Abstract 232: Temperature Profile of Esophageal, Rectal and Tympanic Temperature Probes in a Rodent Model of Cardiopulmonary Bypass Resuscitation from Ventricular Fibrillation Cardiac Arrest

Abstract

BACKGROUND: Exact and valid temperature measurement is crucial to assess the effects of temperature levels on outcome after cardiac arrest (CA). In this study, we assessed the temperature profile in different body locations in our rat ventricular fibrillation (VF) CA model with emergency cardiopulmonary bypass (ECPB) resuscitation. METHODS: Adult Sprague-Dawley rats (400g) were equipped with esophagus (Tes), tympanic (Ttym) and rectal (Trec) temperature probes along standard instrumentation. Following 10 min of VF CA, rats were randomized to normothermic control (NT, 37±0.5°C), mild hypothermic (MH, 33±0.5°C) or deep hypothermic (DH, 27±0.5°C) reperfusion and put on ECPB for 15 min. On ECPB rats were rapidly cooled to and maintained at target temperature. After ECPB and return of spontaneous circulation (ROSC), MH and DH were maintained mild hypothermic with surface cooling/warming. Temperature profiles for the first five rats in the DH group are presented as mean±SD, variances tested by ANOVA and post-hoc Tukey analysis. Results: Before CA, all rats were normothermic with all three probes and cooled passively by 0.8±0.6°C during CA. In the MH and NT group, no differences in temperature measurements were found during the entire experiment, whereas in the DH group, temperature profile of the three probes significantly differed, which is presented below. With start of ECPB, cooling rate was significantly higher according to Tes (2.5±0.7°C/min) versus Ttym (1.4±0.6, p=0.44) or Trec (0.6±0.2, p=0.002) and target temperature reached by Tes within 2.8±1.0 min, but only in two animals by Ttym (4.5±0.7 min) and not at all by Trec. Rewarming rate to mild hypothermia at the end of ECPB did not vary significantly between probes (0.12±0.02) and was reached by 33±4 min. CONCLUSION: Even in a small animal model, temperature differs significantly in measurement locations. But what is true brain temperature? In future studies, measurement of brain temperature might be indicated.