Limits of conventional therapies after prolonged normovolemic cardiac arrest in swine

Patients' outcomes after prolonged cardiac arrest are often grim. The aim of this study was to find the longest period of normovolemic, normothermic, cardiac arrest no-flow after which good neurologic outcome can be achieved with conventional therapies.

Swine (28-37 kg) were subjected to ventricular fibrillation cardiac arrest, after which they were randomized into groups with 13 min (n=6), 15 min (n=6), or 17 min (n=6) of untreated cardiac arrest followed by advanced life support (ALS) for 20 min (epinephrine 0.04 mg/kg every 3 min and vasopressin 0.4 IE/kg every 6 min, no defibrillation attempts), followed by cardiopulmonary bypass (CPB). To mimic an unresuscitable situation after prolonged cardiac arrest, CPB was initiated 20 min after the start of resuscitation, followed by defibrillation attempts. Therapeutic mild hypothermia was applied for 20 h and a final neurologic evaluation (neurologic deficit score, NDS; overall performance category, OPC) was done after 9 days.

In the 13-min group, restoration of spontaneous circulation (ROSC) was achieved in five of six swine, four of which survived to day 9, and all had favorable neurologic outcomes [one swine OPC 1, three swine OPC 2, NDS 15% (IQR 6-21)]. In the 15- and 17-min groups, ROSC was achieved in three of six and two of six swine, respectively, one survived to day 9 with OPC 3 in each group, and NDS values were 45 and 58%, respectively (Kruskal-Wallis test for OPC, p=0.048).

In our model, the limit of normovolemic, normothermic, cardiac arrest no-flow time, followed by ACLS, CPB, and prolonged mild hypothermia, seems to be 13 min.