Similar outcomes with low and standard perioperative urine output targets

Last Updated: 2016-10-31

By Will Boggs MD

NEW YORK (Reuters Health) - Measures of renal function and damage are similar whether perioperative urine output targets are low (0.2 mL/kg/h) or standard (0.5 mL/kg/h), researchers report.

"The most surprising result was the large amount of IV fluid (some 2.3 L) that could be spared in patients using the new, low urine output target," said Dr. Mattias Soop of the University of Manchester, U.K., who was at the University of Auckland in New Zealand when the study was done.

"We had a feeling this lower target would be safe, as indeed we demonstrated, but we did not expect such a high fluid sparing from this simple change in practice," he told Reuters Health by email.

Recent studies have shown that perioperative fluid overloading in an effort to increase urine output markedly increases postoperative morbidity and length of stay.

Dr. Soop and colleagues investigated whether a lower perioperative minimum urine target is safe and fluid sparing when compared with the standard target in a randomized noninferiority trial of 41 patients undergoing elective colon resection.

"This is the first randomized trial to challenge the practice of maintaining an increased diuresis in the perioperative period, an integral part of surgical care since the 1950s," the researchers note.

The primary outcome was the concentration of neutrophil gelatinase-associated lipocalin in urine (uNGAL), a widely validated biomarker of acute tubular damage.

Patients in the low-target group received 2,320 mL less intravenous fluids than did those in the standard group, mostly as a result of smaller fluid boluses.

As designed, the mean urine output was lower in the low-target group (0.83 mL/kg/h) than in the standard-target group (1.00 mL/kg/h), though this difference fell short of statistical significance.

While all participants had a urine output <0.5 mL/kg/h during at least one hour of monitoring, participants in the low-target group had significantly more hours in this range (mean, 21.5 hours vs. 8.6 hours).

Median uNGAL concentrations on postoperative day 1 were noninferior in the low-target group (14.7 mcg/L) versus the standard-target group (18.4 mcg/L, p-noninferiority=0.0011) and were similar between groups during the entire perioperative period, the researchers report in Annals of Surgery, online October 19.

Serum cystatin C, a validated biomarker of acute changes in glomerular filtration, were also similar between low- and standard-target groups on day 1 and throughout the study.

Other measures of renal function did not differ significantly between groups, except for effective renal plasma flow, which increased to a significantly greater extent in the standard-target group.

Postoperative length of stay and complications did not differ significantly between the treatment groups.

"The urine output target for surgical patients should now be lowered during and after major surgery," Dr. Soop said. "This is a significant break with current standard practice. We have demonstrated that this is not only safe but results in marked fluid sparing."

"Our results apply to all major surgery, not just abdominal surgery," he said. "Exceptions include patients with significant pre-existing kidney disease or surgery on the kidneys, who were excluded from this study so we do not yet know the best approach for this small group of patients."

Dr. Soop concluded, "Stop chasing the urine output in surgical patients. While it may be useful to monitor urine output during and after surgery, there is no benefit in accelerating the rate of urine production by additional fluid infusions, as is currently standard practice, and this is likely harmful."

SOURCE: http://bit.ly/2e4W786

Ann Surg 2016.