Weedkiller (Paraquat) Poisoning

Quick Answer

Paraquat (N,N'-dimethyl-4,4'-bipyridinium dichloride) is a highly toxic bipyridyl herbicide with a case fatality rate of 60-90%. There is no specific antidote. Management focuses on immediate gastrointestinal decontamination with activated charcoal or Fuller's earth within 1-2 hours, enhanced elimination with charcoal hemoperfusion if initiated within 4 hours, and supportive care with strict avoidance of supplemental oxygen (unless PaO2 below 40-50 mmHg) due to the oxygen paradox. Immunosuppression with high-dose methylprednisolone and cyclophosphamide (Taipei protocol) and antioxidant therapy (N-acetylcysteine, vitamins C and E) may reduce pulmonary fibrosis. Prognosis is determined by dose ingested, plasma paraquat levels on survival nomogram, and early development of multi-organ failure. Death occurs from progressive pulmonary fibrosis (days 1-3 weeks) or fulminant multi-organ failure (24-72 hours).

ACEM Exam Focus

Primary Exam: Toxicokinetics, mechanism of oxidative injury, redox cycling, lung transport mechanisms (polyamine uptake), renal excretion and concentration in pulmonary tissue.

Fellowship Exam: Immediate management priorities, decontamination techniques, hemoperfusion indications and timing, oxygen paradox management, Taipei protocol for immunosuppression, prognostic indicators (plasma levels, survival nomogram), ethical considerations (futility and palliative care), communication with family about poor prognosis.

OSCE Scenarios: Poisoning station (assessment and management), breaking bad news (poor prognosis and futility), procedural skills (activated charcoal administration, hemoperfusion setup), team leadership in toxicology emergencies.

Key Points

1. Redox cycling mechanism: Paraquat is reduced intracellularly to a free radical, then re-oxidised by oxygen, producing superoxide radicals → oxidative stress, lipid peroxidation, NADPH depletion, and cell death. [1-3]

2. Type I vs II alveolar injury: Phase I (1-3 days): destruction of Type I alveolar cells (gas exchange barrier loss) and Type II cells (surfactant loss, progenitor cell depletion). Phase II (4-14+ days): fibroblast proliferation, collagen deposition, intra-alveolar and interstitial fibrosis → "fossilised lung" with no gas exchange. [4-6]

3. Oxygen paradox: Supplemental oxygen provides more substrate for redox cycling, accelerating pulmonary fibrosis. Maintain SpO2 88-90% (PaO2 60-70 mmHg). Only give oxygen if PaO2 below 40-50 mmHg or for palliative comfort. [7-9]

4. Decontamination window: Activated charcoal (50-100 g adult, 1 g/kg child) or Fuller's earth (100-150 g) within 1-2 hours maximally effective. Gastric lavage only within 1 hour. Skin/eye decontamination immediate with copious irrigation. [10-12]

5. Hemoperfusion timing: Charcoal hemoperfusion most effective within 2-4 hours of ingestion, benefits decline rapidly as paraquat distributes into tissues. May improve survival in moderate ingestions (20-40 mg/kg). [13-15]

6. Taipei protocol: Methylprednisolone 1-2 g/day IV for 3 days then taper, plus cyclophosphamide 15 mg/kg IV loading then 2-4 mg/kg/day, reduces pulmonary fibrosis mortality when combined with antioxidants. [16-18]

7. Prognostic indicators: Plasma paraquat level on Proudfoot nomogram (survival curve), urine dithionite test (deep blue/green = fatal), early renal failure (creatinine rise within 24 hours), rapid decline in SpO2, dose ingested. [19-22]

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Epidemiology

Global Burden

Paraquat remains one of the most lethal herbicides available worldwide, with significant public health impact in agricultural regions where regulations are less stringent.

Incidence and Mortality

• Estimated 300,000-500,000 paraquat poisoning cases annually worldwide
• Case fatality rate 60-90% in most series
• Leading cause of fatal pesticide poisoning in many Asian countries
• Accounts for up to 30% of pesticide-related deaths in regions where widely available [23,24]

Geographic Distribution

• Highest burden: Asia-Pacific (China, Taiwan, Sri Lanka, India, Southeast Asia)
• Significant problem: Central and South America (agricultural regions)
• Rare in high-income countries following bans and restrictions (European Union banned 2007, Australia highly restricted since 1977) [25,26]

Australian Context

Regulatory Status

• Paraquat classified as Schedule 7 (Dangerous Poison) in Australia
• Available only to licensed agricultural users
• Must contain emetic and dye (blue/green colour, vomiting agent)
• Restriction has significantly reduced intentional and accidental exposures but sporadic cases still occur [27,28]

Australian Incidence

• 10-20 cases per year reported to Australian Poisons Information Centre
• Majority: intentional self-harm in rural agricultural workers
• Occupational exposures rare but occur with improper handling or inadequate PPE
• Pediatric accidental exposures very uncommon due to restrictions [29]

Australian Case Series

• Victoria: 15-year review (2005-2020) - 42 cases, 28 deaths (67% mortality) [30]
• NSW: 10-year review - 31 cases, all intentional ingestion, 22 deaths (71% mortality) [31]
• Queensland: Rural regional data - higher incidence in agricultural communities, delayed presentations due to transport distances [32]

Demographics

Age Distribution

• Peak incidence: 30-50 years (working-age adults)
• Intentional: 20-50 years (mental health crises, relationship conflicts)
• Occupational: 30-60 years (agricultural workers)
• Pediatric: Very rare in Australia, more common in countries with less restrictive regulations [33,34]

Sex Distribution

• Intentional self-harm: Male predominance (2-3:1) in most series
• Occupational: Predominantly male (agricultural workforce demographics)
• Accidental pediatric: No significant sex difference [35]

Risk Factors

Paraquat Formulations

Commercial Names (Australia)

• Gramoxone (most common historical brand)
• Weedol
• Pathclear
• Various generic formulations

Concentration

• Commercial formulations: 20% w/v (200 mg/mL) concentrated solution
• Some formulations: 10-15% w/v
• Dilution occurs in spray tanks before application

Appearance

• Concentrated solution: Blue-green or brown colour (dye additive)
• Strong, unpleasant odour
• Added emetic (vomiting agent) in Australian formulations

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Pathophysiology

Paraquat Structure and Properties

Chemical Identity

• N,N'-dimethyl-4,4'-bipyridinium dichloride
• Molecular weight: 257.2 g/mol
• Cationic (positively charged) bipyridyl compound
• Highly water soluble, poorly lipid soluble
• Rapidly absorbed from GI tract, lungs, and damaged skin [1,2]

Pharmacokinetics

• Absorption: GI absorption 5-15% of ingested dose (rapid but incomplete due to caustic effects and vomiting)
• Peak plasma: 1-4 hours post-ingestion
• Volume of distribution: 1.2-1.6 L/kg (predominantly intracellular)
• Protein binding: Negligible
• Elimination: Primarily renal (unchanged via glomerular filtration) with half-life 12-36 hours (prolonged with renal failure) [3,4]

Toxicokinetics: Tissue Distribution

Selective Pulmonary Accumulation The lung is the primary target organ due to active uptake mechanisms:

1. Polyamine Transport System: Alveolar epithelial cells (Type I and II) actively transport polyamines (putrescine, spermidine, spermine) for cellular growth and repair. Paraquat structurally resembles polyamines and is actively concentrated in lung tissue via this system.

2. Concentration Gradient: Lung paraquat concentrations reach 10-20 times higher than plasma levels, explaining pulmonary toxicity disproportionate to other organs.

3. Other Organs: Kidneys (high perfusion, excretion), liver (metabolism), adrenal glands, skeletal muscle, and myocardium also accumulate paraquat but to lesser degrees. [5-7]

Mechanism of Toxicity: Redox Cycling

Step 1: Cellular Uptake

• Paraquat (PQ²⁺) enters cells via polyamine transporters (Type I/II alveolar cells, renal proximal tubular cells, hepatocytes)
• Intracellular concentration increases 10-20-fold compared to plasma [8,9]

Step 2: Enzymatic Reduction

• Intracellular enzymes (NADPH-cytochrome P450 reductase, xanthine oxidase, NADPH dehydrogenase) reduce paraquat
• Reaction: PQ²⁺ + NADPH → PQ•⁺ (paraquat mono-cation radical) + NADP⁺ [10,11]

Step 3: Re-oxidation and ROS Generation

• The paraquat radical rapidly reacts with molecular oxygen
• Reaction: PQ•⁺ + O₂ → PQ²⁺ + O₂•⁻ (superoxide anion)
• This is the redox cycle - paraquat acts as a catalyst, continuously shuttling between oxidised and reduced forms while generating reactive oxygen species (ROS) [12,13]

Step 4: ROS Cascade

• Superoxide (O₂•⁻) is converted by superoxide dismutase (SOD) to hydrogen peroxide (H₂O₂)
• H₂O₂ reacts with Fe²⁺ via Fenton reaction → hydroxyl radical (•OH)
• Hydroxyl radicals are extremely reactive and cause:
  • "Lipid peroxidation: Destruction of cell membranes"
  • "Protein oxidation: Enzyme inactivation, structural damage"
  • "DNA damage: Strand breaks, base modifications"
  • "Mitochondrial dysfunction: ATP depletion, apoptosis [14,15]"

Step 5: NADPH Depletion

• The redox cycle consumes NADPH continuously
• NADPH is required for:
  • Glutathione regeneration (antioxidant defence)
  • Ribose synthesis (cellular repair)
  • Nitric oxide synthase activity
• NADPH depletion impairs cellular recovery and antioxidant capacity [16,17]

Alveolar Injury: Type I vs II Cells

Normal Alveolar Structure

• Type I pneumocytes: Thin, flat cells covering 95% of alveolar surface area. Function: Gas exchange barrier.
• Type II pneumocytes: Cuboidal cells covering 5% of surface area. Functions: Surfactant production, progenitor cells for Type I cell replacement.

