Metabolic and hemodynamic response to hyperventilation in patients with head injuries

The effects of controlled moderate hyperventilation (paCo₂∼31 mmHg) on cardiovascular parameters and whole-body-oxygen-uptake (\(\dot VO_2 \))was studied in 10 patients with head injuries, who were unconscious and artificially ventilated at the time of the investigation. \(\dot VO_2 \)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 \(\dot VO_2 \)(+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.