Right ventricular function during weaning from respirator after coronary artery bypass grafting. Comparison of two different weaning techniques.

Abstract

The purpose of this investigation was to determine right ventricular function during weaning from controlled ventilation comparing a biphasic positive airway pressure ventilatory support system (BiPAP [Respironics]) with pressure support ventilation (PSV). In 22 patients following coronary artery bypass grafting, both weaning techniques were used in randomized chronological order for 60 min each. Right ventricular end-systolic (RVESV) and end-diastolic volume (RVEDV) and ejection fraction (RVEF) were evaluated using the fast-response Swan-Ganz catheter. In comparison to PSV, the BiPAP system resulted in a significantly higher mean pulmonary artery pressure (20.6 +/- 5.0 vs 19.3 +/- 4.2 mm Hg, p = 0.0158), pulmonary vascular resistance index (206 +/- 55 vs 181 +/- 61 dyn.s.cm-5.m2, p = 0.0355), RVESV (92.2 +/- 36.3 vs 77.2 +/- 30.4 ml, p = 0.0017), and RVEDV (176.4 +/- 48.5 vs 161.8 +/- 43.3 ml, p = 0.0061), while the RVEF was significantly lower (46.0 +/- 11.9 vs 51.8 +/- 12.4 percent, p = 0.0012). No differences in left ventricular function or arterial blood gas analyses were measured during both study periods. In summary, the RV afterload was higher with the BiPAP system compared with PSV which suggested that this was due to differences in the respiratory support between both weaning modes. Because of the Frank-Starling mechanism, this higher afterload did cause a small but significant increase in RV volumes and a significant decrease in RV ejection fraction with the BiPAP system.