Phase I: Destructive/Exudative Phase (Days 1-3)

Pathological Findings in Phase I:

• Alveolar epithelial denudation (bare basement membrane)
• Intra-alveolar oedema and haemorrhage
• Hyaline membrane formation
• Neutrophilic and macrophage infiltrates
• Interstitial inflammation [18-20]

Phase II: Proliferative/Fibrotic Phase (Days 4-14+)

If the patient survives the initial destructive phase, a maladaptive repair response occurs:

• gas exchange impossible |

Clinical Consequences of Fibrosis:

• Progressive dyspnoea
• Hypoxaemia refractory to oxygen (oxygen paradox)
• Restrictive lung physiology (↓ FVC, ↓ TLC)
• Radiographic findings: Ground-glass opacities → consolidation → fibrosis
• Death typically 7-21 days post-ingestion from respiratory failure [21-23]

The Oxygen Paradox

Mechanism

• Supplemental oxygen increases arterial and alveolar oxygen tension
• More oxygen available for paraquat redox cycle
• Increased superoxide production → accelerated oxidative damage
• Clinical effect: Oxygen therapy worsens pulmonary fibrosis and hastens death [24,25]

Clinical Thresholds

• Maintain SpO2 88-90% (PaO2 60-70 mmHg)
• Give oxygen ONLY if:
  • PaO2 below 40-50 mmHg (severe hypoxaemia)
  • Palliative care for comfort in terminal patients
• Target permissive hypoxaemia: Accept low oxygen saturation if patient is comfortable [26,27]

Systemic Organ Toxicity

Renal Toxicity

• Paraquat is actively secreted by proximal tubular cells (polyamine transport)
• Direct tubular epithelial cell injury via redox cycling
• Acute tubular necrosis within 24-48 hours
• Consequences:
  • Rapidly rising creatinine
  • Reduced paraquat excretion → higher plasma levels → vicious cycle
  • Often requires renal replacement therapy
• Renal failure is an early marker of severe poisoning and poor prognosis [28,29]

Hepatic Toxicity

• Centrilobular (zone 3) necrosis (similar to paracetamol but via different mechanism)
• Elevated transaminases (AST, ALT) within 2-5 days
• Jaundice, coagulopathy in severe cases
• Usually self-limiting if patient survives other injuries [30,31]

Cardiovascular Toxicity

• Direct myocardial injury via redox cycling
• Arrhythmias, myocarditis, decreased contractility
• Hypotension from capillary leak, gastrointestinal fluid losses, and myocardial depression
• Cardiovascular collapse in fulminant cases (death within 24-72 hours) [32,33]

Gastrointestinal Toxicity

• Corrosive effects of concentrated solution
• Oral, pharyngeal, and oesophageal burns
• Nausea, vomiting, severe abdominal pain
• Haematemesis, melena
• May require analgesia and endoscopic assessment [34,35]

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Clinical Presentation

Timeline Based on Dose Ingested

Fulminant Ingestion (greater than 40 mg/kg)

• Onset: Minutes to 2 hours
• Clinical course: Rapid cardiovascular collapse, multi-organ failure
• Time to death: 24-72 hours despite aggressive treatment
• Features:
  • "Severe gastrointestinal: Vomiting, diarrhoea, abdominal pain, haematemesis"
  • "Early renal failure: Creatinine rising within 12-24 hours"
  • "Cardiovascular: Hypotension, arrhythmias, shock"
  • "Hepatic: Transaminase elevation"
  • "Pulmonary: May have limited pulmonary symptoms (death before fibrosis develops)"

Moderate Ingestion (20-40 mg/kg)

• Onset: 1-6 hours
• Clinical course: Initial GI symptoms → multi-organ involvement → progressive pulmonary fibrosis
• Time to death: 7-21 days (usually from respiratory failure)
• Features by phase:

Small Ingestion (below 20 mg/kg)

• May be asymptomatic or have only mild GI symptoms
• Recovery likely with supportive care
• However, even small ingestions can be fatal in susceptible individuals (pre-existing lung disease, renal impairment) [36,37]

Clinical Features by Organ System

Gastrointestinal (Earliest, most common)

• Oral and pharyngeal burning sensation (immediate)
• Painful swallowing (odynophagia)
• Nausea and profuse vomiting (often bloody)
• Severe abdominal pain
• Diarrhoea (may be bloody)
• Oesophageal/gastric burns (corrosive injury)

Renal (Early marker of severity)

• Oliguria or anuria (within 24-48 hours)
• Rising serum creatinine and urea
• Acute tubular necrosis on urinalysis (granular casts, proteinuria)
• May require renal replacement therapy

Hepatic

• Jaundice (2-5 days)
• Elevated transaminases (AST, ALT, up to 1000s)
• Coagulopathy (elevated INR) in severe cases
• Rarely liver failure as primary cause of death

Pulmonary (Primary cause of death in moderate ingestions)

• Early (1-3 days): Tachypnoea, mild dyspnoea, hypoxaemia may develop
• Intermediate (4-7 days): May temporarily improve ("latent phase")
• Late (7-21 days): Progressive dyspnoea, dry cough, worsening hypoxaemia, fine crackles, cyanosis
• Radiographic progression:
  • "Day 1-2: Normal or mild infiltrates"
  • "Day 3-5: Ground-glass opacities"
  • "Day 6-10: Consolidation"
  • "Day 11+: Fibrosis, honeycombing"

Cardiovascular

• Tachycardia
• Hypotension (from capillary leak, fluid losses, myocardial depression)
• Arrhythmias
• Cardiovascular collapse in fulminant cases

Neurological

• Agitation, confusion (from hypoxia or acidosis)
• Seizures (rare, from severe metabolic disturbance)
• Coma (terminal event)

Physical Examination

Vital Signs

• Tachycardia (HR 100-140/min)
• Hypotension (SBP 80-90 or lower in severe cases)
• Tachypnoea (RR 20-30/min or higher)
• Hypoxaemia (SpO2 may be normal initially, declines with pulmonary fibrosis)
• Fever (from inflammation or infection)

General Examination

• Distress, agitation, or obtunded (depending on severity)
• Cyanosis (late finding in pulmonary fibrosis)
• Signs of dehydration (dry mucous membranes, decreased skin turgor)

Head and Neck

• Oral/pharyngeal burns, erythema, ulceration
• Oropharyngeal pain
• Sialorrhoea (increased secretions)

Cardiovascular

• Tachycardia
• Hypotension
• Muffled heart sounds (if pericardial effusion - rare)
• Gallop rhythm (if myocardial involvement)

Respiratory

• Tachypnoea
• Fine crackles (inspiratory, bibasilar)
• Decreased breath sounds (with consolidation)
• Signs of respiratory distress (accessory muscle use, nasal flaring)

Abdominal

• Tenderness (epigastric, diffuse)
• Guarding
• Possible abdominal distension
• Reduced bowel sounds (paralytic ileus in severe cases)

Neurological

• Altered mental status (agitation, confusion, obtundation)
• May be normal initially, deteriorates with hypoxia or metabolic acidosis

Red Flags (Indicators of Fatal Poisoning)

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Clinical Approach

Immediate Assessment

ABCDE Approach

A - Airway

• Assess patency: May be compromised by decreased consciousness
• Protect airway: Intubate if GCS below 8, unable to protect airway, or respiratory distress
• Use RSI if required
• Note: Rapid sequence intubation with hypoxic precautions (pre-oxygenate carefully - avoid excessive oxygen)

B - Breathing

• Assess respiratory rate, work of breathing, oxygen saturation
• Auscultate lungs (crackles, wheeze, decreased sounds)
• Maintain SpO2 88-90% (permissive hypoxaemia)
• Critical: Only give oxygen if PaO2 below 40-50 mmHg (oxygen paradox)

C - Circulation

• Assess pulse, blood pressure, capillary refill time
• Establish two large-bore IVs (14G or 16G)
• Fluid resuscitation with balanced crystalloid (1L bolus, reassess)
• Monitor for hypotension (correct hypovolaemia but avoid pulmonary edema)

D - Disability

• Assess GCS, pupils, limb movements
• Check blood glucose (hypoglycaemia from liver failure)

E - Exposure

• Full skin examination (dermal exposure)
• Remove contaminated clothing
• Skin decontamination (wash with soap and water)
• Eye decontamination (irrigate with saline for 15 minutes)

History Taking

Critical Information to Obtain

Estimating Ingested Dose

• Concentrated commercial formulation: 20% w/v (200 mg/mL)
• Toxic dose: > 20 mg/kg body weight
• Fatal dose: > 35-40 mg/kg
• Example: 70 kg adult ingesting 50 mL of 20% paraquat:
  • "Amount: 50 mL × 200 mg/mL = 10,000 mg = 10 g"
  • "Dose: 10,000 mg / 70 kg = 143 mg/kg (fatal ingestion)"

Investigations

Immediate Investigations (Within 1 Hour of Presentation)

Bedside Urine Dithionite Test

Procedure:

1. Collect 10 mL urine
2. Add 100 mg sodium dithionite (or 1 g of 1% solution)
3. Add 1 mL 4N NaOH
4. Observe colour change immediately

Colour Interpretation:

• No colour change: No paraquat detected (very small ingestion or delayed > 24 hours)
• Light blue/pink: Low concentration (possible survival)
• Deep blue/green: High concentration (highly likely fatal)

Limitations:

• Qualitative only (no quantitative level)
• False negative if > 24 hours post-ingestion
• False positive with other compounds (rare) [38,39]

Blood Tests

Radiology

Chest X-ray (Serial)

CT Chest

• More sensitive than CXR for early pulmonary changes
• May show ground-glass opacities earlier
• Useful for assessing extent of fibrosis
• Consider in stable patients where prognosis uncertain [40,41]

Proudfoot Survival Nomogram

Method:

1. Obtain plasma paraquat level at time of presentation
2. Plot level against time post-ingestion (in hours)
3. Determine if point falls above or below survival curve

Interpretation:

• Below survival curve: Possible survival with aggressive treatment
• Above survival curve: Near-universal mortality regardless of treatment

Limitations:

• Only valid if ingestion time is known accurately
• Less accurate for staggered ingestions
• Does not account for individual variability
• Australian nomogram may differ from international versions [42,43]

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Management

Immediate Priorities (First Hour)

1. Gastrointestinal Decontamination (CRITICAL - TIME SENSITIVE)

Activated Charcoal

• Dose: 50-100 g for adults (1 g/kg for children)
• Administration: Mix with water to slurry, administer via nasogastric tube if vomiting
• Timing: Most effective within 1-2 hours of ingestion
• Mechanism: Adsorbs paraquat in GI tract, preventing systemic absorption
• Repeat doses: Consider repeat dosing every 4 hours for 24 hours (enhanced elimination via GI dialysis) [44,45]

Fuller's Earth

• Dose: 100-150 g as 15% suspension (1 liter)
• Administration: Single dose via nasogastric tube
• Timing: Within 1-2 hours of ingestion
• Mechanism: High adsorptive capacity for paraquat cations
• Availability: May not be available in all EDs (activated charcoal is acceptable alternative) [46,47]

Gastric Lavage

• Indications: Large, recent ingestion (within 1 hour) and patient presents very early
• Contraindications: Delayed presentation (greater than 1 hour), unprotected airway, corrosive injury risk
• Procedure: Use large-bore orogastric tube, lavage until clear
• Evidence: Limited benefit, potential complications (aspiration, oesophageal injury) [48,49]

2. Skin and Eye Decontamination

Skin Decontamination

• Remove all contaminated clothing immediately
• Wash skin thoroughly with soap and water (minimum 15 minutes)
• Pay special attention to skin folds, nails, and hair
• Use water, not solvents (solvents may increase absorption)

Eye Decontamination

• Immediate irrigation with water or normal saline
• Minimum 15 minutes continuous irrigation
• Use Morgan lens or eye irrigation system if available
• Maintain pH neutral (avoid alkaline solutions)

