FFinalistSouthampton · 2027
Acute care
AKT · Acute care/Toxicology & overdoselow yield

Carbon monoxide poisoning

CO binds haemoglobin (carboxyhaemoglobin) → tissue hypoxia

Overview

Colourless, odourless gas (faulty boilers, fires, generators) that binds haemoglobin with high affinity, causing tissue hypoxia despite a NORMAL SpO2 on pulse oximetry (which cannot distinguish carboxyhaemoglobin). Treated with high-flow 100% oxygen.

Recognise

  • Headache, nausea, dizziness, confusion; "flu-like" with no fever; multiple household members affected
  • Reduced consciousness, seizures; (classic but late/unreliable) cherry-red skin
  • Pulse oximetry reads NORMAL despite hypoxia

Red flags

  • Reduced consciousness, neurological signs, cardiac ischaemia, pregnancy → consider hyperbaric oxygen

Differentials & how to tell them apart

Viral illness/migraineno source/co-exposure, normal COHb
Other cause of reduced GCSglucose, toxicology; COHb level distinguishes
Cyanide co-exposure (smoke)severe acidosis/lactate from a fire — may need hydroxocobalamin

Investigations

Carboxyhaemoglobin level (ABG co-oximetry — not standard SpO2), ECG/troponin (cardiac), glucose; ask about the source/co-exposed people.

Management

High-flow 100% oxygen via non-rebreathe mask; hyperbaric oxygen for severe cases

  1. 1Remove from the source; high-flow 100% oxygen via a non-rebreathe mask (greatly shortens COHb half-life); check COHb and ECG.Gate: A NORMAL SpO2 does NOT exclude CO poisoning — pulse oximetry cannot tell oxyhaemoglobin from carboxyhaemoglobin; use co-oximetry/COHb
  2. 2Severe features (loss of consciousness, neurological/cardiac signs, pregnancy) → discuss hyperbaric oxygen; safety advice + source remediation.
High-flow 100% oxygen (non-rebreathe) — reduces COHb half-life; continue until symptoms resolve/COHb normal
Hyperbaric oxygen — consider for severe features (LOC, neuro/cardiac signs, pregnancy)

Key points

Suspect when a household/group present together with headaches that improve away from home. SpO2 is falsely reassuring. Pregnancy lowers the threshold for hyperbaric oxygen (fetal Hb).

Monitor & prognosis

COHb, neurological status, ECG/troponin; delayed neuropsychiatric sequelae.

Good with early oxygen; delayed neurological sequelae can occur.

Source: TOXBASE; UK CO poisoning guidance