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Abstract

Introduction: Therapeutic hypothermia (TH) is an important treatment for survivors of cardiac arrest. While anecdotally described, no studies have characterized urine output increases during TH induction (“cold diuresis”), nor urine output decreases during TH re-warming (“re-warming anti-diuresis”). An understanding of urine output changes during TH is essential since these patients may exhibit hypovolemia, shock, pulmonary edema or electrolyte abnormalities. Hypothesis: Urine output increases during TH induction and decreases during TH re-warming. Methods: We studied consecutive patients receiving post-cardiac arrest TH at an urban tertiary care center. Using cold intravenous saline, external cooling pads (Arctic Sun) and ice packs, TH was provided to comatose adult survivors of out-of-hospital or in-hospital cardiac arrest as soon as possible after restoration of pulses. We excluded patients <18 years old, with end stage renal disease, who received hemodialysis, or those who died before completing?12 hours of TH. For each TH treatment phase (induction, maintenance, re-warm, and post-TH), we determined fluid input and urine output rates (mL/hr). Using Generalized Estimating Equations and defining post-TH urine output as the baseline, we examined the differences in urine output rates between TH phases, adjusting for fluid input rate, age, sex, location of cardiac arrest, initial arrest ECG rhythm, and vasospressor use. Results: Among 33 patients with complete fluid input and urine output data, mean treatment phase durations were: 1) induction 4.9 hrs (95% CI 4.5-5.4), 2) maintenance 23.1 hrs (22.5-23.6), 3) re-warm 11.1 hrs (10.5-11.7), and 4) post-rewarm 12 hrs (12-12). Mean urine output rates were: 1) induction 162 mL/hr (95% CI: 106-218), 2) maintenance 100 mL/hr (79-121), 3) re-warm 66 mL/hr (50-83), and post-TH 97 mL/hr (70-123). Urine output rate was higher for TH induction than post-TH (p=0.004). There were no significant differences in urine output rates between TH maintenance and post-TH (p=0.88), or TH re-warm and post-TH (p=0.19). Conclusions: Compared with baseline, urine output rate increases during TH induction. Urine output rates do not significantly change during TH maintenance or re-warming.