3. Airway and Breathing Management

Airway Protection

• Intubate if:
  • GCS below 8
  • Unable to protect airway
  • Severe respiratory distress
  • Need for procedures (hemoperfusion)

Oxygen Therapy - CRITICAL PRINCIPLE

• Target SpO2: 88-90% (permissive hypoxaemia)
• Indications for oxygen:
  • PaO2 below 40-50 mmHg on ABG
  • Palliative care for comfort in terminal patients
• Avoid oxygen:
  • Routine administration (accelerates pulmonary fibrosis)
  • SpO2 > 90% if patient is comfortable
• Monitoring: Continuous pulse oximetry, serial ABGs

Mechanical Ventilation

• Use lung-protective strategy if ventilated:
  • Tidal volume 6 mL/kg ideal body weight
  • PEEP 5-10 cmH2O
  • Permissive hypercapnia (accept higher PaCO2)
• Avoid high FiO2 (target FiO2 0.21-0.30 if possible)

4. Circulatory Support

Fluid Resuscitation

• Two large-bore IVs (14G or 16G)
• Initial crystalloid bolus 1L (balanced crystalloid preferred)
• Reassess after each bolus
• Avoid fluid overload (risk of pulmonary edema)
• Monitor urine output, CVP if available

Vasopressors

• If hypotension persists after fluid resuscitation:
  • Noradrenaline infusion (first line)
  • Consider vasopressin or adrenaline in refractory shock
• Target MAP 65-70 mmHg (higher if pre-existing hypertension)

Enhanced Elimination

Charcoal Hemoperfusion (HP)

Indications:

• Plasma paraquat level below survival curve on nomogram
• Ingestion within 4 hours of presentation
• Moderate ingestion (20-40 mg/kg)
• Patient haemodynamically stable

Mechanism:

• Blood passed through cartridge containing activated charcoal
• Paraquat adsorbed to charcoal as blood passes through
• Most effective extracorporeal removal method for paraquat

Timing:

• Initiate within 2-4 hours of ingestion for maximal benefit
• Benefit declines rapidly as paraquat distributes into tissues
• Continue until:
  • Plasma paraquat undetectable
  • Or > 12-24 hours of treatment (diminishing returns)

Procedure:

• Vascular access: Double-lumen haemodialysis catheter (internal jugular or femoral)
• Blood flow: 150-250 mL/min
• Duration: 2-4 hours per session, may repeat daily
• Complications: Thrombocytopenia, hypocalcaemia, hypothermia, vascular access complications

Evidence:

• Improves survival in moderate ingestions when initiated early
• No benefit in fulminant ingestions (greater than 40 mg/kg) or delayed presentations
• Combination with haemodialysis may be used for renal failure [50-52]

Haemodialysis (HD)

• Primary indication: Acute renal failure with metabolic disturbances
• Secondary indication: Adjunct to hemoperfusion for paraquat removal (less effective)
• Indications for dialysis:
  • Severe AKI with rising creatinine, hyperkalaemia, metabolic acidosis
  • Fluid overload unresponsive to diuretics
  • Uraemic symptoms

Continuous Renal Replacement Therapy (CRRT)

• For haemodynamically unstable patients
• Continuous veno-venous haemofiltration (CVVH) or haemodiafiltration (CVVHDF)
• Better haemodynamic tolerance than intermittent HD
• Less efficient paraquat removal than HP

Pharmacological Management

1. Immunosuppressive Therapy (Taipei Protocol)

Rationale:

• Pulmonary fibrosis mediated by inflammatory cascade
• Immunosuppression may reduce fibroblast proliferation and collagen deposition
• Combined with antioxidants for synergistic effect

Taipei Protocol:

• Methylprednisolone:
  • "Loading: 1-2 g IV daily for 3 days"
  • "Taper: Reduce to 40 mg/day over 1-2 weeks"
  • "Duration: Continue for 2-4 weeks or until clinical improvement"
• Cyclophosphamide:
  • "Loading: 15 mg/kg IV single dose (or 750 mg/m²)"
  • "Maintenance: 2-4 mg/kg/day IV or orally"
  • "Duration: Continue for 10-14 days"
• Monitoring:
  • Daily FBC (watch for neutropenia, thrombocytopenia)
  • Liver function tests
  • Urinalysis (haematuria from cyclophosphamide)
  • Blood glucose (steroid-induced hyperglycaemia)

Evidence:

• Improved survival in moderate paraquat poisoning (Level B evidence)
• Combination with antioxidants more effective than either alone
• Most benefit when initiated early (within 24-48 hours)
• May reduce pulmonary fibrosis mortality from 70% to 30-40% in selected patients [53-55]

2. Antioxidant Therapy

N-Acetylcysteine (NAC)

• Dose: 150 mg/kg IV loading over 1 hour, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours (standard paracetamol protocol) OR continuous infusion 20 mg/kg/hour
• Duration: Continue for 3-5 days or until clinical improvement
• Mechanism: Replenishes glutathione, scavenges free radicals
• Evidence: May reduce oxidative damage when combined with immunosuppression (Level C evidence)

Vitamin C (Ascorbic Acid)

• Dose: 2-3 g IV daily
• Mechanism: Water-soluble antioxidant, free radical scavenger
• Evidence: Limited clinical data, theoretical benefit

Vitamin E (Alpha-Tocopherol)

• Dose: 400-800 IU orally twice daily
• Mechanism: Lipid-soluble antioxidant, prevents membrane lipid peroxidation
• Evidence: Limited clinical data, theoretical benefit

3. Supportive Medications

Analgesia

• Oral/pharyngeal burns cause severe pain
• Morphine IV or subcutaneous: 5-10 mg PRN
• Fentanyl: 25-50 mcg IV PRN (more rapid onset)
• Avoid NSAIDs (renal injury risk)

Anti-emetics

• Ondansetron 4-8 mg IV (avoid high doses due to QT prolongation risk with electrolyte disturbances)
• Metoclopramide 10 mg IV (caution with increased seizure risk)

Proton Pump Inhibitor

• Omeprazole 40 mg IV/PO daily
• For stress ulcer prophylaxis and GI mucosal protection

Antibiotics

• Not routinely indicated
• Consider if aspiration pneumonia or secondary infection suspected
• Cover for aspiration: Ceftriaxone 2 g IV daily ± Metronidazole 500 mg IV TDS

Prognostication and Goals of Care

Early Prognostication (Within 24 Hours)

Poor Prognosis Indicators (High Mortality):

• Plasma paraquat level above survival curve on Proudfoot nomogram
• Ingestion > 35-40 mg/kg
• Deep blue/green urine dithionite test
• Creatinine rising within 24 hours
• Early hypoxaemia (SpO2 < 90% within 48 hours)
• Metabolic acidosis (pH < 7.3)
• Multiple organ failure

Futile Care Indications: When multiple poor prognostic indicators are present, aggressive treatment (hemoperfusion, immunosuppression, ICU care) is unlikely to improve survival and may prolong suffering.

Goals of Care Discussion:

• Initiate early (within 12-24 hours)
• Involve family, ICU team, toxicology service
• Discuss realistic prognosis
• Consider palliative care if:
  • Paraquat level well above survival curve
  • Multi-organ failure already present
  • Patient presents late (> 24 hours post-ingestion)

Palliative Care Approach:

• Focus on comfort and symptom management
• Pain control (morphine, fentanyl)
• Dyspnoea management (opioids, fan therapy, oxygen for comfort)
• Anxiety management (benzodiazepines)
• Family support and bereavement care

Long-Term Management (Survivors)

Pulmonary Follow-up

• Serial pulmonary function tests (spirometry, DLCO)
• High-resolution CT chest at 3 months, 6 months, 12 months
• Pulmonary rehabilitation
• Supplemental oxygen if required (for chronic fibrosis, not acute phase)
• Consider lung transplantation in selected cases (rare, ethical considerations)

Renal Follow-up

• Monitor renal function recovery
• May have chronic kidney disease (CKD)
• Nephrology follow-up

Hepatic Follow-up

• LFTs typically normalise
• Monitor for chronic liver disease (rare)

Psychological Support

• Depression, PTSD, anxiety common after intentional poisoning
• Mental health referral
• Suicide prevention strategies
• Family support and counselling

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Indigenous Health Considerations

Aboriginal and Torres Strait Islander Communities

Epidemiology in Indigenous Communities

• Limited specific data on paraquat poisoning in Aboriginal and Torres Strait Islander populations
• Higher rates of pesticide-related injuries in remote agricultural communities
• Increased risk factors: rural residence, occupational exposure, limited access to mental health services

Cultural Safety in Management

• Family involvement: Include family members in discussions and decision-making, respecting cultural protocols around communication and decision-making authority
• Language and communication: Use interpreters if required, avoid medical jargon, be aware of cultural differences in expressing pain and distress
• Traditional healers: Respect and integrate traditional healing practices where appropriate and safe
• Connection to Country: Acknowledge importance of land and community, facilitate return to Country if feasible and safe
• Sorry Business: Understand cultural mourning practices and bereavement protocols if death occurs

Barriers to Care

• Geographic isolation: Remote communities may have delayed presentation due to transport distances
• Limited healthcare access: Few local health services, reliance on aeromedical retrieval (Royal Flying Doctor Service)
• Cultural mistrust: Historical experiences affecting trust in healthcare institutions
• Communication barriers: Language differences, health literacy, cultural concepts of illness

Management Considerations

• Early consultation with Aboriginal and Torres Strait Islander health workers or liaison officers
• Respect family decision-making structures (elders may have decision-making authority)
• Provide culturally appropriate psychosocial support
• Consider involving Indigenous mental health services
• Facilitate connection with community during hospitalisation (virtual or in-person if possible)
• Ensure discharge planning includes community support and follow-up

Specific Recommendations

• Involve local Aboriginal Medical Services in follow-up care
• Provide education on safe pesticide storage and use in agricultural communities
• Support community-based suicide prevention programs
• Train health workers in recognising and responding to pesticide poisoning

Māori Populations (New Zealand)

Cultural Considerations

• Whānau involvement: Include extended family in discussions and care planning
• Manaakitanga: Hospitality and care for patients and family during hospitalisation
• Tikanga: Adhere to cultural protocols around death and dying (including removal of medical equipment from patient if death imminent)
• Karakia: Allow for prayers and spiritual practices
• Tapu: Respect concepts of sacredness, especially around the body and bodily functions

Epidemiology

• Paraquat banned in New Zealand since 2011
• Historical cases may still be relevant for educational purposes
• Current pesticide poisonings typically involve other herbicides/pesticides

Management Principles

• Early involvement of Māori health providers or liaison staff
• Respect whānau decision-making processes
• Provide culturally appropriate bereavement support if death occurs
• Facilitate tikanga practices during hospitalisation and at end of life

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Remote and Rural Emergency Medicine

Challenges in Remote Settings

Geographic Isolation

• Prolonged transport times to tertiary centres (hours to days)
• Limited access to specialist toxicology services
• Delays in initiating advanced therapies (hemoperfusion, ICU care)

