Is prehospital use of active external warming dangerous for patients with accidental hypothermia: a systematic review

Environmental Hypothermia

Although a rare diagnosis in the Emergency Department, hypothermia affects patients in all environments, from urban to mountainous settings. Classic signs of death cannot be interpreted in the hypothermic patient, thus resulting in the mantra, "No one is dead until they're warm and dead." This comprehensive review of environmental hypothermia covers the clinical significance and pathophysiology of hypothermia, pearls and pitfalls in the prehospital management of hypothermia (including temperature measurement techniques and advanced cardiac life support deviations), necessary Emergency Department diagnostics, available rewarming modalities including extracorporeal life support, and criteria for termination of resuscitation.

Effect of a vapor barrier in combination with active external rewarming for cold-stressed patients in a prehospital setting: a randomized, crossover field study

BACKGROUND

Use of a vapor barrier in the prehospital care of cold-stressed or hypothermic patients aims to reduce evaporative heat loss and accelerate rewarming. The application of a vapor barrier is recommended in various guidelines, along with both insulating and wind/waterproof layers and an active external rewarming device; however, evidence of its effect is limited. This study aimed to investigate the effect of using a vapor barrier as the inner layer in the recommended "burrito" model for wrapping hypothermic patients in the field.

METHODS

In this, randomized, crossover field study, 16 healthy volunteers wearing wet clothing were subjected to a 30-minute cooling period in a snow chamber before being wrapped in a model including an active heating source either with (intervention) or without (control) a vapor barrier. The mean skin temperature, core temperature, and humidity in the model were measured, and the shivering intensity and thermal comfort were assessed using a subjective questionnaire. The mean skin temperature was the primary outcome, whereas humidity and thermal comfort were the secondary outcomes. Primary outcome data were analyzed using analysis of covariance (ANCOVA).

RESULTS

We found a higher mean skin temperature in the intervention group than in the control group after approximately 25 min (p < 0.05), and this difference persisted for the rest of the 60-minute study period. The largest difference in mean skin temperature was 0.93 °C after 60 min. Humidity levels outside the vapor barrier were significantly higher in the control group than in the intervention group after 5 min. There were no significant differences in subjective comfort. However, there was a consistent trend toward increased comfort in the intervention group compared with the control group.

CONCLUSIONS

The use of a vapor barrier as the innermost layer in combination with an active external heat source leads to higher mean skin rewarming rates in patients wearing wet clothing who are at risk of accidental hypothermia.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT05779722.

A Rare Case of a Patient Being Alert and Communicative Despite Severe Hypothermia

Hypothermia is defined as a significant drop in core body temperature below 35°C (95°F). It is traditionally staged as mild, moderate, severe, and profound at temperatures of 35°C to 32°C (95°F to 89.6°F), 32°C to 28°C (89.6°F to 82.4°F), <28°C (<82.4°F), and <24°C (75.2°F), respectively. It can also be classified into the same stages by clinical presentations. We present a patient that fits into two different stages based on core body temperature and clinical presentation.  A 58-year-old homeless male with a history of seizures and alcohol use presented via emergency medical services after spending the night outside and uncovered with a core body temperature of 25.1°C (77.1°F) via a urinary bladder thermometer, meeting criteria for severe, near profound, hypothermia. However, he was alert and communicating, shivering, with tachycardia, tachypnea, normal oxygen saturation, and elevated blood pressure, suggestive of mild hypothermia clinically. Passive and active external and internal rewarming were utilized to treat, with the removal of wet clothing, forced air patient warming system, warm blankets, and warm lactated ringers given intravenously. He was soon transferred to the intensive care unit and first returned to normothermic levels after approximately 10 hours from presentation. An electrocardiogram was obtained after resolution of shivering and revealed atrial fibrillation without Osborn waves. He remained in the hospital for the following week to treat his atrial fibrillation, hypothermia-induced rhabdomyolysis, and alcohol withdrawal. He was discharged without neurologic deficits and medically stable with appropriate resources.  This case demonstrates a unique presentation of severe hypothermia. To our knowledge, there has not been a reported case of severe hypothermia that does not involve severe central nervous system depression, severe slowing of vitals, and/or comatose status. These clinical symptoms normally begin during moderate hypothermic levels near 32°C (89.6°F), yet our patient presented without any central nervous system depression and with accelerated vitals that are more consistent with mild hypothermia yet had a core temperature of 25.1°C (77.1°F). Treatment was dictated by his core body temperature rather than clinical presentation. Because of this incongruence between symptoms and true severity of disease in hypothermia, we recommend diagnosis and treatment of hypothermia always be confirmed and based on core body temperature via a low-reading thermometer instead of clinical presentation alone.

