Pulse oximetry oxygen saturation (SpO(2)) does not distinguish carboxy
hemoglobin (COHb) from oxyhemoglobin (O(2)Hb), giving a false impressi
on of the apparent degree of oxyhemoglobin saturation in smokers who h
ave elevated levels of COHb, We questioned whether accounting for smok
ing exposure history could improve description of pulse oximetry by co
rrecting for COHb levels, We evaluated smoking history and %SpO(2) as
predictors of %O-2,Hb and %COHb by CO-oximetry of arterial blood in 18
actively smoking and 18 age-matched nonsmoking patients in a clinical
pilot study. The difference between %SpO(2) and %O(2)Hb was significa
ntly greater (p < 0.001) in the smokers (5.6 +/- 3.1) than the nonsmok
ers (2.1 +/- 2.1). This difference correlated with %COHb (r(p) = 0.789
; p < 0.001) and the smoking exposure score (SES, r(p) = 0.621; p < 0.
001), a six-point index we developed based on whether patients mere ac
tive smokers, refrained from smoking prior to testing, or were exposed
to passive smoking in the home or workplace, The following formula su
mmarizes the correction: %O(2)Hb = 0.882[%SpO(2)] - 0.968[SES] + 9.245
(r(p) = 0.841; SES = 2.478; p < 0.001). This pilot study suggests tha
t smoking exposure history correlates with COHb levels and that correc
tion for smoking exposure improves the accuracy of pulse oximetry.