A Retrospective Study on Carboxyhaemoglobin Half-Life in Acute Carbon Monoxide Poisoning in Patients Treated with Normobaric High Flow Oxygen

Abstract

Objective There has been a vast difference in the reported value for carboxyhaemoglobin (COHb) half-life (COHbt½) in carbon monoxide (CO) poisoning patients breathing 100% normobaric oxygen (O2). This could be due to the fact that all previous studies were performed on heterogeneous groups of patients with different aetiology. We wished to determine the COHbt½ in a homogenous group of acute CO poisoning patients who attempted suicide by burning charcoal and were treated with normobaric high flow oxygen. Methods It was a retrospective descriptive cohort study for a period of 60 months (January 2001 to December 2005). Setting Accident and Emergency Department of Tuen Mun Hospital, serving a population of 1.5 millions. Population We recruited all cases of CO poisoning by burning charcoal for suicidal attempt and we excluded the cases if (1) there was only one COHb measurement; (2) the patient had not received high flow O2 therapy via tightly fitting facial mask with O2 reservoir, given before the first blood sample or throughout the period until a second blood sample was taken; (3) the first COHb was <10%; (4) the second COHb was <2%; (5) there was significant co-poisoning; (6) the patient was haemodynamically unstable; or (7) the time of blood sampling was not documented. We believed that the elimination of COHb under 100% normobaric O2 was constant and followed a simple exponential decay. Results Forty-three (27.4%) cases met all of the selection criteria and the mean COHbt½ was 78±9 minutes. Conclusion We believed that our patients (i.e. CO poisoning patients who committed suicide by burning charcoal) represented a homogenous group of acute CO poisoning of unique aetiology. The estimated COHbt½ would be useful in deciding the length of normobaric oxygen therapy for this group of patients.