Intense monitoring of urine output could be a useful tool in detecting acute kidney injury (AKI), according to a study conducted at the University of Pittsburgh.
Kui Jin, MD, of the University of Pittsburgh and his associates found that, after adjustment for baseline characteristics, intensive monitoring of urine output (UO) was associated with higher rates of AKI, with an odds ratio of 1.22. Intensive UO monitoring also was strongly associated with improved 30-day survival among patients developing AKI.
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This retrospective cohort study included 15,724 adult patients admitted to the center’s ICUs during 2000-2008. All patients had either their UO or serum creatinine (SC) monitored. These patients were then divided into subcohorts that were monitored at one of two different intensities. UO intensive monitoring was defined by hourly recordings, with gaps no greater than 3 hours for the first 48 hours after ICU admission. The group receiving less intensive UO monitoring comprised patients who did not meet intensive monitoring criteria, regardless of their UO in the 7 days following ICU admission. The patients who had their SC intensively monitored had 3 calendar days of samples taken after their ICU admissions. Those who did not meet SC intensive monitoring criteria were placed into the less intensive SC monitoring group.
To understand the effect of the monitoring strategies on detecting the development of AKI, the researchers determined each patient’s baseline, admission, and reference serum creatinine levels. Baseline creatinine was defined as the lowest value in the year prior to hospital admission. Reference creatinine was the baseline creatinine, if available, or the lowest creatinine level recorded within 24 hours after ICU admission. A third method for determining reference creatinine levels was used for some patients, which involved making an estimation based on the Modification of Diet in Renal Disease equation for serum creatinine.
The crude rates of stage 2-3 AKI 7 days after admission to the ICU were similar between patients from both groups that had their UO monitored; 62.5% of intensive and 63.9% of less intensive patients displayed symptoms. After the researchers adjusted for baseline characteristics, however, intensive monitoring of UO was associated with greater rates of stage 2-3 AKI (OR, 1.22; P less than .001). Crude rates were higher in the patients who received intensive monitoring for SC, compared with patients who received less intensive monitoring for SC. Ultimately, Dr. Jin and his associates found that, when caring for patients with or without AKI, fluid management is one of the most important factors. Patients who underwent intensive UO monitoring received less fluid in their first 24 hours (3.6 L) in the ICU, compared with patients who received less intense UO monitoring (4.2 L). Patients who received intensive monitoring of their UO also were less likely to use vasopressors (29.9% vs. 43.3%; P less than .001), suggesting these patients were more hemodynamically stable. Further, the percentage of patients at or above 10% of fluid overload was lower in the group who received intensive monitoring of their UO (2.49% vs. 5.68%; P less than .001), during the first 72 hours in the ICU.
“Our results should help inform clinical decisions and ICU policy around frequency of monitoring of UO, especially for patients at high risk of AKI,” Dr. Jin and his colleagues wrote.
None of the authors had financial disclosures to report. Partial funding was provided by a research grant from C.R. Bard.