Methods
Upper respiratory tract, hypothermia, Polarn 4000, Eberspächer, Esslingen, Germany).
CAR ACCIDENT, HEAT, FIRE
To answer the first question, a representative survey was conducted in Germany. From a list of all German municipal authorities 300 fire brigades were randomly selected and contacted. For this survey a questionnaire was developed. Beside other questions these fire brigades were asked by which means they usually protect entrapped patients after car accidents from hypothermia (For the complete questionnaire please see the supplementary material - supplement In the next part of the work, the most frequently used heat protection procedures used were then examined in volunteers and compared to forced air warming, which is a frequently used and highly effective warming methods in operation rooms [The same methodology was used in both studies except for the different warming methods. Both studies were performed in a crossover fashion. We planned to restrict enrolment to 30 participants in each study due to economic reasons.In the first study (Study A), two active heat protection methods were compared. The first method was the usage of a halogen floodlight as used frequently in preclinical use (Flutlichtstrahler BS 1000, Karl Meister GmbH Feuerwehrtechnik, Reutlingen, Germany). This floodlight is used by many fire brigades in Germany and has a power of 1000 W according to the manufacturer. The floodlight was mounted on a tripod at a height of 1 m and placed at a distance of 2 m from the centre of the volunteer’s body at a right angle to it. The other method used was a forced air warmer intended for preclinical use (Polarn 4000, Eberspächer, Esslingen, Germany). This forced air warmer is operated with diesel fuel and has 4 heating stages with a heat flow between 900 and 4000 watts according to the manufacturer’s specifications. During the test series, only heating level 2 (= 2000 watts) was used. The generated warm air was then transported to the patient via a 1.5 m long and 90 mm wide air hose. A commercially available plastic foil with dimensions of 2 × 2.5 m was used as a warming blanket. The volunteers were covered with the foil and the warm air hose was passed under the foil at the subject’s feet.For study A, 30 subjects were recruited and included after informed and written consent (Fig. CONSORT flow chart of volunteer study AIn the second study (Study B), a passive and an active heat protection method were compared. As a passive method, a disposable fleece blanket as used in prehospital care (Reintex GmbH, Ketsch, Germany) was used. According to the manufacturer, the chosen blanket is produced for use on patients in rescue services, fire brigades and ambulance transport. It is a disposable blanket with a cover made of a non-woven polypropylene fabric and a polyester wool filling. The size is 1.90 m x 1.10 m. The weight of the blanket is given by the manufacturer as approx. 250 g. The active method used was a clinical used forced air warmer (WarmTouch WT 5900, Nellcor Tyco Healthcare Group LP, Pleasanton, USA) with CareQuilt adult full body blanket. The forced air warmer generates an air flow with a constant temperature of 43 °C. The experimental procedure for the volunteers was subsequently identical.For the second study (study B), 32 subjects were recruited and included in the study after informed and written consent (Fig. CONSORT flow chart of volunteer study BParticipating volunteers of both studies had to meet the following inclusion criteria:
Able to understand written informed consentAge ≥18 years, ≤ 65 yearsASA I-IIBody mass index < 30 kg/m²Subjective well-being at the time of the examinationExclusion criteria were defined as:
Upper respiratory tract infectionExisting pregnancyRegular medicationThe following criteria were defined as termination criteria for each experiment:
Core body temperature below 34 °CHeart rate above 120/minHeart rate below 50/minDecrease of SpOPathological ECG changesSubjective malaiseSubject’s wish to stop the test