1540: Shivering, Heat, and Brown Adipose Tissue Activity During Temperature Control After Cardiac Arrest

Introduction: Temperature control (TC) after cardiac arrest remains controversial, with varying temperatures and different effects based on illness severity. Brown adipose tissue (BAT) appears cardioprotective; shivering, heat transmission, and BAT activity remain understudied after cardiac arrest. Methods: This pilot retrospective study evaluated post-cardiac arrest comatose subjects treated with TC at 33-37°C using the Becton Dickinson Arctic Sun (AS). Suppression Ratio 6-hours (SR6) after recovery of spontaneous circulation (ROSC) and Shivering Events (SE) from surface EMG were obtained from the Medtronic BIS Monitor. Shivering intensity was based on EMG SE (minimal, moderate, robust, or HiEMG). Heat Index (HI), Heat Transfer (HT), and Work-to-Cool (W2C) were calculated from AS water temperature and flow data during induction and maintenance phases of TC. Activity of BAT was estimated from peak plasma 12,13-diHOME (1213dH) drawn 6-168 hours post-ROSC. Cerebral Performance Category (CPC) score at 6-months was dichotomized into good (CPC 1-2) and poor (CPC 3-5) categories. Results: 35 subjects were included, with a median age of 63 (55-71) years, 24 (68%) male, 26 (74%) witnessed arrest, 10 (28%) shockable rhythm, and SR6 was 88% (33-98). Target temperature was 33°C in 22 (63%) and 35-37°C in 13 (37%). Good outcome was attained by 7 subjects (20%). Shivering intensity was minimal in 10/32 (31%), moderate in 7 (22%), and robust in 9 (28%). Heat transmittance was greater during induction than maintenance (all p< 0.001). During induction, mean HI was greater for 33°C (15.4 vs 11.5, p=0.002). During maintenance, heat transmittance was greater for 33°C for HI (6.7 vs 3.9, p=0.004), W2C (220 vs 97, p< 0.001), and HT (130 vs 39, p=0.002). The median peak 1213dH was 6.8 (4.2-11.1) ng/ml, was 7.6 (5.2-14.4) ng/ml for minimal shivering vs 4.4 (1.7-8.4, p=0.11) for robust shivering, and was >4.5 ng/ml in 8/10 (80%) minimal shivering vs 4/9 (44%) robust shivering (p=0.17). Conclusions: Heat transmittance was greater during TC induction, and for target temperatures of 33°C vs 35-37°C. While BAT may generate heat and reduce shivering after cardiac arrest, 12,13-diHOME was not lower among robust shivering patients in this small retrospective cohort. Future studies with larger cohorts are needed to test this hypothesis.