Background and purpose: Clinical and experimental studies have shown that marked activation of blood coagulation occurs in cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). Extracorporeal lung and heart assist (ECLHA) is applied in CA patients who cannot be rescued using conventional therapies. We hypothesized that the dose of heparin administered during the pre-arrest period would influence the outcome in a canine model of CA induced by 15 min of normothermia followed by ECLHA, which consists of heparin coating membrane lung and tubing. We therefore investigated the effects of two dose regimes of the pre-arrest heparin for this model.
Methods: Twelve mongrel female dogs were divided into two groups: a group given 200 U/kg heparin (H200, n=6) and a group given 700 U/kg heparin (H700, n=6), group during pre-arrest period. Normothermic ventricular fibrillation (VF) was induced in all dogs for 15 min, followed by 24h of ECLHA with rapidly induced mild hypothermia (33 degrees C) and 120 h of intensive care. Outcome evaluations included: (1) activated coagulation time (ACT); (2) catecholamine dose; (3) hematocrit (Hct) and platelet count; (4) survival rate; (5) neurological deficit scores (NDS); (6) postmortal macroscopic examination with the exception of the brain.
Results: In the H200 group, four dogs died of cardiogenic shock within 28 h. The autopsy revealed extensive patchy hemorrhages in the heart and intestine. In the H700 group, the amount of dopamine was significantly lower (6+/-10mg versus 75+/-41 mg, p<0.05) and the survival rate was significantly higher (100% versus 17%, p<0.05) than in the H200 group. The NDS at 120 h in the H700 group was 18+/-8% and the autopsy revealed an almost normal external appearance of the vital organs. There were no significant differences between groups in either the Hct and platelet count during the 24h of resuscitation, and no bleeding complications were observed.
Conclusion: The use of ECLHA to resuscitate animals in prolonged CA may require a large dose of systemic heparin during the pre-arrest period even if ECLHA circuit was coated with heparin.