Smoke Inhalation Injury

Aka: Smoke Inhalation Injury, Smoke Inhalation, Inhalation Injury, Airway Management in Burn Injury

1. Epidemiology
   1. Leading cause of death from Burn Injury (responsible for 50-80% of burn-related deaths)
   2. Inhalation Injury increases mortality in burn patients by 3 fold
2. Pathophysiology
   1. Upper airway is typically affected (except in steam inhalation which can affect sub-glottic airway)
   2. Inhalation injuries are mediated by chemical lung injury (not typically heat)
      1. Results in large volume fluid influx into the lungs
3. Risk Factors
   1. Entrapment within burning structure
   2. Burns to head, face, neck or chest
4. Signs: Findings suggestive of Smoke Inhalation
   1. Altered Mental Status
      1. Burn Injury alone should not alter mentation
   2. Full thickness facial burns
   3. Singed facial hair (e.g. nasal hair)
   4. Oral and nasal mucosal Burn Injury
   5. Burn Injury occuring in a confined space
   6. Sputum with soot (carbonaceous Sputum)
   7. Hoarseness or Stridor
   8. Bullae in oropharynx or Larynx
   9. Productive Cough
5. Signs: Respiratory distress (late findings)
   1. Dyspnea
   2. Tachypnea
   3. Wheezing
   4. Rhonchi
   5. Hypoxia
   6. Nasal flaring
   7. Accessory muscle use (e.g. intercostal retractions)
6. Labs
   1. Arterial Blood Gas
   2. Serum Lactic Acid
      1. Increased with cyanide Poisoning
      2. No specific Cyanide lab testing in most clinical settings
   3. Carboxyhemoglobin level
      1. Increased with Carbon Monoxide Poisoning
      2. Continuous finger probe Carboxyhemoglobin monitoring is commercially available
   4. Complete Blood Count
   5. Consider serum Troponin
      1. Indicated for Chest Pain, EKG changes or increased cardiovascular risk
7. Imaging
   1. Chest XRay
      1. Typically normal early in course of Inhalation Injury
8. Diagnostics
   1. Electrocardiogram
      1. Observe for Myocardial Ischemia
   2. Pulmonary Function Tests
   3. Nasolaryngoscopy
   4. Bronchoscopy
      1. Evaluate the extent of upper airway and Bronchial injury
9. Complications
   1. Carbon Monoxide Poisoning
   2. Cyanide Poisoning
      1. Results from inhalation of burning materials (e.g. wool, silk, polyurethane, plastics and vinyl)
      2. Consider in residential and industrial fires, especially if concurrent Carbon Monoxide Poisoning
      3. Hypotension may be the only initial finding
      4. Late findings include decreased mental status, Bradycardia, respiratory depression and cardiovascular collapse
   3. Methemoglobinemia
   4. Respiratory injury
      1. Particulate matter and sulfur and nitrogen compounds result in direct lung injury and VQ Mismatch
      2. Causes Hypoxia, airway edema, airway obstruction and ARDS
10. Evaluation
    1. Altered Mental Status
       1. Burn Injury alone is typically associated with alert, Agitated Patient in pain
       2. Decreased level of conciousness suggests other cause
          1. Carbon Monoxide Poisoning
             1. May be associated with Headache, Nausea, Vomiting, Dizziness, myalgias
          2. Cyanide Poisoning
          3. Head Trauma
11. Precautions
    1. Children under age 8 years (esp. under age 2 years) are more susceptible to airway edema
       1. See Advanced Airway in Children
       2. Children have narrow airways at baseline (e.g. 4 mm)
          1. Even 1 mm of circumferential airway edema may drop airway diameter by 50% (increased resistance 16 fold)
       3. Children have a shorter, narrower airway that is unable to cool hot air as it is inspired
          1. Extensive injury to distal Bronchioles and alveoli may occur more easily in children
12. Management
    1. See Burn Injury
    2. Monitoring
       1. Intravenous Access
       2. Oxygen Saturation monitoring
       3. Telemetry monitoring
    3. Interventions: Airway
       1. Supplemental Oxygen 100% Non-Rebreathing Mask
          1. Continue until Carboxyhemoglobin <5% (at least <10% in smokers)
          2. Carbon Monoxide decreases 50% in 60 minutes on Non-Rebreather Mask
          3. Carbon Monoxide decreases 50% in 30 minutes on 100% oxygen while intubated
          4. Cyanide exposure is also common in enclosed structure fires
             1. Hydrogen cyanide forms from burning wool, silk, polyurethane and nylon
       2. Consider hyperbaric oxygen (see indications below)
       3. Consider Advanced Airway and Mechanical Ventilations
          1. Monitor upper airway closely and prophylactically intubate early if airway compromise is suspected
          2. Airway edema peaks at 12 hours after Inhalation Injury
          3. Mechanical Ventilation settings
             1. Keep Tidal Volumes at 3-5 ml/kg
             2. Keep plateau pressures <30 cm H2O
             3. Administer PEEP
          4. Rapid Sequence Intubation precautions
             1. Succinylcholine is typically safe in acute Burn Injury
