Positive end-expiratory pressure influences echocardiographic measures of diastolic function: a randomized, crossover study in cardiac surgery patients.

Abstract

Ultrasonography of the cardiovascular system is pivotal for hemodynamic assessment. Diastolic function is evaluated with a combination of tissue Doppler (e' and a') and pulsed Doppler (E and A) measures of transmitral- and mitral valve annuli velocities. However, accurate echocardiographic evaluation in the intensive care unit or perioperative setting is contingent on relative resistance to positive pressure ventilation and changes in preload. This study aimed to evaluate the effects of positive end-expiratory pressure (PEEP) and positioning on echocardiographic measures of diastolic function. The study was a prospective, randomized, crossover study. Cardiac surgery patients with ejection fraction greater than 45% and averaged e' of 9 or more were included. Postoperatively, anesthetized patients were randomized into six combinations of PEEP (0, 6, 12 cm H2O) and positions (horizontal, Trendelenburg). At each combination, e' (primary endpoint), a', E, and A were obtained with transesophageal echocardiography along with left ventricular area. Image analysis was performed blinded to the protocol. Thirty patients completed the study. PEEP decreased lateral e' from 6.6±3.6 to 5.3±3.0 cm/s (P<0.001) in the horizontal position and from 7.4±4.2 to 6.5±3.3 cm/s (P<0.001) in Trendelenburg. Similar results were found for septal e', a' bilaterally and transmitral pulsed Doppler measures, and PEEP decreased left ventricular area. E/A, E/e', and e'/a' remained unaffected by PEEP and positioning. When evaluating diastolic function by echocardiography, the levels of PEEP and its effect on ventricular area have to be taken into account. In addition, this study dissuades the use of E/e' for tracking changes in left ventricular filling pressures in cardiac surgery patients.