Active Warming

[rock_shoes]

You're essentially correct. We need to rewarm an individual slowly to prevent cold extremty blood from circulating back to the warmer(comparatively) heart and causing it to fibrillate.

Not only the blood temperature but also the pH should be considered. Hypothermic patient's (depending on the severity) have a tendency to be acidotic.

With regard to internal rewarming; one of the most interesting techniques I've seen involves placing a triple lumen central line with a closed loop that warmed fluids are circulated through. I've also seen the exact opposite done for ROSC patients to cool them. If monitored correctly the technique essentially gives the attending physician a "thermostat control" for their patient.