Resource Limitations

• May not have access to:
  • Charcoal hemoperfusion
  • ICU beds with mechanical ventilation
  • Specialist toxicology consultation
  • Laboratory paraquat level testing (send-away testing with delays)

Staffing

• Limited number of medical and nursing staff
• May be solo practitioner or small team
• Limited experience with rare toxicological emergencies

Management in Remote Settings

Immediate Management (ALL Settings Can Provide)

1. Gastrointestinal decontamination: Activated charcoal (available in most rural hospitals)
2. Skin/eye decontamination: Soap and water, saline irrigation (always available)
3. Supportive care: IV fluids, airway management, basic monitoring
4. Oxygen avoidance: This principle applies everywhere (do not give oxygen routinely)

Transfer Considerations

• Early activation: Initiate retrieval as soon as diagnosis suspected (don't wait for confirmation)
• Royal Flying Doctor Service (RFDS): Primary retrieval service for Australia
• Medical Retrieval: Consider medical escort if patient unstable or requires advanced care en route
• Destination: Tertiary centre with:
  • ICU capabilities
  • Charcoal hemoperfusion available
  • Toxicology service

Communication

• Early consultation with:
  • Toxicology information service (state poison centre)
  • Retrieval service
  • Receiving hospital
• Use clinical photos of urine dithionite test if available (can send via telemedicine)

Laboratory Testing

• Urine dithionite test: Can be performed bedside (requires sodium dithionite and NaOH - small rural hospitals may have limited stocks)
• Plasma paraquat level: May require send-away testing (delays in results)
• Basic blood tests: FBC, U&E, LFTs, coagulation, ABG (available in most rural hospitals)

Management Prioritisation

• If transfer delayed (> 6 hours), maximise care at local facility:
  • Repeat activated charcoal doses (every 4-6 hours)
  • Aggressive supportive care (fluids, electrolyte management)
  • Early intubation and ventilation if required (before transport)
  • Prepare patient for safe transport (stabilise as much as possible)

Futility Considerations

• In remote settings with long transfer times and poor prognostic indicators, consider:
  • Is transfer in patient's best interests?
  • Can family be supported at local facility if death likely?
  • Palliative care in local setting vs transfer for futile aggressive care

Remote Healthcare Worker Education

Key Points for Remote Practitioners

1. Recognition: Any herbicide ingestion = treat as potentially paraquat until proven otherwise
2. Decontamination: Activated charcoal immediately if within 2 hours of ingestion
3. Oxygen paradox: Do NOT give oxygen routinely (permissive hypoxaemia)
4. Prognosis: Urine dithionite test provides immediate prognostic information
5. Early retrieval: Activate retrieval early, don't wait for deterioration
6. Goals of care: Have early discussions about treatment goals if poor prognosis

Resources

• State poison information centre (24/7)
• Toxicology guidelines (Therapeutic Guidelines Australia)
• Clinical decision support tools
• Telemedicine consultation with tertiary toxicology services

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Viva Practice

Viva Scenario 1

Stem: A 34-year-old male presents to the emergency department 2 hours after intentional ingestion of approximately 100 mL of weedkiller. He brought the bottle, which is labelled "Gramoxone" (paraquat 20% w/v). On examination, he is alert with GCS 15, HR 110/min, BP 110/70 mmHg, RR 18/min, SpO2 98% on room air. He complains of burning sensation in his mouth and throat and has vomited twice.

Opening Question: What are your immediate management priorities?

Model Answer: This patient has potentially fatal paraquat poisoning requiring immediate intervention. My management priorities are:

1. Immediate decontamination (most time-critical):

• Activated charcoal 50-100 g (1 g/kg) immediately via nasogastric tube (within 2 hours of ingestion)
• Consider gastric lavage if ingestion very recent and patient has protected airway
• Skin and eye decontamination if any exposure

2. Prognostication:

• Perform bedside urine dithionite test immediately
• Send plasma paraquat level for survival nomogram (if available)
• Estimate ingested dose: 100 mL of 20% = 20 g paraquat; in 70 kg adult = 286 mg/kg (fatal dose)

3. Supportive care:

• ABC assessment - patient currently stable but may deteriorate rapidly
• Establish two large-bore IVs, blood tests (FBC, U&E, LFTs, coagulation, ABG)
• Baseline chest X-ray (likely normal initially)
• Maintain SpO2 88-90% (permissive hypoxaemia, do NOT give oxygen)

4. Enhanced elimination:

• Urgent consultation for charcoal hemoperfusion if patient suitable and available
• Timing critical - most effective within 2-4 hours of ingestion

5. Early goals of care discussion:

• Given large estimated dose, prognosis likely poor
• Discuss with patient and family about realistic expectations
• Consider palliative approach if prognostic indicators confirm poor outcome

Follow-up Questions:

1. Explain the mechanism of paraquat toxicity and why oxygen is contraindicated.

Model answer: Paraquat undergoes redox cycling within cells, particularly alveolar epithelial cells. The positively charged paraquat ion is actively taken up by alveolar cells via polyamine transporters, concentrating in lung tissue. Intracellularly, paraquat is reduced to a free radical, then re-oxidised by molecular oxygen, generating superoxide radicals. This continuous redox cycle consumes NADPH (depleting antioxidant defenses) and produces massive oxidative stress, causing lipid peroxidation, mitochondrial dysfunction, and cell death. Supplemental oxygen provides more substrate for this redox cycle, accelerating the oxidative damage and pulmonary fibrosis. Therefore, we maintain permissive hypoxaemia (SpO2 88-90%) and only give oxygen if PaO2 falls below 40-50 mmHg or for palliative comfort. | [1-4, 24-27]

2. What are the phases of pulmonary injury in paraquat poisoning?

Model answer: Pulmonary injury occurs in two distinct phases. Phase I (days 1-3) is the destructive/exudative phase: Type I alveolar cells (gas exchange barrier) and Type II cells (surfactant producers and progenitor cells) are destroyed by oxidative injury, leading to denudation of alveolar basement membrane, pulmonary edema, hemorrhage, and inflammatory cell infiltration. Type II cell death prevents surfactant production and alveolar repair, causing atelectasis. Phase II (days 4-14+) is the proliferative/fibrotic phase: If the patient survives the initial destruction, fibroblasts and myofibroblasts massively proliferate, depositing collagen within alveolar spaces and interstitium. The lung architecture is replaced by dense fibrous tissue ("fossilised lung"), making gas exchange impossible. This progressive, irreversible fibrosis is the primary cause of death in moderate ingestions, typically occurring 1-3 weeks after ingestion. | [4-6, 18-23]

3. What is the Taipei protocol and what is its role in paraquat poisoning?

Model answer: The Taipei protocol is an immunosuppressive regimen developed in Taiwan aimed at reducing the pulmonary fibrosis that causes death in moderate paraquat poisoning. It combines high-dose corticosteroids with cyclophosphamide to dampen the inflammatory cascade and fibroblast proliferation. The protocol typically involves methylprednisolone 1-2 g IV daily for 3 days, then tapering over 1-2 weeks, plus cyclophosphamide 15 mg/kg IV loading dose followed by 2-4 mg/kg/day. Evidence (Level B) suggests it improves survival in moderate ingestions (20-40 mg/kg) when initiated early (within 24-48 hours). It is often combined with antioxidants (N-acetylcysteine, vitamins C and E) which scavenge free radicals and replenish glutathione. However, in fulminant ingestions (greater than 40 mg/kg) or delayed presentations, the benefit is minimal. The protocol carries risks of immunosuppression (infection, neutropenia, bleeding) and should be used in consultation with toxicology and ICU specialists. | [16-18, 53-55]

4. How would you discuss prognosis with this patient and his family?

Model answer: Prognostication in paraquat poisoning depends on several factors and requires careful, honest communication. First, I would explain that paraquat is a highly toxic herbicide with a high mortality rate. I would present the objective data: this patient ingested approximately 100 mL of 20% paraquat solution, which is a dose of approximately 286 mg/kg in a 70 kg adult - well above the fatal threshold of 35-40 mg/kg. I would explain the urine dithionite test and plasma paraquat level results as they become available. If these indicate high levels with poor prognosis, I would have a frank but compassionate discussion that survival is extremely unlikely despite aggressive treatment. I would discuss the limitations of treatment (decontamination window, hemoperfusion timing, immunosuppression risks) and the potential for prolonged suffering with futile aggressive care. I would involve the family in decision-making about goals of care, discuss palliative options if appropriate, and provide psychological support. I would emphasise that the decision is shared between the clinical team, the patient (if able), and the family, respecting their values and wishes while being clear about medical reality. | [36,37, 42,43]

Discussion Points:

• Balancing hope with realistic prognostication
• Ethical considerations of futile care
• Family communication strategies
• Resource allocation (ICU beds, hemoperfusion cartridges)
• Cultural considerations in breaking bad news

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Viva Scenario 2

Stem: You are working in a regional hospital 400 km from the nearest tertiary centre. A 45-year-old female farmer presents 3 hours after accidental ingestion of approximately 30 mL of weedkiller that she had decanted into a water bottle. She has burning mouth pain and has vomited several times. Her urine dithionite test shows light blue colouring. Your hospital does not have hemoperfusion capability. Transfer time by Royal Flying Doctor Service is 6 hours.

Opening Question: What are your management priorities and disposition decisions?

Model Answer: This is a challenging scenario requiring careful assessment of prognosis and disposition given resource limitations.

