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

Background Management 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 (Q si ). 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. Methods This 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 cmH 2 O), 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 CO 2 or N 2 O. PBF and FRC were calculated using CO 2 bolus delivery and the modified differential Fick equation. Shunt was estimated from the number of breaths required to eliminate N 2 O after a 25-breath N 2 O bolus and expressed as Q si . PHM™-derived PBF and Q si were compared to thermodilution CO and calculated Berggren shunt, respectively. Results Studies were completed in 19 animals. Measurements of PBF, FRC and Q si 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