Reliability of Displayed Tidal Volume in Healthy and Surfactant-Depleted Piglets

Volutrauma has been established as the key factor in ventilator-induced lung injury and can only be avoided if tidal volume (V_T) is accurately displayed and delivered. The purpose of this study was to investigate the accuracy of displayed exhaled V_T in a ventilator commonly used in small infants with or without a proximal flow sensor and using 3 methods to achieve a target V_T in both a healthy and lung-injured neonatal pig model.

This was a prospective animal study utilizing 8 male pigs, approximately 2.0 kg (range 1.8-2.2 kg). Intubated, sedated, neonatal pigs were studied with both healthy and injured lungs using the Servo-i ventilator. In pressure-regulated volume control, both with and without a proximal flow sensor, we used 3 methods to set V_T: (1) circuit compliance compensation (CCC) on, set V_T 6-8 mL/kg; (2) CCC off, calculated V_T using the manufacturer's circuit compliance factor; and (3) CCC off, set V_T 10-12 mL/kg to approximate a target V_T of 6-8 mL/kg. Ventilator-displayed exhaled V_T measurements were compared with exhaled V_T measured at the airway opening by a calibrated pneumotachograph. Bland-Altman plots were constructed to show the level of agreement between the two.

CCC improved accuracy and precision of displayed exhaled V_T when the sensor was not used, more markedly in the lung-injured model. Without CCC, the sensor improved accuracy and precision of displayed exhaled V_T, again more markedly in the lung-injured model.

When the Servo-i ventilator is used in neonates, CCC or the in-line sensor should be employed due to the large positive bias and imprecision seen with CCC off and no sensor in-line.