The Clinical Significance of Fluctuations in the Minute-to-minute Urine Flow Rate and in its Minute-to-minute Variability During Septic Events in Critically Ill Patients.

Background: Septic events complicated by hemodynamic instability can lead to decreased organ perfusion, multiple organ failure, and even death. Acute renal failure is a common complication of sepsis, affecting up to 50-70 % of cases, and it is routinely diagnosed by close monitoring of urine output. We postulated that analysis of the minute-to-minute changes in the urine flow rate (UFR) and also of the changes in its minute-to-minute variability might lead to earlier diagnosis of renal failure. We accordingly analyzed the clinical significance of these two parameters in a group of critically ill patients suffering from new septic events.

Methods: The study was retrospective and observational. Demographic and clinical data were extracted from the hospital records of 50 critically ill patients who were admitted to a general intensive care unit (ICU) and developed a new septic event characterized by fever with leukocytosis or leukopenia. On admission to the ICU, a Foley catheter was inserted into the urinary bladder of each patient. The catheter was then connected to an electronic urinometer - a collecting and measurement system that employs an optical drop detector to measure urine flow. Urine flow rate variability (UFRV) was defined as the change in UFR from minute to minute.

Results: Both the minute-to-minute UFR and the minute-to-minute UFRV decreased significantly immediately after each new septic episode, and they remained low until fluid resuscitation was begun (p < 0.001 for both parameters). Statistical analysis by the Pearson method demonstrated a strong direct correlation between the decrease in UFR and the decrease in the systemic mean arterial pressure (MAP) (R = 0.03, p = 0.003) and between the decrease in UFRV and the decrease in the MAP (R = 0.03, p = 0.004). Additionally, both the UFR and the UFRV demonstrated good responses to fluid administration prior to improvement in the MAP.

Conclusion: We consider that minute-to-minute changes in UFR and UFRV could potentially serve as early and sensitive signals of clinical deterioration during new septic events in critically ill patients. We also suggest that these parameters might be able to identify the optimal endpoint for the administration of fluid resuscitative measures in such patients.