Smoke Inhalation Injury

Quick Reference

Critical Alerts

• Early intubation for airway compromise: Supraglottic edema progresses rapidly and unpredictably over 12-24 hours
• Three distinct injury patterns: Thermal (supraglottic), chemical (subglottic/alveolar), systemic toxicity (CO/cyanide)
• CO and cyanide toxicity frequently coexist: Up to 35% of fire victims have significant cyanide levels
• 100% oxygen for ALL smoke inhalation patients: Reduces COHb half-life from 4-5 hours to 60-90 minutes
• Hydroxocobalamin first-line for suspected cyanide: Safe empiric therapy without methemoglobin formation
• Normal SpO₂ does NOT exclude CO poisoning: Pulse oximetry cannot differentiate oxyhemoglobin from carboxyhemoglobin
• Inhalation injury + burns = 20-40% mortality increase: Combined injury substantially worsens prognosis
• Delayed pulmonary edema may occur 24-48 hours post-exposure: Observation period mandatory

Immediate Intubation Indicators

Emergency Treatment Protocol

---

Definition and Classification

Overview

Smoke inhalation injury represents a complex, multisystem injury pattern resulting from exposure to products of combustion in enclosed fires. It is the leading cause of fire-related deaths, accounting for 50-80% of fire fatalities—more than thermal burns themselves. [1,2] The injury encompasses three distinct but frequently overlapping pathophysiologic mechanisms that require simultaneous assessment and treatment. [3]

The Three-Component Injury Model

Modern understanding of smoke inhalation injury recognizes three distinct injury patterns, each with unique pathophysiology, clinical presentation, and treatment requirements. [3,4]

1. Thermal Injury (Supraglottic)

Anatomic Distribution:

• Primarily affects upper airway: nasal passages, oropharynx, larynx
• Rarely extends below vocal cords due to excellent heat dissipation capacity of upper airway
• Exception: Steam inhalation (400× greater heat capacity than dry air) can reach lower airways and alveoli [5]

Pathophysiology:

• Direct thermal damage → mucosal inflammation → progressive edema
• Edema development: typically 2-12 hours, peaks at 24-48 hours post-exposure
• Airway narrowing is exponential (Poiseuille's Law): 50% diameter reduction → 16-fold increase in resistance
• Risk of complete airway obstruction without warning

Clinical Implications:

• Window for safe intubation narrows as edema progresses
• Early prophylactic intubation often safer than delayed emergent intubation
• Once stridor develops, intubation difficulty increases dramatically

2. Chemical Injury (Subglottic/Alveolar)

Mechanism:

• Combustion products cause direct chemical injury to tracheobronchial tree and alveoli
• Particulate matter (soot, carbon) deposits on mucosa → inflammation
• Toxic gases (acrolein, ammonia, chlorine, aldehydes) → mucosal damage
• Mucociliary escalator dysfunction → impaired secretion clearance [6]

Pathophysiologic Cascade:

• Acute phase (0-24h): Bronchospasm, mucosal hyperemia, increased secretions
• Intermediate phase (24-72h): Epithelial sloughing, cast formation (fibrin + debris + mucus)
• Late phase (72h+): ARDS development, pneumonia, respiratory failure

Tissue Effects:

• Increased bronchial blood flow → pulmonary edema
• Impaired surfactant function → atelectasis
• Ciliary dysfunction → mucus plugging and airway obstruction
• Fibrin cast formation → complete airway occlusion possible

3. Systemic Toxicity (Carbon Monoxide and Cyanide)

Carbon Monoxide (CO):

• Present in ALL fires (incomplete combustion of carbon-containing materials)
• Binds hemoglobin with 200-250× greater affinity than oxygen → carboxyhemoglobin (COHb)
• Left-shifts oxyhemoglobin dissociation curve → impaired O₂ delivery to tissues
• Binds myoglobin and mitochondrial cytochrome oxidase → direct cellular toxicity
• Normal PaO₂ with tissue hypoxia ("oxyhemoglobin gap") [7]

Hydrogen Cyanide (HCN):

• Generated from combustion of nitrogen-containing synthetic materials (plastics, polyurethane foam, wool, silk, nylon)
• Increasingly prevalent as modern buildings contain more synthetic materials [8]
• Inhibits cytochrome c oxidase (Complex IV) → blocks mitochondrial respiration
• Cells cannot utilize oxygen despite adequate delivery → cytotoxic hypoxia
• Severe lactic acidosis (lactate often > 10 mmol/L) [9]

Combined Toxicity:

• CO and cyanide frequently coexist (up to 35-50% of smoke inhalation patients) [10]
• Synergistic toxic effects → worse outcomes than either alone
• Cyanide toxicity should be suspected in ANY enclosed-space fire victim with severe acidosis

Epidemiology

Incidence and Mortality:

• 50-80% of fire deaths attributed to smoke inhalation rather than thermal burns [1,2]
• Approximately 20,000-30,000 smoke inhalation injuries annually in United States
• Mortality rate: 5-10% for isolated inhalation injury; 20-40% when combined with burns [11]
• Inhalation injury increases burn mortality by 20% at any given total body surface area (TBSA) [11]

High-Risk Scenarios:

• Enclosed-space fires (residential, vehicular, industrial)
• Delayed rescue or prolonged exposure
• Loss of consciousness at scene (indicates severe CO or cyanide toxicity)
• Structural fires with synthetic materials (furniture, insulation, electronics)
• Fires involving polyvinyl chloride (PVC), polyurethane, or nylon

Prognostic Factors: [12]

• Age > 60 years
• Inhalation injury presence
• Burn size (TBSA)
• Pre-existing cardiopulmonary disease
• Delayed presentation or treatment

---

Pathophysiology

Upper Airway Thermal Injury

Heat Transfer Dynamics:

The upper airway possesses remarkable heat-dissipating capacity through several mechanisms:

• High vascularity → rapid heat transfer to blood
• Turbulent airflow in nasal passages → increased contact time
• Evaporative cooling from moist mucosa
• Reflex glottic closure with superheated air exposure

Result: Only 10-15% of dry air thermal injuries extend below vocal cords. [5]

Exception—Steam Inhalation:

• Water has 4,000 times the heat capacity of air
• Steam carries vastly more thermal energy
• Can overcome upper airway defenses → lower airway thermal injury
• Associated with higher mortality and ARDS development

Edema Formation Timeline:

• 0-2 hours: Often minimal visible changes; deceptive "latent period"
• 2-12 hours: Progressive mucosal edema and erythema
• 12-24 hours: Peak edema; highest risk period for airway obstruction
• 24-48 hours: Gradual improvement if no secondary complications

Critical Concept: Airway obstruction from edema is a progressive, unpredictable process. Early intubation (when easy) is safer than delayed intubation (when difficult or impossible).

Lower Airway Chemical Injury

Toxic Combustion Products:

Subglottic Injury Cascade: [6]

1. Immediate (0-6 hours):

   • Bronchospasm (reflex and inflammatory)
   • Increased mucus production
   • Ciliary dysfunction → impaired clearance

2. Early (6-24 hours):

   • Mucosal hyperemia → increased bronchial blood flow
   • Plasma transudation into airways
   • Epithelial sloughing begins
   • Cast formation (fibrin + cellular debris + mucus)

3. Intermediate (24-72 hours):

   • Extensive cast formation → airway obstruction
   • Atelectasis from mucus plugging
   • Pneumonia risk increases (loss of mucociliary defense)
   • ARDS development in severe cases

4. Late (> 72 hours):

   • Bacterial pneumonia (common complication)
   • Persistent bronchospasm
   • Bronchiolitis obliterans (rare, chronic sequela)
   • Tracheal stenosis (if intubated, rare)

ARDS Development:

• Occurs in 20-30% of severe inhalation injuries [13]
• Typically develops 24-72 hours post-exposure
• Multifactorial: direct chemical injury + systemic inflammation + fluid resuscitation
• Associated with prolonged ventilation and increased mortality

Carbon Monoxide Toxicity

Molecular Mechanisms:

Hemoglobin Binding:

• CO binds heme group of hemoglobin → carboxyhemoglobin (COHb)
• Affinity 200-250× greater than oxygen
• Prevents O₂ binding → reduced oxygen-carrying capacity
• Left-shifts O₂-hemoglobin dissociation curve → impaired O₂ release to tissues [7]

Cellular Toxicity:

• Binds myoglobin → impaired cardiac and skeletal muscle function
• Inhibits cytochrome c oxidase → mitochondrial dysfunction
• Lipid peroxidation → neuronal injury
• May cause delayed neuropsychiatric syndrome (1-4 weeks post-exposure)

Clinical-Pathophysiologic Correlation:

Important: Clinical severity does NOT always correlate with COHb level, particularly if cyanide co-toxicity present.

COHb Half-Life (Critical for Treatment Planning): [7]

• Room air (21% O₂): 4-6 hours
• 100% O₂ (normobaric): 60-90 minutes
• Hyperbaric oxygen (2.5-3.0 ATA): 20-30 minutes

Cyanide Toxicity

Sources in Fire Environments: [8,9]

• Polyurethane foam (furniture, mattresses): Major source
• Wool, silk (natural fibers containing nitrogen)
• Nylon, acrylics (synthetic fabrics)
• Polyvinyl chloride (PVC): Electrical insulation, pipes
• Rubber, paper (certain treatments)

Mechanism of Toxicity:

Cyanide binds to ferric iron (Fe³⁺) in cytochrome c oxidase (mitochondrial Complex IV):

• Blocks electron transport chain → halts oxidative phosphorylation
• Cells unable to utilize O₂ for ATP production
• Shift to anaerobic metabolism → severe lactic acidosis
• PaO₂ and SaO₂ remain NORMAL (oxygen delivered but not utilized) [9]

Clinical Presentation Spectrum:

Diagnostic Clues (Cyanide Often Unrecognized):

• Severe metabolic acidosis (pH less than 7.2) with elevated lactate (> 8-10 mmol/L)
• Normal or elevated mixed venous O₂ saturation (cells not extracting O₂)
• Refractory hypotension despite adequate resuscitation
• "Bitter almond" breath odor (only 40% of population can detect; unreliable)
• Enclosed-space fire + unexplained cardiovascular collapse [10]

Synergistic CO-Cyanide Toxicity:

• Both toxins impair oxygen utilization at cellular level
• CO prevents O₂ delivery; cyanide prevents O₂ utilization
• Combined effect worse than additive
• Treatment of one may partially improve but both require specific therapy

---

Clinical Presentation

History—Critical Elements

Exposure Characteristics (Severity Predictors):

• Enclosed space: Higher concentration of toxic gases
• Duration of exposure: Longer = higher toxin load
• Loss of consciousness at scene: Indicates severe CO or cyanide poisoning
• Type of materials burning: Synthetics → cyanide risk; PVC → chlorine gas
• Rescue time: Prolonged exposure worsens prognosis
• Extrication difficulty: May indicate severe inhalation before escape

Pre-Hospital Course:

• Level of consciousness changes
• Respiratory distress onset and progression
• Any treatment provided (O₂ administration, intubation)
• Time from exposure to presentation

Associated Injuries:

• Cutaneous burns (TBSA estimation)
• Blast injury or trauma
• Jump from height (consider spinal injury)

Symptoms

Respiratory:

