D.3. You are called to see this patient in the postanesthesia care unit (PACU) because of oliguria. How would you evaluate and treat this patient?
Answer:
Oliguria is a decrease in urinary output to less than 0.3 to 0.5 mL/kg/h. ARF is a syndrome characterized by a rapid (hours to weeks) decline in glomerular filtration rate (GFR) and retention of waste products such as urea. Most cases of ARF are reversible, as the kidney is remarkable in its ability to recover from almost complete loss of function. ARF is associated with major in-hospital morbidity and mortality. The diagnosis of ARF usually hinges on changes in serum creatinine, GFR, and urine output.
Causes of renal failure can be grouped into three categories:
Prerenal
Prerenal failure is the most common cause of ARF. It is usually caused by a low flow state, such as hypovolemia or cardiac failure. Evaluation begins with reviewing hemodynamic trends, fluid balance, and relevant studies (eg, echocardiogram). If hypovolemia is suspected, treatment would consist of a fluid bolus. If cardiac output is inadequate, then inotropic support and/or diuretics could be administered. Severe renal hypoperfusion can cause ischemic acute tubular necrosis (ATN); therefore, prerenal azotemia and ischemic ATN are part of a spectrum of manifestations of renal hypoperfusion.
Renal
Intrinsic renal failure is generally due to toxic injury or ischemia resulting in glomerular and tubular damage. Ischemic ATN, unlike prerenal azotemia, is associated with injury to renal parenchyma and does not typically resolve immediately on restoration of renal perfusion. In its more extreme form, renal hypoperfusion can result in bilateral renal cortical necrosis and irreversible renal failure. Urinalysis can show cells or casts that are indicative of ARF. Intrinsic renal failure can be minor and short lived, or it can progress to chronic renal failure, depending on the severity of the insult.
Postrenal
Urinary tract obstruction accounts for less than 5% of cases of ARF. Urinary tract obstruction must be sought and corrected to treat possible causes of postrenal oliguria. This usually requires irrigation or changing of the Foley catheter. Consider the possibility of an intraoperative mishap causing postrenal obstruction.
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