[Protective effects of endovascular cooling treatment on post-resuscitation syndrome and its mechanism].

OBJECTIVE

To investigate the protective function of endovascular cooling method on post-resuscitation syndrome (PRS) in porcine cardiac arrest (CA) model and its mechanism.

METHODS

Ventricular fibrillation (VF) was electrically induced and untreated for 8 minutes in 15 healthy male porcines, cardiopulmonary resuscitation (CPR) was then initiated. All successful recovery animals were randomly divided into two groups by random number table. In normal temperature group, the core temperature was maintained at (38.0±0.5) centigrade for 12 hours. In mild hypothermia group, the mild hypothermia treatment was initiated at 5 minutes after successful resuscitation, the treatment of rapid endovascular cooling was performed to reach the target cooling temperature of (33.0±1.0) centigrade, and then maintained until 6 hours after resuscitation. Rewarming was implemented at the rate of 0.7 centigrade/h until the body temperature reached (38.0±0.5) centigrade. Hemodynamic parameters including heart rate (HR), mean arterial blood pressure (MAP), cardiac output (CO) were continually monitored. Right femoral vein blood was collected before VF and 1, 2, 4, 6, 12 and 24 hours after resuscitation, respectively, and the serum concentrations of E-selectin, soluble thrombomodulin (sTM), and interleukin-1β (IL-1β) were determined with enzyme linked immunosorbent assay (ELISA). The survival of porcines at 24 hours after resuscitation was observed, and the neurological deficit score (NDS) was calculated for the surviving porcines. All animals were sacrificed, and brain, heart and lung tissues were collected, after hematoxylin and eosin (HE) staining, the histopathology changes were evaluated under a light microscopy.

RESULTS

After 8-minute VF, 14 porcines were resuscitated successfully, 7 porcines in normal temperature group and 7 in mild hypothermia group respectively, with the resuscitation success rate of 93.3%. There was no significant difference in body weigh, core temperature, hemodynamics, or blood lactate as well as duration of CPR and the number of defibrillations between the two groups. The core temperature of normal temperature group was maintained at (38.0±0.5) centigrade, while in mild hypothermia group, the hypothermia was reduced to the hypothermia range (33.0±1.0) centigrade until 6 hours, then rewarmed to normothermia gradually [(38.0±0.5) centigrade]. Compared with those before VF, HR was significantly increased after resuscitation in both groups, and MAP and CO were decreased, then they tended to normal. There was no significant difference in hemodynamic parameter at all time points between the two groups. Compared with those before VF, the levels of E-selectin and sTM in serum of the two groups were increased significantly at 1 hour after resuscitation, and they were decreased gradually after reaching the peak at 6 hours, and IL-1β was increased continuously with time. There was no significant difference in E-selectin (μg/L: 1.34±0.52 vs. 1.60±0.61), sTM (μg/L: 19.13±0.34 vs. 19.24±0.73), or IL-1β (ng/L: 25.73±0.87 vs. 25.32±0.25) before VF between normal temperature group and mild hypothermia group (all P > 0.05). The levels of E-selection, sTM and IL-1β in mild hypothermia group were significantly lower than those in normal temperature group from 2 hours after resuscitation [E-selection (μg/L): 11.15±2.73 vs. 16.04±3.23, sTM (μg/L): 49.67±3.32 vs. 62.22±1.85, IL-1β (ng/L): 140.51±6.66 vs. 176.29±18.51, all P < 0.05], and E-selection decreased to the baseline level at 12 hours (μg/L: 1.17±0.65 vs. 1.60±0.61, P > 0.05). The 24-hour survival rates of two groups were both 100%. The NDS score of mild hypothermia group was obviously lower than that of normal temperature group (150.0±6.6 vs. 326.4±12.3, P < 0.05). In normal temperature group, neuronal cell necrosis was observed in the cerebral cortex at 24 hours after resuscitation, and nucleus was deeply stained. The myocardial necrosis and alveolar collapse was found. Meanwhile the infiltration of inflammatory cell could be found in the myocardium and alveolar. The brain, lung and myocardium injury were significantly milder in mild hypothermia group as compared with those in normal temperature group.

CONCLUSIONS

The intravascular cooling therapy was a safe and effective method for inducing mild hypothermia after resuscitation. This cooling effect was fast and reliable, and the rewarming speed was controllable and stable. The protective mechanism of mild hypothermia on PRS may be related to inhibiting systemic inflammatory response and reducing vascular endothelial cell injury.