Protection against cold in prehospital care: wet clothing removal or addition of a vapor barrier.

OBJECTIVE: The purpose of this study was to evaluate the effect of wet clothing removal or the addition of a vapor barrier in shivering subjects exposed to a cold environment with only limited insulation available. METHODS: Volunteer subjects (n = 8) wearing wet clothing were positioned on a spineboard in a climatic chamber (-18.5°C) and subjected to an initial 20 minutes of cooling followed by 30 minutes of 4 different insulation interventions in a crossover design: 1) 1 woolen blanket; 2) vapor barrier plus 1 woolen blanket; 3) wet clothing removal plus 1 woolen blanket; or 4) 2 woolen blankets. Metabolic rate, core body temperature, skin temperature, and heart rate were continuously monitored, and cold discomfort was evaluated at 5-minute intervals. RESULTS: Wet clothing removal or the addition of a vapor barrier significantly reduced metabolic rate (mean difference ± SE; 14 ± 4.7 W/m(2)) and increased skin temperature rewarming (1.0° ± 0.2°C). Increasing the insulation rendered a similar effect. There were, however, no significant differences in core body temperature or heart rate among any of the conditions. Cold discomfort (median; interquartile range) was significantly lower with the addition of a vapor barrier (4; 2-4.75) and with 2 woolen blankets (3.5; 1.5-4) compared with 1 woolen blanket alone (5; 3.25-6). CONCLUSIONS: In protracted rescue scenarios in cold environments with only limited insulation available, wet clothing removal or the use of a vapor barrier is advocated to limit the need for shivering thermogenesis and improve the patient's condition on admission to the emergency department.

Validity and reliability of the Cold Discomfort Scale: a subjective judgement scale for the assessment of patient thermal state in a cold environment.

Complementary measures for the assessment of patient thermoregulatory state, such as subjective judgement scales, might be of considerable importance in field rescue scenarios where objective measures such as body core temperature, skin temperature, and oxygen consumption are difficult to obtain. The objective of this study was to evaluate, in healthy subjects, the reliability of the Cold Discomfort Scale (CDS), a subjective judgement scale for the assessment of patient thermal state in cold environments, defined as test-retest stability, and criterion validity, defined as the ability to detect a difference in cumulative cold stress over time. Twenty-two healthy subjects performed two consecutive trials (test-retest). Dressed in light clothing, the subjects remained in a climatic chamber set to -20 °C for 60 min. CDS ratings were obtained every 5 min. Reliability was analysed by test-retest stability using weighted kappa coefficient that was 0.84 including all the 5-min interval measurements. When analysed separately at each 5-min interval the weighted kappa coefficients were was 0.48-0.86. Criterion validity was analysed by comparing median CDS ratings of a moving time interval. The comparison revealed that CDS ratings were significantly increased for every interval of 10, 15, and 30 min (p < 0.001) but not for every interval of 5 min. In conclusion, in a prehospital scenario, subjective judgement scales might be a valuable measure for the assessment of patient thermal state. The results of this study indicated that, in concious patients, the CDS may be both reliable and valid for such purpose.

Being cold when injured in a cold environment--patients' experiences.

BACKGROUND: Patients in prehospital care, irrespective of diseases or trauma might experience thermal discomfort because of a cold environment and are at risk for decreasing body temperature which can increase both morbidity and mortality. OBJECTIVE: To explore patients' experiences of being cold when injured in a cold environment. METHOD: Twenty persons who had been injured in a cold environment in northern Sweden were interviewed. Active heat supply was given to 13 of them and seven had passive heat supply. The participants were asked to narrate their individual experience of cold and the pre- and post-injury event, until arrival at the emergency department. The interviews were transcribed verbatim, then analyzed with qualitative content analysis. RESULTS: Patients described that they suffered more from the cold than because of the pain from the injury. Patients who received active heat supply experienced it in a positive way. Two categories were formulated: Enduring suffering and Relief of suffering. CONCLUSION: Thermal discomfort became the largest problem independent of the severity of the injuries. We recommend the use of active heat supply to reduce the negative experiences of thermal discomfort when a person is injured in a cold environment.

