A Prospective Observational Study of the Association between Cabin and outside Air Temperature, and Patient Temperature Gradient during Helicopter Transport in New South Wales

Abstract

The prevalence of hypothermia in patients following helicopter transport varies widely. Low outside air temperature has been identified as a risk factor. Modern helicopters are insulated and have heating; therefore outside temperature may be unimportant if cabin heat is maintained. We sought to describe the association between outside air, cabin and patient temperature, and having the cabin temperature in the thermoneutral zone (18-36 o C) in our helicopter-transported patients. We conducted a prospective observational study over one year. Patient temperature was measured on loading and enginesoff. Cabin and outside air temperature were recorded for the same time periods for each patient, as well as in-flight. Previously identified risk factors were recorded. Complete data was obtained for 133 patients. Patients' temperature increased by a median of 0.15 o C (P=0.013). There was no association between outside air temperature or cabin temperature and patient temperature gradient. The best predictor of patient temperature on landing was patient temperature on loading (R 2 =0.86) and was not improved significantly when other risk factors were added (P=0.63). Thirty-five percent of patients were hypothermic on loading, including those transferred from district hospitals. No patient loaded normothermic became hypothermic when the cabin temperature was in the thermoneutral zone (P=0.04). A large proportion of patients in our sample were hypothermic at the referring hospital. The best predictor of patient temperature on landing is patient temperature on loading. This has implications for studies that fail to account for pre-flight temperature.

A review of the burns caseload of a physician‐based helicopter emergency medical service

“…Just under one quarter (23.6%) of body temperatures that were recorded at destination were ≤35 C, while a comparable service in the UK found similar rates of hypothermia among adult burns patients (19%). 15 A high proportion of interhospital patients were found to be hypothermic prior to transport (32%) in another recent publication by GSA-HEMS, 16 which may account for some of these findings; however, it may be that hypothermia is a complication of burns more common to retrieval medicine. A European study of pre-hospital burns care demonstrated that each drop in temperature by 1 C significantly increases mortality.…”

Body temperature change and outcomes in patients undergoing long-distance air medical transport

“…We divided T before and T after into three groups: hyperthermia (N38.0°C ), normothermia (36.0-37.9°C), and hypothermia (b36.0°C) [4]. The following patient categories described body temperature change: hypothermia both before and after air transport ("hypo to hypo"); hypothermia before air transport and normothermia after air transport ("hypo to normo"); hypothermia before air transport and hyperthermia after air transport ("hypo to hyper"); normothermia before air transport and hypothermia after air transport ("normo to hypo"); normothermia both before and after air transport ("normo to normo"); normothermia before air transport and hyperthermia after air transport ("normo to hyper"); hyperthermia before air transport and hypothermia after air transport ("hyper to hypo"); hyperthermia before air transport and normothermia after air transport ("hyper to normo"); and hyperthermia both before and after air transport ("hyper to hyper").…”

“…For example, one emergency medical center in our region conducts air medical transport for approximately 250 patients a year from isolated islands. Distances range from 100 to 1000 km, and transport usually takes from 30 min to 5 h. These flights cover longer distances and require longer duration than those in previous studies [1][2][3][4]6].…”

“…However, the flight duration in previous studies was relatively short (range, 18-35 min) [1][2][3][4]6]. Also, the evaluated outcome in previous studies was body temperature change between before and after air transport.…”

“…Air medical transport is common in emergency settings and is now the global standard. Although ambient air temperature decreases with altitude, several studies showed that the body temperature of most adult patients did not decline significantly during air medical transport [1][2][3][4][5][6]. Studies also show that body temperature change is not associated with flight duration [1,2,5,6] and outside air temperature [1][2][3][4].…”