Non-invasive monitoring of pulmonary blood flow, functional residual capacity, and shunt index in a porcine model

Abstract

BackgroundManagement of mechanically ventilated patients can be improved with monitoring of key pulmonary function parameters that facilitate individualization and optimization. The VQm Pulmonary Health Monitor™ (PHM) (Rostrum Medical Innovations Inc., Vancouver, Canada) is a new monitor that continuously measures pulmonary blood flow (PBF), functional residual capacity (FRC) and a novel parameter: shunt index (Qsi). The goal of this study was to provide an initial assessment of the performance of the VQm PHM™ when compared with reference measures of PBF, FRC and intra-pulmonary shunt.MethodsThis was a prospective, experimental, large animal (porcine) study. After baseline measurements, three interventions were performed: increased cardiac output (CO) using dobutamine infusion, increased PEEP (from 4 to 12 cmH2O), and experimental shunt induced by an extracorporeal circuit. PBF, FRC and shunt were measured by the VQm Pulmonary Health Monitor™ (PHM) before and after each intervention. The PHM™ uses sequential gas delivery to deliver targeted alveolar concentrations of CO2 or N2O. PBF and FRC were calculated using CO2 bolus delivery and the modified differential Fick equation. Shunt was estimated from the number of breaths required to eliminate N2O after a 25-breath N2O bolus and expressed as Qsi. PHM™-derived PBF and Qsi were compared to thermodilution CO and calculated Berggren shunt, respectively.ResultsStudies were completed in 19 animals. Measurements of PBF, FRC and Qsi obtained from the PHM™ trended as expected following each intervention. The mean difference between paired values of PBF was − 0.2 ± 0.9 L/min and the 95% limits of agreement were 1.5 and − 1.9 L/min. Concordance was 94.1%. The mean baseline FRC was 1.7 pm 0.4 L and increased to 2.0 pm0.6 L, following the increase in PEEP (p = 0.0078). For shunt (Qsi), the mean values during low (1 L/min) and high (50% of baseline CO) shunt value were 40 pm 4 and 27 pm 5, respectively, p = 0.002.ConclusionsPBF obtained through the modified differential Fick equation and Qsi obtained through N2O uptake and decay dynamics by the VQm PHM™ provide comparable results to reference standards. FRC measurements trended as expected following interventions.