A simple method of maintaining chilled saline in the prehospital setting

Mild therapeutic hypothermia has been shown to improve neurologic outcomes after sudden cardiac arrest. Therapeutic hypothermia should be started as soon as return of spontaneous circulation occurs. However, saline is difficult to keep chilled in the prehospital environment. We sought to determine whether a cooler and ice packs could keep saline cold under prehospital conditions.

In phase 1 of the experiment, two 1000-mL bags of prechilled 0.9% normal saline were placed in a cooler with 3 ice packs. An additional bag of 1000-mL 0.9% normal saline remained outside the cooler as a control. Over 9 consecutive days, we measured the ambient air temperature and the temperature of each bag of saline every 4 hours. In phase 2 of the experiment, the cooler was kept sealed, and the temperature of the saline was measured after 24 hours.

The mean temperatures over 24 hours ranged as follows: ambient temperature, 24°C to 27.2°C; bottom bag, 0.6°C to 3.5°C; top bag, 1.4°C to 5.7°C; and control bag, 9.8°C to 26.8°C. A t test was used to compare the chilled saline against the control bag. Statistical significance (P < .05) was achieved at all times. In phase 2 of the experiment, after 24 hours, 100% of the bottom bags and 93% of the top bags were less than 6°C.

Our data demonstrate that saline can be kept chilled in ambulances for 24 hours using ice packs and coolers. The estimated cost is less than $50.00 per ambulance. Using coolers and ice packs is an inexpensive way for emergency medical service agencies to initiate prehospital hypothermia.