Protection against cold in prehospital care: evaporative heat loss reduction by wet clothing removal or the addition of a vapor barrier--a thermal manikin study.

INTRODUCTION: In the prehospital care of a cold and wet person, early application of adequate insulation is of utmost importance to reduce cold stress, limit body core cooling, and prevent deterioration of the patient's condition. Most prehospital guidelines on protection against cold recommend the removal of wet clothing prior to insulation, and some also recommend the use of a waterproof vapor barrier to reduce evaporative heat loss. However, there is little scientific evidence of the effectiveness of these measures. OBJECTIVE: Using a thermal manikin with wet clothing, this study was conducted to determine the effect of wet clothing removal or the addition of a vapor barrier on thermal insulation and evaporative heat loss using different amounts of insulation in both warm and cold ambient conditions. METHODS: A thermal manikin dressed in wet clothing was set up in accordance with the European Standard for assessing requirements of sleeping bags, modified for wet heat loss determination, and the climatic chamber was set to -15 degrees Celsius (°C) for cold conditions and +10°C for warm conditions. Three different insulation ensembles, one, two or seven woollen blankets, were chosen to provide different levels of insulation. Five different test conditions were evaluated for all three levels of insulation ensembles: (1) dry underwear; (2) dry underwear with a vapor barrier; (3) wet underwear; (4) wet underwear with a vapor barrier; and (5) no underwear. Dry and wet heat loss and thermal resistance were determined from continuous monitoring of ambient air temperature, manikin surface temperature, heat flux and evaporative mass loss rate. RESULTS: Independent of insulation thickness or ambient temperature, the removal of wet clothing or the addition of a vapor barrier resulted in a reduction in total heat loss of 19-42%. The absolute heat loss reduction was greater, however, and thus clinically more important in cold environments when little insulation is available. A similar reduction in total heat loss was also achieved by increasing the insulation from one to two blankets or from two to seven blankets. CONCLUSION: Wet clothing removal or the addition of a vapor barrier effectively reduced evaporative heat loss and might thus be of great importance in prehospital rescue scenarios in cold environments with limited insulation available, such as in mass-casualty situations or during protracted evacuations in harsh conditions.

The effect of active warming in prehospital trauma care during road and air ambulance transportation - a clinical randomized trial.

BACKGROUND: Prevention and treatment of hypothermia by active warming in prehospital trauma care is recommended but scientific evidence of its effectiveness in a clinical setting is scarce. The objective of this study was to evaluate the effect of additional active warming during road or air ambulance transportation of trauma patients. METHODS: Patients were assigned to either passive warming with blankets or passive warming with blankets with the addition of an active warming intervention using a large chemical heat pad applied to the upper torso. Ear canal temperature, subjective sensation of cold discomfort and vital signs were monitored. RESULTS: Mean core temperatures increased from 35.1°C (95% CI; 34.7-35.5°C) to 36.0°C (95% CI; 35.7-36.3°C) (p < 0.05) in patients assigned to passive warming only (n = 22) and from 35.6°C (95% CI; 35.2-36.0°C) to 36.4°C (95% CI; 36.1-36.7°C) (p < 0.05) in patients assigned to additional active warming (n = 26) with no significant differences between the groups. Cold discomfort decreased in 2/3 of patients assigned to passive warming only and in all patients assigned to additional active warming, the difference in cold discomfort change being statistically significant (p < 0.05). Patients assigned to additional active warming also presented a statistically significant decrease in heart rate and respiratory frequency (p < 0.05). CONCLUSIONS: In mildly hypothermic trauma patients, with preserved shivering capacity, adequate passive warming is an effective treatment to establish a slow rewarming rate and to reduce cold discomfort during prehospital transportation. However, the addition of active warming using a chemical heat pad applied to the torso will significantly improve thermal comfort even further and might also reduce the cold induced stress response. TRIAL REGISTRATION: ClinicalTrials.gov: NCT01400152.