• Dyspnea (indicates chemical injury or systemic toxicity)
• Cough (often productive with black/carbonaceous sputum)
• Hoarseness (WARNING: suggests laryngeal edema)
• Stridor (EMERGENCY: critical airway narrowing)
• Chest pain (CO-induced myocardial ischemia or pneumonitis)
• Wheezing (bronchospasm from chemical irritation)

Neurologic (CO or Cyanide Toxicity):

• Headache (early CO symptom; very common)
• Dizziness, lightheadedness
• Confusion, altered mental status
• Visual changes, blurred vision
• Syncope or near-syncope
• Seizures (severe toxicity)

Cardiovascular:

• Chest pain (myocardial ischemia from CO or hypoxia)
• Palpitations (arrhythmias)
• Hypotension (cyanide, distributive shock)

Physical Examination

General Appearance:

• Level of consciousness (GCS less than 8 = intubation)
• Respiratory distress: tachypnea, accessory muscle use, nasal flaring
• Agitation or lethargy (hypoxia, toxicity)
• Odor: bitter almonds (cyanide, unreliable); smoke odor on clothing

Head, Eyes, Ears, Nose, Throat (HEENT):

Respiratory Examination:

• Tachypnea (> 24 breaths/min suggests significant injury)
• Accessory muscle use (impending respiratory failure)
• Wheezing (bronchospasm; treat with bronchodilators)
• Rhonchi (secretions, mucus plugging)
• Crackles (pulmonary edema, pneumonitis)
• Decreased breath sounds (atelectasis, pneumothorax if barotrauma)

Cardiovascular:

• Tachycardia (hypoxia, stress response, toxicity)
• Hypotension (cyanide, cardiogenic shock from CO, distributive shock)
• Arrhythmias (myocardial toxicity from CO or hypoxia)
• Elevated JVP (fluid overload; beware in burn resuscitation)

Skin:

• Cherry-red coloration (COHb; CLASSIC but RARE less than 5% of cases; DO NOT wait for it) [7]
• Cyanosis (severe hypoxemia; late finding)
• Burns: document TBSA, depth, distribution
• Peripheral perfusion (capillary refill, temperature)

Neurologic:

• Focal neurologic deficits (uncommon; consider trauma or stroke)
• Seizure activity (severe CO or cyanide toxicity)

---

Red Flags and Emergency Indicators

Airway Compromise—Immediate Action Required

Key Principle: "When in doubt, intubate early." Delayed intubation may be impossible once edema progresses.

Severe Systemic Toxicity Indicators

Carbon Monoxide:

• COHb > 25% (serious toxicity; consider HBO)
• COHb > 40% (life-threatening; HBO strongly recommended)
• Syncope or loss of consciousness
• Cardiac ischemia (chest pain, ECG changes, troponin elevation)
• Neurologic symptoms (confusion, seizures, coma)
• Pregnancy (fetus at higher risk; lower threshold for HBO)

Cyanide Toxicity (Treat Empirically if Suspected): [9,10]

• Severe metabolic acidosis: pH less than 7.2, lactate > 8-10 mmol/L
• Refractory hypotension: Not responding to fluids/pressors
• Cardiovascular collapse: Unexplained in fire victim
• Cardiac arrest at scene or in ED
• Enclosed-space fire + severe acidosis: Empiric hydroxocobalamin

Treatment Principle: Cyanide levels NOT rapidly available. Empiric treatment with hydroxocobalamin is SAFE and recommended when clinical suspicion exists.

Indicators of Severe Inhalation Injury

• Prolonged enclosed-space exposure (> 15-20 minutes)
• Loss of consciousness at scene
• Significant facial burns with singed nasal hairs and carbonaceous sputum
• Respiratory distress on presentation
• Hypoxemia despite supplemental oxygen
• Bronchoscopic evidence of severe injury (see grading below)

---

Diagnostic Approach

Laboratory Evaluation

Immediate Essential Tests:

Special Considerations:

CO-Oximetry (NOT Standard Pulse Oximetry):

• Pulse oximetry measures only two wavelengths → cannot differentiate COHb from O₂Hb
• SpO₂ will read falsely NORMAL/ELEVATED in CO poisoning (dangerous)
• CO-oximetry required (measures 4+ wavelengths: O₂Hb, COHb, MetHb, Deoxyhemoglobin) [7]
• Critical Point: "Normal" SpO₂ does NOT exclude CO poisoning

Cyanide Levels:

• Rarely available in real-time (send for confirmation only)
• DO NOT delay treatment waiting for cyanide level
• Diagnose clinically: enclosed fire + severe acidosis + elevated lactate
• Empiric hydroxocobalamin is safe [9]

Lactate as Surrogate Marker:

• Elevated lactate (> 8-10 mmol/L) in fire victim → presume cyanide toxicity [10]
• Lower lactate (4-8 mmol/L) can occur with CO toxicity alone
• Serial lactate helps assess treatment response

Imaging

Chest X-Ray (CXR):

Computed Tomography (CT) Chest:

• Not routinely indicated in acute phase
• May show ground-glass opacities, consolidation earlier than CXR
• Useful if complications suspected (pneumothorax, pulmonary embolism)
• Consider if discrepancy between clinical severity and CXR findings

Important: Early normal imaging does NOT exclude inhalation injury. Radiographic changes lag clinical injury by 12-48 hours.

