ALTERATIONS IN PHARMACOKINETICS OF CARBOXYHEMOGLOBIN PRODUCED BY OXYGEN UNDER PRESSURE

The pharmacokinetic effect of elevated oxygen partial pressures in the elimination of carboxyhemoglobin (COHb) by O-2 administration was stu died in an inflatable hyperbaric chamber. A double crossover prospecti ve analysis between the modified Gamow bag and non-rebreather (NRB) ma sk O-2 was conducted among 12 healthy, adult volunteers who smoked fiv e cigarettes sequentially within a 60-min period. COHb levels were mea sured using co-oximetry before and after smoking. Subjects inspired hy perbaric oxygen (HBO2) and normobaric oxygen (NBO2) in separate trials for 40 min. Mean COHb levels (1.16 +/- 0.28 g/dl) post-smoking were r epresentative of low-level poisoning. NBO2 consisted of a NRB mask at a rate of 15 liter/min outside the Gamow bag. HBO2 was delivered insid e the Gamow bag with a demand valve regulator mask at a Po-2 of 1.58 a tm abs. A significant increase in the half-life (t1/2) of COHb was obs erved for each subject in the Gamow bag (P < 0.05; repeated measures a nalysis of variance). Average t1/2 for COHb was 26.3 +/- 3.7 min (n = 12) and 71.3 +/- 9.9 min (n = 12) while breathing HBO2 and NBO2, respe ctively. Pharmacokinetic modeling was performed using PCNONLIN softwar e for each subject. Both zero and first order elimination kinetics wer e tested and the model of best fit determined using the Akaike Informa tion Criterion for each subject. A significant shift in COHb eliminati on from a zero to first order mechanism with elevation in O-2 partial pressure was observed (P = 0.002; McNemar's test). HBO, provides a pha rmacokinetic advantage over NRB mask O-2 in eliminating mild carboxyhe moglobinemia.