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), and at different stages of cooling: 30°C, 25°C, and 18°C.

For 3 months, a prospective study was conducted on patients who underwent pulmonary thromboendarterectomy.

This was a single-center study done in a university teaching hospital.

Patients who underwent pulmonary thromboendarterectomy during the inclusion period.

Hemodynamic and biological data were recorded from arterial and venous blood gas samples withdrawn first at normothermia, then at 30°C, 25°C, and 18°C.

24 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 18°C, the median venoarterial difference of O₂ bound to hemoglobin was 2.22 [1.68-2.58] and 0.03 mL [0.01-0.07] of O₂/100 mL of blood, respectively (p < 0.001). Whereas the median venoarterial differences in dissolved O₂ were 0.78 [0.66-0.92] and 1.09 mL [1.03-1.32] of O₂/100 mL of blood, respectively (p = 0.0013).

There were VO₂ and OE decreases of more than half their baseline values at 18°C. Given that metabolic needs are essentially supplied by dissolved O₂ during cooling from 30°C to 18°C, the authors suggest that PaO₂ should be increased during the period of cooling and/or deep hypothermia to prevent hypoxia.