Mechanical Ventilation in the Emergency Department

Quick Answer

One-liner: Mechanical ventilation is life-saving support for respiratory failure, requiring immediate implementation of lung-protective strategies to prevent ventilator-induced lung injury while optimizing oxygenation and ventilation.

Emergency physicians must initiate ventilation with lung-protective settings (tidal volume 6-8 mL/kg predicted body weight, plateau pressure below 30 cmH2O) from the first breath. The LOV-ED trial (PMID: 29049118) demonstrated that early implementation of lung-protective ventilation in the ED significantly reduces ARDS development and improves outcomes. Critical errors include using actual body weight instead of predicted body weight, allowing plateau pressures greater than 30 cmH2O, and failing to recognize patient-ventilator dyssynchrony.

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ACEM Exam Focus

Primary Exam Relevance

• Anatomy: Tracheobronchial tree, lung zones, dead space (anatomical 2 mL/kg vs physiological)
• Physiology: Compliance (ΔV/ΔP), resistance (ΔP/flow), work of breathing, V/Q matching, oxygen delivery (DO2 = CO × CaO2 × 10)
• Pharmacology: Sedation (propofol, midazolam, ketamine), analgesia (fentanyl, morphine), neuromuscular blockade (rocuronium, cisatracurium)

Fellowship Exam Relevance

• Written: Initial ventilator settings, ARDS ventilation strategy, troubleshooting high peak pressures, auto-PEEP recognition, weaning parameters
• OSCE: Ventilator setup, managing patient-ventilator dyssynchrony, ARDS protocol implementation, discussing disposition with ICU
• Key domains tested: Medical Expert (ventilator modes, settings), Communicator (explaining ventilation to family), Leader (coordinating ICU transfer)

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Key Points

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Epidemiology

Australian/NZ Specific

• ANZICS APD Registry: 12,000+ mechanically ventilated patients annually across Australia/NZ ICUs
• ED ventilation times: Median 2-4 hours in ED before ICU transfer (metropolitan); up to 12-24 hours in regional/remote settings
• Indigenous populations: Aboriginal and Torres Strait Islander patients have 3-5× higher rates of chronic respiratory disease requiring ventilation
• RFDS retrievals: Mechanical ventilation is required in 15-20% of critical care retrievals

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Pathophysiology

Respiratory Failure Mechanisms

Type I (Hypoxemic): V/Q mismatch, shunt, diffusion impairment

• Examples: Pneumonia, ARDS, pulmonary edema, pulmonary embolism
• PaO2 below 60 mmHg on room air despite supplemental oxygen
• Responds to increased FiO2 and PEEP (recruitment)

Type II (Hypercapnic): Alveolar hypoventilation

• Examples: COPD, asthma, neuromuscular disease, CNS depression
• PaCO2 greater than 50 mmHg with pH below 7.35
• Requires increased minute ventilation (RR × TV)

Ventilator-Induced Lung Injury (VILI)

High Tidal Volumes → Alveolar Overdistension (Volutrauma)
High Plateau Pressure → Barotrauma (Pneumothorax)
Cyclic Opening/Closing → Atelectrauma
Inflammatory Cascade → Biotrauma → Multi-Organ Failure

Why It Matters Clinically: The ARDSNet trial (PMID: 10793162) showed that reducing tidal volume from 12 mL/kg to 6 mL/kg decreased mortality from 39.8% to 31.0%. Every breath delivered in the ED matters—protective ventilation must start immediately.

Auto-PEEP Mechanism

In obstructive disease (asthma, COPD), prolonged expiratory time is needed for complete exhalation. If expiratory time is insufficient:

Breath 1 (500 mL) + Breath 2 (500 mL) → Stacking → ↑ Intrathoracic Pressure → ↓ Venous Return → Cardiovascular Collapse

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Clinical Approach

Recognition: Indications for Mechanical Ventilation

Absolute Indications:

• Apnea or respiratory arrest
• Severe hypoxemia despite maximal non-invasive support (PaO2 below 50 mmHg on NRB)
• Inability to protect airway (GCS ≤8)
• Severe acidosis (pH below 7.15) with respiratory cause

Relative Indications:

• Progressive respiratory distress (RR greater than 35, accessory muscle use)
• Impending airway obstruction
• Anticipated clinical course (e.g., pre-procedural for agitated patient)
• Hemodynamic instability requiring high work of breathing reduction

Initial Assessment

Primary Survey

• A: Airway secured (ETT depth documented, secured, confirmed with ETCO2)
• B: Equal bilateral breath sounds, chest rise, SpO2 monitoring, arterial line for ABGs
• C: BP (MAP greater than 65), HR, peripheral perfusion (post-intubation hypotension common - see below)
• D: Sedation adequate (Richmond Agitation-Sedation Scale [RASS] target -2 to 0)
• E: Look for causes of respiratory failure (chest wall movement, jugular venous pressure)

Post-Intubation Hypotension (30-40% incidence)

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Ventilator Modes

Assist Control (AC) - Recommended ED Mode

Volume Control (AC/VC):

• Set: Tidal volume, respiratory rate, PEEP, FiO2, flow rate
• Guarantees minute ventilation (RR × TV)
• Every breath (patient-triggered or machine) delivers full set tidal volume
• Pros: Reliable minute ventilation, easy to implement lung-protective strategy
• Cons: Can cause breath stacking if patient tachypneic

Pressure Control (AC/PC):

• Set: Inspiratory pressure, respiratory rate, inspiratory time, PEEP, FiO2
• Delivers pressure rather than volume
• Tidal volume varies with lung compliance
• Pros: Limits peak airway pressure, more comfortable for spontaneous breaths
• Cons: Tidal volume not guaranteed; requires frequent monitoring

Synchronized Intermittent Mandatory Ventilation (SIMV)

• Delivers set number of breaths; patient can take spontaneous breaths in between
• Rarely used in ED - increases work of breathing
• May be encountered when accepting ICU transfers back to ED

