🌫️ Chapter 127: Carbon Monoxide Poisoning

COHb → left shift of oxyhaemoglobin curve · Cherry red colour (uncommon) · Headache, confusion, coma · 100% oxygen (half-life 90 min vs 5h room air) · Hyperbaric oxygen (neurological symptoms, COHb >25%) · Co-oximetry · Neuropsychological sequelae

🔍 Core Concepts: Carbon Monoxide Poisoning

📌 Mechanism
CO binds haemoglobin with 210x affinity of O2 → carboxyhaemoglobin (COHb). Shifts O2 dissociation curve left → tissue hypoxia. Also binds myoglobin, cytochrome oxidase → direct cellular toxicity.
⚠️ Clinical Features
Mild (COHb 10-20%): headache, nausea, confusion. Moderate (20-40%): fatigue, visual changes, tachycardia, tachypnoea. Severe (>40%): coma, seizures, cardiovascular collapse. Cherry red skin is rare.
📊 Diagnosis
COHb by co-oximetry (ABG machine cannot measure). Pulse oximetry overestimates SpO2 (cannot distinguish COHb from oxyHb). ABG shows normal PaO2 with low O2 content.
💨 100% Oxygen (Mainstay)
Half-life COHb: room air 4-5h; 100% O2 90 min; hyperbaric O2 (2.5-3 ATA) 30 min. Give via non-rebreather mask immediately.
⚡ Hyperbaric Oxygen (HBO)
Indications: COHb >25%, neurological symptoms (loss of consciousness, seizures, focal deficits), cardiac ischaemia, pregnancy with COHb >15-20%. Reduces risk of delayed neurological sequelae.
🧠 Delayed Neurological Sequelae
Occurs days to weeks after recovery: memory loss, parkinsonism, personality changes. Hyperbaric oxygen may reduce risk.

🩺 Stepwise Approach: Carbon Monoxide Poisoning

1
Remove from source & give high-flow O2
100% oxygen via non-rebreather mask immediately. Half-life of COHb 90 min on 100% O2 (vs 5h on room air). Intubate if comatose.
2
Confirm diagnosis (co-oximetry)
Draw blood for COHb (ABG machine cannot measure). Pulse oximetry unreliable (overestimates SpO2). PaO2 normal but oxygen content low.
3
Assess severity (neurological, cardiac)
GCS, focal deficits, seizures, ECG for ischaemia, troponin. Pregnancy test if applicable.
4
Hyperbaric oxygen (HBO) indications
COHb >25%, loss of consciousness, neurological symptoms (seizures, focal deficits), cardiac ischaemia, pregnancy with COHb >15-20%, severe metabolic acidosis. HBO reduces delayed neurological sequelae.
5
Monitor for delayed sequelae
Neurological symptoms may recur days to weeks later (memory loss, parkinsonism). MRI may show basal ganglia changes.
6
Disposition
Asymptomatic with COHb <10% may be discharged after 4-6h observation. Symptomatic patients or COHb >10-15% require admission. PICU for severe cases.