Makindo Medical Notes

Related Subjects: |Carbon monoxide poisoning |Cyanide toxicity

Oxygen Saturation measurements are unreliable in the presence of methaemoglobinaemia (metHb) or carbon monoxide (CO) poisoning. Pulse oximetry may appear normal despite severe hypoxia because CO “tricks” the oximeter into reporting a falsely high saturation.

🔎 About

• Always assess the wider context: Was this smoke inhalation only, or is there a risk of drug/alcohol overdose as well?
• Consider if the patient needs naloxone (opioids), or treatment for co-ingestants such as alcohol or sedatives.
• In smoke inhalation, also consider CO poisoning and cyanide toxicity.

⚠️ Aetiology

• Toxic components of smoke: carbon monoxide, hydrogen cyanide, irritant aldehydes.
• Thermal injury to the airway causing oedema and obstruction.

🚨 Risk Factors

• Exposure to fire/smoke in an enclosed space.
• Prolonged entrapment, impaired consciousness, or reduced GCS.
• Associated burns (especially facial and airway burns).

🩺 Clinical Features

• Upper airway injury: hoarseness, harsh cough, stridor, painful swallowing, voice change.
• Signs of facial burns: singed nasal hairs, soot in mouth/nasal secretions, inflamed oropharynx.
• Respiratory compromise: laryngospasm, bronchospasm, cyanosis.
• Systemic toxicity: confusion, headache, reduced GCS, seizures, coma (suggesting CO or cyanide).
• Carboxyhaemoglobin level >10% is considered significant (lower thresholds in children, pregnant women, and cardiac patients).

Lung injury from inhaled smoke and chemicals is a major cause of morbidity and mortality in burn victims, even without extensive external burns.

🔬 Investigations

• FBC, U&E, CRP.
• Arterial blood gas (ABG) with co-oximetry → essential to measure COHb and metHb.
• Check lactate – high levels suggest possible cyanide toxicity.
• Cyanide levels (if available, though not rapid).
• CXR: may be normal early, but can show pulmonary oedema or infection later.
• Pulmonary function (spirometry/PEFR) once stable.

⚠️ Complications

• Airway obstruction from progressive oedema.
• ARDS (non-cardiogenic pulmonary oedema).
• Ventilator-associated pneumonia (common if intubated).
• Hydrogen cyanide poisoning → may require hydroxocobalamin (preferred) or dicobalt edetate.
• CO poisoning → may require hyperbaric oxygen in severe cases (e.g. neurological symptoms, cardiac ischaemia, pregnancy with COHb >15%).

💊 Management

• Immediate ABCs – expert airway assessment; early intubation if any suspicion of impending obstruction.
• 100% high-flow O₂ via non-rebreather mask (or advanced airway if required).
• Bronchodilators, mucolytics, humidified O₂ for airway irritation.
• Hydroxocobalamin IV for suspected cyanide toxicity (especially with high lactate & cardiovascular collapse).
• Consider hyperbaric oxygen for severe CO poisoning (as above).
• Supportive care: IV fluids, pain management, treat burns/trauma.
• Specialist input: Burns/plastics, ENT/maxillofacial, ICU.

📚 References

• Management of acute smoke inhalation injury
• Current clinical management of smoke inhalation injuries
• NICE CKS: Burns and smoke inhalation
• Resuscitation Council (UK) guidance