Maternal blood-gas tensions (PAO2-PaO2), physiological shunt and Vd/Vt during general anaesthesia for Caesarean section.

Measurements of maternal blood-gas tensions, (PAO2-PaO2), calculated pulmonary venous admixture (physiological shunt) and deadspace/tidal volume ratio (VD/VT) were made in 14 patients undergoing Caesarean section. Measurements were carried out after induction of general anaesthesia, and before delivery, with the patient tilted to the left. With a mean inspired oxygen concentration of 67.5% mean PaO2 was 44.3 kPa, mean (PAO2-PaO2) 18.4 kPa, mean Vd/Vt 32% and mean physiological shunt 9.5%. The findings are compared with published values for non-anesthetized pregnant patients.