Field torso-warming modalities: a comparative study using a human model.

OBJECTIVE: To compare four field-appropriate torso-warming modalities that do not require alternating-current (AC) electrical power, using a human model of nonshivering hypothermia. METHODS: Five subjects, serving as their own controls, were cooled four times in 8 degrees C water for 10-30 minutes. Shivering was inhibited by buspirone (30 mg) taken orally prior to cooling and intravenous (IV) meperidine (1.25 mg/kg) at the end of immersion. Subjects were hoisted out of the water, dried, and insulated and then underwent 120 minutes of one of the following: spontaneous warming only; a charcoal heater on the chest; two flexible hot-water bags (total 4 liters of water at 55 degrees C, replenished every 20 minutes) applied to the chest and upper back; or two chemical heating pads applied to the chest and upper back. Supplemental meperidine (maximum cumulative dose of 3.5 mg/kg) was administered as required to inhibit shivering. RESULTS: The postcooling afterdrop (i.e., the continued decrease in body core temperature during the early period of warming), compared with spontaneous warming (2.2 degrees C), was less for the chemical heating pads (1.5 degrees C) and the hot-water bags (1.6 degrees C, p < 0.05) and was 1.8 degrees C for the charcoal heater. Subsequent core rewarming rates for the hot-water bags (0.7 degree C/h) and the charcoal heater (0.6 degree C/h) tended to be higher than that for the chemical heating pads (0.2 degree C/h) and were significantly higher than that for spontaneous warming rate (0.1 degrees C/h, p < 0.05). CONCLUSION: In subjects with shivering suppressed, greater sources of external heat were effective in attenuating core temperature afterdrop, whereas sustained sources of external heat effectively established core rewarming. Depending on the scenario and available resources, we recommend the use of charcoal heaters, chemical heating pads, or hot-water bags as effective means for treating cold patients in the field or during transport to definitive care.

Protection against cold in prehospital care-thermal insulation properties of blankets and rescue bags in different wind conditions.

INTRODUCTION: In a cold, wet, or windy environment, cold exposure can be considerable for an injured or ill person. The subsequent autonomous stress response initially will increase circulatory and respiratory demands, and as body core temperature declines, the patient's condition might deteriorate. Therefore, the application of adequate insulation to reduce cold exposure and prevent body core cooling is an important part of prehospital primary care, but recommendations for what should be used in the field mostly depend on tradition and experience, not on scientific evidence. OBJECTIVE: The objective of this study was to evaluate the thermal insulation properties in different wind conditions of 12 different blankets and rescue bags commonly used by prehospital rescue and ambulance services. METHODS: The thermal manikin and the selected insulation ensembles were setup inside a climatic chamber in accordance to the modified European Standard for assessing requirements of sleeping bags. Fans were adjusted to provide low (< 0.5 m/s), moderate (2-3 m/s) and high (8-9 m/s) wind conditions. During steady state thermal transfer, the total resultant insulation value, Itr (m2 C/Wclo; where C = degrees Celcius, and W = watts), was calculated from ambient air temperature (C), manikin surface temperature (C), and heat flux (W/m2). RESULTS: In the low wind condition, thermal insulation of the evaluated ensembles correlated to thickness of the ensembles, ranging from 2.0 to 6.0 clo (1 clo = 0.155 m2 C/W), except for the reflective metallic foil blankets that had higher values than expected. In moderate and high wind conditions, thermal insulation was best preserved for ensembles that were windproof and resistant to the compressive effect of the wind, with insulation reductions down to about 60-80% of the original insulation capacity, whereas wind permeable and/or lighter materials were reduced down to about 30-50% of original insulation capacity. CONCLUSIONS: The evaluated insulation ensembles might all be used for prehospital protection against cold, either as single blankets or in multiple layer combinations, depending on ambient temperatures. However, with extended outdoor, on-scene durations, such as during prolonged extrications or in multiple casualty situations, the results of this study emphasize the importance of using a windproof and compression resistant outer ensemble to maintain adequate insulation capacity.