A randomized, controlled trial comparing arteriovenous to venovenous rewarming of severe hypothermia in a porcine model.

Background: The purpose of this study was to evaluate active rewarming using continuous arteriovenous rewarming (CAVR) and continuous venovenous rewarming (CVVR) methods during severe hypothermia using an electromagnetic fluid warmer. Rapid rewarming using these techniques is superior to passive rewarming and is possible with commercially available equipment.
Methods: Eighteen swine (55-65 kg) were assigned to CAVR, CVVR, or control. Vascular access was obtained via central lines (8.5-French) in all subjects. Subjects were cooled to 27 degrees C (80.6 degrees F) in an ice bath, and then dried, covered, and connected to the rewarming device. The carotid artery (CAVR) or internal jugular vein (CVVR) was used for circuit inflow. Warmed 39 degrees C (102.2 degrees F) blood was returned via the femoral vein. Hemodynamic parameters and temperatures (pulmonary artery and rectal) were recorded until reaching an endpoint of a pulmonary artery temperature of 37 degrees C (98.6 degrees F).
Results: Mean rewarming time in the CAVR group was 2 hours 14 minutes, with a mean rewarming rate of 4.5 degrees C/h (8.1 degrees F/h, 0.034 degrees C/kg/h). Total circulating volume averaged 65 L. CVVR averaged 3 hours 8 minutes, with a mean rewarming rate of 3.2 degrees C/h (5.8 degrees F/h, 0.024 degrees C/kg/h). Total circulating volume averaged 67 L. Controls averaged 10 hours 42 minutes, with a mean rate of 0.9 degrees C/h (1.7 degrees F/h, 0.007 degrees C/kg/h). The CAVR group was faster than the CVVR group in both the rewarming rate and total time to rewarming (p = 0.034 and p = 0.040, respectively). Both experimental groups were significantly different from controls in rewarming rate and total time to rewarming (p < 0.001).
Conclusion: CAVR offers the most rapid rate of rewarming. CVVR offers a rapid rate using less invasive procedures. Both techniques are markedly superior to passive rewarming methods typically used during early resuscitation.