Bronchoscopy—Gold Standard for Diagnosis [14]

Indications:

• Suspected moderate-to-severe inhalation injury
• Facial burns with singed nasal hairs and/or carbonaceous sputum
• Diagnostic uncertainty requiring direct visualization
• Therapeutic suctioning of casts/debris in intubated patients

Timing:

• Ideally within 24 hours of injury
• Can be performed at bedside (flexible bronchoscopy)
• Repeat bronchoscopy may be needed for therapeutic suctioning

Bronchoscopic Findings and Grading:

Abbreviated Injury Score (AIS)—Most Widely Used: [14]

Prognostic Correlation:

• Grade 0-1: Generally favorable prognosis; supportive care often sufficient
• Grade 2: Moderate injury; increased pneumonia/ARDS risk
• Grade 3-4: High risk of ARDS (up to 60%), prolonged ventilation, mortality 20-40% [14]

Therapeutic Bronchoscopy:

• Serial bronchoscopy with suctioning for cast removal
• Reduces atelectasis and pneumonia risk
• May improve oxygenation and ventilation
• Particularly important in severe grades (3-4)

Electrocardiogram (ECG)

Indications:

• All patients with COHb > 10%
• Chest pain or cardiac symptoms
• Age > 40 years or cardiac risk factors

Findings Suggesting CO-Induced Cardiac Toxicity:

• ST-segment changes (ischemia)
• T-wave inversions
• Arrhythmias (SVT, VT, AF)
• Conduction abnormalities
• QTc prolongation

Significance: Cardiac ischemia from CO → strong indication for hyperbaric oxygen therapy.

---

Treatment and Management

General Principles

1. Airway security is paramount: Early intubation when indicated
2. 100% oxygen for ALL patients: Treat CO, maximize O₂ delivery
3. Empiric cyanide antidote if high suspicion: Hydroxocobalamin is safe
4. Aggressive pulmonary toilet: Bronchoscopy, suctioning, bronchodilators
5. Fluid resuscitation if burns present: Parkland formula
6. Monitor for delayed complications: ARDS, pneumonia, pulmonary edema

Airway Management

Indications for Intubation:

Absolute Indications:

• Stridor
• Severe respiratory distress
• Hypoxemia (SpO₂ less than 90%) despite high-flow oxygen
• Altered mental status (GCS ≤ 8)
• Apnea or impending respiratory arrest

Relative Indications (Lower Threshold, Prophylactic):

• Progressive hoarseness
• Significant facial or neck burns
• Extensive oropharyngeal edema on examination
• Bronchoscopic evidence of severe supraglottic injury
• Need for transfer to another facility (edema may worsen en route)
• Anticipated clinical course (e.g., large burn requiring massive resuscitation)

Intubation Technique Considerations:

Key Principle: "Intubate early while easy, not late when difficult."

Oxygen Therapy

100% Oxygen—MANDATORY for ALL Smoke Inhalation Patients: [7]

Rationale:

• Competitively displaces CO from hemoglobin → reduces COHb half-life
• Maximizes oxygen delivery to tissues
• Treats both CO toxicity and tissue hypoxia from inhalation injury

Delivery Methods:

Duration:

• Continue 100% O₂ until COHb less than 5% (normal less than 2% non-smokers; less than 5-10% smokers)
• Typically requires 60-90 minutes on 100% normobaric O₂ [7]
• If symptoms persist despite COHb normalization, consider HBO or cyanide toxicity

Hyperbaric Oxygen Therapy (HBO)

Mechanism:

• Increases dissolved oxygen in plasma (independent of hemoglobin)
• Reduces COHb half-life to 20-30 minutes (vs. 60-90 min with normobaric 100% O₂)
• May reduce delayed neuropsychiatric sequelae of CO poisoning [15]
• Pressures typically 2.5-3.0 atmospheres absolute (ATA)

Indications for HBO (Based on Evidence and Guidelines): [15]

Strong Indications:

• COHb > 25%
• COHb > 20% with symptoms
• Loss of consciousness at any time
• Neurologic symptoms (confusion, seizures, focal deficits, coma)
• Cardiac ischemia (chest pain, ECG changes, troponin elevation)
• Pregnancy (any COHb > 15%; fetal hemoglobin binds CO more avidly)
• Severe metabolic acidosis (pH less than 7.1)
• Refractory symptoms despite normobaric 100% O₂

Relative Indications:

• Age less than 2 years (developing brain at risk)
• COHb 15-25% with mild symptoms
• Prolonged exposure (> 30 minutes)

Contraindications:

• Untreated pneumothorax (relative; requires chest tube first)
• Severe hemodynamic instability (relative; stabilize first)
• Unavailability of HBO facility (do not delay other treatment)

Practical Considerations:

• Coordinate with hyperbaric center early if indicated
• Do NOT delay intubation, antidote therapy, or resuscitation to arrange HBO
• Continue 100% normobaric O₂ until HBO available
• Transfer may be required; ensure airway secured before transport

Evidence Summary: HBO for CO poisoning remains somewhat controversial. Some studies show reduced delayed neuropsychiatric syndrome; others show no benefit. [15] Nonetheless, HBO is widely recommended for severe CO poisoning by major toxicology and hyperbaric medicine societies.

Cyanide Antidote Therapy

Clinical Decision-Making:

Cyanide levels are NOT rapidly available. Treat empirically based on clinical suspicion.

