title: Minute-to-minute urine flow rate variability: a new renal physiology variable.
abstract: BACKGROUND
  Urine 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.
  
  
  METHODS
  Seven 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.
  
  
  RESULTS
  The 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).
  
  
  CONCLUSIONS
  The 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.
authors: Department of Acute Care Surgery and Trauma, Kaplan Medical Center, Rehovot, Israel.
authors: Yoram
authors: Y
authors: Klein
authors: Mor
authors: M
authors: Grinstein
authors: Stephen M
authors: SM
authors: Cohn
authors: Jacob
authors: J
authors: Silverman
authors: Moti
authors: M
authors: Klein
authors: Hanoch
authors: H
authors: Kashtan
authors: Micha Y
authors: MY
authors: Shamir
mesh_terms: D000818:Animals; D001810:Blood Volume / Q000502:physiology*; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D020896:Hypovolemia / Q000175:diagnosis / Q000503:physiopathology; D013552:Swine; D013997:Time Factors; D014554:Urination / Q000502:physiology*