Right ventricular myocardial function in ARF patients - PEEP as a challenge for the right heart

Objective: To examine the hemodynamic effects of external positive end-expiratory pressure (PEEP) on right ventricular (RV) function in acute respiratory failure (ARF) patients. Design: Prospective, with retrospective analysis on the basis of RV volume response to PEEP. Setting: General intensive care unit in a university teaching hospital. Patients: 20 mechanically ventilated ARF patients (mean lung injury score = 2.6 +/- 0.45 SD). Intervention: Incremental levels of PEEP (0 - 5 - 10 - 15 cmH(2)O) were applied and RV hemodynamics were studied by means of a Swan-Ganz catheter with a fast-response thermistor for right ventricular ejection fraction (RVEF) measurement. According to their response to PEEP 15, two groups of patients were defined: group a (9 patients) with unchanged or increased RV end-diastolic volume index (RVEDVI) and group B (11 patients) with decreased RVEDVI. Measurements and results: At zero PEEP (ZEEP) the hemodynamic parameters of the two groups did not differ. In group A, cardiac index (CI) and stroke volume index (SI) decreased at all PEEP levels (5, 10, and 15 cmH(2)O), while RVEF started to decrease only at a PEEP of 10 cmH(2)O (-10.8%), and RVES(systolic)VI increased only at PEEP 15 cmH(2)O (+21.5%). RVEDVI was not affected by PEEP. In group B, CI and SI decreased at all PEEP levels (5, 10, and 15 cmH(2)O). Similarly, RVEDVI started to decrease at PEEP 5 cmH(2)O, while RVESVI decreased only at PEEP 15 cmH(2)O (-21.4%). RVEF was not affected by PEEP in this group. In each patient the slope of the relationship between RVEDVI and right ventricular stroke work index (RVSWI), expressing RV myocardial performance, was studied. This relationship was significant (no change in RV contractility) in 8 of 11 patients in group B and in only 2 patients in group A. In 4 patients in group A, PEEP shifted the RVSWI/RVEDVI ratio rightward in the plot, indicating a decrease in RV myocardial performance in these patients. Conclusions: PEEP affects RV function in ARF patients. The decrease in cardiac output is more often associated with a preload decrease and no change in RV contractility. On the other hand, the finding of increased RV volumes with PEEP may be associated with a reduction in RV myocardial performance. Thus, these results suggest that assessment of RV function by PEEP and preload recruitable stroke work may disclose otherwise unpredictable alterations in RV function.