Comparing the effects of rapid and gradual cooling following acute hyperthermia on body temperature and inflammatory response

Abstract

Hyperthermia negatively impacts human and animal health and may cause morbidity and mortality if recovery is not properly managed. The study objective was to evaluate the effects of two cooling methods on body temperature and the inflammatory response after acute heat stress (HS) exposure in a pig model for human hyperthermia. Male pigs (88.7 ± 1.6 kg BW) were exposed to thermoneutral conditions (TN; n = 12; 19.5 ± 0.1°C) for 6 hrs, or HS (36.4 ± 0.1°C) for 3 hrs, followed by a 3 hr recovery period of either rapid cooling (HSRC; n = 12; immediate TN exposure and ice water dousing) or gradual cooling (HSGC; n = 12; gradual decrease to TN temperature). Rectal (TR) and gastrointestinal temperatures (TGI) were obtained every 15 min. Blood samples were collected from 6 pigs per treatment at 60, 180, 210 and 240 min to determine TNFα and IL‐1ß concentrations. TR was increased (p < 0.01) in HSRC and HSGC pigs compared to TN controls during HS (1.2°C) and recovery (0.6°C), and was reduced (p < 0.01; 0.4°C) in HSRC versus HSGC pigs during the recovery period. TGI was increased (p < 0.01) in HSRC and HSGC compared to TN pigs during HS (1.6°C and 1.5°C, respectively) and recovery (1.2°C and 1.3°C, respectively), but was similar (40.8°C) in HSRC and HSGC pigs during both periods. During HS, HSRC and HSGC pigs had increased TNFα concentrations (p < 0.04; 27.5%), but IL‐1ß concentrations were similar (p > 0.60; 10.2 pg/mL) to TN controls. In the recovery period, HSRC pigs tended to have increased TNFα concentrations (p < 0.07; 41.2%) compared to HSGC pigs. In summary, although rapid cooling was more effective than gradual cooling in reducing TR during HS recovery it had no effect on TGI and this differential may be linked to the increased inflammatory response observed in HSRC pigs.