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Kevin Wolf ACF Abstract FY12

"Incidence and Risk Factors of Post-Rewarding "Rebound Hypothermia" in Cardiac Arrest Patients Undergoing Therapeutic Hypothermia"

Conference Name: American College of Emergency Physicians (ACEP) Research Forum

Study Objectives: Guidelines recommend initiating therapeutic hypothermia as soon as possible after return of spontaneous circulation in patients with witnessed cardiac arrest. However, the incidence of complications, such as overcooling and rebound hyperthermia may increase without careful monitoring of temperature. Post-rewarming 'rebound hyperthermia', defined as a temperature of 38.5°C or greater, may worsen survival and outcome. The purpose of this study was to determine the incidence and risk factors associated with post-rewarming rebound hyperthermia (RH).

Methods: This retrospective, cohort study was performed using a database of visits to the ED chest pain unit of a tertiary referral center. During a four-year study period, all patients undergoing therapeutic hypothermia (to a central target temperature of 33°C, using endovascular cooling) following cardiac arrest were eligible for the study. Patients less than 18 years old, trauma cases, pregnancy and cardiogenic shock cases were excluded. Electronic dispatch, patient care reports, and hospital records were reviewed by three independent reviewers. Our main outcome was the incidence of post-rewarming RH within 48 hours after cooling withdrawal. Analysis of risk factors was performed as follows: 24 potentially relevant risk factors for RH were assessed by univariate analysis with chi-square test for categorical variables and simple logistic regression for continuous variables. Collected data also included the rate of medical complications, death or severe disability (modified Rankin Scale 4-6).

Results: During the study period, 93 consecutive adult patients were treated with therapeutic hypothermia following out-of-hospital cardiac arrest (70% male, age 56.8 + 17 years). RH was documented in 23 patients (24.7%; 95% CI 16.0-33.5) within 48 hours after cooling withdrawal. Post-rewarming RH was associated with an increased risk of death (70% vs 41%, p< 0.001) as well as severe disability (93% vs 68%, P<0.001). Infectious complications were observed in 8 patients with RH (34.8%; 95% CI 15.3-54.2), but no patient developed severe sepsis or septic shock. The biological changes that occurred during rewarming manifested principally as hypokalemia (< 3.5 mmol/l) in 74% of patients with RH (p=0.06). No statistical correlation was found between predictor variables and the incidence of RH in this population.

Conclusions: Post-rewarming RH was observed in 25% of patients within 48 hours after cooling withdrawal and was associated with significant disability and mortality. No statistical correlation was found between predictor variables and the incidence of RH in our population.