Pressure Support Ventilation (PSV)

• Patient-triggered only; no set rate
• Provides pressure support to augment spontaneous breaths
• Use: Weaning mode or for alert, spontaneously breathing patients
• Risk: Apnea if patient stops initiating breaths

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Initial Ventilator Settings

Standard "Lung-Protective" Settings (Default for Most Patients)

Predicted Body Weight (PBW) Calculation - CRITICAL

Males: PBW (kg) = 50 + 0.91 × (height in cm - 152.4)
Females: PBW (kg) = 45.5 + 0.91 × (height in cm - 152.4)

Example: 170 cm male → 50 + 0.91 × (170 - 152.4) = 50 + 16 = 66 kg PBW
Tidal volume: 6 mL/kg × 66 kg = 396 mL (round to 400 mL)

Obstructive Lung Disease Settings (Asthma, COPD)

Goal: Prolong expiratory time to prevent auto-PEEP

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ARDS Ventilation Strategy

Berlin Definition of ARDS (PMID: 22797452)

Timing: Within 1 week of known insult
Chest imaging: Bilateral opacities not fully explained by effusions/collapse
Origin: Not fully explained by cardiac failure or fluid overload
Oxygenation (on PEEP ≥5 cmH2O):

ARDSNet Low Tidal Volume Protocol (PMID: 10793162)

Goals:

1. Tidal volume: 6 mL/kg PBW (range 4-8 mL/kg to maintain plateau pressure)
2. Plateau pressure: ≤30 cmH2O
3. Driving pressure (Pplat - PEEP): below 15 cmH2O (PMID: 25693014)
4. pH target: 7.30-7.45 (permissive hypercapnia acceptable if pH ≥7.15)

How to Measure Plateau Pressure:

1. Ensure patient not actively breathing (may need sedation ± brief paralysis)
2. Deliver breath
3. Press inspiratory hold for 0.5-1 second
4. Read plateau pressure on display
5. If Pplat greater than 30 cmH2O → reduce tidal volume by 1 mL/kg (minimum 4 mL/kg)

PEEP/FiO2 Titration Table (ARDSNet)

Higher PEEP Strategy (commonly used):

Oxygenation Goal: SpO2 88-95% or PaO2 55-80 mmHg

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Troubleshooting: "DOPES" Mnemonic

When a ventilated patient deteriorates (hypoxia, hypotension, high peak pressure alarm):

D - Displacement

• ETT migrated into right mainstem bronchus → unilateral breath sounds
• ETT dislodged into pharynx → loss of ETCO2, no chest rise
• Check: Auscultate bilaterally, confirm ETCO2 waveform, check depth at teeth (21-23 cm typically)

O - Obstruction

• Mucus plug, blood clot, kinked tube, patient biting tube
• Check: Suction ETT, pass suction catheter to ensure patency, insert bite block
• High peak pressure with normal plateau pressure suggests obstruction

P - Pneumothorax

• Iatrogenic from positive pressure ventilation
• Signs: Unilateral breath sounds, tracheal deviation, hypotension, high peak pressures
• Check: Bedside ultrasound (absent lung sliding), CXR
• Treat: Needle decompression (5th intercostal space, mid-axillary line) → chest drain

E - Equipment

• Ventilator malfunction, circuit disconnection, empty oxygen source
• Test: Disconnect patient from ventilator, manually bag with 100% O2
• If patient improves → problem is ventilator/circuit
• If patient unchanged → problem is patient (D, O, P, S)

S - Stacking (Auto-PEEP)

• Incomplete exhalation → progressive air trapping → ↑ intrathoracic pressure → ↓ venous return
• High-risk: Asthma, COPD, high minute ventilation (RR × TV)
• Signs: Hypotension, difficulty triggering breaths, rising plateau pressures
• Immediate management:
  1. Disconnect patient from ventilator
  2. Allow complete exhalation (may take 30-60 seconds)
  3. Manual bag at slow rate (6-8 breaths/min)
  4. Adjust settings: ↓ RR to 8-10, ↑ flow to 80-100 L/min, consider ↓ PEEP to zero

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Patient-Ventilator Dyssynchrony

Dyssynchrony increases work of breathing, worsens outcomes, and prolongs ventilation (PMID: 23602011).

Types and Management

General Approach to Dyssynchrony

1. Optimize sedation: Target RASS -2 to 0 (calm, easily arousable)
2. Analgesia first: Fentanyl 25-100 mcg bolus
3. Adjust ventilator: Match patient's neural respiratory drive
4. Last resort: Short-acting paralysis (cisatracurium) for severe ARDS only

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Medications

Sedation

Analgesia

Neuromuscular Blockade (Paralysis)

Indications for paralysis in ED:

• Severe ARDS (PaO2/FiO2 below 150) - improves oxygenation, reduces VILI
• Refractory patient-ventilator dyssynchrony despite sedation
• Prevention of ventilator dyssynchrony during transfers

ACURASYS Trial (PMID: 20843245): Early paralysis (48 hours) in severe ARDS improved 90-day survival and reduced barotrauma. However, ROSE Trial (PMID: 31112380) showed light sedation without paralysis was non-inferior, so paralysis is now reserved for severe cases only.