Immediate management (at regional hospital):

1. Activated charcoal: 1 g/kg immediately (within 3 hours of ingestion)
2. Baseline investigations: FBC, U&E, LFTs, coagulation, ABG, chest X-ray
3. Supportive care: IV fluids, analgesia, anti-emetics
4. Prognostic assessment:
   • Estimated dose: 30 mL of 20% = 6 g; in 60 kg adult = 100 mg/kg (fatal dose)
   • Urine dithionite test: Light blue (moderate concentration)
   • Plasma level: Send for nomogram (results may be delayed)
5. Avoid oxygen: Maintain SpO2 88-90%

Disposition decision factors:

• Factors favouring transfer:

  • Light blue dithionite test (may be below survival curve)
  • Early presentation (3 hours)
  • Younger patient, may tolerate aggressive treatment better
  • Plasma level if available and below survival curve

• Factors against transfer:

  • Estimated dose 100 mg/kg (well above fatal threshold)
  • No hemoperfusion capability locally, limited benefit if plasma level high
  • 6-hour transfer time (hemoperfusion window closing)
  • May prolong dying process with transport and futile aggressive care

Decision framework:

1. Obtain plasma paraquat level: If level can be processed quickly and shows below survival curve → transfer for hemoperfusion and ICU care
2. If plasma level not available or above survival curve: Have frank discussion with patient and family about likely futility of aggressive care, consider palliative approach locally with family support
3. If uncertain: Discuss with retrieval service and receiving toxicology consultant to reach consensus on transfer decision

Communication:

• Be honest about prognosis and limitations
• Present options clearly with rationale
• Respect patient and family values and wishes
• Involve local medical consultant and retrieve team in decision-making

Follow-up Questions:

1. How does the timing of presentation and availability of hemoperfusion affect prognosis?

Model answer: Timing is critical in paraquat poisoning. Decontamination with activated charcoal is most effective within 1-2 hours of ingestion, declining rapidly after 2 hours. Hemoperfusion is most effective when initiated within 2-4 hours of ingestion, as paraquat rapidly distributes from plasma into tissues (particularly lung). Beyond 4-6 hours, hemoperfusion has minimal impact on survival. In this scenario, the patient presented at 3 hours but transfer time is 6 hours (total 9 hours before potential hemoperfusion). This delay significantly reduces the likelihood of benefit from hemoperfusion. Combined with the estimated dose of 100 mg/kg (well above fatal threshold), the prognosis is poor regardless of transfer. However, if plasma paraquat level were available and showed a level below the survival curve, there may still be benefit from immunosuppressive therapy and ICU support, potentially justifying transfer. | [13-15, 44-52]

2. What are the principles of remote toxicology management when definitive therapy is not available locally?

Model answer: In remote settings, the focus shifts to interventions that can be performed locally and optimal use of retrieval services. Key principles: (1) Maximise decontamination - administer activated charcoal immediately, consider repeat dosing if prolonged care before transfer. (2) Provide full supportive care - IV fluids, airway management, analgesia, anti-emetics - stabilise patient as much as possible before transport. (3) Avoid harmful interventions - strict oxygen avoidance to prevent accelerating pulmonary fibrosis. (4) Early prognostication - bedside tests (urine dithionite) and available laboratory tests help determine who may benefit from transfer versus who may be better served with palliative care locally. (5) Early retrieval activation - don't wait for deterioration; if transfer may be beneficial, initiate retrieval early to stay within therapeutic windows. (6) Clear communication - involve toxicology consultants and receiving centre early via telemedicine to reach consensus on management and disposition. (7) Goals of care discussions - have early, honest discussions with patients and families about realistic expectations and treatment options. | [27,28, 38,39]

3. How would you approach the ethical considerations around potentially futile transfer?

Model answer: This is a complex ethical decision requiring careful weighing of benefits and burdens. Principles to consider: (1) Beneficence - acting in the patient's best interest by providing care that may improve outcomes versus avoiding interventions that may prolong suffering. (2) Non-maleficence - avoiding harm from futile aggressive treatment or from denying potentially beneficial treatment. (3) Autonomy - respecting the patient's values and wishes (if capacity intact) and involving family in shared decision-making. (4) Justice - appropriate use of limited retrieval resources (ICU beds, aircraft, personnel). In this scenario, the estimated dose of 100 mg/kg, combined with delayed potential hemoperfusion, suggests survival is extremely unlikely even with transfer. However, there is residual uncertainty (urine test light blue, patient relatively stable). The ethical approach would be to: (a) obtain all available prognostic information (plasma level if possible), (b) discuss prognosis transparently with patient and family, (c) present options with clear rationale for each, (d) respect the patient's autonomous choice if they wish to pursue aggressive treatment despite poor prognosis, (e) provide palliative care if they choose comfort-focused approach, (f) support the decision whichever way it goes. | [36,37]

Discussion Points:

• Remote medicine decision-making under uncertainty
• Resource allocation and stewardship
• Professional duty versus patient autonomy
• Communication strategies in resource-limited settings
• Palliative care in regional and remote contexts

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Viva Scenario 3

Stem: A 28-year-old male was transferred to your tertiary ICU 4 hours after paraquat ingestion. He has received activated charcoal. Plasma paraquat level at 4 hours post-ingestion is 2.5 µg/mL. His current vitals: GCS 14, HR 95, BP 105/65, RR 16, SpO2 96% on room air. Creatinine is 150 µmol/L (baseline unknown), LFTs normal, chest X-ray normal. The family is requesting "everything possible be done."

Opening Question: How do you interpret this plasma level and what is your management plan?

Model Answer: Interpretation of plasma level: On the Proudfoot survival nomogram, a plasma paraquat level of 2.5 µg/mL at 4 hours post-ingestion falls below the survival curve, indicating a possibility of survival with aggressive treatment. This represents a moderate ingestion, potentially in the 20-40 mg/kg range.

Management plan:

1. Enhanced elimination - URGENT:

• Charcoal hemoperfusion immediately (within 4-hour window)
• Aim for 2-4 hours per session, may repeat daily if indicated
• Consider concurrent haemodialysis if renal function deteriorates

2. Immunosuppressive therapy (Taipei protocol):

• Methylprednisolone 1 g IV daily for 3 days, then taper
• Cyclophosphamide 15 mg/kg IV loading dose, then 2-4 mg/kg/day
• Monitor FBC daily (watch for neutropenia, thrombocytopenia)
• Continue for 10-14 days or until clinical improvement

3. Antioxidant therapy:

• N-acetylcysteine 150 mg/kg loading, then infusion for 3-5 days
• Vitamin C 2-3 g IV daily
• Vitamin E 400-800 IU PO BID

4. Supportive care:

• Maintain SpO2 88-90% (oxygen paradox - do NOT give oxygen routinely)
• IV fluids to maintain renal perfusion (but avoid overload)
• Monitor urine output closely (AKI may develop)
• Baseline chest X-ray, repeat daily or if respiratory symptoms develop
• Analgesia for oral/pharyngeal burns (morphine)

5. Monitoring:

• Daily FBC, U&E, LFTs, coagulation
• Repeat plasma paraquat levels (if available)
• Serial ABGs (monitor for acidosis, hypoxaemia)
• Daily chest X-rays (watch for pulmonary changes)

6. Communication with family:

• Explain that prognosis is uncertain but survival is possible with aggressive treatment
• Outline treatment plan, risks, and expected course
• Set realistic expectations: May require prolonged ICU stay, possible complications
• Discuss potential for deterioration despite treatment
• Prepare for goals of care discussions if condition worsens

Follow-up Questions:

1. Explain the Proudfoot survival nomogram and how it is used.

Model answer: The Proudfoot survival nomogram is a prognostic tool developed by Proudfoot and colleagues in the 1970s. It plots plasma paraquat concentration (µg/mL) on the y-axis against time post-ingestion (hours) on the x-axis. Two curves are drawn: one for survivors and one for non-survivors. To use the nomogram: (1) Obtain an accurate time of ingestion, (2) Draw a plasma paraquat level at a known time post-ingestion, (3) Plot the point on the nomogram, (4) Determine if the point falls above or below the survival curve. A point below the survival curve indicates possible survival with treatment, while a point above the curve indicates near-universal mortality regardless of treatment. The nomogram is based on hundreds of cases and has good prognostic accuracy when ingestion time is known accurately. Limitations: Not accurate for staggered ingestions, does not account for individual variability or comorbidities, and Australian nomograms may differ slightly from international versions due to formulation differences. | [42,43]

2. What are the major complications you anticipate and how would you manage them?

Model answer: Major complications and management: (1) Acute kidney injury - Already developing (creatinine 150 µmol/L). Manage with careful fluid balance, avoid nephrotoxins, may require renal replacement therapy if severe AKI with hyperkalaemia, acidosis, or fluid overload. (2) Pulmonary fibrosis - Monitor daily CXR, early ground-glass changes may progress to consolidation then fibrosis. Manage with permissive hypoxaemia, consider lung-protective ventilation if intubation required. Immunosuppression aims to reduce fibrosis. (3) Hepatic injury - Transaminitis may develop. Supportive care, monitor coagulation, treat hypoglycaemia if liver failure develops. (4) Infection - Immunosuppression increases infection risk. Vigilant monitoring, early antibiotics if infection suspected, consider prophylactic strategies. (5) Cardiovascular instability - Hypotension from capillary leak or myocardial injury. Fluid resuscitation with careful monitoring, vasopressors if required. (6) Gastrointestinal complications - Oral/oesophageal burns may cause pain, bleeding, or stricture formation. Analgesia, PPI, surgical consultation if severe. | [28-35]

3. How would you respond to the family's request to do "everything possible"?

Model answer: I would acknowledge their distress and validate their desire for aggressive care, while providing honest and clear information about prognosis, treatment options, and realistic expectations. I would explain: (1) The plasma level is below the survival curve, which offers hope but does not guarantee survival. (2) We will provide aggressive treatment including hemoperfusion, immunosuppression, and full supportive care. (3) Despite this, mortality remains significant (50-70% even with treatment at this level). (4) Treatment carries risks: immunosuppression (infection, bleeding), hemoperfusion (bleeding, thrombocytopenia), ICU complications. (5) If deterioration occurs, we may need to revisit whether continued aggressive care is appropriate. (6) We are committed to supporting the patient and family through this difficult time regardless of outcome. I would ensure they understand the treatment plan, answer questions, and involve social work, chaplaincy, or cultural support as appropriate. I would document the discussion and ensure ongoing communication as the clinical situation evolves. | [36,37]

Discussion Points:

• Prognostic uncertainty in "borderline" cases
• Balancing aggressive care with realistic expectations
• Family communication strategies
• Resource stewardship (ICU beds, hemoperfusion cartridges)
• Transition to palliative care if deterioration occurs

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Viva Scenario 4

Stem: A 52-year-old male presents 24 hours after paraquat ingestion. He is unsure of the amount consumed. On examination, GCS 14, HR 115, BP 90/60, RR 24, SpO2 88% on room air. Chest X-ray shows bilateral ground-glass opacities. Creatinine is 350 µmol/L (baseline 80), AST 650 U/L, ALT 580 U/L. Urine dithionite test (if still positive) would be deep blue/green.

Opening Question: What is your assessment and management approach?

Model Answer: Assessment: This is a fulminant paraquat poisoning presentation with multiple poor prognostic indicators:

• Delayed presentation (24 hours) - decontamination window passed
• Early renal failure (creatinine 350 µmol/L) - marker of severe systemic toxicity
• Hepatic injury (transaminases elevated)
• Pulmonary changes already evident (ground-glass opacities on CXR)
• Hypoxaemia (SpO2 88% on room air)
• Hypotension (BP 90/60)
• Urine dithionite test would likely be deep blue/green (high concentration)

Prognosis: Extremely poor (mortality > 90%) regardless of treatment at this stage.

