• Micha Y Shamir, Yoram Klein, Mor Grinstein, Stephen M Cohn, Jacob Silverman, and Hanoch Kashtan.
• Department of Acute Care Surgery and Trauma, Kaplan Medical Center, Rehovot, Israel.
• Anesth. Analg.. 2012 Oct 1;115(4):843-7.

BackgroundUrine output is a surrogate for tissue perfusion and is typically measured at 1-hour intervals. Because small urine volumes are difficult to measure in urine collection bags, considerable over- or underestimation is common. To overcome these shortcomings, digital urine meters were developed. Because these monitors measure urine volume in 1-minute intervals, they provide minute-to-minute measurements of the urine flow rate (UFR). In a previous study, we observed that the minute-to-minute variability in the UFR disappeared during hypovolemia. The aim of this study was to describe the minute-to-minute variability in the UFR as a new physiological variable and to show its relationship to blood volume depletion.MethodsSeven adult pigs were used in this study. The UFR, minute-to-minute UFR, mean arterial blood pressure, heart rate, and base excess were measured at euvolemia and during gradual hemorrhaging (10%, 20%, and 30% of estimated blood volume). Variance and wavelet spectral analysis were used to measure the disappearance of the minute-to-minute UFR variability.ResultsThe UFR decreased from 2.2 ± 0.2 to 1.0 ± 0.1 mL/min after a 10% estimated blood volume loss (±1 SE, n = 7, P = 0.0348). The variance in the minute-to-minute UFR decreased from 1.4 ± 0.3 to 0.4 ± 0.1 mL/min (±1 SE, n = 7, P = 0.046).ConclusionsThe UFR and its minute-to-minute variability decrease during hemorrhaging. The variability in the UFR may be useful as an aid for the diagnosis of hypovolemia.

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