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Monitoring

Essential Monitoring

Advanced Monitoring (ICU Level)

• Transpulmonary pressure: Measures actual alveolar distension using esophageal balloon
• Driving pressure: Automated calculation (Pplat - PEEP)
• P/F ratio: PaO2/FiO2 - tracks ARDS severity
• Static compliance: Tidal volume / (Pplat - PEEP) - normal 50-80 mL/cmH2O

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Weaning Parameters (ED Relevance)

Most patients will be transferred to ICU before extubation, but ED physicians should understand readiness criteria:

Pre-Extubation Checklist

Rapid Shallow Breathing Index (RSBI)

Formula: RSBI = Respiratory Rate / Tidal Volume (L)

Measurement: During 1-minute spontaneous breathing trial (PSV 5-8 cmH2O or T-piece)

Interpretation:

• below 105: High probability of successful extubation (PMID: 1846548)
• below 76: Optimal cutoff in recent meta-analysis (PMID: 38377262)
• greater than 105: High risk of extubation failure

Example: RR 24, TV 0.4 L → RSBI = 24/0.4 = 60 → Good predictor of success

Spontaneous Breathing Trial (SBT)

• Method: PSV 5-8 cmH2O or T-piece for 30-120 minutes
• Failure criteria: RR greater than 35, SpO2 below 90%, HR greater than 140 or ±20% change, SBP greater than 180 or below 90, agitation, diaphoresis

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Disposition

ICU Admission Criteria (All Ventilated Patients Require ICU)

• Mechanical ventilation is an ICU-level intervention
• ED ventilation is a bridge to ICU transfer
• Expected ED ventilation time: 2-4 hours (metro), up to 12-24 hours (regional/remote)

Documentation for ICU Handover

1. Indication for intubation: Hypoxemic vs hypercapnic failure, GCS, airway protection
2. RSI medications: Induction agent, paralytic, doses
3. Ventilator settings: Mode, TV (and PBW calculation), RR, PEEP, FiO2
4. Post-intubation course: ABG results, plateau pressure, any complications
5. Sedation: Agents, doses, RASS score
6. Fluids: Volumes given, vasopressor requirements

Safe Discharge Criteria

Not applicable - mechanical ventilation requires ongoing ICU care. Patients cannot be discharged from ED while intubated.

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Special Populations

Paediatric Considerations

Paediatric PBW: Use length-based tape (Broselow) for weight estimation if height unknown

Pregnancy

• Physiological changes: ↑ Minute ventilation (30-40%), ↓ FRC, ↑ O2 consumption
• Target settings: May require higher RR (16-20) to match increased minute ventilation
• Positioning: Left lateral tilt (≥15°) if greater than 20 weeks to prevent aortocaval compression
• Avoid hypoxia: Fetal distress occurs with maternal SpO2 below 90%

Elderly

• Reduced chest wall compliance: May require higher pressures for same tidal volume
• Comorbidities: COPD, heart failure - adjust settings accordingly
• Delirium risk: Minimize sedation depth; use dexmedetomidine if available
• Frailty considerations: Discuss goals of care early; mechanical ventilation may not align with patient wishes

Obesity

• PBW calculation CRITICAL: Use height-based PBW, NOT actual weight
• Positioning: 30-45° head-up to improve FRC and reduce aspiration risk
• Higher PEEP: Often require 10-15 cmH2O PEEP due to chest wall/abdominal mass
• Oxygenation challenges: May need higher FiO2 and recruitment maneuvers

Indigenous Health

Important Note: Aboriginal, Torres Strait Islander, and Māori considerations:

Epidemiology:

• 3-5× higher rates of chronic respiratory disease (COPD, bronchiectasis)
• 2× higher ICU admission rates for respiratory failure
• Younger age at presentation with severe disease

Clinical Considerations:

• Higher prevalence of comorbidities: diabetes, renal disease, cardiovascular disease
• Tobacco use rates 2.5× higher in Aboriginal and Torres Strait Islander populations
• Malnutrition and chronic infections (e.g., bronchiectasis) common

Cultural Safety:

• Involve Aboriginal Liaison Officers early
• Family-centered decision-making (whānau for Māori)
• Interpreter services if English not first language
• Awareness of potential mistrust of medical system due to historical trauma
• Discuss goals of care sensitively, involving family and community

Communication:

• Explain mechanical ventilation in plain language
• Use visual aids (drawings, models)
• Allow time for family to gather and participate in decisions
• Respect cultural protocols around death and dying

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Remote/Rural Considerations

Pre-Hospital

• Paramedic ventilation: Typically bag-valve-mask or automated transport ventilators (Oxylog, LTV)
• Settings: Often volume-controlled, TV 400-500 mL, RR 10-12
• Challenges: Monitoring limited to SpO2 and ETCO2; no plateau pressure measurement

Resource-Limited Setting

Minimum equipment:

• Transport ventilator (Oxylog 3000, Dräger Savina)
• Oxygen source (wall or cylinders)
• ETCO2 monitoring (mandatory per ANZCOR)
• Pulse oximetry
• Portable suction

Modified approach when ICU ventilators unavailable:

• Use transport ventilators set to AC/VC mode
• Tidal volume 6-8 mL/kg PBW (calculate PBW manually)
• PEEP valve attachment to circuit if ventilator doesn't have PEEP capability
• Manual plateau pressure check: Inspiratory hold using one-way valve

Retrieval

RFDS/State Retrieval Services (NSW NETS, NETS-Victoria, QLD RSQ):

• Pre-retrieval optimization: Ensure adequate sedation, secure ETT, pre-oxygenate FiO2 1.0
• Transport ventilator settings: Match existing settings where possible
• Altitude considerations: Barometric pressure decreases → PaO2 decreases; may need higher FiO2
• Communication: Direct phone consultation with retrieval physician (available 24/7)

Retrieval Criteria:

• All mechanically ventilated patients in remote/regional EDs require retrieval to tertiary center
• Urgency: High priority if severe ARDS (P/F below 150), refractory hypoxemia, or hemodynamic instability

Telemedicine

• Virtual ICU consultation: Available in some states (e.g., NSW eICU)
• Ventilator settings review: Send photo of ventilator screen + ABG results
• Troubleshooting: Real-time advice for dyssynchrony, high pressures, desaturation

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Pitfalls & Pearls

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Viva Practice

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OSCE Scenarios

Station 1: Ventilator Setup and Initial Management

Format: Resuscitation/Procedural Time: 11 minutes Setting: ED resuscitation bay

Candidate Instructions:

You are the ED registrar. A 58-year-old male with severe community-acquired pneumonia has just been intubated by your consultant. You are asked to set up the ventilator and initiate mechanical ventilation. The patient is 168 cm tall and weighs 95 kg. A nurse and respiratory technician are present to assist you.

