Carboxyhemoglobin levels in carbon monoxide poisoning: do they correlate with the clinical picture?

OBJECTIVE It is commonly written that carboxyhemoglobin (COHb) measurements correlate with the clinical presentation of patients poisoned with carbon monoxide (CO). However, the evidence supporting this concept is scanty. The present study was performed to analyze COHb measurements in a large population of patients with CO poisoning to determine whether clinically significant correlates exist. METHODS Records of all patients treated with hyperbaric oxygen for acute CO poisoning at a single private academic medical center from 1978 to 2005 were reviewed. The COHb measurements were analyzed with regard to sex, age, source of CO, loss of consciousness, endotracheal intubation, arterial pH, and death. RESULTS Data from 1603 CO-poisoned patients were reviewed, and 1407 were included in the final analysis. Statistically higher COHb measurements were associated with male sex (24.2% +/- 11.2% vs 21.5% +/- 11.6), adult age range (24.0% +/- 11.0% vs 19.5% +/- 10.3%), poisoning by CO from fires (25.7% +/- 12.1%) or motor vehicles (22.7% +/- 24.7%), loss of consciousness (24.3% +/- 12.2% vs 22.3% +/- 9.4%), lower arterial pH, and death (32.1% +/- 12.8% vs 23.1% +/- 0.9%). CONCLUSIONS Despite the fact that statistically significant differences in average COHb measurements were seen with regard to a number of variables, the clinical significance of these differences appeared to be minimal. Moreover, the utility of COHb measurements as predictors of clinical status in CO poisoning was not apparent. At least in part, this likely relates to delay and interval oxygen administration before obtaining COHb measurements.