What is the best way to keep the patient warm during technical rescue? Results from two prospective randomised controlled studies with healthy volunteers

BACKGROUND

Accidental hypothermia is a manifest problem during the rescue of entrapped victims and results in different subsequent problems as coagulopathy and wound infection. Different warming methods are available for the preclinicial use. However, their effectiveness has hardly been evaluated.

METHODS

In a first step a survey among German fire brigades was performed with questions about the most used warming methods. In a second step two crossover studies were conducted. In each study two different warming method were compared with forced air warming - which is the most frequently used and highly effective warming method in operation rooms (Study A: halogen floodlight vs. forced air warming; Study B: forced air warming vs. fleece blanket). In both studies healthy volunteers (Study A: 30 volunteers, Study B: 32 volunteers) were sitting 60 min in a cold store. In the first 21 min there was no subject warming. Afterwards the different warming methods were initiated. Every 3 min parameters like skin temperature, core body temperature and cold perception on a 10-point numeric rating scale were recorded. Linear mixed models were fitted for each parameter to check for differences in temperature trajectories and cold perception with regard to the different warming methods.

RESULTS

One hundred fifty-one German fire brigades responded to the survey. The most frequently used warming methods were different rescue blankets (gold/silver, wool) and work light (halogen floodlights). Both studies (A and B) showed significantly (p < 0.05) higher values in mean skin temperature, mean body temperature and total body heat for the forced air warming methods compared to halogen floodlight respectively fleece blanket shortly after warming initiation. In contrast, values for the cold perception were significantly lower (less unpleasant cold perception) during the phase the forced air warming methods were used, compared to the fleece blanket or the halogen floodlight was used.

CONCLUSION

Forced air warming methods used under the standardised experimental setting are an effective method to keep patients warm during technical rescue. Halogen floodlight has an insufficient effect on the patient's heat preservation. In healthy subjects, fleece blankets will stop heat loss but will not correct heat that has already been lost.

TRIAL REGISTRATION

The studies were registered retrospectively on 14/02/2022 on the German Clinical Trials registry (DRKS) with the number DRKS00028079.

Prehospital Active and Passive Warming in Trauma Patients

OBJECTIVE

Hypothermia is common among trauma patients and can lead to a serious rise in morbidity and mortality. This study was performed to investigate the effect of active and passive warming measures implemented in the prehospital phase on the body temperature of trauma patients.

METHODS

In a multicenter, multinational prospective observational design, the effect of active and passive warming measures on the incidence of hypothermia was investigated. Adult trauma patients who were transported by helicopter emergency medical services (HEMS) or ground emergency medical services with an HEMS physician directly from the scene of injury were included. Four HEMS/ground emergency medical services programs from Canada, the United States, and the Netherlands participated.

RESULTS

A total of 80 patients (n = 20 per site) were included. Eleven percent had hypothermia on presentation, and the initial evaluation occurred predominantly within 60 minutes after injury. In-line fluid warmers and blankets were the most frequently used active and passive warming measures, respectively. Independent risk factors for a negative change in body temperature were transportation by ground ambulance (odds ratio = 3.20; 95% confidence interval, 1.06-11.49; P = .03) and being wet on initial presentation (odds ratio = 3.64; 95% confidence interval, 0.99-13.36; P = .05).

CONCLUSION

For adult patients transported from the scene of injury to a trauma center, active and passive warming measures, most notably the removal of wet clothing, were associated with a favorable outcome, whereas wet patients and ground ambulance transport were associated with an unfavorable outcome with respect to temperature.

