Induced hypothermia by central venous infusion: Saline ice slurry versus chilled saline

Objective: Surface cooling improves outcome in selected comatose survivors of cardiac arrest. Internal cooling with considerable volumes of intravenous cold saline may accelerate hypothermia induction. This study compares core temperatures in swine after central catheter infusions of saline ice slurry (saline with smoothed 100-μm-size ice particles) vs. an equal volume of chilled saline. We hypothesized that slurry would achieve core hypothermia (32-34°C) more consistently and at a faster rate. Design: A total of 11 swine were randomized to receive microparticulate ice slurry, chilled saline infusion, or anesthesia alone in a monitored laboratory setting. Interventions: Intravenous bolus (50 mUkg) of slurry or chilled 1.5% NaCl saline. Slurry was composed of a 1:1 mixture of ice and distilled H 2 O plus NaCl. Measurements: Cerebral cortex, tympanic membrane, inferior vena cava, rectal temperatures, electrocardiogram, arterial blood pressure, and arterial oxygen saturation were recorded for 1 hr after bolus. Main Results: Compared with anesthetized controls, core brain temperatures of the saline and slurry groups dropped by 3.4 ± 0.4°C and 5.3 ± 0.7°C (p =.009), respectively. With an infusion rate of 120 mUmin, cooling rates for the saline and slurry groups were -11.6 ± 1.8°C/hr and -18.2 ± 2.9°C/hr, respectively, during the first 20 mins. Four of four animals in the slurry group vs. zero of four animals in the saline group achieved target cortical temperatures of <34°C. Conclusions: Cold intravenous fluids rapidly induce hypothermia in swine with intact circulation. A two-phase (liquid plus ice) saline slurry cools more rapidly than an equal volume of cold saline at 0°C. Ice-slurry could be a significant improvement over other cooling methods when rate of cooling and limited infusion volumes are important to the clinician.