title: Urine flow is a novel hemodynamic monitoring tool for the detection of hypovolemia.
abstract: BACKGROUND
  Noticeable changes in vital signs indicating hypovolemia occur only after 15% of the blood volume is lost. More sensitive variables (e.g., cardiac output, systolic pressure variation and its Δdown component) are invasive and difficult to obtain in the early phase of bleeding. Lately, a new technology for continuous optical measurements of minute-to-minute urine flow rates has become available. We performed a preliminary evaluation to determine whether urine flow can act as an early and sensitive warning of hypovolemia.
  
  
  METHODS
  Eleven patients (ASA physical status I-II) undergoing posterior spine fusion surgery were studied prospectively. Study variables included heart rate, blood pressure (systolic and diastolic), systolic pressure variation and Δdown, minute urinary flow, hemoglobin, blood and urinary sodium, and creatinine in the blood and urine. Urine flow rate was measured using URINFO 2000™ (FlowSense Medical, Misgav, Israel). After recording baseline variables, 10 mL/kg of the patient's blood was shed and a second set of variables was recorded. Subsequently, hypovolemia was reversed by infusing colloid solution (hetastarch 6%) followed by recording a third set of variables. These 3 observations were then compared.
  
  
  RESULTS
  An average of 614 ± 143 mL (mean ± SD) of blood was shed. During phlebotomy, the mean urine flow rate decreased from 5.7 ± 8 mL/min to 1.07 ± 2.5 mL/min. Systolic blood pressure and hemoglobin also decreased. Δdown increased. After rehydration, urine flow, blood pressure, and Δdown values returned to baseline. The hemoglobin concentration decreased whereas other variables did not change significantly.
  
  
  CONCLUSIONS
  Urine flow rate is a dynamic variable that seems to be a reliable indicator of changes in blood volume. These results justify further investigation.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Hadassah-Hebrew University Medical Center, POB 12000, Jerusalem 91120, Israel. shamir61@gmail.co
authors.forename: Micha Y
authors.initials: MY
authors.lastname: Shamir
authors.forename: Leonid
authors.initials: L
authors.lastname: Kaplan
authors.forename: Rachel S
authors.initials: RS
authors.lastname: Marans
authors.forename: Dafna
authors.initials: D
authors.lastname: Willner
authors.forename: Yoram
authors.initials: Y
authors.lastname: Klein
mesh_terms: D000293:Adolescent; D000328:Adult; D016063:Blood Loss, Surgical / Q000503:physiopathology; D005240:Feasibility Studies; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D020896:Hypovolemia / Q000175:diagnosis / Q000503:physiopathology / Q000652:urine*; D008297:Male; D016343:Monitoring, Intraoperative / Q000379:methods*; D011446:Prospective Studies; D014554:Urination / Q000502:physiology*; D055815:Young Adult