High Suspicion for Cyanide Toxicity (Treat Empirically): [9,10]

• Enclosed-space fire exposure
• Severe metabolic acidosis: pH less than 7.2, lactate > 8-10 mmol/L
• Refractory hypotension despite adequate resuscitation
• Cardiovascular collapse or cardiac arrest in fire victim
• Concomitant COHb elevation with severe acidosis

Hydroxocobalamin (Vitamin B12a)—First-Line Agent: [9]

Mechanism:

• Binds cyanide → cyanocobalamin (non-toxic) → renally excreted
• Direct cyanide scavenging without methemoglobin formation

Dosing:

• 5 grams IV over 15 minutes (reconstitute in 200 mL NS)
• May repeat second 5-gram dose if inadequate response or severe toxicity
• Pediatric dose: 70 mg/kg (maximum 5g first dose)

Advantages:

• Extremely safe (essentially non-toxic)
• No methemoglobin formation (unlike nitrite-based antidotes)
• Can be given empirically without harm if cyanide not present
• Compatible with CO treatment (no worsening of O₂ delivery)

Adverse Effects (Minimal):

• Red discoloration of skin, mucous membranes, urine (expected; warn patient)
• Transient hypertension (usually clinically insignificant)
• Allergic reactions (rare)
• Interferes with colorimetric lab tests (e.g., serum creatinine may be falsely elevated for 24h)

Cyanide Antidote Kit (Alternative, Less Preferred): [9]

Components:

1. Amyl nitrite pearls (inhaled)
2. Sodium nitrite 300mg IV
3. Sodium thiosulfate 12.5g IV

Mechanism:

• Nitrites induce methemoglobinemia → methemoglobin binds cyanide (competitive binding)
• Thiosulfate enhances cyanide metabolism (rhodanese pathway) → thiocyanate (excreted)

Disadvantages:

• Nitrites create methemoglobin → reduces oxygen-carrying capacity
• Dangerous in CO co-toxicity (CO already reduces O₂ delivery; MetHb worsens this)
• Hypotension from nitrite-induced vasodilation
• More complex administration

Current Recommendation: Hydroxocobalamin is strongly preferred in smoke inhalation given frequent CO co-toxicity. [9,10]

Sodium Thiosulfate Alone:

• May be used as adjunct to hydroxocobalamin
• Safe, enhances cyanide elimination
• Less effective as monotherapy (slower onset)

Bronchodilator Therapy

Indication: Bronchospasm (wheezing on examination)

Agents:

Caution: Excessive beta-agonist use may cause tachycardia, arrhythmias (especially with CO-induced cardiac toxicity).

Bronchoscopy and Pulmonary Toilet

Therapeutic Bronchoscopy Indications: [14]

• Cast formation visible on bronchoscopy
• Mucus plugging with atelectasis
• Deteriorating oxygenation/ventilation despite mechanical ventilation
• Severe bronchoscopic grade (3-4)

Technique:

• Flexible bronchoscopy via ETT (requires ≥ 7.5mm ETT)
• Suction casts, carbonaceous material, mucus
• May require serial procedures (q 8-12h initially if significant debris)
• Lavage with normal saline if needed

Adjunctive Pulmonary Toilet:

• Frequent ETT suctioning (q 1-2h initially)
• Chest physiotherapy (if not contraindicated by burns)
• Adequate humidification of inspired gases
• N-acetylcysteine nebulization (mucolytic; limited evidence but sometimes used)

Mechanical Ventilation Strategies

General Principles:

• Lung-protective ventilation (tidal volume 6-8 mL/kg ideal body weight)
• Target plateau pressure less than 30 cm H₂O
• PEEP to maintain oxygenation (typically 5-10 cm H₂O; titrate to FiO₂)
• Minimize FiO₂ as oxygenation improves (target SpO₂ 92-96%)

High-Frequency Percussive Ventilation (HFPV):

• Alternative mode used in some burn centers [16]
• Delivers high-frequency, low tidal volume breaths superimposed on conventional breaths
• Theoretical benefits: improved secretion clearance, better gas exchange, lower peak pressures
• Evidence: Some observational studies suggest benefit; no large RCTs [16]
• Not standard of care; conventional ventilation appropriate for most patients

ARDS Management (if develops):

• Follow ARDSNet protocol
• Tidal volume 6 mL/kg IBW
• Plateau pressure less than 30 cm H₂O
• Higher PEEP strategies
• Prone positioning for refractory hypoxemia
• Consider neuromuscular blockade if severe ARDS (PaO₂/FiO₂ less than 150)

Fluid Resuscitation (If Burns Present)

Parkland Formula (if burns ≥ 15-20% TBSA):

• 4 mL × body weight (kg) × %TBSA = total fluid in first 24 hours
• Give 50% in first 8 hours, 50% in subsequent 16 hours
• Use lactated Ringer's solution

Caution in Inhalation Injury:

• Aggressive fluid resuscitation may worsen pulmonary edema
• Balance burn resuscitation needs with pulmonary status
• Early intubation if large fluid volumes anticipated
• Monitor urine output (target 0.5 mL/kg/h), serum lactate, base deficit

Pharmacologic Adjuncts (Limited Evidence)

N-Acetylcysteine (NAC):

• Mucolytic agent
• Nebulized 20% solution 3-5 mL q 4-6h
• May help with secretion clearance
• Antioxidant properties (theoretical benefit; unproven in inhalation injury)

Heparin/N-Acetylcysteine Nebulization:

• Some burn centers use nebulized heparin (to reduce fibrin cast formation) + NAC
• Evidence limited to small case series; no large trials [17]
• Not standard of care but may be considered in severe cases

Corticosteroids:

• NOT recommended routinely
• No proven benefit; may increase infection risk
• Exception: pre-existing asthma/COPD exacerbation

Prophylactic Antibiotics:

• NOT recommended
• Risk of selecting resistant organisms
• Treat documented infections based on culture data

Supportive Care

• Analgesia: Opioids for pain control (burns, procedures)
• Sedation: If intubated (propofol, benzodiazepines)
• Stress ulcer prophylaxis: PPI or H2 blocker
• DVT prophylaxis: Pharmacologic (LMWH, heparin) unless contraindicated
• Nutrition: Early enteral feeding if feasible; burn patients have high metabolic demands
• Glucose control: Target 140-180 mg/dL (stress hyperglycemia common)

---

Complications

Early Complications (0-72 Hours)

Airway Obstruction:

• Progressive upper airway edema
• Late recognition → difficult/impossible intubation
• Prevention: Early intubation when indicated

Acute Respiratory Distress Syndrome (ARDS): [13]

