Pathophysiology of the perioperative low output syndrome

Surgery in high-risk cardiac patients is now possible due to improvements in medical techniques. These patients are, however, more likely to develop a low cardiac output syndrome in the perioperative period. The condition may be precipitated by surgery, especially in those with underlying ischaemic heart disease, the initial cardiac insult being followed by diminished contractility and compensatory changes in perfusion pressures due to the release of endogenous catecholamines. Catecholamine release induces myocardial irritability and there is a subsequent increase in heart rate and decrease in cardiac output. As a result, contractility may decrease even further, and the downward spiral worsens. This article reviews current progress in the understanding of the pathophysiology of the low cardiac output syndrome with reference to the various parameters used to assess cardiac function, and the effects of drug therapy on these parameters.