Abstract
Background and Aims
Therapeutic hypothermia or targeted temperature management (TTM) has been standard treatment for cardiac arrest survivors with suspected hypoxic ischemic brain injury for improvement in both survival and neurological outcomes. TTM is consisted of an induction phase of quickly lowering the temperature to target temperature (ranging from 32°C -36°C) as soon as possible, a hypothermia maintenance phase of keeping the body temperature at target temperature for at least 24 hours, a rewarming phase of slowly rewarming the temperature to normothermia, and a normothermia phase of keeping the body temperature at normothermia. During the dynamic changes in body temperature, cold-diuresis is a commonly described phenomenon. However, limited studies have characterized cold-induced diuresis during TTM. In this study, we sought to determine urine output changes during post cardiac arrest therapeutic hypothermia.
Method
This retrospective cohort study included adult patients who underwent TTM after out-of-hospital cardiac arrest and were admitted to the intensive care unit for post cardiac arrest care between January 2012 and August 2018. The exclusion criteria of this study were as follows: 1) deceased status before the completion of all phase of TTM; 2) previous end stage kidney disease patients, 3) undergoing renal replacement therapy due to AKI within 48 hours of TTM termination; 4) terminal cancer less than 6 months of life expectancy or previously cerebral performance category (CPC) 3 or more. The neurologic outcome was assessed using the CPC score after 1 month. Good neurologic outcome was defined as a CPC score of 1, 2 and poor neurologic outcome as a CPC score of 3 to 5. The post cardiac arrest protocol recommends a target temperature of 33°C unless the patient is hemodynamically unstable or has a bleeding tendency or severe infection. Rewarming rate was 0.15°C/hr or 0.25°C/hr. TTM was conducted with the use of temperature managing devices with a feedback loop system (Artic Sun Energy Transfer Pads, Medivance Corp., Louisville, CO, USA; Cool Guard Alsius Icy Heat Exchange Catheter, Alsius Corporation, Irvine, CA, USA). We calculated the hourly IV fluid input and urine output rates for each TTM phase. To compare the mean of urine volume between each TTM phase, we used repeated measure analysis of variance (ANOVA).
Results
178 Patients included in the analysis. We observed a increase in urine output rates during hypothermia induction. This effect persisted even after adjustment for variable clinical confounders, including intravenous fluid input rate, mean arterial pressure (MAP), initial shockable rhythm, SOFA score, body mass index, and IV furosemide use. However, we did not detect any evidence of urine output increases or decreases during the hypothermia maintenance or rewarming phases. By repeating measures ANOVA and a linear mixed model, it was confirmed that there is a difference in urine output for each TTM phase. Even after the post hoc analysis was calibrated with several variables, only the hypotheria induction phase differed significantly from the urine output of the phase.
Conclusion
Although our results are some limitations, the findings support the potential presence of cold-induced dieresis, but not rewarm anti-diuresis during TTM. Our study may not fully capture the extent of renal impairment in post cardiac arrest undergoing TTM. However, our objective was to characterize urine output during TTM in post cardiac arrest patients. This has important implications for fluid management in patients undergoing TTM.
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