Fresh gas flow in the Bain circuit during laparoscopy

Twenty-two women were studied during laparoscopy with abdominal insufflation of carbon dioxide. A bain anaesthetic breathing circuit was used with a fresh gas flow (VFG) of 110 ml.min-1.kg-1, and controlled ventilation was applied with a minute ventilation (VE) of 175 ml.min-1.kg-1. Arterial blood gases were analysed at the end of the operation. Nineteen of the women (86 per cent) were found to have a PaCO2 within the range for normocapnia (i.e., 4.7-5.9 kPa (35-45 mmHg), two were hypocapnic with a PaCO2 of 4.4 and 4.5 kPa (33 and 34 mmHg) respectively and one was found to have a PaCO2 of 6.2 kPa (46.5 mmHg). It was concluded that the carbon dioxide absorbed from the abdomen during laparoscopy demands fresh gas flows that are higher than normally used in the Bain circuit if a PaCO2 within the normal range is to be obtained. A simultaneous increase in VFG and VE of about 45 per cent is sufficient to achieve normocapnia.