Abstract
In neonates, small changes in tidal volumes (VT) may lead to complications. Previous studies have shown a significant difference between ventilator-measured tidal volume and tidal volume delivered (actual VT). We evaluated the accuracy of three different ventilators to deliver small VT during volume-controlled ventilation.
We tested Servo 300, 840 ventilator and Evita 4 Neoflow ventilators with lung models simulating normal and injured neonatal lung compliance models. Gas volume delivered from the ventilator into the test circuit (VTV) and actual VT to the test lung were measured using Ventrak respiration monitors at set VT (30 ml). The gas volume increase of the breathing circuit was then calculated.
Tidal volumes of the SV300 and PB840 in both lung models were similar to the set VT and the actual tidal volumes in the injured model (20.7 ml and 19.8 ml, respectively) were significantly less than that in the normal model (27.4 ml and 23.4 ml). PB840 with circuit compliance compensation could not improve the actual VT. VTV of the EV4N in the normal and the injured models (37.8 ml and 46.6 ml) were markedly increased compared with set VT, and actual VT were similar to set VT in the normal and injured model (30.2 ml and 31.9 ml, respectively). EV4N measuring VT close to the lung could match actual VT to almost the same value as the set VT, however the gas volume of the breathing circuit was increased.
If an accurate value for the patient's actual VT is needed, this VT must be measured by a sensor located between the Y-piece and the tracheal tube.