Editors

MikaValtonen

JouniKurola

Carbon Monoxide Poisoning

Carbon monoxide (CO) is formed by incomplete combustion. Air CO levels exceeding 0.01% will cause poisoning symptoms and levels exceeding 0.2% cause immediate death.
Carbon monoxide poisoning leading to death is most often caused by a domestic fire or suicide. Accidental poisonings are caused by petrol-driven motors running at idle in a closed space, by various heaters that use fuels or gas, and also by traditional wood-burning heaters. The severity of poisoning is dependent both on the concentration of CO and on the exposure time.
Regular pulse oximetry does not distinguish between carboxyhaemoglobin (COHb) and oxyhaemoglobin (OHb) and thus gives false normal results even for a severely anoxic victim.
If carbon monoxide poisoning is associated with a burn injury, a burn centre should be consulted.

As the binding affinity of CO for haemoglobin is 210 times that of oxygen, CO reduces the blood oxygen transport capacity.
The release of oxygen from haemoglobin to tissues is impaired.
- The dissociation curve is shifted to the left.
A direct cyanide-like effect blocking cell respiration

Clinical suspicion based on the history of events is of primary importance.
- Fire victim
- Person found unconscious in a wood-heated apartment, a car or garage
The level of carboxyhaemoglobin (COHb %) in arterial blood should be measured.
- For equivalent carbon monoxide and carboxyhaemoglobin levels, see Table T1.
- A COHb level exceeding 10% always signifies poisoning.
The partial pressure of oxygen in arterial blood is normal.
There is often also respiratory alkalosis Blood Gas Analysis and Acid-Base Balance.

Administration of 100% oxygen should be started immediately.
- Reservoir mask, securing the airway, as necessary
Oxygen therapy should be continued until symptoms subside and COHb levels fall below 5%.
- The half-life of COHb is about 5 h when breathing air, 80-100 min. when breathing 100% oxygen, and 20 min. with hyperbaric oxygen therapy.
- COHb levels should be extrapolated back to the end of exposure (levels falling by about 50% an hour when breathing 100% oxygen).

There is no clear evidence for the benefit of HBOT in carbon monoxide poisoning.
HBOT is recommended for severe carbon monoxide poisoning.
Minimizing the delay to treatment will improve the prognosis.
Primarily, carboxyhaemoglobin should be measured in the emergency unit and other severe causes of disturbed consciousness should be excluded before transfer.
Find out about locally available units with HBOT and relevant policies.

The patient is or has been unconscious.
Besides headache, the patient has other neurological symptoms.
The patient has severe cardiovascular symptoms.
The blood concentration of COHb extrapolated back to the time of exposure is > 40%, even if the patient is asymptomatic.
The blood concentration of COHb is > 20% and the patient is pregnant.
- There is a high risk of foetal poisoning.