Traumatisme et température

Le patient traumatisé est exposé à l’hypothermie. La mortalité des traumatisés hypothermes est multipliée par quatre ou cinq. Les interactions de l’hypothermie avec l’hémostase et le système cardiovasculaire sont délétères. Les effets sur la coagulation sont multiples et concourent directement à la surmortalité faisant de l’hypothermie une composante majeure de la « triade létale ». Les causes d’hypothermie chez le patient traumatisé sont multiples : 1) environnementales, le risque augmente quand la température ambiante diminue ; 2) cliniques, le risque augmente avec la gravité ; et aussi 3) thérapeutiques, par exemple par la perfusion de solutés à température ambiante. Une prise en charge optimale repose sur une mesure précoce et un monitorage continu de la température corporelle. L’objectif thérapeutique est de maintenir une température corporelle au moins égale à 36 °C. Limiter le déshabillage du patient, le protéger du froid avec une couverture de survie, l’installer rapidement dans une ambulance chauffée, recourir à des dispositifs de réchauffement actifs, perfuser des solutés réchauffés sont les éléments fondamentaux de la prise en charge d’un patient traumatisé, potentiellement hypotherme.

Accidental hypothermia: characteristics, outcomes, and prognostic factors-A nationwide observational study in Japan (Hypothermia study 2018 and 2019)

Aim

This study describes the clinical characteristics and outcomes as well as the prognostic factors of patients with accidental hypothermia (AH) using Japan’s nationwide registry data.

Methods

The Hypothermia study 2018 and 2019, which included patients aged 18 years or older with a body temperature of 35°C or less, was a multicenter registry conducted at 87 and 89 institutions throughout Japan, with data collected from December 2018 to February 2019 and December 2019 to February 2020, respectively.

Results

In total, 1363 patients were enrolled in the registry, of which 1194 were analyzed in this study. The median (interquartile range) age was 79 (68–87) years, and the median (interquartile range) body temperature at the emergency department was 30.8°C (28.4–33.6°C). Forty‐three percent of patients with AH had a mild condition, 35.2% moderate, and 21.9% severe. AH occurred in an indoor setting in 73.4% and was caused by acute medical illness in 49.3% of patients. A total of 101 (8.5%) patients suffered from cardiopulmonary arrest on arrival at the hospital. The overall 30‐day mortality rate was 24.5%, the median (interquartile range) intensive care unit stay was 4 (2–7) days, and the median (interquartile range) hospital stay was 13 (4–27) days. In the multivariable logistic analysis, the prognostic factors were age (≥75 years old), male, activities of daily living (needing total assistance), cause of AH (trauma, alcohol), Glasgow Coma Scale score, and potassium level (>5.5 mEq/L).

Conclusion

The mortality rate of AH was 24.5% in Japan. The prognostic factors developed in this study may be useful for the early prediction, prevention, and awareness of severe AH.

Is prehospital use of active external warming dangerous for patients with accidental hypothermia: a systematic review

BACKGROUND

Optimal prehospital management and treatment of patients with accidental hypothermia is a matter of frequent debate, with controversies usually revolving around the subject of rewarming. The rule of thumb in primary emergency care and first aid for patients with accidental hypothermia has traditionally been to be refrain from prehospital active rewarming and to focus on preventing further heat loss. The potential danger of active external rewarming in a prehospital setting has previously been generally accepted among the emergency medicine community based on a fear of potential complications, such as "afterdrop", "rewarming syndrome", and "circum-rescue collapse". This has led to a reluctancy from health care providers to provide patients with active external rewarming outside the hospital. Different theories and hypotheses exist for these physiological phenomena, but the scientific evidence is limited. The research question is whether the prehospital use of active external rewarming is dangerous for patients with accidental hypothermia. This systematic review intends to describe the acute unfavourable adverse effects of active external rewarming on patients with accidental hypothermia.

METHODS

A literature search of the Cochrane Library, MEDLINE, EMBASE, the Cumulative Index to Nursing and Allied Health Literature (CINAHL], and SveMed+ was carried out, and all articles were screened for eligibility. All article formats were included.

RESULTS

Two thousand three hundred two articles were screened, and eight articles met our search criteria. Three articles were case reports or case series, one was a prospective study, two were retrospective studies, one article was a literature review, and one article was a war report from the Napoleonic Wars.

CONCLUSIONS

One of the main findings in this article was the poor scientific quality and the low number of articles meeting our inclusion criteria. When conducting this review, we found no scientific evidence of acceptable quality to prove that the use of active external rewarming is dangerous for patients with accidental hypothermia in a prehospital setting. We found several articles claiming that active external rewarming is dangerous, but most of them do not cite references or provide evidence.