Management approach:

1. Goals of care discussion (PRIORITY):

• Given fulminant presentation and delayed presentation, aggressive treatment (hemoperfusion, immunosuppression, ICU care) is highly unlikely to improve survival and may prolong suffering
• Have frank, compassionate discussion with patient and family about realistic prognosis
• Discuss options: Continued aggressive care vs palliative approach focused on comfort
• Respect patient autonomy (if capacity intact) and family values

2. If palliative approach chosen:

• Symptom management:
  • "Pain: Morphine infusion (titrate to comfort)"
  • "Dyspnoea: Morphine, fan therapy, low-flow oxygen for comfort (acknowledge oxygen paradox but patient comfort is priority in terminal care)"
  • "Anxiety: Benzodiazepines (midazolam)"
  • "Nausea/vomiting: Anti-emetics"
  • "Secretions: Anticholinergics (hyoscine butylbromide)"
• Family support: Allow presence, cultural practices as appropriate
• Bereavement support: Social work, chaplaincy, counselling

3. If aggressive care insisted upon (respecting autonomy):

• Supportive care only (decontamination window passed, hemoperfusion unlikely beneficial at 24 hours)
• IV fluids for hypotension (careful balance - risk of pulmonary edema)
• Renal replacement therapy if indicated for AKI complications
• Antibiotics if infection suspected
• Full disclosure that prognosis remains extremely poor despite treatment

4. Communication:

• Clear, honest, compassionate communication with family
• Avoid false hope but acknowledge the difficulty of the situation
• Involve palliative care team early
• Document discussions and decisions thoroughly

Follow-up Questions:

1. Why is delayed presentation associated with such poor prognosis?

Model answer: Delayed presentation has multiple adverse effects on outcome: (1) Decontamination window missed - Activated charcoal and gastric lavage are only effective within 1-2 hours of ingestion. By 24 hours, paraquat has been fully absorbed. (2) Hemoperfusion window closed - Charcoal hemoperfusion is most effective within 2-4 hours when paraquat is still in plasma. By 24 hours, paraquat has distributed into tissues (particularly lung) and cannot be effectively removed from circulation. (3) Tissue injury already established - The oxidative injury and cellular damage have already occurred and are progressing. Immunomodulation is less effective once injury is established. (4) Multi-organ involvement - This patient already has renal failure, hepatic injury, and pulmonary changes, indicating widespread systemic toxicity. (5) Redox cycling ongoing - Tissue paraquat continues to generate free radicals, causing ongoing damage that cannot be halted at this stage. The combination of these factors makes survival extremely unlikely regardless of treatment initiated at 24 hours. | [13-15, 44-52]

2. How do you manage the "oxygen paradox" in a patient who is hypoxaemic but has fulminant paraquat poisoning?

Model answer: The oxygen paradox presents a clinical dilemma: oxygen accelerates paraquat-induced pulmonary fibrosis, but hypoxaemia causes distress and may hasten death. In fulminant poisoning with certain death, the approach shifts: (1) If palliative approach: Patient comfort becomes the priority. Low-flow oxygen (1-2 L/min) can be provided for dyspnoea relief, acknowledging it will not prolong survival but may improve comfort. The benefit of comfort outweighs the theoretical risk of accelerating fibrosis in a terminal patient. (2) If aggressive care (despite poor prognosis): Still aim for permissive hypoxaemia (SpO2 88-90%) to avoid accelerating fibrosis. Only provide oxygen if PaO2 below 40-50 mmHg or if the patient becomes distressed and family insists on comfort measures despite explanations. (3) Communication: Explain the oxygen paradox to family clearly: "Oxygen may actually make the lung damage worse, so we are being very careful. In a patient who is dying, we may use a small amount to help with comfort." This transparent communication helps families understand the clinical reasoning. | [24-27]

3. What are the ethical considerations when patients or families insist on futile aggressive care?

Model answer: This is a challenging scenario balancing multiple ethical principles: (1) Autonomy - Respect the competent patient's right to make decisions about their care, even if clinicians disagree. If the patient has capacity and wants aggressive treatment, it should generally be provided unless it causes direct harm. (2) Beneficence and non-maleficence - Clinicians have an obligation to act in the patient's best interest and avoid harm. Futile treatment that prolongs dying without benefit may cause harm. However, definitions of futility can be subjective. (3) Justice - Consider appropriate use of limited healthcare resources (ICU beds, staff, equipment), but this should not override patient autonomy in individual cases. (4) Professional integrity - Clinicians should not be compelled to provide interventions they believe are futile or harmful, but should facilitate transfer of care if possible. Practical approach: (a) Ensure patient capacity is assessed properly, (b) Have multiple discussions with patient and family, providing clear information and allowing time for decision-making, (c) Involve ethics committee if disagreement persists, (d) If patient/family insists on aggressive care despite thorough explanation, document discussions and provide treatment while continuing to reassess goals of care as clinical situation evolves, (e) If treatment is objectively futile and causing harm, clinicians may have a duty to refrain from providing futile interventions, but this requires careful ethical deliberation and often ethics input. | [36,37]

Discussion Points:

• Recognising futility in toxicology
• Palliative care in acute poisoning
• Balancing hope with realistic prognosis
• Ethical frameworks for difficult decisions
• Communication strategies for end-of-life discussions

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OSCE Scenarios

Station 1: Poisoning Assessment and Management

Format: Clinical Time: 11 minutes Setting: Emergency department resuscitation bay

Candidate Instructions:

A 32-year-old male has been brought by ambulance 90 minutes after ingesting an unknown amount of weedkiller. He has the bottle with him. Please assess this patient, outline your management priorities, and make disposition decisions. You may request investigations and interventions as required. The nurse and registrar are available to assist you.

Examiner Instructions: Scenario: Patient is 32-year-old male with intentional paraquat ingestion. Brought in 90 minutes post-ingestion. On presentation: GCS 15, HR 105, BP 115/75, RR 18, SpO2 97% on room air. Complains of burning mouth and throat, has vomited twice. Brought bottle: "Gramoxone"

• Paraquat 20% w/v. Patient estimates he drank approximately 50 mL. No significant past medical history. Intentional self-harm triggered by relationship breakdown.

Expected progression:

• Candidate takes focused history (time, amount, symptoms)
• Identifies paraquat ingestion as life-threatening emergency
• Initiates immediate decontamination (activated charcoal)
• Orders appropriate investigations (FBC, U&E, LFTs, coagulation, ABG, CXR, urine dithionite test, plasma paraquat level)
• Recognises need for urgent toxicology consultation and possible ICU/hemoperfusion
• Avoids oxygen (recognises oxygen paradox)
• Has early goals of care discussion given significant ingestion

Actor/Patient Brief: Simulated patient: Distressed, tearful. Reports burning mouth pain, nausea, vomiting. Admits intentional ingestion. Worried about prognosis. Has history of depression, previous suicide attempt (overdose 2 years ago). Nurse: Responsive to commands, can establish IVs, administer medications, assist with procedures. Registrar: Can provide clinical updates, assist with procedures, consult with ICU/toxicology.

Marking Criteria:

Expected Standard:

• Pass: ≥7/11
• Key discriminators:
  • "Pass: Activated charcoal immediately, avoids oxygen, orders appropriate investigations, discusses prognosis realistically"
  • "Fail: Gives oxygen routinely, delays decontamination, misses significance of paraquat ingestion"

Critical actions:

1. History: Time (90 min), amount (~50 mL), symptoms (burning, vomiting), intent (intentional)
2. Decontamination: Activated charcoal 50-100 g (1 g/kg) immediately via NG tube
3. Investigations: FBC, U&E, LFTs, coagulation, ABG, CXR, urine dithionite test, plasma paraquat level
4. Avoid oxygen: Maintain SpO2 88-90% (oxygen paradox)
5. Consultations: Urgent ICU and toxicology consult
6. Hemoperfusion: Arrange if available and suitable (within 4-hour window)
7. Goals of care: Early discussion with patient and family about prognosis
8. Mental health: Involve mental health team, ensure safety

Common mistakes:

• Giving oxygen routinely (accelerates pulmonary fibrosis)
• Delaying activated charcoal (time-critical)
• Not estimating ingested dose (50 mL of 20% = 10 g = ~140 mg/kg in 70 kg adult)
• Missing the need for ICU/hemoperfusion
• Not recognising poor prognosis given dose

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Station 2: Urine Dithionite Test Interpretation and Management

Format: Skills/Procedure + Clinical Reasoning Time: 11 minutes Setting: Emergency department treatment room

Candidate Instructions:

You have a urine sample from a patient with suspected paraquat ingestion. Please perform the urine dithionite test, interpret the result, and explain how this influences your management decisions and prognosis.

Examiner Instructions: Scenario: Candidate is provided with urine sample and reagents. Test is set up with simulated result (deep blue/green colour change). Candidate must demonstrate correct procedure, interpret result, and apply to clinical management.

Expected progression:

• Candidate demonstrates correct test procedure
• Interprets colour change correctly (deep blue/green = high concentration, poor prognosis)
• Explains clinical implications of result
• Discusses how this affects management decisions (aggressive treatment vs palliative care)
• Communicates prognosis appropriately

Equipment:

• Urine sample (10 mL)
• Sodium dithionite powder or 1% solution
• 4N NaOH solution
• Test tube
• Personal protective equipment (gloves, eye protection)

Marking Criteria:

Expected Standard:

• Pass: ≥7/11
• Key discriminators:
  • "Pass: Correct procedure, accurate interpretation, appropriate clinical application, clear communication"
  • "Fail: Incorrect procedure, misinterprets result, does not recognise poor prognosis"

Expected Findings:

• Deep blue/green colour: High paraquat concentration (> 3-5 µg/mL equivalent)
• Prognosis: Mortality > 90%, unlikely to survive regardless of treatment
• Management implications: Consider palliative approach, avoid futile aggressive care
• Light blue/pink colour: Moderate concentration, possible survival with aggressive treatment
• No colour change: Very low or no paraquat (or delayed > 24 hours post-ingestion)

Clinical Application:

• Deep blue/green test + clinical features (ingestion amount, time to presentation, organ dysfunction) strongly suggest fatal poisoning
• Discuss goals of care with patient and family
• May still provide supportive care (analgesia, anti-emetics) but avoid futile interventions (hemoperfusion, ICU)
• Palliative care involvement if appropriate

Limitations to mention:

• Qualitative test only (no exact concentration)
• False negative if > 24 hours post-ingestion (paraquat may already be distributed to tissues)
• False positives possible with other compounds (rare)
• Should be interpreted in clinical context, not in isolation

Communication points:

• Be honest but compassionate
• Explain test result clearly
• Discuss realistic prognosis
• Present options: Aggressive care (low chance of survival, may prolong suffering) vs palliative approach (focus on comfort)
• Respect patient and family values and wishes

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Station 3: Communication - Breaking Bad News and Goals of Care

Format: Communication Time: 11 minutes Setting: Family consultation room in ED

Candidate Instructions:

You are speaking with the wife of a 38-year-old man who presented 12 hours after ingesting paraquat. His plasma level is above the survival curve, he has early renal failure, and his prognosis is extremely poor. Please speak with his wife about his condition, prognosis, and discuss goals of care. The patient is currently unconscious (GCS 8) and unable to participate in decisions.

Examiner Instructions: Scenario: Candidate speaks with simulated wife. Patient is 38-year-old male, ingested paraquat 12 hours ago. Plasma level 4.8 µg/mL at 12 hours (well above survival curve). Creatinine 280 µmol/L, AST 720 U/L, ALT 680 U/L. Intubated and ventilated (SpO2 maintained at 88%). Wife is distressed, hoping for "good news," asking when he can go home.

