[Establishment of porcine model of prolonged cardiac arrest and cardiopulmonary resuscitation electrically induced by ventricular fibrillation].

OBJECTIVE: To investigate the optimal injury time point of cardiac arrest (CA) induced electrically, and establish a reproducible prolonged CA and cardiopulmonary resuscitation (CPR) model in pigs.

METHODS: Forty healthy domestic male pigs were randomly divided into four groups, which were ventricular fibrillation (VF) 8, 10, 11, and 12 minutes groups, each group for 10 animals. In these groups, VF was induced by alternating current delivered to right ventricular endocardium and untreated for 8, 10, 11, and 12 minutes, respectively, followed by 6 minutes of CPR procedure. The resuscitation and survival outcomes were recorded. Hemodynamic parameters and arterial blood gases of animals after successful resuscitation were measured and recorded for 6 hours. Those successful resuscitation animals were regularly evaluated for the neurological deficit score (NDS) and survival outcomes every 24 hours till 96 hours after resuscitation.

RESULTS: The shortest duration of CPR (minute: 6.9±1.3) and the highest successful ratio of the first defibrillation (7/10) were observed in group VF 8 minutes, and the ratio of successful resuscitation was 100%. The best coronary perfusion pressure (CPP) during the CPR, less neurological impairment, longer survival time, more stable hemodynamics, and shorter time for arterial pH and lactate level restoring to the original state after CPR were also observed in group VF 8 minutes, and no severe damage was found in those animals. The longest duration of CPR (minute: 10.3±2.9) and the lowest successful ratio of the first defibrillation (1/10) were observed in group VF 12 minutes, and only 4 animals achieved restoration of spontaneous circulation (ROSC), and no animal survived to CPR 96 hours. The worst CPP during CPR and the highest NDS after resuscitation were also found in VF 12 minutes animals compared to those animals in the other groups. The injuries caused by ischemia and hypoxia in groups VF 10 minutes and VF 11 minutes were in between those of the groups VF 8 minutes and VF 12 minutes, and the duration of CPR were (7.0±2.1) minutes and (8.2±2.6) minutes. There were 9 and 7 animals achieved ROSC in groups VF 10 minutes and VF 11 minutes correspondingly, and 6 and 4 animals survived to 96 hours respectively. Obviously unstable hemodynamics was observed during the period of CPR 2 hours in the two groups. At CPR 1 hour, the heart rates (HR, beats/min) in groups VF 10 minutes and VF 11 minutes increased to 172 (155, 201) and 168 (136, 196) respectively, and the mean arterial pressures (MAP, mmHg, 1 mmHg = 0.133 kPa) declined to 97 (92, 100) and 81 (77, 100), the cardiac output (CO, L/min) decreased to 5.0 (4.0, 5.8), 3.7 (3.0, 5.4) correspondingly. Distinct injuries were found in the two groups [CPR 24-96 hours NDS in groups VF 10 minutes and VF 11 minutes: 180 (110, 255)-20 (0, 400) and 275 (223, 350)-240 (110, 400)], and the arterial pH of the two group decreased to 7.26±0.09 and 7.23±0.09 respectively, and the level of lactate (mmol/L) increased to 9.17±1.48 and 12.80±2.71 correspondingly at CPR 0.5 hour. Significantly lower pH was observed in group VF 11 minutes compared to group VF 8 minutes at CPR 0.5 hour (7.23±0.09 vs. 7.33±0.04, P < 0.05). The highest level of lactate (mmol/L) was also found at the same time point in group VF 11 minutes, which recovered to normal slowly, and was still significantly higher than groups VF 8, 10, 12 minutes (7.58±3.99 vs. 2.55±1.53, 2.13±2.00, 3.40±2.30, all P < 0.05) at CPR 4 hours.

CONCLUSIONS: The longer duration of CA was, the more severe damage would be, the longer CPR time would be required, and the harder of the animals to achieve ROSC. In this prolonged CA and CPR porcine model, 10-11 minutes for untreated VF, was an optimal time point with appropriate successful rate of resuscitation, survival outcomes, and post-resuscitation injuries. Therefore, we recommended 10-11 minutes might be the rational length of no-flow time in this model.