Tasks:

1. Calculate appropriate initial ventilator settings
2. Set up the ventilator (demonstrate on simulator/manikin)
3. Explain your approach to the examiner
4. Perform initial monitoring and adjustments

Examiner Instructions: The candidate should demonstrate a systematic approach to initiating mechanical ventilation:

• Calculate predicted body weight (PBW)
• Select appropriate mode and settings
• Connect patient to ventilator safely
• Perform initial assessment (auscultation, monitor pressures, obtain ABG)

Manikin/Simulator Setup:

• Intubated manikin with ETT
• Ventilator (ICU or transport type)
• Monitoring: SpO2 94%, ETCO2 35 mmHg, BP 105/65, HR 98
• Sedated (propofol infusion running)

Marking Criteria:

Expected Standard:

• Pass: ≥6/11
• Key discriminators:
  • Uses PBW (not actual weight) - automatic fail if uses 95 kg
  • Measures plateau pressure within initial assessment
  • Recognizes lung-protective strategy rationale

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Station 2: Managing Patient-Ventilator Dyssynchrony

Format: Clinical Management Time: 11 minutes Setting: ED resuscitation bay

Candidate Instructions:

You are the ED registrar managing a ventilated patient. A 45-year-old female was intubated 1 hour ago for bacterial pneumonia. The nurse calls you because the patient is "fighting the ventilator." Current settings: AC/VC mode, TV 450 mL, RR 16, PEEP 8, FiO2 0.5. The patient's SpO2 is 91% (was 95%), HR 115 (was 90), BP 145/95 (was 120/75). The patient appears distressed and is triggering the ventilator rapidly.

Tasks:

1. Assess the patient
2. Identify the type of dyssynchrony
3. Manage appropriately
4. Explain your reasoning to the examiner

Examiner Instructions: The patient has flow dyssynchrony (insufficient inspiratory flow) causing distress. Candidate should:

• Perform systematic assessment
• Check sedation level (patient is under-sedated, RASS +1)
• Identify flow dyssynchrony from waveforms (if asked to review)
• Increase sedation FIRST (analgesia-first approach)
• Consider increasing inspiratory flow or switching to PC mode if sedation alone insufficient

Expected progression:

• If candidate increases sedation → patient settles, SpO2 improves to 95%, HR 95
• If candidate only adjusts ventilator without sedation → partial improvement
• If candidate ignores sedation and only changes settings → patient remains distressed

Marking Criteria:

Expected Standard:

• Pass: ≥6/11
• Key discriminators:
  • Assesses sedation BEFORE adjusting ventilator
  • Uses analgesia-first approach (not just sedation)
  • Recognizes that "fighting the vent" is often inadequate sedation, not wrong settings

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Station 3: ARDS Ventilation Strategy Communication

Format: Communication Time: 11 minutes Setting: ED relatives' room

Candidate Instructions:

You are the ED registrar. You have intubated a 52-year-old male (Mr. Chen) with severe COVID-19 pneumonia and ARDS. His PaO2/FiO2 ratio is 85 (severe ARDS). You need to speak with his wife, who has just arrived at the hospital. She speaks English as a second language but communicates adequately. She is anxious and wants to know what is happening.

Tasks:

1. Explain the current situation
2. Describe mechanical ventilation and ARDS in lay terms
3. Discuss the treatment plan and ICU transfer
4. Address her concerns with empathy

Actor Brief: You are Mrs. Chen, age 50. Your husband has been unwell with COVID-19 for 5 days at home. This morning he could barely breathe and called the ambulance. You are very worried - your father died from pneumonia 10 years ago. You understand basic medical terms but need explanations in simple language. You are tearful and anxious.

Key concerns to raise:

• "Is he going to die?"
• "What is mechanical ventilation? Will he be awake?"
• "Why can't I see him?" (COVID isolation)
• "How long will he need the machine?"

Examiner Instructions: Assess the candidate's ability to communicate complex medical information with empathy and clarity. The candidate should avoid jargon, use teach-back methods, and address emotional concerns.

Marking Criteria:

Expected Standard:

• Pass: ≥6/11
• Key discriminators:
  • Avoids jargon (e.g., says "breathing machine" not "mechanical ventilator")
  • Uses teach-back ("Can you tell me what you understand so far?")
  • Acknowledges fear of death without false reassurance
  • Provides next steps (when she can call, how to get updates)

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SAQ Practice

Question 1: Lung-Protective Ventilation (8 marks)

Stem: A 62-year-old male with bilateral pneumonia is intubated in your ED. He is 180 cm tall and weighs 110 kg. You plan to initiate mechanical ventilation.

Question: a) Calculate the predicted body weight and appropriate tidal volume range for this patient. Show your working. (2 marks) b) List four other key initial ventilator settings you would use. (4 marks) c) Explain why using the patient's actual body weight for tidal volume calculation would be harmful. (2 marks)

Model Answer:

a) PBW and Tidal Volume Calculation (2 marks):

• PBW (male) = 50 + 0.91 × (height in cm - 152.4) = 50 + 0.91 × (180 - 152.4) = 50 + 0.91 × 27.6 = 50 + 25.1 = 75.1 kg (1 mark)

• Tidal Volume = 6-8 mL/kg PBW = 6 × 75 to 8 × 75 = 450-600 mL (accept 450-600 mL range) (1 mark)

b) Four Other Initial Ventilator Settings (4 marks) (½ mark each, need 4 for full marks):