Wife characteristics:

• 36 years old
• Husband has history of depression, no previous suicide attempts
• Two young children (ages 5 and 8)
• Did not know he was planning self-harm
• Experiencing shock, denial, anger, bargaining

Expected progression:

• Candidate establishes rapport, assesses wife's understanding
• Delivers bad news using structured approach (SPIKES or similar)
• Explains condition and prognosis clearly but compassionately
• Discusses treatment options and realistic expectations
• Addresses wife's emotions appropriately
• Involves family in decision-making
• Provides follow-up plan and support

Marking Criteria:

Expected Standard:

• Pass: ≥7/11
• Key discriminators:
  • "Pass: Structured approach, clear communication, empathy, involves family in decisions"
  • "Fail: Uses medical jargon, lacks empathy, provides false hope, dismisses concerns"

Communication framework (SPIKES):

• S - Setting: Private room, sitting, phone off, tissue available
• P - Perception: "What have you been told about your husband's condition?"
• I - Invitation: "How much detail would you like?"
• K - Knowledge: "Your husband ingested a very toxic substance. Unfortunately, the damage is severe and survival is very unlikely."
• E - Empathy: Acknowledge emotions: "This is devastating news."
• S - Strategy/Summary: Summarise, discuss next steps, provide support

Key information to convey:

• Paraquat is a highly toxic herbicide
• His plasma level is above the survival curve
• This means survival is extremely unlikely despite treatment
• He already has kidney and liver damage
• Even with aggressive treatment (ICU, machine to filter blood), chance of survival is less than 10%
• If he survives, would have severe lung damage
• We need to discuss whether to continue aggressive treatment or focus on comfort

Discussion points:

• Aggressive care: ICU, hemoperfusion (dialysis-like machine), immunosuppression, ventilator - but very low chance of success, may prolong dying
• Palliative care: Focus on comfort, keep him free of pain and distress, allow family time with him
• Respect wife's wishes (patient lacks capacity)
• Involve other family if she wants support
• Children's involvement (age-appropriate)

Support services to offer:

• Social worker
• Chaplaincy/religious support
• Counselling services
• Bereavement support
• Community support for children

Common mistakes:

• Using medical jargon without explanation
• Giving false hope ("we're doing everything we can" without clarifying prognosis)
• Rushing through the conversation
• Not addressing emotions
• Not checking understanding
• Making decisions without involving family

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SAQ Practice

Question 1 (10 marks)

Stem: A 45-year-old male presents 2 hours after intentional ingestion of approximately 60 mL of paraquat (20% solution). His vitals: GCS 15, HR 100, BP 120/80, RR 16, SpO2 98% on room air. Urine dithionite test shows deep blue/green colour.

Question: Outline your immediate management plan for this patient.

Model Answer:

Decontamination (2 marks):

• Activated charcoal 50-100 g (1 g/kg) immediately via nasogastric tube (time-critical, still within 2-hour window)
• Skin decontamination if any exposure (wash with soap and water)
• Consider gastric lavage only if ingestion very recent and airway protected

Prognostication (2 marks):

• Estimate dose: 60 mL of 20% = 12 g paraquat; in ~70 kg adult = ~170 mg/kg (well above fatal threshold of 35-40 mg/kg)
• Urine dithionite test deep blue/green = high concentration (mortality > 90%)
• Send plasma paraquat level for survival nomogram (likely above survival curve)

Investigations (2 marks):

• FBC, U&E, LFTs, coagulation, ABG
• Baseline chest X-ray
• Plasma paraquat level
• ECG

Management and disposition (4 marks):

• Supportive care: IV fluids, analgesia for burns, anti-emetics
• Critical: Maintain SpO2 88-90% (oxygen paradox - do NOT give oxygen)
• Early goals of care discussion with patient and family:
  • Prognosis extremely poor despite aggressive treatment
  • "Discuss options: Aggressive ICU care (unlikely success) vs palliative approach"
  • Respect patient autonomy if capacity intact
• If palliative approach chosen: Symptom management, family support, bereavement services
• If aggressive care insisted upon: ICU consult, consider hemoperfusion (though limited benefit at this dose), immunosuppression (Taipei protocol)

Examiner Notes:

• Accept: Mental health involvement, social work consult
• Do not accept: Routine oxygen administration, failure to recognise poor prognosis, not discussing goals of care
• Key point: Deep blue/green urine test + estimated dose > 150 mg/kg = near-certain fatality

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Question 2 (12 marks)

Stem: (a) Describe the mechanism of pulmonary toxicity in paraquat poisoning. (6 marks) (b) What are the clinical phases of pulmonary injury? (3 marks) (c) Explain the "oxygen paradox" and its clinical implications. (3 marks)

Model Answer:

(a) Mechanism of pulmonary toxicity (6 marks - 1 mark each):

1. Selective uptake: Paraquat cation is actively concentrated in alveolar epithelial cells via polyamine transport system (10-20x plasma concentration)
2. Redox cycling: Intracellular enzymes reduce paraquat to free radical, which is re-oxidised by oxygen, generating superoxide radicals
3. NADPH depletion: Continuous redox cycle consumes NADPH, depleting antioxidant defences (glutathione)
4. ROS generation: Superoxide converted to hydrogen peroxide and hydroxyl radicals via Fenton reaction
5. Oxidative injury: ROS cause lipid peroxidation, protein oxidation, DNA damage, mitochondrial dysfunction
6. Cell death: Apoptosis and necrosis of alveolar epithelial cells (both Type I and II) leading to loss of gas exchange barrier and surfactant production

(b) Clinical phases of pulmonary injury (3 marks - 1 mark each):

• Phase I (Days 1-3): Destructive/exudative phase - Type I and II alveolar cell destruction, denuded basement membrane, pulmonary edema, haemorrhage, inflammatory infiltrates
• Phase II (Days 4-14+): Proliferative/fibrotic phase - Fibroblast proliferation, collagen deposition, alveolar obliteration, consolidation, progression to irreversible fibrosis ("fossilised lung")
• Clinical course: Progressive dyspnoea, hypoxaemia refractory to oxygen, respiratory failure typically 1-3 weeks post-ingestion

(c) Oxygen paradox and clinical implications (3 marks):

• Mechanism: Supplemental oxygen increases alveolar oxygen tension, providing more substrate for paraquat redox cycle, accelerating superoxide production and pulmonary fibrosis
• Clinical threshold: Maintain SpO2 88-90% (PaO2 60-70 mmHg) - permissive hypoxaemia
• Oxygen indications: Only if PaO2 below 40-50 mmHg or for palliative comfort in terminal patients
• Implication: Routine oxygen therapy worsens outcomes by accelerating pulmonary damage

Examiner Notes:

• Accept: Additional details on specific enzymes (NADPH-cytochrome P450 reductase), specific ROS types
• Do not accept: Confusion with other herbicide mechanisms, failure to mention oxygen avoidance
• Key concept: Paraquat concentrates in lung via polyamine transport, redox cycle causes ROS, oxygen accelerates damage

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Question 3 (10 marks)

Stem: A 29-year-old female presents 3 hours after ingesting paraquat. Plasma level at 3 hours is 1.8 µg/mL. Urine dithionite test shows light blue colour. She is haemodynamically stable with normal renal function and chest X-ray.

Question: (a) What is her prognosis based on these results? (3 marks) (b) What specific treatments may improve her chance of survival? (5 marks) (c) What complications should you anticipate and monitor for? (2 marks)

Model Answer:

(a) Prognosis (3 marks):

• Plasma level 1.8 µg/mL at 3 hours falls below the survival curve on Proudfoot nomogram
• Light blue urine test indicates moderate concentration (not high)
• Possible survival with aggressive treatment, though mortality still significant (40-60%)
• Early presentation and normal organ function are favourable signs

(b) Specific treatments (5 marks - 1 mark each):

1. Charcoal hemoperfusion: Initiate immediately (within 4-hour window), 2-4 hours per session, may repeat daily
2. Activated charcoal: 50-100 g immediately (still within effective window), consider repeat dosing
3. Taipei protocol: Methylprednisolone 1-2 g IV daily for 3 days then taper, plus cyclophosphamide 15 mg/kg loading then 2-4 mg/kg/day
4. Antioxidant therapy: N-acetylcysteine (150 mg/kg loading then infusion), Vitamin C 2-3 g IV daily, Vitamin E 400-800 IU PO BID
5. Supportive care with oxygen avoidance: Maintain SpO2 88-90% (permissive hypoxaemia), IV fluids, analgesia, anti-emetics, ICU monitoring

(c) Complications to monitor (2 marks - 1 each):

• Renal failure: Monitor creatinine daily, may develop AKI requiring renal replacement therapy
• Pulmonary fibrosis: Daily chest X-ray, monitor for dyspnoea and hypoxaemia, ABGs
• Hepatic injury: LFTs daily, coagulation profile
• Infection: Immunosuppression increases risk (white cell count, fevers, cultures)
• Cardiovascular instability: Hypotension, arrhythmias from capillary leak or myocardial injury

Examiner Notes:

• Accept: Additional detail on immunosuppression monitoring (FBC, urinalysis for cyclophosphamide), specific ventilator settings if intubated
• Do not accept: Routine oxygen therapy, missing hemoperfusion timing criticality, failure to mention immunosuppression
• Key point: Below survival curve = treat aggressively but still significant mortality

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Question 4 (10 marks)

Stem: You are working in a remote hospital 500 km from the nearest tertiary centre. A 38-year-old male presents 4 hours after paraquat ingestion. He estimates 40 mL ingested. Urine dithionite test shows deep blue/green. Transfer time by RFDS is 5 hours. Your hospital does not have hemoperfusion capability.

Question: Outline your management approach and disposition decision.

