The "ICE" study: feasibility of inexpensive commercial coolers on mobile EMS units

Prehospital postresuscitation induced hypothermia (IH) has been shown to reduce neurological complications in comatose cardiac-arrest survivors. Retrofitting ambulances to include equipment appropriate to initiate hypothermia, such as refrigeration units for cooled saline, is expensive. The objective of this nonhuman subject research study was to determine if inexpensive, commercially available coolers could, in conjunction with five reusable ice packs, keep two 1 L bags of precooled 0.9% normal saline solution (NSS) at or below 4°C for an average shift of eight to 12 hours in a real-world environment, on board in-service Emergency Medical Service (EMS) units, over varying weather conditions in all seasons.

The coolers were chosen based on availability and affordability from two nationally available brands: The Igloo MaxxCold (Igloo Products Corp., Katy, Texas USA) and Coleman (The Coleman Company, Wichita, Kansas USA). Both are 8.5 liter (nine-quart) coolers that were chosen because they adequately held two 1 L bags of saline solution, along with the reusable ice packs designated in the study design, and were small enough for ease of placement on ambulances. Initial testing of the coolers was conducted in a controlled environment. Thereafter, each EMS unit was responsible to cool the saline to less than 4°C prior to shift. Data were collected by emergency medical technicians, paramedics, and resident physicians working in seven different ambulance squads. Data analysis was performed using repeated measurements recorded over a 12-hour period from 19 individual coolers and were summarized by individual time points using descriptive statistics.

Initial testing determined that the coolers maintained temperatures of 4°C for 12 hours in a controlled environment. On the ambulances, results based on the repeated measurements over time revealed that the saline solution samples as defined in the protocol, remained consistently below 4°C for 12 hours. Utilizing the lower bound of the 2-sided 95% exact binomial confidence intervals, there was less than a five percent chance that saline samples could not be maintained below 4°C for 12 hours, even during the summer months.

Simple, commercially available coolers can maintain two 1 L bags of 0.9% NSS at 4°C for 12 hours in ambulances in varying environmental conditions. This suggests that EMS agencies could inexpensively initiate prehospital IH in appropriate cases.