Hypothermia in trauma victims at first arrival of ambulance personnel: an observational study with assessment of risk factors

Hypothermia is common in trauma victims. In several studies on severe trauma injury, hypothermia has been reported as occurring in up to two third of the patients [1]. Hypothermia is associated with aggravated injury and increased mortality [2, 3]. A body temperature below 35 °C is an independent risk factor of mortality in trauma victims [4, 5]. Hypothermia induced coagulopathy and cardiovascular, neurological, renal and hematologic effects, all contribute to increased morbidity and mortality [1, 6]. In addition, the lower the initial body temperature, the greater the incidence of hypothermia. Controlling body temperature is thus a priority in the early management of trauma victims [1]. Dedicated guidelines have been recently published [1]. Yet, hypothermia is underdiagnosed and undertreated, particularly during initial management of severe trauma, and only a few studies have focused on prehospital management of trauma victims’ body temperature [1].

The HypoTraum study has shown that risk factors predictive of hypothermia on arrival at the hospital emergency department (ED) relate to the victim’s environment, the severity of the injury, and prehospital management, especially during transport to hospital [7]. On the other hand, circumstances leading hypothermia, from trauma onset to rescue team arrival, remain less clear. Such information should help to optimize body temperature control, and improve management and final outcome.

The aim of the present study was to investigate the risk factors associated with hypothermia, not on arrival at hospital, but at the time of arrival of the emergency medical services (EMS) team at the scene of the accident.

The prevalence of hypothermia was high (29%) on EMS arrival at the scene of the accident and especially noteworthy as patient body temperature was measured after a median delay of only 30 min after the accident. Because of this high incidence and because hypothermia in an independent risk factor of mortality in trauma victims, we recommend the routine early measurement and monitoring of body temperature in all trauma victims.

In this prehospital setting, three independent factors predictive of hyperthermia were identified at the scene of the accident: a low level of consciousness of the victim as given by the GCS, a low air temperature (median 17 °C in this study), and a wet victim. The risk of hypothermia was at least two-fold higher in wet patients, even if these patients accounted for only 11% of the overall population (49/461). A patient who is drenched should benefit from special measures. Usually this means being undressed, dried, and provided with thermal protection. These actions are particularly important as there are no specific interventions that can compensate for injury severity (as given here by the RTS). Undressing, however, should be reserved for wet patients only as it becomes an independent risk factor of hypothermia on arrival at hospital [7]. Blankets were frequently used before MICU arrival and moreover after (74%) [7]. In contrast, active warming was very rarely used during management by the MICU (3%) [7].

The incidence of hypothermia recorded in our earlier study on arrival at the hospital ED was considerably lower (14% vs 29%). This may have been due in part to patient warming by the medical team during transport to hospital in 78% of cases, even if harmful interventions such as infusion of unwarmed fluid may have taken place [7]. In the present study, only 50% of patients (232/461) benefitted from warming (covered by blanket) before EMS arrival and hypothermia was controlled in fewer than 50% of cases whatever the measures taken by the medical team.

The main risk factors for hypothermia on arrival of trauma victims at the hospital ED were severity of injury (especially head injury) and certain aspects of medical care (e.g. orotracheal intubation) [7]. However, the nature of the injury was not an independent risk factor for hypothermia in an early prehospital setting, maybe because the interval between the accident and body temperature measurement was too short for the expression of all adverse effects.

Initial measurement of body temperature is crucial in the initial assessment of trauma patients. We strongly feel that body temperature should be considered as a vital parameter along with blood pressure and heart rate. Continuous monitoring should be performed where possible, particularly in severely injured patients. Only one non invasive device allowed pre-hospital was validated for continuous monitoring when we started this study [9]. A few more devices are now available [1]. This underlines the special attention currently being paid to temperature management in trauma patients.

Precocious, prehospital hypothermia diagnosis is the key to optimal hypothermia management. In this study, hypothermia was corrected (or avoided) before hospital arrival in two thirds of patients. As the Hypotraum study was conducted in France, involvement of an emergency physician in the prehospital setting and relatively short transportation times may have contributed to hypothermia management. First-aid rescuers must also be trained to manage temperature, and long transportation times need to be used to correct hypothermia.

The strength of our study was the exploration of a wide variety of factors (environmental and other) poorly documented in an early prehospital setting [3, 13‐15]. Data collection was facilitated by the way the French EMS system is organized. In France, mobile intensive care units with an emergency physician aboard are sent out to accident scenes. However, the system was also a potential limitation of our study as, in the case of the most serious accidents, the fire brigade may have preceded the medical team on scene, commencing first warming measures, such as blankets, before MICU arrival and initial assessment. Conversely, patients most in need of medical management may have had protracted periods outside on the ground before they could be moved. In contrast less severely injured patients could be managed without MICU, however, such minor trauma patients are not at high risk of hypothermia. Nevertheless, it is unlikely that the determinants of the onset of hypothermia on EMS arrival are influenced by the EMS system. Furthermore, the time from accident to MICU arrival, the position of the patient, and the presence of a blanket were not significantly different between patients with and without hypothermia. Finally, it cannot be excluded that the respective impact of ambient temperature, wetness and patient’s injury severity on body temperature could be different in other locations.

Early preventive or corrective measures should help reduce the incidence of hypothermia in a prehospital setting. These measures should be initiated as soon as EMS arrive at the accident scene. Body temperature measurement and immediate thermal protection should be routine, and special attention should be given to patients who are wet. These measures should be followed by optimal patient management during transport to hospital (warming of infusion fluids and ambulance heating) as previously documented.