Classification and Management of Renal Failure

Classification and Management of Renal Failure

ARF

Acute renal failure (ARF) is a sudden decrease in renal function resulting in inability of the kidneys to excrete wastes. Oliguria (a condition in which a patient does not produce enough urine) is the clinical manifestation of renal failure. This is manifested by accumulation of creatinine and urea in the blood (uremia) and is often accompanied by reduced urine production. Acute renal failure can be divided into pre-renal, renal, and post-renal types depending on its causes.

Pre-Renal Renal Failure

Pre-renal renal failure (pre renal azotemia) results from an acute decrease in renal perfusion or renal blood flow. Pre-renal renal failure is rapidly reversible if the underlying cause (hypovolemia, congestive heart failure) is corrected. Elderly patients are uniquely susceptible to pre-renal renal failure because of their predisposition to hypovolemia (poor fluid intake). Reduced renal blood flow (congestive heart failure, shock, liver dysfunction) may be a result of anesthetic drug-induced decreases in perfusion pressure, particularly in the presence of hypovolemia associated with the intraoperative period.

Renal Azotemia

Renal azotemia is usually due to intrinsic renal disease, renal ischemia, or nephrotoxins. Intrinsic renal diseases that result in ARF are categorized according to the primary site of injury (renal tubules, intrstittium, glomerulus, renal vasculature). Injury to the renal tubules is most often due to ischemia or nephrotoxins (aminoglycoside antibiotics, radiographic contrast agents). Prerenal azotemia and ischemic tubular necrosis present as a continuum with the initial decreases in renal blood flow leading to ischemia of the renal tubular cells. The principal functional derangements in patients with acute oliguria are sudden and profound decreases in the glomerular filtration rate (GFR) that are sufficient to cause ARF manifesting as increased serum urea and creatinine concentrations, retention of sodium and water, and development of acidosis and hyperkalemia. Although some cases of ischemic ARF are reversible if the underlying cause is corrected, irreversible cortical necrosis can occur if the ischemia is severe or prolonged. ARF due to acute interstitial nephritis is most often caused by allergic reactions to drugs.

Post-Renal Azotemia

Is the result of urinary tract obstruction or disruption, as with prostatic hypertrophy or cancer of the prostate or cervix. It is important to diagnose post-renal causes of ARF promptly because the potential for recovery is inversely related to the duration of the obstruction.