Effect of Deep Hypothermia (18°C) on Dioxygen Metabolism During Pulmonary Thromboendarterectomy Surgery

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

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

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

Participants: Patients who underwent pulmonary thromboendarterectomy during the inclusion period.

Interventions: Hemodynamic and biological data were recorded from arterial and venous blood gas samples withdrawn first at normothermia, then at 30°C, 25°C, and 18°C.

Measurements and main results: 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).

Conclusion: 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.