Renal dysfunction in patients with cardiac disease and after cardiac surgery

Chronic renal dysfunction is relatively common in patients with advanced cardiac disease and is typically secondary to several pathophysiologic processes. These processes include decreased renal blood flow due a low cardiac output state and renal vasoconstriction secondary to the neurohumoral response to such low output state. They also include renal disease secondary to the same disorders, which may have caused cardiac disease such as atherosclerosis. Finally, hypertension and drug-induced changes in intraglomerular hemodynamics may contribute to renal dysfunction. An understanding of these processes is important to the cardiac intensivist. More frequently, however, it is acute or acute on chronic renal dysfunction that requires intervention in the cardiac or cardiothoracic ICU. The incidence of this complication varies from 15% to 20%. Although the pathogenesis of acute renal failure (ARF) in this setting mostly involves hemodynamic factors, humoral and pharmacologic factors may also play a role. The development of ARF is associated with a worse prognosis and prolongation of hospital stay. When severe ARF supervenes and dialysis therapy is needed, the mortality rate approaches 50% to 80%. Because of such epidemiology, morbidity, and mortality, the prevention of renal failure is a frequent and important therapeutic goal in the cardiothoracic ICU. No randomized controlled trials, however, have yet shown evidence that clinically important pharmacologic protection can be achieved. On the other hand, the use of preoperative clonidine may provide a degree of statistically significant renal protection. Maintenance of urine output with diuretics may be practically advantageous. The most important aspect of renal protection, however, remains prompt and effective optimization of central hemodynamics. Maintenance of adequate intravascular filling, cardiac output, and arterial blood pressure is paramount. Several drugs such as phosphodiasterase inhibitors and catecholamines can be used to sustain the central circulation. The use of these drugs may restore renal perfusion and urine output. In some patients, extracorporeal cardiac support may become necessary Finally, if necessary, dialysis therapy should be performed using continuous renal replacement techniques because they offer superior hemodynamic stability and volume control. Such techniques may also result in the removal of myocardial depressant factors and may improve myocardial contractility.