could not find a minimum hourly rate stated in any of my references, but did find evidence to indicate that along with the amount of water being excreted, it is also important to know if there is any interference with these mechanisms since they will affect the final urine volume that is formed:
- glomerular filtration
- tubular reabsorption
- tubular secretion
"a urine volume less than 30 ml/hr in an adult is cause for concern if it persists
. one must be constantly aware that persistent oliguria in the severely volume-depleted patient can result in renal tubular damage
." (page 43, fluid & electrolyte balance: nursing considerations
, 4th edition, by norma m. metheny).
"normal urine output averages about 1 ml/kg body weight/hour, or approximately 1500 ml in a 24-hour period in a healthy adult. the urine output can be as small as 1000 ml or as great as 2000 ml in a 24-hour period, which is an average of approximately 40-80 ml/hour in a healthy adult. children have lesser amounts of urine volume, based on their age and weight. when the body is under stress, urine output may be less than normal because of increased aldosterose and antidiuretic hormone secretion. . .low or high urine volumes may indicate a fluid imbalance. urine osmolality and specific gravity give further information on this issue. . . .this value depends on the amount of antidiuretic hormone that is in the blood stream and the rate that solutes are excreted through the kidneys. . .on average, urine osmolality should be approximately 1.5 times that of the serum osmolality. . .it is important to understand and discriminate between the differences in water diuresis and solute diuresis. a low urinary specific gravity, a low urinary osmolality, and a normal or elevated serum sodium level can indicate either a lack of antidiuretic hormone or the inability of the renal tubules to respond properly. these findings indicate water diuresis. solute diuresis occurs when impaired tubular absorption of a solute occurs. symptoms of solute diuresis are a high urinary specific gravity, a high urinary osmolality, and a normal or low serum sodium level. solute diuresis may occur in such states as diabetes mellitus or the correction of bladder obstruction. . .based on this. . .it is apparent that the amount of solute and the amount of waste product in the urine can influence volume
. in other words, urine volume would be increased in conditions that cause high levels of solute in the urine. the amount of circulating volume in the extracellular space also affects urine volume. hypovolemia can result in decreased urinary output. hypervolemia can cause increased urinary output in the presence of normal renal function." (page 361, intravenous therapy: clinical principles and practice
, by judy terry, leslie baranowski, rose anne lonsway and carolyn hedrick, published by the intravenous nurses society, 1995).