Predicted normocapnea in infants and children using the Bain circuit with controlled ventilation

Abstract

We have constructed a nomogram for fresh gas flow (VFG) and minute ventilation (VE) for paediatric anaesthesia during controlled ventilation using the Bain coaxial Mapleson D circuit. VFG was based upon the assumption of a high fresh gas utilization because of a low VFG/VE ratio (0.67) and known figures of carbon dioxide elimination. The formulas VFG = 27.8 x VCO2 and VE = 1.5 x VFG were used to calculate the necessary flows to generate normocapnea. The nomogram was evaluated in 59 children (6-62 kg, age 5 months-14 years). PaCO2 (mean +/- s.d.) was 5.0 +/- 0.5 kPa (38 +/- 4 mmHg) with a total range of 3.9-6.3 kPa (29-47 mmHg). Ninety percent of the children had a PaCO2 of 5.7 kPa (43 mmHg) or lower. There was no correlation between body weight and PaCO2. Hence, there was no difference in mean values between children below or above a body weight of 20 kg.