[Carbomonoxyhemoglobin and methemoglobin in patients with and without a smoking history during ambulatory anesthesia. Consequences for the use of pulse oximetry].

Carboxyhemoglobin (COHb) and methemoglobin (MetHb) in venous blood were determined by oximetry in 1000 non-hospitalised preoperative patients. 370 of them were smokers (S), 630 non-smokers (NS). In addition, in five S we compared the oxygen saturation measured by pulse oximetry (SaO2, p) with that measured by in vitro oximetry (SaO2) and that calculated with reference to COHb (SaO2,korr). MetHb (0.66 +/- 0.21%, mean +/- standard deviation) was found to be of no relevance. COHb in S (5.12 +/- 2.25%, maximum 12.4%) was significantly higher than in NS (1.82 +/- 0.3%, range 0.9%-4.0%) and is therefore of importance in S for the oxygen transport and for the interpretation of SaO2, p, which overestimated SaO2 at a COHb level of 4.4 +/- 0.7% by 4.5 +/- 0.9%. The difference between SaO2, korr (calculated according to Forstner) differed from SaO2 by 0.66 +/- 0.5% only. We conclude that there is an indication for in vitro oximetry in non hospitalised smokers or cases of unknown smoking history. If oximetry is not available, both a reduction of O2-binding hemoglobin and an overestimation of SaO2 by pulse oximetry in an order of ten per cent should be taken into account. To compensate for dyshemoglobin fractions, pulse oximetry using more than two wavelengths is desirable.