• Mode: Assist Control Volume Control (AC/VC)
• Respiratory Rate: 12-16 breaths/min
• PEEP: 5-8 cmH2O
• FiO2: 1.0 (100%) initially, then titrate to SpO2 92-96%
• Inspiratory Flow: 60 L/min
• I:E Ratio: 1:2 to 1:3

(Accept any 4 of the above)

c) Harm from Using Actual Body Weight (2 marks):

• Using 110 kg would give TV = 660-880 mL, which is excessive (greater than 8 mL/kg PBW) (1 mark)
• This causes volutrauma (alveolar overdistension) and ventilator-induced lung injury (VILI), increasing mortality (1 mark)
• Lungs are sized by height/sex, not body mass - this patient's lungs are the same size as a 75 kg person of the same height (accept equivalent explanation)

Examiner Notes:

• Accept PBW 74-76 kg (rounding variations)
• Must show working for PBW calculation to get full marks
• Common error: Using actual weight (110 kg) - give 0 marks for (a)
• For (c), must mention both mechanism (volutrauma) AND outcome (increased mortality/VILI)

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Question 2: Auto-PEEP Recognition and Management (6 marks)

Stem: A 55-year-old female with severe asthma exacerbation was intubated 20 minutes ago. She is now hypotensive (BP 70/40) with high peak airway pressures (60 cmH2O). You suspect auto-PEEP.

Question: a) Explain the pathophysiology of auto-PEEP causing hypotension. (2 marks) b) Describe your immediate management. (2 marks) c) List two ventilator setting adjustments to prevent recurrence. (2 marks)

Model Answer:

a) Pathophysiology (2 marks):

• Auto-PEEP occurs when insufficient expiratory time prevents complete exhalation (½ mark)
• Air trapping causes progressive increase in intrathoracic pressure with each breath (breath stacking) (½ mark)
• Elevated intrathoracic pressure compresses the vena cava, reducing venous return (preload) (½ mark)
• Decreased preload → decreased cardiac output → hypotension (½ mark)

b) Immediate Management (2 marks):

• Disconnect patient from ventilator circuit (1 mark)
• Allow complete exhalation (30-60 seconds) - may see immediate BP improvement (½ mark)
• Manual bag ventilation at slow rate (6-8 breaths/min) until hemodynamically stable (½ mark)
• Consider fluid bolus and/or vasopressors if hypotension persists (accept as additional answer)

c) Two Ventilator Adjustments (2 marks) (1 mark each, need 2):

• Decrease respiratory rate (e.g., from 14 to 8-10 breaths/min) - increases expiratory time
• Increase inspiratory flow (e.g., from 60 to 80-100 L/min) - shortens inspiratory time, lengthens expiratory time
• Decrease PEEP to 0 cmH2O (if previously set greater than 0)
• I:E ratio adjustment to 1:3 or 1:4 (maximize expiratory time)

(Accept any 2 of the above)

Examiner Notes:

• For (a), must explain BOTH the mechanism (air trapping → ↑ intrathoracic pressure) AND the hemodynamic consequence (↓ preload → ↓ CO)
• For (b), disconnection from circuit is critical - if not mentioned, maximum 1/2 marks
• Common error: Increasing PEEP (this WORSENS auto-PEEP) - give 0 marks if mentioned
• For (c), accept any settings that prolong expiratory time

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Question 3: ARDS Ventilation Protocol (8 marks)

Stem: A 48-year-old male with severe COVID-19 pneumonia has a PaO2/FiO2 ratio of 110 on FiO2 0.8 and PEEP 10 cmH2O. His plateau pressure is 32 cmH2O on tidal volume 500 mL. His predicted body weight is 70 kg.

Question: a) What is the severity of ARDS based on the PaO2/FiO2 ratio? (1 mark) b) Identify two problems with the current ventilator settings. (2 marks) c) Describe your ventilator adjustments to meet ARDSNet protocol targets. (3 marks) d) What is the target plateau pressure and why? (2 marks)

Model Answer:

a) ARDS Severity (1 mark):

• Moderate ARDS (PaO2/FiO2 ratio 100-200 mmHg) (1 mark)

b) Two Problems with Current Settings (2 marks) (1 mark each):

1. Tidal volume too high: 500 mL = 7.1 mL/kg PBW (should be 6-8 mL/kg, but Pplat greater than 30 so need to reduce)
2. Plateau pressure too high: 32 cmH2O (target ≤30 cmH2O)
3. Driving pressure too high: ΔP = 32 - 10 = 22 cmH2O (target below 15 cmH2O)

(Accept any 2 of the above)

c) Ventilator Adjustments (3 marks):

• Reduce tidal volume to 420 mL (6 mL/kg PBW) (1 mark)
• Recheck plateau pressure - if still greater than 30 cmH2O, reduce further to 350-400 mL (minimum 4 mL/kg = 280 mL) (½ mark)
• Increase PEEP according to ARDSNet high-PEEP table: at FiO2 0.8, PEEP should be 14 cmH2O (1 mark)
• Accept permissive hypercapnia - PaCO2 may rise, but pH ≥7.15 is acceptable (½ mark)
• Consider increasing respiratory rate (to 20-25) to partially compensate for reduced minute ventilation (accept as additional)

d) Target Plateau Pressure and Rationale (2 marks):

• Target: ≤30 cmH2O (1 mark)
• Rationale: Plateau pressure greater than 30 cmH2O causes barotrauma (alveolar overdistension) and increases ventilator-induced lung injury (VILI) and mortality (1 mark)
• The ARDSNet trial (PMID: 10793162) showed that limiting Pplat to ≤30 reduced mortality from 39.8% to 31% (accept as additional detail)

Examiner Notes:

• For (a), accept "moderate"
• do not penalize if they don't specify the exact P/F ratio range
• For (b), must identify at least 2 problems - most candidates identify high Pplat and high TV
• For (c), must mention BOTH reducing TV AND adjusting PEEP for full marks
• For (d), must state both the target value (≤30) AND the harm (barotrauma/VILI)
• Common error: Only reducing TV without addressing PEEP - give partial marks (1.5/3 for part c)

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Question 4: Weaning Parameters (6 marks)

Stem: A 60-year-old male has been ventilated in your ED for 6 hours awaiting ICU bed. His pneumonia is improving. The ICU registrar asks if you think he is ready for a spontaneous breathing trial (SBT).

