Individualised flow-controlled ventilation versus pressure-controlled ventilation in a porcine model of thoracic surgery requiring one-lung ventilation A laboratory study

BACKGROUND Flow-controlled ventilation (FCV) enables precise determination of dynamic compliance due to a continuous flow coupled with direct tracheal pressure measurement. Thus, pressure settings can be adjusted accordingly in an individualised approach. OBJECTIVE The aim of this study was to compare gas exchange of individualised FCV to pressure-controlled ventilation (PCV) in a porcine model of simulated thoracic surgery requiring one-lung ventilation (OLV). DESIGN Controlled interventional trial conducted on 16 domestic pigs. SETTING Animal operating facility at the Medical University of Innsbruck. INTERVENTIONS Thoracic surgery was simulated with left-sided thoracotomy and subsequent collapse of the lung over a period of three hours. When using FCV, ventilation was performed with compliance-guided pressure settings. When using PCV, end-expiratory pressure was adapted to achieve best compliance with peak pressure adjusted to achieve a tidal volume of 6 ml kg(-1) during OLV. MAIN OUTCOME MEASURES Gas exchange was assessed by the Horowitz index (= PaO2/FIO2) and CO2 removal by the PaCO2 value in relation to required respiratory minute volume. RESULTS In the FCV group (n = 8) normocapnia could be maintained throughout the OLV trial despite a significantly lower respiratory minute volume compared to the PCV group (n = 8) (8.0 vs. 11.6, 95% confidence interval, CI -4.5 to -2.7 l min(-1); P < 0.001), whereas permissive hypercapnia had to be accepted in PCV (PaCO2 5.68 vs. 6.89, 95% CI -1.7 to -0.7 kPa; P < 0.001). The Horowitz index was comparable in both groups but calculated mechanical power was significantly lower in FCV (7.5 vs. 22.0, 95% CI -17.2 to -11.8 J min(-1); P < 0.001). CONCLUSIONS In this porcine study FCV maintained normocapnia during OLV, whereas permissive hypercapnia had to be accepted in PCV despite a substantially higher minute volume. Reducing exposure of the lungs to mechanical power applied by the ventilator in FCV offers a possible advantage for this mode of ventilation in terms of lung protection.