Comparison of pulmonary artery pressure measurements in the supine and lateral positions

Pulmonary artery pressure monitoring, with the patient in both the supine and lateral position, constitutes an essential element of assessment in the critically ill. Previous work offers conflicting results regarding the accuracy of pulmonary artery pressure measurements obtained with the patient in the lateral position. Additionally, recent studies question the most appropriate thoracic surface landmark for use as the zero point for pulmonary artery pressure monitoring. The purpose of this study was to identify a reliable surface landmark to be used as the zero point for pulmonary artery pressure monitoring, as well as to determine if use of that zero point provided accurate pulmonary artery pressure measurements when the patient was in either the left or right 60° lateral position. Specifically, these questions were related to the post-operative cardiac surgical patient. Thirty-five post-operative cardiac patients, with pulmonary artery catheters in situ, were prospectively enrolled in this correlational study. All subjects underwent repositioning between the supine and both the left and right 60° lateral position on two occasions each, once while being mechanically ventilated and once while breathing spontaneously. Pulmonary artery pressure measurements, including Pulmonary Artery Systolic, Diastolic, Mean and Capillary Wedge Pressure, were recorded prior to, two minutes following and ten minutes following repositioning. For each subject a surface landmark was identified which corresponded with the mid-point of the thorax in each of the left and right 60° lateral position. Results showed that the dependent mid-clavicular line was the most frequent surface landmark for the zero-point (83% and 74% left and right respectively). Following change of position, pulmonary artery pressure measurements were variable. In the spontaneously breathing subject these differences had resolved and all pulmonary artery pressure measurements were statistically reliable 10 minutes after repositioning. In subjects being mechanically ventilated, despite some differences remaining, the Pulmonary Capillary Wedge Pressure measurement was statistically reliable 10 minutes after repositioning. This study concludes that clinical practitioners can confidently obtain accurate Pulmonary Capillary Wedge Pressure measurements in both the spontaneously breathing and mechanically ventilated post-operative cardiac surgical patient positioned in either the left or right 60° lateral positio