             2. Hyperkalemia risk starts at 5 days post-injury (protocols recommend avoiding 48 hours after burn)
          5. Endotracheal Tube precautions
             1. Place at least a 7.5 Endotracheal Tube (otherwise more difficult suctioning, bronchoscopy)
             2. Have a back-up smaller Endotracheal Tube, in case unable to pass the larger ET Tube (airway edema)
             3. Use lower ET Tube cuff pressure to prevent trachea-esophageal fistula
       4. Endotracheal Intubation indications
          1. Includes all standard intubation indications
             1. See Advanced Airway
             2. Respiratory Failure
             3. Altered Mental Status
             4. Unprotected airway or inability to handle own secretions
          2. Expectation of further tracheal edema within next 24 hours
          3. Hoarseness or increasing Stridor (upper airway obstruction)
          4. Supraglottic edema and inflammation on bronchoscopy or Nasolaryngoscopy
          5. Severe Third Degree Burns to face or oropharynx
          6. Circumferential neck burn
          7. Prolonged transport and tenuous airway status
          8. Respiratory Muscle Fatigue
          9. Hypoventilation (PCO2>50 mmHg and pH <7.20)
          10. Hypoxemia despite maximal Supplemental Oxygen
              1. Carbon Monoxide >20% may require intubation due to Hypoxemia
    4. Other interventions
       1. Intravenous crystalloid
          1. See Burn Management (includes Parkland Formula)
          2. Maintain urinary output of 0.5 to 1 mL/kg/hour
       2. Opioid Analgesics
       3. Airway adjuncts to consider
          1. Bronchodilators (e.g. Nebulized Albuterol) for Wheezing, or Asthma Exacerbation
          2. Humidified oxygen (decreases thickness of secretions)
          3. Nebulized Epinephrine
             1. Consider for temporary stabilization of upper airway symptoms until definitive management
          4. Inhaled Mucolytics (may help clear Fibrin, mucus and debris from airway)
             1. Inhaled N-Acetylcysteine
             2. Inhaled Heparin
          5. Systemic Corticosteroids may be indicated in certain inhalations
             1. Examples: Nitrogen oxide, Zinc Oxide, sulfur trioxide, titanium tetrachloride
             2. Discuss with poison control, pulmonology or burn center
       4. Cyanokit (IV Hydroxycobalamin)
          1. Empiric therapy for suspected cyanide Poisoning
          2. Indications (Paris Fire Brigade Protocol)
             1. Known Smoke Inhalation in an enclosed space AND
             2. One of the following criteria
                1. Altered Mental Status
                2. Soot in nares or mouth
                3. Full cardiopulmonary arrest (without full body burns incompatible with life)
          3. Dosing
             1. Hydroxycobalamin (Vitamin B12a) 70 mg/kg up to 5 grams IV over 15 minutes
             2. May give a second dose up to 5 grams
          4. Efficacy
             1. Resulted in 50% ROSC rate in full arrest Smoke Inhalation patients
             2. Much safer empiric therapy than the Lily Kit (Methemoglobinemia, Hypotension)
             3. Hydroxycobalamin neutralizes Cyanide without affecting cellular oxygen use
          5. Adverse Effects
             1. Skin Flushing
             2. Red pigmented urine
          6. References
             1. Fortin (2006) Clin Toxicol 44 (suppl 1):37-44 +PMID:16990192 [PubMed]
             2. Borron (2007) Ann Emerg Med 49(6): 794-801 +PMID:17481777 [PubMed]
13. Disposition
    1. Monitor in Emergency Department for at least 4-6 hours
       1. Observe with serial exams, Vital Signs and diagnostics
       2. Discharge with close interval follow-up if normal observation without significant airway symptoms
    2. Hospitalization indications
       1. Enclosed space inhalation exposure for >10 minutes
       2. Sputum with soot
       3. pAO2 <60 mmHg
       4. Metabolic Acidosis
          1. Increased Anion Gap and Lactic Acidosis with cyanide Poisoning
       5. Carboxyhemoglobin >15%
       6. A-a Gradient >100 mmHg on 100% Supplemental Oxygen
       7. Significant symptoms or signs (Central facial burns, painful Swallowing or bronchospasm)
    3. Hyperbaric oxygen therapy indications
       1. Base Excess < -2 mmol/L
       2. Carboxyhemoglobin >25% (or >20% in pregnancy, in which fetal Hemoglobin is more CO avid)
       3. Cerebellar symptoms (e.g. Ataxia) or Altered Mental Status
       4. Pulmonary Edema
       5. Cardiac Arrhythmia or Acute Coronary Syndrome
       6. Very young or very old
14. References
    1. Lafferty in Alcock (2013) Smoke Inhalation Injury, Medscape EMedicine (accessed 12/11/2013)
    2. Latenser in Bope (2011) Burn Treatment Guidelines, Conn's Current Therapy, Elsevier, p. 1151
    3. Schwartz in Cydulka (2011) Tintinalli's Emergency Medicine 7ed, McGraw Hill, New York (accessed 12/11/2013)
       1. http://www.accessmedicine.com/content.aspx?aID=6385384
    4. Weir (2020) Crit Dec Emerg Med 34(12): 3-11