Carboxyhaemoglobin can be measured with standard blood tests

EDITOR—In their editorial about carbon monoxide poisoning, Walker and Hay note that it is tissue poisoning rather than merely the effects of carboxyhaemoglobin that contributes to its toxicity.1 We recently reported that metabolic acidosis was a better indicator of the severity of poisoning than carboxyhaemoglobin,2 as the acidosis reflects tissue poisoning.

Walker and Hay concentrate on cerebral toxicity. The heart, however, as the next most vulnerable organ may help to give a clue to the diagnosis. We reviewed 139 electrocardiograms from patients with acute severe carbon monoxide poisoning who had been referred for treatment with hyperbaric oxygen, and we found that 41% were abnormal (unpublished data). Previously, 3% of patients presenting with unstable angina were found to have significant carbon monoxide intoxication.3 Thus the possibility of carbon monoxide poisoning should be considered when patients present with non-specific symptoms and have abnormalities on their electrocardiograms. Patients with known coronary disease who present with unstable angina and carbon monoxide intoxication should be given high flow oxygen via a tight fitting mask and reservoir bag (aiming to give 100%) in addition to standard treatment.

Arterial blood gases need not be used to measure carboxyhaemoglobin, as venous and arterial concentrations are not significantly different.4 Thus carboxyhaemoglobin can be measured simultaneously with other standard blood tests, without the need for an additional arterial puncture.

Doctors should inform Employment Medical Advisory Service

EDITOR—Walker and Hay's editorial was timely but did not put the issue into a proper public health context.1 A review by the Institute for Environment and Health on the health effects of carbon monoxide in the home is a useful starting point.2

About 50 people die from carbon monoxide poisoning in the home every year; about 30 ofthose deaths are associated with natural gas or liquefied petroleum gas. These figures remain similar year after year, but in 1998–9 the provisional data show a small increase. The risk of death from carbon monoxide poisoning associated with gas at 0.4 per million is, however, much lower than that from falls in the home (22.8 per million), poisoning (13.2 per million), and fire (7.5 per million). Nevertheless, carbon monoxide poisoning tends to affect old and disadvantaged people and is preventable.

The Health and Safety Executive is currently undertaking a fundamental review of gas safety and, in its discussion document, invites comments on a range of gas related issues such as carbon monoxide poisoning, monitors, and others.3

Doctors, especially in accident and emergency departments, need to be more aware of the possibility of carbon monoxide poisoning. The general public is already showing an increased awareness. Doctors can also help in another way. When a faulty appliance is reported and subsequently investigated, and especially when people in the household concerned show symptoms, the appliance is usually disabled and a notification of suspected carbon monoxide poisoning made to the local office of the Health and Safety Executive. Such a report puts in train a detailed investigation which may be unnecessary if, as is frequently the case, the incident is not one of carbon monoxide poisoning. It would be extremely helpful if details of patients' investigations (including carboxyhaemoglobin concentrations) could be released on request to a doctor in the Employment Medical Advisory Service so that the investigation by the Health and Safety Executive can be quickly concluded if no poisoning has occurred or, if it has, completed with full knowledge of the extent of the poisoning.