Original Article

The Temperature-Corrected Versus the Uncorrected PO₂ During Hypothermic Cardiopulmonary Bypass-Correlation with Oxyhemoglobin Saturation

Department of Anesthesiology and Department of Biostatistics and Epidemiology, American University of Beirut, Beirut, Lebanon

^* Address correspondence to: Anis S. Baraka, MD Professor and Chairman of Anesthesiology American University of Beirut Beirut, Lebanon

Abstract

In 8 adult patients undergoing cardiopulmonary bypass, the perfusion flow was altered from 2.4 to 1.8 and 1.2 L/min/m2 during hypothermia (26.5 ± 2.3°C). Following rewarming of the patients to 37°C, the perfusion flow was also altered from 2.4 to 1.8 and 1.2 L/min/m². The resulting mixed venous oxyhemoglobin saturation (SvO₂) was measured in vivo by in-line oximetry at the actual body temperature, and was correlated with the corresponding temperature-corrected and uncorrected mixed venous oxygen tension (PvO₂) as measured in the lab at 37°C. Venous blood at the entrance of the oxygenator was used for continuous in-line oximetry, blood gas sampling, and for measuring body temperature.

Correlation of SvO₂ at the different perfusion flows with the corresponding temperature-corrected PvO₂ during hypothermia is shifted to the leftofthecorrelation following rewarming ofthe patients to 37°C. In contrast, correlation of SvO₂ with the uncorrected PvO₂ is not significantly different from the normothermic relationship. Also, the uncorrected PvO₂ and SvO₂ during hypothermia at a perfusion flow of 1.2 L/min/m² were not significantly different from that achieved during normothermia at a flow of 2.4 L/min/m² Thus, maintenance of the temperature-uncorrected PO₂ during hypothermia at the normal normothermic value facilitates clinical interpretation and reflects a normal oxyhemoglobin saturation, irrespective of changing the body temperature.