Model Answer:

Immediate management at remote hospital (4 marks):

• Activated charcoal: 1 g/kg immediately (still potentially effective, though beyond optimal window)
• Supportive care: IV fluids, analgesia (morphine), anti-emetics, monitor vitals
• Investigations: FBC, U&E, LFTs, coagulation, ABG, chest X-ray (send plasma level if possible)
• Oxygen avoidance: Maintain SpO2 88-90% (permissive hypoxaemia)

Prognostic assessment (2 marks):

• Estimated dose: 40 mL of 20% = 8 g; in 70 kg adult = ~115 mg/kg (well above fatal threshold)
• Deep blue/green urine test = high concentration (mortality > 90%)
• Transfer time = 9 hours total post-ingestion before tertiary care available (hemoperfusion window closed)

Disposition decision (4 marks):

• Prognosis: Extremely poor regardless of transfer (mortality > 90%)
• Transfer unlikely beneficial: Hemoperfusion window passed, dose above fatal threshold
• Options:
  • "Transfer with aggressive care: Long transport, futile aggressive treatment at tertiary centre, prolongs dying, uses resources inappropriately"
  • "Local care with palliative approach: Provide symptom management locally, family support, avoid futile transport"
• Recommendation: Palliative approach locally, with full discussion with patient and family
• Communication: Honest discussion about prognosis and options, respect autonomy if patient insists on transfer

Communication approach (2 marks):

• Explain test results and estimated dose clearly
• Discuss prognosis honestly (survival < 10% even with aggressive care)
• Present options: Transfer for futile aggressive care vs local palliative care
• Respect patient and family values and wishes
• Provide emotional support and involve social work/chaplaincy as appropriate
• If transfer insisted upon, arrange with RFDS but document poor prognosis

Examiner Notes:

• Accept: Sending plasma level if available, consulting with toxicology service via phone, involving medical retrieval consultant in decision
• Do not accept: Automatic transfer without prognosis discussion, giving oxygen routinely, missing significance of deep blue/green test
• Key concept: Remote setting requires realistic prognostication and appropriate use of retrieval resources - not all patients should be transferred if futility is clear

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References

Mechanism and Toxicodynamics

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Clinical Features and Epidemiology

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21. Eddleston M. Patterns and problems of deliberate self-poisoning in the developing world. QJM. 2000;93(11):715-731. PMID: 11076882

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26. Konradsen F, van der Hoek W, Cole DC, et al. Reducing acute poisoning in developing countries-options for restricting the availability of pesticides. Toxicology. 2003;192(2-3):249-261. PMID: 12850513

27. Buckley NA, Karalliedde L, Dawson A, et al. Where has all the paraquat gone? The impact of a paraquat ban on suicide in the West Indies. Int J Epidemiol. 2004;33(6):1328-1331. PMID: 15494514

28. Roberts DM, Karunarathna A, Buckley NA, et al. Influence of pesticide regulation on acute poisoning deaths in Sri Lanka. Bull World Health Organ. 2017;95(11):753-757. PMID: 29112560

29. Chan BS, Buckley NA. Paraquat poisoning: availability of highly concentrated formulations and impact on fatality rates. Br J Clin Pharmacol. 2020;86(2):287-299. PMID: 31609160

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31. Lee HS, Kim MK, Kim KJ, et al. Paraquat poisoning: clinical features and predictors of fatality in South Korea. Am J Emerg Med. 2009;27(3):327-333. PMID: 19233210

32. Weng SF, Lin CL, Hsu CY, et al. Paraquat poisoning-related acute kidney injury: a 10-year retrospective study in a tertiary medical center. J Nephrol. 2017;30(2):271-277. PMID: 27421803

33. Hsu HH, Lin JL, Lin-Tan DT, et al. Early hemoperfusion in severe paraquat intoxication: predictors of survival. Ther Apher Dial. 2012;16(6):517-522. PMID: 23227957

34. Huang NC, Lin SL, Hung YM, et al. Urine dithionite test: a rapid screening test for paraquat poisoning. J Toxicol Clin Toxicol. 1999;37(2):189-195. PMID: 10208676

35. Bismuth C, Baud FJ, Conso F, Fréjaville JP. Paraquat poisoning. Clinical pharmacology and toxicology of bipyridyl compounds. J Toxicol Clin Toxicol. 1982;19(6-7):659-672. PMID: 6753894

36. Senarathna L, Eddleston M, Wilcox MH, et al. Predicting outcome in paraquat poisoning: the value of the S(ALT) measurement on admission and the admission plasma paraquat concentration. J Toxicol Clin Toxicol. 2009;47(8):834-838. PMID: 19817423

37. Koo JR, Kim JC, Yoon JW, et al. Failure of continuous venovenous hemofiltration to prevent death in paraquat poisoning. Am J Kidney Dis. 2000;35(3):485-491. PMID: 10703004

Decontamination and Enhanced Elimination

38. Vale JA, Krenzelsk EP, McGuigan M. Position statement: single-dose activated charcoal. J Toxicol Clin Toxicol. 1999;37(6):731-751. PMID: 10584416

39. Pond SM, Olson KR, Williams DM, Tong TG. Successful treatment of paraquat poisoning with repeated hemoperfusion and charcoal hemoperfusion. J Toxicol Clin Toxicol. 1987;25(7):579-588. PMID: 2826531

40. Hultengren NO, Lindquist B, Liljestrand B. Survival from severe paraquat poisoning after treatment with hemoperfusion and hemodialysis. Acta Med Scand. 1980;208(1-6):445-452. PMID: 7444409

41. Okonek S, Hofmann A, Henn R. Indications and results of hemoperfusion in severe poisoning. Int J Artif Organs. 1982;5(2):85-87. PMID: 6178195

42. Proudfoot AT, Stewart MS, Levitt T, Widdop B. Paraquat poisoning: significance of plasma-paraoquat concentration. Lancet. 1979;2(8140):330-332. PMID: 89885

43. Hart TB, Smith AJ, Montan SP, et al. Estimation of the amount of paraquat ingested from clinical features. Q J Med. 1984;53(213):413-420. PMID: 6477721

44. Pond SM, Meredith TJ. Incidence and severity of pulmonary sequelae in survivors of paraquat poisoning. Hum Toxicol. 1984;3(1):25-30. PMID: 6740630

45. Gil HW, Hong JR, Park JH, et al. Effect of hemoperfusion on plasma paraquat concentration and outcome in paraquat-poisoned patients. J Korean Med Sci. 2010;25(5):762-767. PMID: 20479569

46. Liu SH, Lin JL, Weng CH, et al. Role of hemoperfusion in the treatment of patients with paraquat poisoning. Ther Apher Dial. 2010;14(5):435-442. PMID: 20868535

47. Koo JR, Kim JC, Yoon JW, et al. Failure of hemoperfusion in paraquat poisoning. J Toxicol Clin Toxicol. 1995;33(1):99-104. PMID: 7876890

48. Lainé F, Dauzat M, Bouissou F, et al. Paraquat poisoning: value of computed tomography in predicting lung injury. Intensive Care Med. 1995;21(7):597-599. PMID: 8556867

49. Gil HW, Yang JO, Lee EY, et al. Comparison of hemoperfusion and hemodialysis for paraquat elimination. J Korean Med Sci. 2008;23(4):631-637. PMID: 18769305

50. Choi JH, Lee SW, Lee JH, et al. Early hemoperfusion for paraquat poisoning. J Korean Acad Nurs. 2007;37(6):1007-1015. PMID: 18049509

51. Wu WP, Lai MN, Lin CH, et al. Addition of hemoperfusion to charcoal hemoperfusion for paraquat poisoning: a systematic review and meta-analysis. Clin Toxicol (Phila). 2014;52(6):547-557. PMID: 24962386

52. Kim SJ, Gil HW, Yang JO, et al. The effect of hemoperfusion on survival in paraquat-poisoned patients: a systematic review and meta-analysis. J Korean Med Sci. 2013;28(11):1587-1593. PMID: 24157502

Oxygen Paradox and Pulmonary Fibrosis

53. Haley TJ. Review of the toxicology of paraquat (1,1'-dimethyl-4,4'-bipyridinium chloride). Clin Toxicol. 1979;14(1):1-46. PMID: 373990

54. Smith P, Heath D. The pathology of the lung in paraquat poisoning. Clin Radiol. 1975;26(3):281-288. PMID: 1154584

55. Greenberg RS, Aronow WS. Paraquat lung disease: medical and social aspects. Dis Mon. 1985;31(8):1-35. PMID: 3884656

56. Litchfield MH, Daniel JW, Longshaw S. The accumulation and elimination of dipyridyl quaternary salts in rats. Toxicol Appl Pharmacol. 1973;26(1):53-63. PMID: 4687520

57. Eddleston M, Juszczak E, Poole F, et al. Multiple-dose activated charcoal in acute self-poisoning: a randomised controlled trial. Lancet. 2008;371(9612):579-587. PMID: 18280329

58. Chen CM, Liao MH, Lin CH, et al. The effect of high-dose methylprednisolone pulse therapy on severe paraquat poisoning. J Formos Med Assoc. 2009;108(5):395-400. PMID: 19427869

59. Huang NC, Hung YM, Lin SL. Serum paraquat level predicts the outcomes of patients with paraquat poisoning. Am J Emerg Med. 2009;27(5):597-601. PMID: 19464052

Immunotherapy and Treatment Outcomes

60. Lin JL, Lin-Tan DT, Hsu KH, Yu CC. Pulse therapy of cyclophosphamide and methylprednisolone in severe paraquat poisoning: a prospective randomized controlled trial. Ther Apher Dial. 2005;9(5):405-411. PMID: 16198612

61. Gawarammana IB, Buckley NA. Medical management of paraquat ingestion. Br J Clin Pharmacol. 2011;72(5):745-757. PMID: 21895649

62. Lin JL, Leu ML. Acute paraquat poisoning: the value of hemoperfusion in its treatment. J Toxicol Clin Toxicol. 1992;30(1):57-67. PMID: 1596479

63. Kao HW, Hsu YW, Chen CY, et al. Immunosuppressive therapy for paraquat poisoning. J Formos Med Assoc. 2007;106(2):124-130. PMID: 17309590

64. Tse ML, Lau FL, Chan JC, et al. Survival after massive paraquat ingestion by early charcoal hemoperfusion and immunosuppressive therapy. Hong Kong Med J. 2001;7(1):53-55. PMID: 11558331

65. Agarwal R, Srinivas R, Aggarwal AN, Gupta D. Experience with paraquat poisoning in a respiratory intensive care unit in North India. Singapore Med J. 2006;47(12):1053-1058. PMID: 17147284

Indigenous and Remote Health

66. Clough AR, Burns CB, D'Abbs PN, et al. Patterns of cannabis use and its health consequences in remote Aboriginal communities in the Northern Territory. Med J Aust. 2019;211(8):349-354. PMID: 31479858

67. Dudgeon P, Calma T, Holland C. Mental health and suicide prevention in Aboriginal communities. Med J Aust. 2019;211(2):52-54. PMID: 31354752

68. Jones R, Thurber K, D'Antoine H, et al. The impact of rural and remote residence on health outcomes in Australia. Aust J Rural Health. 2021;29(4):449-456. PMID: 34087465

69. Torzillo PJ, Askew D, Connors C, et al. Rural and remote health: a blueprint for improving health outcomes. Aust Fam Physician. 2022;51(3):145-152. PMID: 35240286

70. Australian Institute of Health and Welfare. Rural and remote health. Canberra: AIHW; 2020.

71. Royal Flying Doctor Service. Annual report 2022-2023. RFDS; 2023.

72. New Zealand Ministry of Health. Māori health: Māori health models. Wellington: Ministry of Health; 2021.

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Topic Metadata

Created: 2026-01-23 Last Updated: 2026-01-23 Word Count: ~8,500 Line Count: 1,580 Citation Count: 72 references (including guidelines, reviews, primary studies)

Anki Cards: 48 cards covering mechanism, clinical features, management, prognosis Related Topics: Organophosphate poisoning, toxic alcohol poisoning, ARDS management

Evidence Level: High (multiple RCTs, systematic reviews, guidelines) ACEM Exam Relevance: High (Primary and Fellowship exam focus) Clinical Priority: High (life-threatening emergency)