Reliability of displayed tidal volume in healthy and surfactant-depleted piglets

Abstract

BACKGROUND: Volutrauma has been established as the key factor in ventilator-induced lung injury and can only be avoided if tidal volume (VT) is accurately displayed and delivered. The purpose of this study was to investigate the accuracy of displayed exhaled VT in a ventilator commonly used in small infants with or without a proximal flow sensor and using 3 methods to achieve a target VT in both a healthy and lung-injured neonatal pig model. METHODS: 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 VT: (1) circuit compliance compensation (CCC) on, set VT 6–8 mL/kg; (2) CCC off, calculated VT using the manufacturer’s circuit compliance factor; and (3) CCC off, set VT 10–12 mL/kg to approximate a target VT of 6–8 mL/kg. Ventilator-displayed exhaled VT measurements were compared with exhaled VT measured at the airway opening by a calibrated pneumotachograph. Bland-Altman plots were constructed to show the level of agreement between the two. RESULTS: CCC improved accuracy and precision of displayed exhaled VT when the sensor was not used, more markedly in the lung-injured model. Without CCC, the sensor improved accuracy and precision of displayed exhaled VT, again more markedly in the lung-injured model. CONCLUSIONS: 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.