Physiological dead space during general anaesthesia for Caesarean section.

The physiological dead space and its components were determined during general anaesthesia for Caesarean section in seventeen patients and compared with similar values for seventeen patients undergoing abdominal hysterectomy under general anaesthesia. The physiological dead space was smaller in the pregnant patients, due to a smaller alveolar dead space. The anatomical dead space was similar in both groups. A lowered physiological dead space suggests that there will be a decrease in the pulmonary ventilation perfusion ratio (V/Q) during Caesarean section; this could result from better perfusion of the ventilated alveoli than in the non-pregnant group, due to the increased cardiac output of pregnancy. An improvement in alveolar perfusion should also produce more efficient carbon dioxide elimination in pregnant patients, when compared to non-pregnant subjects.