Flow requirements for the Bain breathing circuit during anaesthesia for Caesarean section

Abstract

We studied the relationship between arterial carbon dioxide tension (PaCO2) and fresh gas flow (FGF) during use of the Bain breathing circuit for Caesarean section anaesthesia. Thirty-one patients undergoing Caesarean section were anaesthetised using the Bain circuit with intermittent positive pressure ventilation. The PaCO2 were measured at FGF of 70ml·kg-1·min-1, 80 ml·kg-1min-1, and 100ml·kg-1·min-1. The FGF requirement to maintain a given PaCO2 during Caesarean section anaesthesia is the same as the requirements for nonpregnant subjects, despite the increase in carbon dioxide production associated with pregnancy. This is probably because the total FGF determined by body weight and given during Caesarean section anaesthesia is 15-20 per cent higher than nonpregnant levels, due to the weight gain associated with pregnancy. A FGF of 100 mlçkg-1 of pregnant weight/min maintains PaCO2 of 4.44 kPa predelivery, which is in the desirable range of PaCC2 during Caesarean section. © 1986 Canadian Anesthesiologists.