Carbon Monoxide Toxicity

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🚨 Carbon Monoxide (CO) Poisoning → Invisible, odourless, colourless gas ⚠️. Not detected by a pulse oximeter ❌ (SpO₂ unreliable). Diagnosis = 🩸 ABG with carboxyhaemoglobin (CoHb). Prognosis depends on ⏱️ rapid removal from source + 100% O₂ therapy. Normal CoHb <10% (up to 10% in smokers 🚬). Severe >30% 🟥.

ℹ️ About

• CO binds Hb with 240× affinity of O₂ → forms CoHb 🩸.
• Shifts O₂–Hb curve left ⬅️ → impaired O₂ release to tissues.
• Also inhibits mitochondrial cytochrome oxidase → blocks electron transport chain → cellular hypoxia ⚡.
• Half-life: 320 min (room air) → 80 min (100% O₂) → 20–30 min (HBOT).

🔎 Aetiology

• 🏠 Faulty boilers, heaters, poorly ventilated gas appliances.
• 🚗 Vehicle exhaust fumes in enclosed space.
• 🔥 House fires (common in winter).
• ⚙️ Occupational exposure: welders, industrial workers.

🩺 Clinical Features

• Early: Headache 🤕, dizziness, nausea, malaise.
• Neuro: Confusion, irritability, seizures, coma 🧠.
• Cardiac: Chest pain, arrhythmias, ischaemia ❤️.
• Skin: "Rosy/pink" appearance 🌹 (misleading sign).
• Delayed sequelae: Memory loss, personality change, parkinsonism (post-hypoxic encephalopathy) 🧠⏳.

🔬 Investigations

• 🩸 ABG: CoHb level (gold standard). Often lactic acidosis from hypoxia.
• FBC: check for polycythaemia in chronic cases.
• U&E, lactate, CK/troponin (myocardial/renal injury).
• ECG: arrhythmias, ischaemia.
• CT head: if coma or persistent neurological symptoms.

📊 Assessing CoHb Levels

• Normal: 1–3% (non-smokers), up to 10% in smokers 🚬.
• >10% = exposure, >20% = symptomatic, >30–40% = severe 🔴.
• Pregnancy: fetal Hb binds CO tighter → increased risk 👶.

💊 Management

• 📞 Call NPIS/TOXBASE for guidance.
• ABC + 100% O₂ at 15 L/min via non-rebreather until CoHb <5%.
• 💉 IV fluids: correct dehydration & support renal function.
• ❤️ ECG & cardiac monitoring for ischaemia/arrhythmias.
• 🧠 Neuro checks for cerebral oedema. Consider mannitol if raised ICP.
• HBOT: if CoHb >25%, neuro/cardiac involvement, pregnancy, or coma.

⚠️ Complications

• 🧠 Delayed neuro sequelae: memory deficits, cognitive decline, parkinsonism.
• ❤️ Cardiac: MI, arrhythmias, heart failure.
• 📉 Multi-organ dysfunction due to persistent hypoxia.
• 👶 Pregnancy: fetal death or developmental issues.

🛡️ Prevention

• 🏠 CO detectors near bedrooms & gas appliances.
• 🔧 Regular servicing of boilers, heaters, chimneys.
• 🌬️ Ensure proper ventilation of fuel-burning appliances.
• 📢 Public education campaigns (esp. winter months).

Case 1 – “Flu” at home that isn’t

A 34-year-old and two family members develop morning headache, nausea, dizziness that improve when outside; boiler recently serviced. Vitals normal; SpO₂ 98% on air (can be falsely reassuring). ABG with co-oximetry shows COHb 18%. Manage with 100% high-flow oxygen via non-rebreather until COHb <5% and symptoms settle; do ECG/troponin and neuro exam. Ventilate the property, switch off the appliance, and advise calling the UK Gas Emergency Service (0800 111 999)/Gas Safe engineer to inspect. Discharge with CO alarm advice and safety-netting for neuro symptoms.

Case 2 – High-risk exposure (pregnancy)

A 28-year-old pregnant woman has syncope and confusion after time in a garage with a running car; exam: mild ataxia. SpO₂ 99% on air; COHb returns at 12% (maternal) but fetus is more vulnerable. Start 100% oxygen immediately, continuous fetal monitoring, labs/ECG. Discuss hyperbaric oxygen with a specialist (consider for pregnancy, neurological signs, loss of consciousness, cardiac