The effect of body position upon pulmonary artery and pulmonary capillary wedge pressure in critically ill patients.

Critically ill subject, with a wide range of diagnoses and with pulmonary artery flow-directed balloon-tipped catheters in place, were studies to determine the effect of body position change on pulmonary artery and pulmonary capillary wedge pressure. The head of the bed was raised from a supine flat position to 20 and 45 degrees, respectively. The transducer was repositioned and zeroed at the phlebostatic level before each measurement was obtained. Subjects were analyzed for pressure changes by four major approaches: (1) The sample as a whole, (2) the sample divided according to presence and type of ventilatory support, (3) the sample divided according to degree of pulmonary artery mean pressure elevation in the supine flat position, and (4) the sample divided according to degree of pulmonary capillary wedge pressure elevation in the supine flat position. Subjects with normal to mild elevation of pulmonary artery mean pressures in the supine flat position demonstrated a statistically significant change in pulmonary artery end-diastolic pressure (p < 0.03) when body position was adjusted from the 20 degree angle to the 45 degree angle of elevation. No other statistically significant changes in pulmonary artery pressures were noted. Relatively large standard deviations existed in many of the pressure differences. The study finds that pulmonary artery pressures vary insignificantly when they are obtained in critically ill individuals with the head of the bed elevated. Further study is recommended, however, before pressure are routinely obtained in a position other than he supine flat position.