12th March 2024

Carbon monoxide poisoning

Carbon monoxide (CO) poisoning occurs when there is poor ventilation and incomplete combustion, such as in low-quality housing with a faulty boiler. It is a colourless and odourless gas. CO binds to haemoglobin and myoglobin more readily than oxygen and causes a left shift in the oxygen dissociation curve. Hence, tissue ischaemia can occur despite a normal PaO2. CO poisoning symptoms vary from headaches, nausea and dizziness to altered mental state, weakness, seizures or ‘cherry red’ lips.

Pulse oximetry will give a falsely high reading; VBG/ABG and carboxyhaemoglobin levels are needed for diagnosis. If CO poisoning is suspected, then immediate high flow 100% oxygen is essential. Hyperbaric oxygen therapy indications include pregnancy, persistent confusion, neurological signs (not including headache), evidence of ischaemia on ECG and significant loss of consciousness.