• Develops in 20-30% of severe inhalation injuries
• Onset typically 24-72 hours post-exposure
• Diffuse alveolar damage, pulmonary edema, impaired gas exchange
• Management: Lung-protective ventilation, PEEP, supportive care
• Mortality 30-40% in severe ARDS

Pneumonia:

• Loss of mucociliary clearance, mucosal damage → infection risk
• Aspiration risk if altered mental status
• Typical organisms: S. aureus (including MRSA), Pseudomonas, Klebsiella
• Diagnosis: Clinical + radiographic + microbiologic (BAL culture)
• Treatment: Broad-spectrum antibiotics tailored to culture results

Pulmonary Edema:

• Cardiogenic: Fluid overload during resuscitation (especially with burns)
• Non-cardiogenic: Chemical injury, ARDS, neurogenic (rare)
• May be delayed 24-48 hours (especially with phosgene, nitrogen oxides)

Cardiovascular Complications:

• Myocardial infarction (CO-induced ischemia)
• Arrhythmias (CO, hypoxia, electrolyte abnormalities)
• Cardiogenic shock (severe CO toxicity, myocardial stunning)
• Distributive shock (cyanide, systemic inflammation)

Acute Kidney Injury (AKI):

• Rhabdomyolysis (prolonged immobilization, compartment syndrome)
• Hypoperfusion (shock, hypotension)
• Nephrotoxins (contrast, aminoglycosides)
• Management: Fluid resuscitation, avoid nephrotoxins, RRT if severe

Delayed Complications (> 72 Hours)

Ventilator-Associated Pneumonia (VAP):

• High risk in intubated smoke inhalation patients
• Prevention: Head of bed elevation, chlorhexidine oral care, daily sedation vacations, spontaneous breathing trials

Barotrauma:

• Pneumothorax, pneumomediastinum from mechanical ventilation
• Higher risk with high peak pressures, large tidal volumes

Tracheal Stenosis:

• Rare complication from prolonged intubation
• Thermal or chemical injury to tracheal mucosa + mechanical injury from ETT cuff
• May present weeks to months later with dyspnea, stridor

Chronic Sequelae:

Delayed Neuropsychiatric Syndrome (DNS) from CO: [15]

• Occurs in 10-30% of CO poisoning cases
• Onset 1-4 weeks after exposure (after initial recovery)
• Symptoms: Cognitive impairment, memory deficits, personality changes, parkinsonism
• May be persistent or improve over months
• HBO may reduce risk (controversial)

Bronchiolitis Obliterans:

• Rare chronic sequela of severe chemical inhalation injury
• Progressive fibrosis of small airways
• Presents with progressive dyspnea, obstructive pattern on PFTs
• Treatment: Corticosteroids (limited efficacy), lung transplant for severe cases

Post-Traumatic Stress Disorder (PTSD):

• Psychological trauma from fire event
• Screening and mental health support important

---

Prognosis and Prognostic Factors

Mortality Predictors [11,12]

Independent Risk Factors for Mortality:

Combined Burn + Inhalation Injury:

• 20% TBSA burn alone: ~5% mortality
• 20% TBSA burn + inhalation: ~20-25% mortality
• Inhalation injury adds ~20% absolute mortality increase [11]

Prognostic Scoring Systems: [12]

Baux Score (Age + %TBSA):

• less than 60: Low mortality risk
• 60-80: Moderate risk

• 80: High risk

• 100: Very high mortality

Modified Baux Score (Age + %TBSA + 17 if inhalation injury):

• Adds 17 points for inhalation injury presence
• More accurate than original Baux score

Bronchoscopic Grade and Prognosis: [14]

Key Prognostic Principle: Severity of inhalation injury (by bronchoscopy) is one of the strongest predictors of outcome.

Functional Outcomes

Most survivors recover pulmonary function within 6-12 months, but some have persistent abnormalities:

• Mild obstructive defect (10-20% of cases)
• Reactive airway disease (may require inhaled bronchodilators)
• Exercise intolerance (reduced VO₂ max)

Neurologic outcomes after CO poisoning:

• Complete recovery: 50-70%
• Mild persistent deficits: 20-30%
• Severe persistent deficits or DNS: 10-30%
• HBO may improve outcomes (evidence mixed) [15]

---

Disposition

Admission Criteria

Mandatory Admission:

• Any patient intubated for inhalation injury
• COHb > 15%
• Moderate-severe inhalation injury (bronchoscopic grade ≥ 2)
• Respiratory symptoms (dyspnea, wheezing, hypoxemia)
• Altered mental status from CO or cyanide
• Cardiac symptoms or ischemia
• Burns requiring admission (TBSA ≥ 10-15%, critical areas)
• Significant acidosis (lactate > 4, pH less than 7.3)

Observation (Possible Discharge After 6-12 Hours if Improving):

• Brief exposure, minimal symptoms
• COHb less than 10% and normalizing with 100% O₂
• Normal mental status
• No respiratory distress
• Normal vital signs
• Reliable patient with good follow-up

ICU vs. Floor Admission

ICU Admission Indications:

• Intubated patients
• Hemodynamic instability (hypotension, arrhythmias)
• Severe respiratory distress or hypoxemia
• Severe acidosis or elevated lactate (> 4 mmol/L)
• Altered mental status
• High-dose vasopressor or inotrope requirement
• Severe burns (TBSA > 20%)
• Bronchoscopic grade 3-4

Floor Admission Acceptable:

• Mild inhalation injury (grade 0-1)
• Stable vital signs
• Improving respiratory status
• COHb normalizing
• Mild symptoms only

Transfer Criteria

Consider Transfer to Burn Center if:

