Fluid replacement during hypothermia

Hypothermia produces acidosis, depressed cardiac function, hypovolemia and hypotension. This study was designed to examine the cardiovascular dynamics involved with restoration of the hypovolemia before rewarming. Mixed breed splenectomized adult dogs (n = 16) were anesthetized with pentobarbital and cooled to a right atrial temperature of 25 degrees C at a rate of 3 degrees C X h-1. The animals were maintained at 25 degrees C for 6 h and rewarmed at 3 degrees C X h-1. Group 1 was given no fluid, Group 2 was given saline (20% of plasma volume infused in 10 min). 2 h after reaching 25 degrees C and Group 3 received saline just prior to rewarming. The hematocrit was elevated in all groups (p less than 0.05) upon cooling, but did not differ between groups even after saline was given. Cardiac output (Co) at 25 degrees C was 35% of precooled values. Group 2 increased their Q by 15% with fluid and this Q was maintained at higher levels than Groups 1 or 3 for the next 4 h. Plasma volume, heart rate, and cardiac contractility returned to control levels upon rewarming, but Q remained low (less than 10%). The level of Q at the start of rewarming did not affect the final level of Q.