FRESH GAS REQUIREMENTS OF AN ENCLOSED AFFERENT RESERVOIR BREATHING SYSTEM IN ANAESTHETIZED, SPONTANEOUSLY VENTILATING CHILDREN

We have determined the minimum fresh gas flow rate (F) for use with the Ohmeda enclosedafferent reservoir breathing system (EAR) in 10 anaesthetizedchildren breathing spontaneously. First, we determined the F required to prevent rebreathing asdetected by increased total ventilation (E) and end-tidal carbon dioxide partial pressure.Second, we used a mathematical model to calculate the degreeof rebreathing occurring at each F.A F equal to the predictedalveolar ventilation was sufficient to prevent clinically detectablerebreathing in all pateints. From the model, no rebreathingoccurred when F//E was 0.78 or more. We have shown previously thatthe EAR functions efficiently during controlled ventilationwith a F = 0.6x weight^0.5.As this F is slightly greaterthan the predicted alveolar ventilation, we suggest that theEAR may be used with a F =0.6 x weight ^0.5 regardless of the mode of ventilation.