• Inhalation injury + burns TBSA > 10%
• Severe inhalation injury requiring advanced ventilatory support
• Need for HBO not available at current facility
• Pediatric patient with significant injury
• Electrical or chemical burns

American Burn Association (ABA) Burn Center Referral Criteria (relevant to inhalation):

• Inhalation injury
• Burn injury with concomitant trauma
• Burns in patients with pre-existing medical conditions
• Burns and associated injuries requiring specialized care

Pre-Transfer Stabilization:

• Secure airway (intubate if any concern; edema may worsen during transport)
• 100% oxygen
• IV access, fluid resuscitation initiated
• Antidotes given (hydroxocobalamin if cyanide suspected)
• Stabilize hemodynamics
• Contact receiving facility and hyperbaric center if HBO planned

Discharge Instructions (If Outpatient Observation Completed)

Return Precautions:

• Worsening shortness of breath
• Chest pain
• Confusion, dizziness, severe headache
• Hoarseness or difficulty swallowing
• Any new or worsening symptoms

Follow-Up:

• Primary care or pulmonology follow-up in 1-2 weeks
• Neuropsychiatric evaluation if CO exposure (assess for DNS at 2-4 weeks)
• Pulmonary function testing if persistent respiratory symptoms

Activity:

• Rest for 24-48 hours
• Avoid strenuous activity until cleared by physician
• No driving for 24 hours (CO effects, medications)

---

Special Populations

Pregnancy

Fetal Considerations:

• Fetal hemoglobin binds CO more avidly than adult hemoglobin
• Fetal COHb levels higher and persist longer than maternal levels
• Fetal hypoxia risk even with maternal COHb normalization
• Teratogenic effects possible (especially first trimester)

Management Differences:

• Lower threshold for HBO: Consider if maternal COHb > 15-20% (vs. > 25% in non-pregnant)
• Longer duration of 100% O₂ therapy (until maternal COHb less than 2%)
• Fetal monitoring (if viable gestational age)
• Multidisciplinary care (Obstetrics, Neonatology, Toxicology)

Pediatrics

Differences from Adults:

• Smaller airway diameter → faster obstruction with edema
• Higher minute ventilation → greater toxin exposure per kg
• Lower threshold for intubation
• Fluid resuscitation for burns ≥ 10-15% TBSA (vs. ≥ 20% in adults)
• Hydroxocobalamin dosing: 70 mg/kg (max 5g)

Elderly

Increased Mortality Risk:

• Age > 60 is independent predictor of mortality
• Pre-existing cardiopulmonary disease common → less reserve
• Higher risk of CO-induced myocardial ischemia
• Consider early HBO if significant CO exposure

---

Quality Metrics and Documentation

Performance Indicators

Essential Documentation

History:

• Enclosed space? Duration of exposure?
• Loss of consciousness at scene?
• Type of materials burning?
• Time from exposure to presentation?

Examination:

• Airway: hoarseness, stridor, oropharyngeal edema?
• Respiratory: distress, wheezing, crackles?
• Neurologic: GCS, confusion, focal deficits?
• Skin: facial burns, singed hairs, soot?

Diagnostics:

• COHb level (with co-oximetry)
• Lactate, pH
• Bronchoscopy findings (grade)
• CXR findings

Treatment:

• Time to 100% oxygen initiation
• Intubation details (timing, indication, difficulty)
• Antidote administration (hydroxocobalamin, timing, dose)
• HBO referral/transfer if indicated

Disposition:

• Admission location (ICU vs. floor)
• Transfer arrangements if needed
• Follow-up plan

---

Key Clinical Pearls

Diagnostic Pearls

• SpO₂ is UNRELIABLE in CO poisoning: Always obtain co-oximetry (COHb level)
• Normal CXR initially is common: Does NOT exclude inhalation injury; imaging lags clinical injury by 12-48 hours
• Lactate > 8-10 mmol/L in fire victim = cyanide until proven otherwise: Treat empirically with hydroxocobalamin
• Hoarseness or stridor = airway emergency: Intubate early while still possible
• Three injury patterns often coexist: Assess for thermal (supraglottic), chemical (subglottic), and systemic (CO/cyanide) injury simultaneously
• Bronchoscopy is diagnostic and prognostic: AIS grade predicts ARDS, pneumonia, mortality
• Enclosed-space fire + unconsciousness = severe toxicity: Presume significant CO and cyanide exposure

Treatment Pearls

• 100% oxygen for ALL smoke inhalation patients: Start immediately; do not delay for lab confirmation
• Intubate early when indicated: "When in doubt, intubate"—edema progression unpredictable
• Hydroxocobalamin is safe empiric therapy: No harm if cyanide not present; do not wait for cyanide level
• Avoid nitrite-based cyanide antidotes in smoke inhalation: Methemoglobin formation worsens oxygen delivery (already compromised by CO)
• Large ETT (≥ 7.5mm) for intubation: Allows therapeutic bronchoscopy
• HBO for severe CO poisoning: Consider if COHb > 25%, neurologic symptoms, cardiac ischemia, pregnancy
• Serial bronchoscopy for severe injury: Therapeutic cast/debris removal improves outcomes
• Lung-protective ventilation if ARDS develops: Tidal volume 6 mL/kg IBW, plateau pressure less than 30 cm H₂O

Prognostic Pearls

• Inhalation injury + burns = 20% mortality increase: Combined injury much worse than either alone
• Bronchoscopic grade 3-4 → high ARDS risk (50-70%): Anticipate need for prolonged ventilation
• Age > 60 + inhalation injury = poor prognosis: Consider early aggressive intervention
• Delayed neuropsychiatric syndrome (DNS) occurs in 10-30% of CO poisoning: Follow-up neuropsychiatric assessment at 2-4 weeks
• Most pulmonary function recovers within 6-12 months: Reassure patients with mild persistent symptoms

