The performance of two intensive care humidifiers at high gas flows

High continuous flow breathing systems are now available to provide fresh gas flows well in excess of 100 l.min-1 in continuous positive airway pressure systems used for respiratory support. The performance of two commonly used intensive care humidifiers, the Kendal Conchatherm and the Fisher and Paykel FP310 have been assessed at flows of 50, 75, 100, 125 and 150 l.min-1. Their performance when using two humidifiers connected in parallel and in series was also studied. At a fresh gas flow of 100 l.min-1 the single Conchatherm gave an absolute water vapour concentration of 15.6 g.m-3 and the single FP310 11.9 g.m-3. At all flows the best results were achieved using two Conchaterm humidifiers in series. It is concluded that with high continuous flow breathing systems the humidification achieved with conventional humidifiers may be inadequate and it may be necessary to combine two humidifiers to obtain clinically useful humidification.