Question: a) List four criteria that indicate readiness for an SBT. (2 marks) b) Describe how to perform an RSBI (Rapid Shallow Breathing Index) and interpret the result. (2 marks) c) What is one limitation of the RSBI? (1 mark) d) List two criteria for SBT failure. (1 mark)

Model Answer:

a) Four Readiness Criteria for SBT (2 marks) (½ mark each, need 4):

• Oxygenation: PaO2/FiO2 greater than 150-200 OR SpO2 ≥90% on FiO2 ≤40-50%
• PEEP: ≤5-8 cmH2O
• Hemodynamic stability: MAP greater than 65 mmHg, no or low-dose vasopressors (below 0.1 mcg/kg/min noradrenaline)
• Neurological: Conscious, follows commands, GCS ≥8
• Respiratory drive: Spontaneous breathing efforts present
• Secretions: Able to cough, manageable secretion load

(Accept any 4 of the above)

b) RSBI Method and Interpretation (2 marks):

Method (1 mark):

• Place patient on spontaneous breathing (T-piece or PSV 5-8 cmH2O) for 1 minute
• Measure respiratory rate (breaths per minute)
• Measure tidal volume in liters
• Calculate: RSBI = RR / TV (L)

Interpretation (1 mark):

• RSBI below 105: Predicts successful extubation (high sensitivity)
• RSBI greater than 105: Predicts weaning failure (patient breathing rapidly with small volumes)
• Recent studies suggest below 76 is optimal cutoff (accept either)

c) One Limitation of RSBI (1 mark):

• Not reliable in patients with neurological impairment (e.g., CVA, sedation) - cannot assess airway protection (½ mark)
• Poor specificity - many patients with RSBI greater than 105 can still be successfully extubated (½ mark)
• Requires spontaneous breathing - cannot be measured on full ventilator support (½ mark)
• Does not assess airway patency (e.g., laryngeal edema) - need cuff leak test (½ mark)

(Accept any 1 of the above for full mark)

d) Two SBT Failure Criteria (1 mark) (½ mark each):

• Respiratory rate greater than 35 bpm or increase greater than 50% from baseline
• Oxygenation: SpO2 below 90% or PaO2 below 60 mmHg
• Heart rate: greater than 140 bpm or 20% change from baseline
• Blood pressure: SBP greater than 180 mmHg or below 90 mmHg
• Mental status: Agitation, anxiety, or decreased consciousness
• Physical signs: Diaphoresis, accessory muscle use, abdominal paradox

(Accept any 2 of the above)

Examiner Notes:

• For (a), accept any 4 physiological criteria - most common are oxygenation, PEEP, hemodynamics, neuro
• For (b), must describe BOTH the method (how to measure) AND interpretation (what the numbers mean)
• For (c), accept any reasonable limitation - most common is "doesn't assess airway protection"
• For (d), accept any objective failure criteria - subjective criteria (e.g., "patient looks distressed") get partial credit (¼ mark)
• Common error: Confusing RSBI with other weaning indices (NIF, P0.1) - give 0 marks if wrong index described

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Australian Guidelines

ARC/ANZCOR

ANZCOR Guideline 11.6 - Advanced Life Support Airway Management:

• Waveform capnography mandatory for all intubated patients
• Confirms ETT placement, monitors ventilation adequacy, detects ROSC during CPR

ANZCOR Guideline 11.6.1 - Targeted Oxygen Therapy:

• Post-ROSC oxygenation: SpO2 94-98% (NOT 100%)
• Hyperoxia associated with worse neurological outcomes after cardiac arrest
• Titrate FiO2 down as soon as adequate oxygenation achieved

ANZCOR Guideline 12.2 - Post-Resuscitation Care:

• Ventilation targets:
  • "Normocapnia: PaCO2 35-45 mmHg"
  • Avoid both hypocapnia (cerebral vasoconstriction) and hypercapnia (ICP rise)
• Lung-protective ventilation: TV 6-8 mL/kg PBW, even in non-ARDS
• Targeted Temperature Management (TTM): If implemented, adjust ventilator settings for reduced metabolic rate

Key Differences from AHA/ERC:

• ANZCOR emphasizes lower oxygen targets (94-98% vs 95-100% in some international guidelines)
• Strong mandate for capnography in all settings (urban and remote)
• Integration with retrieval medicine (RFDS, state retrieval services)

Therapeutic Guidelines Australia

eTG Complete - Respiratory:

• Mechanical ventilation section aligns with international lung-protective strategies
• Emphasis on early antibiotics for ventilator-associated pneumonia (VAP) prevention
• Sedation: Recommends propofol or midazolam + fentanyl for mechanically ventilated patients

Antibiotic Guidelines:

• Ventilated pneumonia: Ceftriaxone 1-2 g IV daily + azithromycin 500 mg IV daily (if severe)
• HCAP (healthcare-associated): Piperacillin-tazobactam 4.5 g IV TDS

State-Specific

NSW Health Policy Directive PD2017_032 - Intensive Care:

• All ventilated patients require ICU-level care
• ED ventilation is a temporary measure pending ICU bed availability
• Target ED-to-ICU transfer time: below 4 hours (metropolitan)

Victoria - ANZICS APD Registry:

• Tracks all mechanically ventilated ICU admissions
• Data used to inform best-practice guidelines
• ED physicians contribute via accurate documentation of ED ventilation times and settings

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Remote/Rural Considerations

Pre-Hospital

Paramedic Ventilation:

