Lung Protection during Cardiac Surgery

Abstract

Despite the improvement in the cardiopulmonary bypass (CPB) techniques as well as the postoperative intensive care, impaired pulmonary function is a well documented (by enormous experimental and clinical evidence) complication of cardiopulmonary bypass, resulting in increased morbidity and mortality. Preoperative preparation and evaluation, monitoring, induction, and maintenance of anesthesia for patients requiring CPB for heart surgery remains a vital and incredibly important aspect of anesthetic management. Planning for maintenance of anesthetic depth, neuromuscular relaxation, and prevention of awareness during CPB is important during the prebypass period. Paralysis is vital to prevent shivering during cooling and rewarming, which will increase myocardial oxygen consumption. In the time prior to initiation of bypass as well as the maintenance of bypass and separation periods, episodes of transient or prolonged hypotension due to either surgical necessity or patient hemodynamic instability may place patients at risk for awareness. Processed EEG as in use of the bispectral index (BIS) during anesthesia for cardiac surgery has been shown to help prevent awareness and guide use of anesthetic medications and agents. Impaired pulmonary function is a well-documented and fairly common complication, occurring in about 25% of patients after CPB for cardiac surgery; in the most severe cases acute respiratory distress syndrome results and contributes to significant postoperative morbidity and mortality. The reported increased mortality and morbidity of this early postoperative pulmonary dysfunction after cardiac surgery may be related to the duration of mechanical ventilation, neurological, renal and infectious complications, ICU and hospital stays, and subsequently increased mortality. Despite the well-documented impairment of pulmonary function even after uncomplicated CPB, effective precautions and ideal management strategies for this problem are still under debate. The scope of this review is, therefore, to highlight the path of genetic and pathophysiological mechanisms involved in this injury, and the possible perioperative therapeutic options and manipulations that could be implemented, in order to alleviate the expected post-operative lung dysfunction.