ICU and trauma06 / 13
Carbon monoxide poisoning for forearm fixation27-year-old man, 74 kg, found drowsy beside a petrol generator running in a closed room
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Know this first
- Pulse oximetry and PaO2 do not detect carbon monoxide poisoning.
- Carboxyhaemoglobin half-life: roughly 4 hours breathing air, a little over 1 hour on 100% oxygen.
- HBOT: loss of consciousness, cardiac involvement, acidosis, or HbCO over 25%.
- Cyanide comes from burning plastics, fabrics and paper, not from engine exhaust alone.
The patient
27-year-old man, 74 kg, found drowsy beside a petrol generator running in a closed room; fell and fractured his forearm.
Headache and vomiting; unconscious briefly at the scene, now GCS 14. Pulse oximeter reads 99%.
CO-oximetry: carboxyhaemoglobin 28%; lactate 3.4 mmol/L; troponin rising. ECG: sinus tachycardia, no ST change.
Urgent open reduction of the forearm. Vitals: BP 132/80, HR 118, RR 24, temperature 36.8 °C.
The examiner asks
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Consider
What are your concerns?
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- A 27-year-old with significant CO poisoning and myocardial injury, for urgent forearm fixation. Patient
- As a trauma patient: he fell while unconscious, so I look for head and other injuries.
- His SpO2 of 99% means nothing; the oximeter can't see carboxyhaemoglobin. Disease
- CO grips haemoglobin about 200 times harder than oxygen, and poisons mitochondria too.
- Urgent, not emergency: if the hand is perfused, oxygen treatment comes first. Surgery
Prepare
How do you assess and treat him before surgery?
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- Diagnosis is by CO-oximetry on a blood gas; his level is 28%. (Disease)
- 100% oxygen now: half-life drops from about 4 hours to just over 1.
- He meets hyperbaric criteria: lost consciousness, cardiac injury and a level above 25%.
- No fire, so cyanide is unlikely; persistent acidosis means more severe CO injury and favours hyperbaric oxygen.
- Continuous ECG and serial troponin for his myocardial injury.
Plan
How do you anaesthetise him?
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- Surgery waits for hyperbaric treatment, as long as his hand is perfused. Surgery
- Regional block suits him: I can keep assessing his mental state, with oxygen on. Disease
- If he needs GA: FiO2 1.0 until his level is normal.
- No hypotension or tachycardia to load his injured myocardium.
- Monitored bed after, with cognitive follow-up for late sequelae. After surgery
Crisis
Under the block he develops runs of ventricular ectopy and 2 mm ST depression; BP 140/86, HR 124. What do you do?
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- Myocardial ischaemia from CO: 100% oxygen, tell the surgeon to pause. Crisis
- 12-lead ECG, troponin, electrolytes, and a gas with carboxyhaemoglobin.
- Treat pain and anxiety to slow his rate.
- If magnesium is low: 1–2 g over 15 minutes.
- Cardiac involvement adds weight to hyperbaric treatment; cardiology review. After surgery
Crisis
Forty minutes into recovery, with the axillary block in place, he starts fitting; SpO2 88%, BP 158/92, HR 128. Your management?
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- Fitting soon after a plexus block: LAST until proven otherwise; any local anaesthetic infusion stopped. Crisis
- Call for help, get the lipid kit, 100% oxygen and secure his airway.
- Benzodiazepine for the seizure: midazolam 1–5 mg IV.
- He is over 70 kg: lipid 20% about 100 mL over 2–3 minutes, then 250 mL over 15–20 minutes.
- If LAST is excluded: CO brain injury, a head injury from his fall, hypoglycaemia.
- CT head, then hyperbaric oxygen; neurology follow-up for late deficits. After surgery
Fatal mistakes
- Trusting a normal pulse oximeter reading.
- Withholding high-flow oxygen.
- Missing his myocardial injury.
Checked against: Miller 10e
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