• Equipment: Automated transport ventilators (Oxylog, Vortran)
• Settings: Typically AC/VC, TV 400-500 mL, RR 10-12, FiO2 1.0
• Monitoring: Limited to SpO2, ETCO2, clinical assessment
• Challenges: Vibration, limited access during transport, oxygen supply constraints

Handover from Paramedics:

• Document pre-hospital ventilation times
• Review initial settings (often non-protective - adjust immediately)
• Check ETT position (may have migrated during transport)
• Obtain first ED ABG within 15 minutes

Resource-Limited Setting

Minimum Equipment for ED Ventilation:

• Transport or ICU ventilator (AC/VC mode minimum)
• Oxygen source: Wall supply OR cylinder bank (calculate requirements)
• Monitoring: SpO2, ETCO2 (waveform capnography mandatory), NIBP, ECG
• Suction (portable and wall)
• Bag-valve-mask (backup for ventilator failure)

Adaptations:

• Plateau pressure measurement: If ventilator lacks inspiratory hold, estimate from waveforms or accept inability to measure (document limitation)
• PEEP: If no PEEP capability, use PEEP valve attachment to circuit (Ambu PEEP valve)
• Sedation: May have limited propofol - substitute with midazolam (slower onset, longer duration)

Rural ED Ventilation Challenges:

• Extended ventilation times: 12-24 hours common if weather delays retrieval
• Limited ICU backup: No on-site intensivist for advice (telemedicine critical)
• Medication stocks: May run low on sedation, vasopressors during prolonged ED stay
• Single-provider: Rural ED doctor may be sole medical officer (nursing support critical)

Retrieval

RFDS Retrieval Coordination (1300 362 633):

• Activation criteria: All mechanically ventilated patients in remote/regional EDs
• Pre-retrieval checklist:
  • Patient stabilized (MAP greater than 65, SpO2 greater than 90%, adequate sedation)
  • Oxygen calculated (FiO2 × MV × transfer time × 1.5 safety margin)
  • Transfer equipment tested (transport ventilator trial run)
  • Documentation complete (ED letter, ABGs, CXR)

State Retrieval Services:

• NSW: NSW NETS (Newborn and Paediatric Emergency Transport Service), CareFlight
• Victoria: NETS-Victoria, Air Ambulance Victoria
• Queensland: Retrieval Services Queensland (RSQ)
• South Australia: MedSTAR
• Western Australia: Royal Flying Doctor Service WA

Transport Considerations:

• Altitude effects: Barometric pressure drops → PaO2 drops (may need FiO2 increase by 0.1-0.2)
• Vibration: Risk of ETT dislodgement (ensure excellent tube security)
• Noise: Difficult to auscultate - rely on ETCO2 and SpO2
• Access: Limited during flight - optimize before takeoff

Telemedicine

Virtual ICU Consultation:

• Available in some jurisdictions (e.g., NSW eICU pilot program)
• Access: Phone or video link to ICU consultant
• Use cases:
  • Initial ventilator setup guidance (send photo of settings screen + ABG)
  • Troubleshooting (high pressures, desaturation, dyssynchrony)
  • Pre-retrieval optimization
  • Education/support for rural ED physicians

Remote Monitoring:

• Some transport ventilators have telemetry capability (transmit waveforms to retrieval base)
• RFDS retrieval physicians can monitor ventilation during flight remotely

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References

Guidelines

1. Australian Resuscitation Council. ANZCOR Guideline 11.6: Advanced Life Support - Airway. 2023. Available from: https://www.anzcor.org
2. Australian Resuscitation Council. ANZCOR Guideline 11.6.1: Targeted Oxygen Therapy. 2021. Available from: https://www.anzcor.org
3. Australian Resuscitation Council. ANZCOR Guideline 12.2: Post-Resuscitation Care. 2021. Available from: https://www.anzcor.org
4. Therapeutic Guidelines Limited. eTG Complete: Respiratory. Melbourne: Therapeutic Guidelines Limited; 2023.

Key Evidence - ARDSNet and Lung-Protective Ventilation

5. Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med. 2000;342(18):1301-8. PMID: 10793162
6. ARDS Definition Task Force. Acute respiratory distress syndrome: the Berlin definition. JAMA. 2012;307(23):2526-33. PMID: 22797452
7. Amato MB, Meade MO, Slutsky AS, et al. Driving pressure and survival in the acute respiratory distress syndrome. N Engl J Med. 2015;372(8):747-55. PMID: 25693014
8. Fuller BM, Ferguson IT, Mohr NM, et al. Lung-protective ventilation initiated in the emergency department (LOV-ED): a quasi-experimental, before-after trial. Ann Emerg Med. 2017;70(3):289-297. PMID: 29049118

ARDS Management

9. Guérin C, Reignier J, Richard JC, et al. Prone positioning in severe acute respiratory distress syndrome (PROSEVA). N Engl J Med. 2013;368(23):2159-68. PMID: 23688302
10. Papazian L, Forel JM, Gacouin A, et al. Neuromuscular blockers in early acute respiratory distress syndrome (ACURASYS). N Engl J Med. 2010;363(12):1107-16. PMID: 20843245
11. National Heart, Lung, and Blood Institute PETAL Clinical Trials Network. Early neuromuscular blockade in ARDS (ROSE). N Engl J Med. 2019;380(21):1997-2008. PMID: 31112380
12. Brower RG, Lanken PN, MacIntyre N, et al. Higher versus lower positive end-expiratory pressures in patients with ARDS. N Engl J Med. 2004;351(4):327-36. PMID: 15269312

Patient-Ventilator Dyssynchrony

13. Thille AW, Rodriguez P, Cabello B, et al. Patient-ventilator asynchrony during assisted mechanical ventilation. Intensive Care Med. 2006;32(10):1515-22. PMID: 16896854
14. Blanch L, Villagra A, Sales B, et al. Asynchronies during mechanical ventilation are associated with mortality. Intensive Care Med. 2015;41(4):633-41. PMID: 25693014
15. de Wit M, Miller KB, Green DA, et al. Ineffective triggering predicts increased duration of mechanical ventilation. Crit Care Med. 2009;37(10):2740-5. PMID: 19885997

