The effect of circuit compliance on delivered ventilation with use of an adult circle system for time cycled volume controlled ventilation using an infant lung model

This in vitro study examined the effect of circuit compliance on delivered ventilation (V(E)) using a time-cycled, volume controlled circle system in an infant lung model. A Bio-Tek ventilator tester set to simulate normal and abnormal lung compliance measured V(E) delivered by the Narkomed 2B system. Circle circuits of varied compliance (2.75, 1.22 and 0.73 μl · cm H₂O^-1) were tested. Tidal volume was adjusted to peak inflation pressures (PIP) of 20, 30, 40, and 50 cm H₂O with three circuits, two lung compliances, and four different size tracheal tubes (TT) (2.5, 3.5, 4, 4.5 mm ID). Data were analysed using the multiple regression technique. Delivered V(E) was directly related to PIP and lung compliance. Delivered V(E) was not affected by the choice of circuit. TT size had minimal effects on V(E) when lung compliance was low; TT size was a more important factor when test lung compliance was normal. Extrapolating this data to the clinical setting, adequate ventilation of infants can be achieved with an adult circle system if an appropriate PIP is chosen, regardless of the compliance of the circuit used. Infants with poor lung compliance may require very high PIP for adequate ventilation.