Postobstructive diuresis. Studies in a dialyzed patient with a solitary kidney

Fluid and electrolyte abnormalities

Patients with cancer are at risk for developing a variety of fluid and electrolyte disturbances caused by the disease process or by complications from therapy. An understanding of the pathophysiology of these potential abnormalities allows the clinician to manage patients expectantly and to avoid severe metabolic disarray by correcting imbalances promptly.

Assessment of the nephron segments involved in post-obstructive diuresis in man, using lithium clearance

The phenomena of post-obstructive diuresis and natriuresis have been studied using the lithium clearance technique in 10 patients with high pressure chronic retention. Following relief of obstruction there was a significant increase in both sodium and water excretion. There was a coincident reduction in the fractions of sodium and water reabsorbed in both proximal and distal nephron segments. This study demonstrates for the first time that following relief of chronic obstructive uropathy in man, changes in sodium and water excretion are due to altered handling in both proximal and distal nephron segments.

Effects of obstruction on renal functions

Following ureteral obstruction there is a progressive fall in glomerular filtration rate (GFR) due to a reduction in single nephron glomerular filtration rate (SNGFR) and a reduced number of filtering nephrons. Renal plasma flow also declines after a transient, prostaglandin-dependent increase, due to afferent and efferent arteriolar vasoconstriction. The vasoactive hormones thromboxane A2 and angiotensin II are implicated in the pathogenesis of the vasoconstriction following ureteral obstruction and they also reduce the glomerular ultrafiltration coefficient by causing mesangial contraction. Ureteral obstruction also leads to profound changes in renal tubular cell function. These include altered sodium and water handling resulting in a post-obstructive diuresis and natriuresis and a failure to dilute or concentrate the urine. Potassium and divalent cation exchange is also affected, as is urinary acidification. Furthermore, the response of the tubule to hormones such as antidiuretic hormone and parathyroid hormone is impaired. The pathophysiology of these alterations in renal function is discussed.

Post-obstructive urinary concentrating defect. A case study in the role of prostaglandins

A child with post-obstructive urinary concentrating defect was studied for the possible pathophysiological role of prostaglandins and an eventual therapeutic approach. Increased urinary excretion of prostaglandins was corrected by indomethacin, with resultant increased nephrogenous cyclic AMP and partial improvement in the concentrating defect. The addition of a thiazide restored urinary concentration. These results add clinical support to the conception of the important role of prostaglandins in the mechanism of post-obstructive hyposthenuria. This therapeutic regimen is advocated for prolonged post-obstructive concentrating defect.

Post-obstructive diuresis

A patient with post-obstructive diuresis is described. Inappropriate losses of salt and water occurred, with urine volume exceeding half the glomerular filtration rate. Additionally, excessive urinary excretion of potassium, bicarbonate, calcium, phosphate, magnesium and urate took place in the presence of subnormal blood levels. Transient proteinuria was also observed. This case demonstrates that serious electrolyte disturbances can occur after relief of urinary tract obstruction and the evidence suggests these may be due to disordered proximal tubule function.

Hyperkalemic distal renal tubular acidosis associated with obstructive uropathy

We studied renal function in 13 patients with obstructive uropathy and hyperkalemic metabolic acidosis to characterize the pathogenesis of this disorder. Base-line fractional potassium excretion was lower in all patients than in controls with similar glomerular filtration rates. Acetazolamide was given to 11 patients but failed to increase fractional potassium excretion to normal. In five patients, impaired potassium excretion was associated with decreased ammonium excretion, a urinary pH below 5.5 (5.18 +/- 0.07, mean +/- S.E.M.), and aldosterone deficiency. In the remaining eight patients, the urinary pH did not fall below 5.5 (6.4 +/- 0.2) with acidosis, and we failed to lower the urinary pH and increase fractional potassium excretion to normal by administering a mineralocorticoid and sodium sulfate. A syndrome of hyperkalemic distal renal tubular acidosis may occur in patients with obstructive uropathy. In some patients, this syndrome results from a defect in hydrogen and potassium secretion in the distal nephron rather than from aldosterone deficiency. Obstructive uropathy should be included in the differential diagnosis of hyperkalemic acidosis and renal insufficiency.

Nature of the acidifying defect after the relief of ureteral obstruction

Nature of the acidifying defect observed after relief of ureteral obstruction. The acidifying capacity of the normal and experimental kidney was studied in rats three hours after release of complete unilateral ureteral obstruction or after unilateral release of unilateral ureteral obstruction, mean plasma bicarbonate concentration was 23.5 mEq/liter, and plasma pH, 7.45. Urine pH from the postreleased kidney was 7.47 and 6.01 from the control side. Net acid escretion averaged 0.97 muEq/min in the experimental kidney. Fractional excretion of bicarbonate averaged 0.02% in the control and 3.17% in the experimental kidney. In eight animals with unilateral release of bilateral ureteral obstruction, mean plasma bicarbonate was 16.9 mEq/min and plasma pH was7.35. Mean urine pH in the postreleased Kidney was 6.11, net acid excretion averaged 2.01 plus or minus 0.69 muEq/min and fractional bicarbonate excretion averaged 0.84%.