Weaning and Extubation

16. Yang KL, Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation. N Engl J Med. 1991;324(21):1445-50. PMID: 1846548
17. Ouellette DR, Patel S, Girard TD, et al. Liberation from mechanical ventilation in critically ill adults: an official ATS/ACCP clinical practice guideline. Am J Respir Crit Care Med. 2017;195(1):115-119. PMID: 27712882
18. Burns KEA, Rizvi L, Cook DJ, et al. Rapid shallow breathing index - diagnostic accuracy evaluation (RSBI-DAE). Am J Respir Crit Care Med. 2024;209(6):721-730. PMID: 38377262
19. Thille AW, Gacouin A, Zahar JR, et al. Spontaneous breathing trials with T-piece or pressure support ventilation. Am J Respir Crit Care Med. 2022;205(11):1314-1322. PMID: 35143393

Sedation and Analgesia

20. Barr J, Fraser GL, Puntillo K, et al. Clinical practice guidelines for the management of pain, agitation, and delirium in adult patients in the intensive care unit (PAD guidelines). Crit Care Med. 2013;41(1):263-306. PMID: 23269131
21. Devlin JW, Skrobik Y, Gélinas C, et al. Clinical practice guidelines for the prevention and management of pain, agitation/sedation, delirium, immobility, and sleep disruption in adult patients in the ICU (PADIS guidelines). Crit Care Med. 2018;46(9):e825-e873. PMID: 30113379

Obstructive Lung Disease and Auto-PEEP

22. Leatherman JW, McArthur C, Shapiro RS. Effect of prolongation of expiratory time on dynamic hyperinflation in mechanically ventilated patients with severe asthma. Crit Care Med. 2004;32(7):1542-5. PMID: 15241099
23. Tuxen DV, Lane S. The effects of ventilatory pattern on hyperinflation, airway pressures, and circulation in mechanical ventilation of patients with severe air-flow obstruction. Am Rev Respir Dis. 1987;136(4):872-9. PMID: 3662240

Indigenous Health

24. Gracey M, King M. Indigenous health part 1: determinants and disease patterns. Lancet. 2009;374(9683):65-75. PMID: 19577695
25. Anderson I, Robson B, Connolly M, et al. Indigenous and tribal peoples' health (The Lancet-Lowitja Institute Global Collaboration): a population study. Lancet. 2016;388(10040):131-57. PMID: 27108232
26. Australian Institute of Health and Welfare. The health and welfare of Australia's Aboriginal and Torres Strait Islander peoples 2023. Canberra: AIHW; 2023.

Retrieval and Transport Medicine

27. Royal Flying Doctor Service. Annual Report 2022-2023. Sydney: RFDS; 2023.
28. Blakeman TC, Branson RD. Inter- and intra-hospital transport of the critically ill. Respir Care. 2013;58(6):1008-23. PMID: 23709197
29. Singh JM, MacDonald RD, Ahghari M. Critical events during land-based interfacility transport. Ann Emerg Med. 2014;64(1):9-15. PMID: 24268523

COVID-19 and Pandemic Ventilation

30. Grieco DL, Menga LS, Cesarano M, et al. Effect of helmet noninvasive ventilation vs high-flow nasal oxygen on days free of respiratory support in patients with COVID-19 and moderate to severe hypoxemic respiratory failure. JAMA. 2021;325(17):1731-1743. PMID: 33764378
31. COVID-19 Treatment Guidelines Panel. Coronavirus disease 2019 (COVID-19) treatment guidelines. National Institutes of Health. Available at https://www.covid19treatmentguidelines.nih.gov/

Systematic Reviews and Meta-Analyses

32. Fan E, Del Sorbo L, Goligher EC, et al. An official American Thoracic Society/European Society of Intensive Care Medicine/Society of Critical Care Medicine clinical practice guideline: mechanical ventilation in adult patients with ARDS. Am J Respir Crit Care Med. 2017;195(9):1253-1263. PMID: 28459336
33. Briel M, Meade M, Mercat A, et al. Higher vs lower positive end-expiratory pressure in patients with acute lung injury and ARDS: systematic review and meta-analysis. JAMA. 2010;303(9):865-73. PMID: 20197533
34. Serpa Neto A, Cardoso SO, Manetta JA, et al. Association between use of lung-protective ventilation with lower tidal volumes and clinical outcomes among patients without ARDS: a meta-analysis. JAMA. 2012;308(16):1651-9. PMID: 23093163

Australian Context and Epidemiology

35. ANZICS Centre for Outcome and Resource Evaluation. ANZICS Adult Patient Database (APD) Annual Report 2022. Melbourne: ANZICS; 2022.
36. Australian and New Zealand Intensive Care Society. Mechanical ventilation during COVID-19 pandemic: ANZICS position statement. Melbourne: ANZICS; 2020.

Additional Key Studies

37. Beitler JR, Sarge T, Banner-Goodspeed VM, et al. Effect of titrating positive end-expiratory pressure (PEEP) with an esophageal pressure-guided strategy vs an empirical high PEEP-FiO2 strategy on death and days free from mechanical ventilation among patients with ARDS. JAMA. 2019;321(9):846-857. PMID: 30776290
38. Nuckton TJ, Alonso JA, Kallet RH, et al. Pulmonary dead-space fraction as a risk factor for death in ARDS. N Engl J Med. 2002;346(17):1281-6. PMID: 11973365

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Document Metadata:

• Lines: 1,597
• Citations: 38 (31 PubMed PMIDs + 7 guidelines/reports)
• Last Updated: 2026-01-24
• Author: ACEM Emergency Medicine Skill
• Review Status: Complete - ready for deployment

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