Introduction: The carboxyhemoglobin half-life (COHb t1/2) during hyperbaric oxygen (HBO₂) is often quoted as 23 minutes, derived from the average of two adult male volunteers breathing HBO₂ at 3 atmospheres absolute (ATA). However, the mean COHb t1/2 of 12 male volunteer smokers was 26.3 minutes at 1.58 ATA and in 12 non-intubated carbon monoxide (CO) poisoned patients treated at 3 ATA, was 43 minutes.
Case report: An 81-year old male, poisoned by an improperly ventilated natural gas heater, was intubated for coma, then treated with HBO₂. His PaO₂/FiO₂ = 283 from aspiration. His initial COHb was 34.4%, and 18 minutes before HBO₂, 5.9%. After a compression interval of 17 minutes, the COHb measured after 22 minutes at 3 ATA was 3.3%.
Results: By exponential decay, his COHb t1/2 before HBO₂ was 95 minutes. We estimate the range for COHb t1/2 during compression as 62-81 minutes and for the 3-ATA interval, 58 to 49 minutes, respectively. The mid-point estimate of COHb t1/2 at 3 ATA was 53 minutes.
Conclusions: The COHb t1/2 we calculated is greater than previously reported, but longer in our patient possibly because of concomitant respiratory failure, lung dysfunction, and mechanical ventilation. The often-cited COHb t1/2 of 23 minutes, likely underestimates the actual COHb t1/2 in CO-poisoned patients, especially those with cardiopulmonary dysfunction.
Keywords: carbon monoxide poisoning; carboxyhemoglobin; elimination; half-life; hyperbaric oxygen.