The alveolar-arterial difference in oxygen tension increases with temperature-corrected determination during moderate hypothermia

Moderate hypothermia (32-33 degrees C) occurs in anesthetic practice. Howev er, intrapulmonary gas exchange and the effect of temperature correction of blood gases on. oxygen and carbon dioxide exchange have not been investiga ted in these patients. We investigated alveolar-arterial difference in oxyg en tension (AaDO(2)) and arterial to end-tidal difference in carbon dioxide (Pa-ETCO2) during rewarming of eight ASA physical status I patients from h ypothermia of 32 degrees C. Anesthesia wits maintained with fentanyl/prapof al. AaDO(2) and Pa-ETCO2 were assessed by analyzing arterial blood gases an d saturated water vapor pressure, uncorrected or corrected to actual body t emperature. The respiratory quotient (RQ) was measured by calorimetry. Afte r temperature correction of blood gases and water vapor pressure, the AaDO( 2) was significantly higher at 33 and 32 degrees C compared with 36 degrees C (56 +/- 13 and 64 +/- 14 vs 39 +/- 10 mm Hg; P < 0.05 and P < 0.01). The deterioration of pulmonary oxygen exchange was not detected if arterial bl ood gases and water vapor pressure were not corrected. The RQ did not chang e during moderate hypothermia compared with 36 degrees C. The temperature-c orrected Pa-ETCO2 was not affected by hypothermia. We conclude that AaDO(2) is increased during moderate hypothermia. This is only detected when water vapor pressure and arterial blood gases are corrected to actual body tempe rature. Implications: We investigated intrapulmonary oxygen and carbon diox ide exchange during moderate hypothermia (32 degrees C) in eight patients. If oxygen, carbon dioxide, and water vapor pressure were corrected to actua l body temperature, the alveolar-arterial oxygen tension difference was inc reased during hypothermia. The carbon dioxide tension difference and the re spiratory quotient were unaffected by hypothermia.