The presence of one of the causes of true volume depletion is usually evident from the history. A fluid loss severe enough to produce renal insufficiency should be associated with at least some of the characteristic physical findings of this disorder, including decreased skin turgor, dry mucous membranes, flat neck veins, and postural tachycardia with or without hypotension.
Oliguria is present in most individuals.
Rapid reduction of chronically elevated blood pressure is another source of acute prerenal azotemia. If renal arteriolar hyperplasia is present as an adaptive change, it protects the glomerular capillaries from the elevated systemic pressure. However, these vessels have an impaired ability to dilate when the blood pressure is lowered abruptly, which can result in a decrease in tissue perfusion. Continued control of the blood pressure permits arteriolar hyperplasia to regress and renal function to improve over a period of one to three months. The major questions that must be addressed are the type of fluid to be used and the rate at which it should be given.