The initial management of the oliguric patient is to exclude urinary tract obstruction. Anuria is usually due to urinary catheter obstruction and is remedied by flushing. It should be noted that anuria is uncommon in patients with either impending or established oliguric acute tubular necrosis, who frequently continue passing urine volumes of up to 20 ml/h.
Obstruction of the urinary tract can be confirmed by ultrasound of the renocalyceal system which may demonstrate hydronephrosis. Patients with evidence of obstruction require urgent intervention to provide free drainage of urine.
Elevated intra-abdominal pressure can be an important factor in producing oliguria and may follow abdominal trauma or postoperative intra-abdominal bleeding. Occasionally it may be associated with ascites under tension. The mechanism of oliguria secondary to raised intra-abdominal pressure is not clearly established but is probably due to a combination of increased renal vascular resistance, reduction in cardiac output, and direct pressure on the renal pelvis.
A bedside estimate of intra-abdominal pressure can be conveniently obtained by transducing a urinary catheter (water manometer) or femoral venous line. A clinically significant elevated pressure is more than 30 mmHg above the pubis. An abdomen generating such pressures in the presence of oliguria should be considered for decompression.
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