Renal dysfunction after off-pump coronary artery bypass surgery- risk factors and preventive strategies

Postoperative renal dysfunction is a relatively common and one of the serious complications of cardiac surgery. Though off-pump coronary artery bypass surgery technique avoids cardiopulmonary bypass circuit induced adverse effects on renal function, multiple other factors cause postoperative renal dysfunction in these groups of patients. Acute kidney injury is generally defined as an abrupt and sustained decrease in kidney function. There is no consensus on the amount of dysfunction that defines acute kidney injury, with more than 30 definitions in use in the literature today. Although serum creatinine is widely used as a marker for changes in glomerular filtration rate, the criteria used to define renal dysfunction and acute renal failure is highly variable. The variety of definitions used in clinical studies may be partly responsible for the large variations in the reported incidence. Indeed, the lack of a uniform definition for acute kidney injury is believed to be a major impediment to research in the field. To establish a uniform definition for acute kidney injury, the Acute Dialysis Quality Initiative formulated the Risk, Injury, Failure, Loss, and End-stage Kidney (RIFLE) classification. RIFLE, defines three grades of increasing severity of acute kidney injury - risk (class R), injury (class I) and failure (class F) - and two outcome classes (loss and end-stage kidney disease). Various perioperative risk factors for postoperative renal dysfunction and failure have been identified. Among the important preoperative factors are advanced age, reduced left ventricular function, emergency surgery, preoperative use of intraaortic balloon pump, elevated preoperative serum glucose and creatinine. Most important intraoperative risk factor is the intraoperative haemodynamic instability and all the causes of postoperative low output syndrome comprise the postoperative risk factors. The most important preventive strategies are the identification of the preoperative risk factors and therefore the high risk groups by developing clinical scoring systems. Preoperative treatment of congestive cardiac failure and volume depletion is mandatory. Avoidance of nephrotoxic drugs and prevention of significant hemodynamic events that may insult the kidney are essential. Perioperative hydration, aggressive control of serum glucose, haemodynamic monitoring and optimization of ventricular function are important strategies. Several drugs have been evaluated with inconsistent results. Dopamine and diuretics once thought to be renoprotective has not been shown to prevent renal failure. Mannitol is probably effective if given before the insult takes place. Some of the newer drugs like fenoldopam, atrial natriuretic peptide, N-acetylcysteine, clonidine and diltiazem have shown some promise in preventing renal dysfunction but more studies are needed to establish their role of renoprotection in cardiac surgery.