Pitfalls to Avoid

• Relying on SpO₂ to exclude CO poisoning: Will read falsely normal/high
• Waiting for "cherry-red" skin to diagnose CO: Rare finding (less than 5%); unreliable
• Delaying intubation in progressive hoarseness: Window for safe intubation closes rapidly
• Assuming normal initial CXR excludes significant injury: Radiographic changes lag by 12-48 hours
• Not considering cyanide in fire victims with severe acidosis: Often overlooked; empiric treatment safe
• Using nitrite-based cyanide kit in smoke inhalation: Worsens oxygen delivery (methemoglobin formation)
• Excessive fluid resuscitation without early intubation: Pulmonary edema risk
• Discharging patients after brief observation without adequate monitoring: Delayed complications (edema, pulmonary edema) can occur 24-48 hours post-exposure

---

References

1. Rehberg S, Maybauer MO, Enkhbaatar P, et al. Pathophysiology, management and treatment of smoke inhalation injury. Expert Rev Respir Med. 2009;3(3):283-297. doi:10.1586/ers.09.21

2. Mlcak RP, Suman OE, Herndon DN. Respiratory management of inhalation injury. Burns. 2007;33(1):2-13. doi:10.1016/j.burns.2006.07.007

3. Huzar TF, George T, Cross JM. Carbon monoxide and cyanide toxicity: etiology, pathophysiology and treatment in inhalation injury. Expert Rev Respir Med. 2013;7(2):159-170. doi:10.1586/ers.13.9

4. Walker PF, Buehner MF, Wood LA, et al. Diagnosis and management of inhalation injury: an updated review. Crit Care. 2015;19:351. doi:10.1186/s13054-015-1077-4

5. Albright JM, Davis CS, Bird MD, et al. The acute pulmonary inflammatory response to the graded severity of smoke inhalation injury. Crit Care Med. 2012;40(4):1113-1121. doi:10.1097/CCM.0b013e3182374a67

6. Cancio LC. Airway management and smoke inhalation injury in the burn patient. Clin Plast Surg. 2009;36(4):555-567. doi:10.1016/j.cps.2009.05.008

7. Weaver LK. Carbon monoxide poisoning. N Engl J Med. 2009;360(12):1217-1225. doi:10.1056/NEJMcp0808891

8. Baud FJ, Barriot P, Toffis V, et al. Elevated blood cyanide concentrations in victims of smoke inhalation. N Engl J Med. 1991;325(25):1761-1766. doi:10.1056/NEJM199112193252502

9. Borron SW, Baud FJ, Barriot P, et al. Prospective study of hydroxocobalamin for acute cyanide poisoning in smoke inhalation. Ann Emerg Med. 2007;49(6):794-801. doi:10.1016/j.annemergmed.2007.01.026

10. Fortin JL, Giocanti JP, Ruttimann M, et al. Prehospital administration of hydroxocobalamin for smoke inhalation-associated cyanide poisoning: 8 years of experience in the Paris Fire Brigade. Clin Toxicol (Phila). 2006;44 Suppl 1:37-44. doi:10.1080/15563650600811961

11. Steinvall I, Elmasry M, Abdelrahman I, et al. Mortality-predictive factors in severe burns. Burns. 2015;41(3):536-545. doi:10.1016/j.burns.2014.10.009

12. Chai J, Luo H, Wang C, et al. Prognostic scoring systems in burns: a review. Burns. 2011;37(8):1288-1295. doi:10.1016/j.burns.2011.07.017

13. Dancey DR, Hayes J, Gomez M, et al. ARDS in patients with thermal injury. Intensive Care Med. 1999;25(11):1231-1236. doi:10.1007/s001340051061

14. Mosier MJ, Pham TN, Park DR, et al. Predictive value of bronchoscopy in assessing the severity of inhalation injury. J Burn Care Res. 2012;33(1):65-73. doi:10.1097/BCR.0b013e318234d92f

15. Weaver LK, Hopkins RO, Chan KJ, et al. Hyperbaric oxygen for acute carbon monoxide poisoning. N Engl J Med. 2002;347(14):1057-1067. doi:10.1056/NEJMoa013121

16. Chung KK, Wolf SE, Renz EM, et al. High-frequency percussive ventilation and low tidal volume ventilation in burns: a randomized controlled trial. Crit Care Med. 2010;38(10):1970-1977. doi:10.1097/CCM.0b013e3181eb9d0b

17. Desai MH, Mlcak R, Richardson J, et al. Reduction in mortality in pediatric patients with inhalation injury with aerosolized heparin/N-acetylcysteine therapy. J Burn Care Rehabil. 1998;19(3):210-212. doi:10.1097/00004630-199805000-00004

18. Gigengack RK, Ijzermans AC, van Vught LA, et al. Advances in airway management and mechanical ventilation in inhalation injury. Curr Opin Anaesthesiol. 2020;33(6):774-780. doi:10.1097/ACO.0000000000000929

19. Tintinalli JE, Ma OJ, Yealy DM, et al. Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 9th ed. New York, NY: McGraw-Hill Education; 2020.

20. Dries DJ, Endorf FW. Inhalation injury: epidemiology, pathology, treatment strategies. Scand J Trauma Resusc Emerg Med. 2013;21:31. doi:10.1186/1757-7241-21-31

21. Enkhbaatar P, Pruitt BA Jr, Suman O, et al. Pathophysiology, research challenges, and clinical management of smoke inhalation injury. Lancet. 2016;388(10052):1437-1446. doi:10.1016/S0140-6736(16)31458-1

22. Hall AH, Rumack BH. Hydroxycobalamin/sodium thiosulfate as a cyanide antidote. J Emerg Med. 1987;5(2):115-121. doi:10.1016/0736-4679(87)90074-6