Early illness severity and therapeutic hypothermia process in post-cardiac arrest patients

Abstract

Purpose: Severity of illness is an important determinant of the response to therapeutic interventions. Post-cardiac arrest (PCA) patients with different levels of illness severity may respond differently to therapeutic hypothermia (TH). This study examined whether the cooling rates and temperature curves varied between PCA patients with different categories of early illness severity. Materials and methods: We performed a retrospective review of data from adults treated with TH after out-of-hospital CA in a tertiary hospital between 1/1/2005 and 12/31/2009. Subjects were stratified by categories of PCA illness severity based on neurological examination and sequential organ failure assessment scores at presentation: Category II (moderate coma with mild cardiopulmonary dysfunction), III (moderate coma with moderate to severe cardiopulmonary dysfunction), or IV (severe coma with loss of brainstem reflexes). Associations between the category and time to target temperature (>34 °C) were assessed using Cox Regression. Duration of induction and rewarming (time to >36 °C), incidence of overcooling (38 °C), area of out-of-range (>34 °C or 37 °C) were compared between groups using Kruskal–Wallis test. Results: Of 283 out-of-hospital CA patients screened, 173 (61.1%) received TH, and 68 (24%) had complete temperature data. TH was delivered using cold saline and cooling blanket, except for two patients treated with endovascular cooling who were excluded. There was no significant association between the category and time to target temperature. Median (IQR) induction time in the category IV [151(102–398) min] was shorter than in the category II [357(328–638) min] or III [400(303–575) min] (p = 0.036). The incidence of overcooling and hyperthermia, area of out-of-range, and area of fever burden in the category II were slightly higher than the other categories (p > 0.05). Conclusion: The time needed to achieve target temperature of the PCA patients in severe coma with loss of brainstem reflexes may be shorter than the others in early illness severity categories.