Fresh gas formulae do not accurately predict end-tidal PCO2 in paediatric patients.

To determine the fresh gas flow (FGF) requirements in paediatric patients, we measured the FGFs needed to maintain distal end-tidal PCO2 (PETCO2) values at 30 and 38 mmHg in patients weighing between 3.8 and 20 kg ventilated with either a Sechrist Infant Ventilator IV-100B or an Air-Shields Ventimeter and a Mapleson D circuit. The FGF requirement was 500 ml.kg-1.min-1 to maintain a PETCO2 of 30 mmHg and 250 ml.kg-1.min-1 to maintain a PETCO2 of 38 mmHg when minute ventilation greater than or equal to FGF. When these formulae were used in a subsequent group of similar patients, a wide variation in PETCO2 measurements were obtained. We conclude that the safest and most accurate approach to determine the FGF requirement of paediatric patients is to continuously monitor the PETCO2 in each patient and to adjust the FGF accordingly.