Right Ventricular Function During Weaning From Respirator After Coronary Artery Bypass Grafting: Conclusion
However, the increase in RV volumes with the BiPAP system compared with PSV could result from the increase in after load, a decrease in contractility, or both With respect to the similar RVPSP in both weaning modes, the higher volumes with the BiPAP system indicate a rightward shift of the pressure volume curve compared with PSV. This may be attributed to a decrease in contractility as suggested during inspiration by mechanical ventilation or if levels of PEEP above 15 cm H2O were applied. We cannot exclude changes in RV systolic function with the BiPAP system compared with PSV, but we did not evaluate load-independent indices of systolic function to evaluate RV contractility. It seems likely that the increase in RV volumes and the decrease in RVEF with the BiPAP system compared with PSV might be explained by a compensatory RV reaction to the increased afterload, according to the Frank-Starling mechanism.’ Despite the higher afterload in our patients, this mechanism was able to maintain the RV stroke work, the RVSV, and an adequate flow from the right to the left ventricle, ie, RV pump function.
In accordance to Valentine et al, the differences in cardiovascular performance between the BiPAP system and PSV were negligible in our patients, but the lower RVEF and the higher RV volumes with the BiPAP system may indicate an encroachment on RV function with the BiPAP system compared with PSV More info canadian health&care mall. This may become clinically relevant in patients with a markedly depressed RV function or dilatation. Although there is no evidence in the present study, the RV dilatation may increase RV wall stress and O2 requirements while O2 supply decreases.’ The reduced O2 supply/demand ratio may cause RV ischemia and RV, and subsequently, left ventricular failure.’ Therefore, the ability to utilize the Frank-Starling mechanism seems potentially limited, especially if baseline RV function is impaired.’ In contrast to the intact RV increasing levels of PEEP,’’ volume loading or different ventilatory modes induce a more pronounced circulatory response if RV function is impaired due to myocarditis cardiac contusion, right coronary artery stenosis or experimental occlusion,’’’ experimental increase in RV afterload or if RV function is impaired after extracorporeal circulation. Therefore, we might suggest that the small hemodynamic differences between the BiPAP system and PSV may become relevant in markedly impaired RV function, but further investigation is necessary to prove this speculation.
In summary, this study demonstrates that the BiPAP system compared with PSV may cause a higher RVEDV and RVESV and a depression in RVEF. In accordance with the Frank-Starling mechanism, this reaction seems to be a hemodynamic compensation to the increase in RV afterload with the BiPAP system which is attributed to differences in respiratory support created by both weaning techniques. No clinically relevant differences in hemodynamic or respiratory function were found between the BiPAP system and PSV during weaning after uneventful elective coronary artery bypass surgery.