Smoke inhalation

OVERVIEW

• Smoke is a complicated heterogeneous mixture of potentially toxic gases, chemical fumes, asphyxiants and particulate debris
• Smoke inhalation is commonly seen in patients with burns as a result of fire
• it is associated with high morbidity and mortality
• Consider concomitant carbon monoxide and/or cyanide poisoning (cyanide is produced by the combustion of plastics, wools and various polymers)

MECHANISM

• thermal injury to the airway and respiratory tract from steam and heated products of combustion
• chemical injury to the upper and lower respiratory tract due to irritant gases produced by thermal degradation and combustion e.g. nitrogen oxides, phosgene, HCl, etc
• systemic effects from lung-mediated absorption of toxic agents
• asphyxia due to oxygen consumption by fire and the production of asphyxiants such as carbon dioxide

ASSESSMENT

• suspect more severe smoke inhalation effects if exposed to fire in a confined space
• assess for airway injury and respiratory compromise
  — features of airway burns
  — upper airways: singed nasal airs, facial burns, soot in nose and pharynx, stridor, hoarseness
  — lower airways: wheeze, dyspnea, APO, ARDS
• suspect significant systemic toxicity if severity of presentation is out of keeping with degree of burns (e.g. coma, seizures, shock)
  — CO and/or CN, metHb

Investigations

• lactate (>10 mM is sensitive and specific for CN toxicity in the absence of severe burns)
• COHb
• methemoglobin
• CN levels (only useful for retrospective diagnosis)
• CXR
• spirometry/ PEFR
• other investigations appropriate to mechanism (e.g. associated trauma)

SpO2 is unreliable in the presence of metHb or CO poisoning

MANAGEMENT

Resuscitation

• ensure secure airway, early intubation is often appropriate if evidence of airway burns
• provide high flow oxygen (ideally FiO2 1.0 for carbon monoxide poisoning
• treat bronchospasm (e.g. salbutamol, iprotropium)
• treat ARDS/ non-cardiogenic pulmonary edema

Specific therapy

• treat coexistent burns
• treat suspected cyanide toxicity
  —sodium thiosulfate and hydroxocobalamin are preferred for suspected severe toxicity
• treat treat methemoglobinemia with methylene blue
• treat carbon monoxide therapy
  — high flow O2 (ideally FiO2 1.0) until asymptomatic, 24 hours if pregnant
  — the role of hyperbaric oxygen is controversial

Supportive care and monitoring

Disposition

• if no other injuries and asymptomatic at 6 hours then smoke inhalation patients can be discharge home with GP follow up
• patients with any respiratory symptoms should be admitted for observation, as delayed pneumonitis/ APO/ ARDS may occur
• pateints with severe effects need ICU admission

References and Links

LITFL

• CCC — Carbon Monoxide Poisoning
• CCC — Hyperbaric oxygen and carbon monoxide poisoning
• CCC — Cyanide Poisoning
• Toxicology Conundrum 038 — Smoking is deadly (2010)

FOAM and web resources

• EMCrit — Podcast 122 – Cardiac Arrest after the Toxicology of Smoke Inhalation with Lewis Nelson (2014)