Which sign indicates the second phase of acute renal failure?
A. Daily doubling of urine output (4 to 5 L/day).
B. Urine output less than 400 ml/day.
C. Urine output less than 100 ml/day.
D. Stabilization of renal function.
Correct Answer: A. Daily doubling of urine output (4 to 5 L/day).
Daily doubling of the urine output indicates that the nephrons are healing. This means the patient is passing into the second phase (diuresis) of acute renal failure. The GFR is stable albeit at a level determined by the severity of the initial event. This cellular repair and reorganization phase results in slowly improving cellular function and sets the stage for improvement in organ function.
Option B: The initiation phase of ATN occurs when renal blood flow (RBF) decreases to a level resulting in severe cellular ATP depletion that in turn leads to acute cell injury and dysfunction. Renal tubular epithelial cell injury is a key feature of the Initiation Phase.
Option C: The extension phase is ushered in by two major events: continued hypoxia following the initial ischemic event and an inflammatory response. It is during this phase that renal vascular endothelial cell damage likely plays a key role in the continued ischemia of the renal tubular epithelium, as well as, the inflammatory response observed with ischemic ARF. During this phase, cells continue to undergo injury and death with both necrosis and apoptosis being present predominantly in the outer medulla
Option D: During the recovery phase cellular differentiation continues, epithelial polarity is reestablished and normal cellular and organ function returns. Thus, renal function can be directly related to the cycle of cell injury and recovery.
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