Low systemic vascular resistance after cardiopulmonary bypass: Incidence, etiology, and clinical importance

Background. Low systemic vascular resistance during and immediately after c ardiac surgery in which cardiopulmonary bypass is utilized is a well-known phenomenon, characterized as vasoplegia, which appears with an incidence ra nging between 5% and 15%. The etiology is not completely elucidated and the clinical importance remains speculative. Methods: In this prospective clin ical trial, we assessed the incidence of postoperative low systemic vascula r resistance in 800 consecutive patients undergoing elective coronary arter y bypass grafting and/or valve replacement. We have attempted to identify t he predictive factors responsible for the presence of low systemic vascular resistance and we have examined the subsequent postoperative outcome of th ose patients who developed early postoperative vasoplegia. The severity of vasoplegia was divided into three groups according either to the value of s ystemic resistance and/or the dose of vasoconstrictive agents necessary to correct the hemodynamic. Results: Six hundred twenty-five patients (78.1%) did not develop vasoplegia, 115 patients (14.4%) developed a mild vasoplegi a, and 60 patients (7.5%) suffered from severe vasoplegia. Low systemic vas cular resistance did not affect hospital mortality but was the cause for de layed extubation and prolonged stay on the intensive care unit (ICU). Logis tic regression analysis identified temperature and duration of cardiopulmon ary bypass, total cardioplegic volume infused, reduced left ventricular fun ction, and preoperative treatment with angiotensin-converting enzyme (ACE)- inhibitors, out of 25 parameters, as predictive factors for early postopera tive vasoplegia. Conclusion. The occurrence of low systemic vascular resist ance following cardiopulmonary bypass is as high as 21.8%. The etiology of this clinical condition is most probably multifactorial. Mortality is not a ffected by vasoplegia, but there is a trend to higher morbidity and prolong ed stay in the ICU.