ESTIMATION OF THE PULMONARY CAPILLARY WEDGE PRESSURE FROM TRANSESOPHAGEAL PULSED DOPPLER-ECHOCARDIOGRAPHY OF PULMONARY VENOUS FLOW - INFLUENCE OF THE RESPIRATORY CYCLE DURING MECHANICAL VENTILATION

Objective:Pulsed Doppler measurement of pulmonary venous flow (PVF) in the left superior pulmonary vein has been suggested as a noninvasive method to evaluate pulmonary capillary wedge pressure (PCWP). In previ ous studies, PVF was measured at end-expiration, and it is unknown to what extent PVF is affected by the respiratory cycle. It is hypothesiz ed that phasic variations of PVF during mechanical ventilation may be used to estimate PCWP. Design: Prospective clinical study. Setting: Te rtiary care university hospital. Participants: Thirty patients undergo ing elective cardiac surgery. Interventions: At multiple intervals dur ing the surgery, the PVF was measured with transesophageal pulsed Dopp ler echocardiography, and measurements of PCWP and airway pressure wer e simultaneously obtained. Measurements and Results: Components of PVF evaluated were the systolic (X), diastolic (Y), and atrial (Z) waves with their velocity-time integrals (VTI). The systolic fraction (SF = VTI X/[VTI X + VTI Y]) and respiratory variations of each component of PVF were determined and compared with PCWP. There was a greater respi ratory variation of the X wave (X expiratory-X inspiratory/X expirator y) in patients with PCWP <18 mmHg than in patients with PCWP greater t han or equal to 18 mmHg (0.19 +/- 0.19 v 0.14 +/- 0.13, respectively, p < 0.01). PVF components measured at end-expiration that related best with PCWP were the X/Y peak velocities (r = -0.53), VTI X/VTI Y ratio (r = -0.42), and the SF (r = -0.49). When measured during end-inspira tion. the relation of the X/Y ratio, VTI X/VTI Y,and SF with the PCWP were r = -0.54, r = -0.41, and r = -0.50, respectively. Conclusions: I t has been documented that PVF velocity is influenced by the respirato ry cycle during mechanical ventilation in patients undergoing cardiac surgery, and the magnitude of this variation is influenced by PCWP. Ho wever, it is not actually possible to predict PCWP accurately using th ese findings. Further studies are needed in which preload is varied ac utely to confirm the usefulness of the results. Copyright (C) 1998 by W.B. Saunders Company.