Equipment to prevent, diagnose, and treat hypothermia: a survey of Norwegian pre-hospital services

Accidental hypothermia represents a challenge in the pre-hospital setting during all seasons and is identified as an independent risk factor for increased mortality and morbidity in trauma patients [1–4]. Trauma patients lose temperature at the accident site, during transport, and in the emergency department [5, 6]. The definition of hypothermia is usually a core temperature below 35°C, but there is a considerable individual difference at what temperature the clinical effects occur [7].

Data are limited on the incidence of hypothermia in Scandinavian trauma patients. Studies from the United States and Australia show an incidence of hypothermia in trauma patients from 1.6 to 15.7% [1–3, 8]. The risk of hypothermia increases with injury severity and has been reported to occur in over 40% of trauma patients presenting signs of hypoperfusion [9].

Knowledge concerning current treatment practices and use of equipment among rescue personnel for treating and preventing hypothermia outside hospitals is limited and warrants further investigation. One retrospective study of military personnel found that despite introduction of new wrapping concepts and active heating equipment, wool blanket was the most used utility [10]. A survey of American mountain rescue teams found that most teams preferred active warming during evacuation, with chemical heat packs as the dominant method [11]. A survey of EMS personnel in one region in Norway found that wool blankets and hot iv fluids were the most preferred interventions among rescue personnel with hypothermic patients [12].

The aim of this study was to identify equipment available for diagnosis, prevention, and treatment of hypothermia in Norwegian pre-hospital services, defined as the ground ambulance service (AS), helicopter emergency medical service (HEMS), fixed wing air ambulance service (FW), and the national search and rescue service (SAR).

The AS is operated through 18 health trusts and conducted approximately 600,000 missions in 2010, serving a population of 4.9 million. The number of ground ambulances was estimated to be around 490 units in daily operation during the study period. HEMS consisted of twelve physician-staffed ambulance helicopters operating from eleven bases, FW of nine planes assigned to seven bases, and SAR had ten helicopters assigned to six bases. Other organisations that handle patients outside the hospital (primary care, non-governmental organisations like the Red Cross, alpine rescue teams, and ski patrols) also provide initial treatment but were not included in this study.

Structured telephone interviews were performed in the period of April-August 2011 and were guided by a questionnaire on the following topics: available insulation materials, active warming equipment, protocols on how to insulate patients, hypothermia thermometers and preferred anatomical measuring sites, pre-warmed i.v. fluids, and infusion heating devices (questionnaire available from corresponding author.). A hypothermia thermometer was defined as a thermometer designed to measure temperature below 32°C. Optional equipment not stored in the units and equipment designed for incubators were excluded. The study was approved by the regional research ethics committee.

In the AS, the primary contact was the head of each health trust’s ambulance department who either responded personally or referred to personnel with better knowledge of the current status. The respondents had to have knowledge of organisational structure and guidelines and detailed knowledge of the current equipment setup in their service. All respondents were asked if there was an equal equipment setup for the whole area and to report the number of ambulance units in their service. In cases of reported variation in equipment setup, a questionnaire was to be distributed electronically to all local station managers in the area. Respondents in the three aero-medical services (FW, HEMS, and SAR) consisted of one of the medical crew members on call.

Data were entered into a standardised database and analysed in a spreadsheet (Microsoft Excel 2010, Microsoft Corp, Redmond, WA, US). Ambiguous answers were interpreted in consensus among the authors, and respondent confirmations were sought when needed.

18 (43%) of the respondents reported having equipment for providing active warming, which was available in most HEMS (58%) and SAR service units (70%), but to a lesser degree in the FW (44%) and AS (14%) units. Heating pads were most frequent, followed by hot water bottles and heating blankets.

Protocols describing how to insulate patients were present for 73% of AS and 70% of SAR units. The minority of HEMS (42%) and FW (22%) units was reported to have such protocols.

All air services reported having hypothermia thermometers, in contrast to the AS in which 12% of the units had them. The reported anatomical measuring sites were rectal, oesophageal, and tympanic.

Hot i.v. fluids were available in all SAR units and the majority of AS (91%) and HEMS services (92%) but in only one of the FW bases (11%). Infusion warmers were available to a small number of the units (0-20%).

The 100% response rate makes this survey a valid overview of the equipment to prevent, diagnose, and treat hypothermia in the Norwegian pre-hospital services.

The insulation material was largely similar within the SAR and FW services, while greater regional differences emerged within the HEMS and AS. Hospital duvets were present in almost all units. The study also showed that “bubble wrap” were common in all services except FW, which has some insulating effect and also acts as a vapour barrier [13, 14].

Active warming equipment was unavailable to most AS units (14%) but fairly common in FW (44%), HEMS (58%), and SAR (70%) units. The main heat source in the survey was heat packs. In the Scandinavian countries there are no current consensus regarding which role active warming devices should have in pre-hospital care. In cases of mild to moderate hypothermia in a patient with intact shivering response, the effect of active warming on core temperature have been questioned [15]. The rate of re-warming will largely be the same as if heat were not added because shivering effectively re-establishes the temperature balance. The main benefits of active re-warming are in these cases to reduce energy consumption and increase comfort [15, 16]. In patients with impaired shivering response due to severe hypothermia, injury, disease, intubation or use of drugs, insulation alone may not be sufficient to maintain core temperature and these patients may require active warming [17, 18].

Head cover intended for patient use was present in the equipment setup of all SAR bases but to a lesser extent in the other services.

A written procedure describing how to insulate patients who either are hypothermic or in danger of becoming hypothermic was reported by the majority of respondents in the AS (73%) and SAR (70%) services. In HEMS and FW, the minority reported having such a protocol (42%, 22% respectively). The appropriateness of the content and personnel compliance was not included in the study aim and was not assessed. The presence of protocols may be viewed as an indicator of whether or not hypothermia prevention and treatment receives attention.

In addition to clinical signs and environmental clues, a reliable measurement of the core temperature is important in assessing the degree of hypothermia. This study shows that the majority of the AS units lack suitable tools for diagnosing hypothermia. Oesophageal and rectal measurements correspond well with pulmonary artery blood temperature and were the measurement sites reported in the aero-medical services [19]. The ambulance service reported rectal and tympanic temperature as measurement locations. Tympanic measurement without isolation of the ear canal may be inaccurate in the pre-hospital environment, especially if the victim has been submerged [20]. ERC Guidelines 2010 recommend the use of oesophageal, rectal, urinary bladder, or tympanic measurement to determine core temperature in hypothermic patients [21]. A survey of Norwegian rescue workers showed that rectal temperature was the most common measuring site in the vehicle ambulance services, consistent with our findings [12].

Depending on ambient temperature, significant temperature loss occurs in the i.v. tube and infusion bag and is a potential factor for iatrogen heat loss [22–24]. Outside the hospital, it is almost impossible to deliver fluid to patients at near body temperature without specially designed equipment. In most cases, giving intravenous fluids with the intention to re-warm the patient will therefore be counterproductive [25, 26]. Heated storage cabinets were reported to be available in almost all AS (91%), HEMS (92%), and SAR units (100%). Infusion heaters were reported only in a small number of the services.

The most common equipment types used to treat and prevent hypothermia in Norwegian pre-hospital services are duvets, plastic “bubble wrap”, and cotton blankets. Active external heating devices and suitable thermometers were available in only a few of the ground ambulance services. The findings in this survey may reflect a lack of consensus in how to best prevent and treat hypothermia in the pre-hospital setting. Further research on the effects of the various wrapping concepts is needed.