The impact of mild hypothermia on coagulation and cerebral microcirculation after cardiopulmonary resuscitation in rabbits

Abstract

Objective To study the effects of mild hypothermia (MH) on blood coagulation and cerebral microcirculation in rabbits after cardiopulmonary resuscitation (CPR). Method A total of 24 New Zealand rabbits were randomly (random number) divided equally into normothermic group (NT) and MH group. CPR model was established by ventricular fibrillation induced by using alternating current. The rabbits of NT group were observed for 12 h in room temperature after restoration of spontaneous circulation (ROSC). The mild hypothermia was induced in the rabbits of group MH by surface cooling after ROSC, and maintained for 12 h after the aimed low temperature reached. The PT (prothrombin time), APTT (activated partial thromboplastin time), INR (international normalized ratio of prothrombin), D-dimmer (DD) , blood platelet count (BPC) , anti-thrombin Ⅲ activity (AT-Ⅲ) and protein C activity (PC) were measured before CPR and 4 h, 8 h and 12 h after ROSC, and at the same time the cerebral microcirculation was measured by using PERIMED Multichannel Laser Doppler system. One-way ANOVA or Mann-Whitney rank was used to determine the statistical significance between two groups. LSD-t test was used for multiple comparisons,t test for comparisons of means between two independent samples, and Pearson correlation test for correlation analysis. Results The PT, APTT and INR showed a trend of gradually shortening during the course. The APTT in 12 h after ROSC was significantly shorter than that before CPR (23.32 ±5.19 vs. 29.53 ±5.10,P = 0.025), and the activity of AT- Ⅲ and PC were decreased significantly. Compared with the group NT,the PT, APTT and INR in group MH were increased significantly, while there were no differences in the activity of AT- Ⅲ, PC and D-D between two groups. The rates of cerebral microcirculation in group NT before CPR and 4 h, 8 h and 12 h after ROSC were 401.60 ± 11.76 mL/min, 258.86 ± 34. 58 mL/min,317.59 ± 23.36 mL/min and 371.98 ± 5.79 mL/min, respectively, and those in group MT were 398.18 ±12.91 mL/min, 336.19 ± 19.27 mL/min, 347.76 ± 13.80 mL/min and 383.78 ± 3.29 mL/min, respectively. There were significant differences between two groups at each interval after ROSC (4 h: t = - 6.025,df=16, P=0.000;8 h: t= -2.942, df=12, P=0.012;12 h: t= -3.959, df=8, P=0.004). The Pearson correlation test showed that the rate of cerebral microcirculation was positive correlated with APTT after ROSC (4 h:R =0.503,P=0.033;8 h:R=0. 565,P=0. 035;12 h:R=0. 774,P=0. 009), and was not correlated with the other blood coagulants. Conclusions The mild hypothermia led to the inhibition of blood coagulation and improved the cerebral microcirculation concomitantly, which may be one of the mechanism of cerebral protection. Key words: cardiopulmonary resuscitation; coagulopathy; microcirculation; therapeutic hypothermia; rabbits