Objectives: The aim of this physiological pilot study was to investigate the effect of deep hypothermia on oxygen extraction (OE) and consumption (VO2) in normothermic conditions (36-37°C) then at different stages of cooling: 30°C, 25°C and 18°C. Design: For three months, we conduct a prospective study on patients that underwent pulmonary thromboendarterectomy. Settings: This is a single center study done in a university teaching hospital. ParticipantsPatients that underwent pulmonary thromboendarterectomy during the inclusion period. InterventionsHemodynamic and biological data were recorded from arterial and venous blood gas samples withdrawn first at normothermia, then at 30°C, 25°C and 18°C.. Measurements and Main Results24 patients were included in the final analysis. Indexed VO2 decreased from 65.9 ml to 25.1 ml of O2/min/m2 between 36°C and 18°C (p<0.001). The OE decreased from 18% to 9% between 36°C and 18°C (p<0.001). At normal temperature and at 18°C, the median venoarterial difference of O2 bound to hemoglobin was 2.22 [1.68-2.58] and 0.03 [0.01-0.07] ml of O2/100 ml of blood, respectively (p<0.001). Whereas the median venoarterial difference of dissolved O2 was 0.78 [0.66-0.92] and 1.09 [1.03-1.32] ml of O2/100 ml of blood, respectively (p=0.0013). Conclusion: There is a VO2 and OE decrease of more than half of their baseline value at 18°C. Seeing that the metabolic needs are essentially supplied from dissolved O2 during cooling from 30°C to 18°C, we suggest that PaO2 should be increased during the period of cooling and/or of deep hypothermia to prevent hypoxia.
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