Rapid induction of cerebral hypothermia by aortic flush during normovolemic cardiac arrest in pigs

Objective: Induction of deep cerebral hypothermia before reperfusion might improve neurologic outcome after cardiac arrest. We hypothesized that an aortic flush with cold saline during cardiac arrest is able to induce deep cerebral hypothermia and that the cooling efficiency can be enhanced by a) increasing the arteriovenous pressure gradient during the flush with vasopressin; b) improving the cerebral microcirculation during the flush with the thrombolytic agent alteplase; and c) increasing the arteriovenous pressure gradient further with venting the right heart by draining blood during the flush. Design: Prospective randomized experimental study. Setting: University research laboratory. Subjects: Twenty-four pigs Large White breed (31-42 kg). Interventions: After 10 mins of ventricular fibrillation, pigs received an aortic flush (100 mL/kg, 4 degrees C, flow rate 35 mL/kg/min) into the descending aorta via a balloon catheter. The animals were subjected randomly to either an aortic flush with saline, saline plus vasopressin 1.2 IU/kg, saline plus alteplase 1 mg/kg, saline plus a combination of vasopressin 1.2 IU/kg and alteplase 1 mg/kg, or saline plus vasopressin 1.2 IU/kg and venting the right heart. Arterial and venous pressures and brain temperatures were recorded for an observation time of 10 mins after flush. Measurements and Main Results: A sufficient arteriovenous pressure gradient and deep cerebral hypothermia were only achieved with a flush containing vasopressin (brain temperature 16.1 +/- 1.3 degrees C in the vasopressin group vs. 35.4 +/- 1.5 degrees C in the saline group, p < .001); combining vasopressin with alteplase, or venting the right heart, did not further enhance the cooling efficiency of the flush. Conclusions: A cold saline aortic flush with vasopressin rapidly decreases brain temperature during prolonged normovolemic cardiac arrest in pigs. Whether deep cerebral hypothermia induced before reperfusion can improve neurologic outcome after cardiac arrest needs further investigation in large animal outcome studies.