Metabolic and hemodynamic response to hyperventilation in patients with head injuries

The effects of controlled moderate hyperventilation (paCo2 approximately 31 mmHg) on cardiovascular parameters and whole-body-oxygen-uptake (VO2) was studied in 10 patients with head injuries, who were unconscious and artificially ventilated at the time of the investigation. VO2 was measured with the Beckmann Metabolic Measurement Cart and also calculated from cardiac output and arterio-mixed venous oxygen content difference. A mean increase in VO2 (+ 19.6% of control) was observed after 2 h of hyperventilation. Cardiac output remained unchanged. This resulted in a decrease of venous oxygen content and impaired full oxygenation of the blood. Our results indicate that hyperventilation should not be a routine procedure. Close monitoring of arterial and venous blood gases is recommended, when hyperventilation is applied.