Prehospital treatment of hypothermia

Complications with hot, cold and altitude environments in disaster management

INTRODUCTION

Disaster management is the process of preparing, responding and recovering to an emergency whether that be natural or man-made. It is a time-consuming, resource-heavy process with the aim of reducing the risk of certain events and, where not possible, reducing the impact of said disaster, ensuring that the risks have been identified and appropriate rescue and recovery plan is in place.

METHODS

We carried out a thorough literature search on the complications of hot, cold and altitude environments in disaster management and distilled the learnings into this article.

RESULTS

The incidence of disasters of natural, man-made and complex origin is likely to continue increasing as global temperatures continue to rise.

CONCLUSION

Disaster management in the extreme environments of hot, cold and high altitude is fraught with unique challenges, especially around the physiological response of rescuers, resource constraints and logistics. Recognising these challenges is an important aspect of planning and preparation for disaster management in these environments.

Impact of rescue collapse on mortality rate in severe accidental hypothermia: A matched-pair analysis

AIM

To assess the impact of the occurrence of cardiac arrest associated with initial management on the outcome of severely hypothermic patients who were rewarmed with Extracorporeal Life Support (ECLS).

METHODS

We collected the individual data of patients in a state of severe accidental hypothermia who were found with spontaneous circulation and rewarmed with ECLS, from cardiac surgery departments. Patients were divided into two groups: those with a subsequent cardiac arrest (RC group); and those with the retained circulation (HT3 group), and compared by using a matched-pair analysis. The mortality rates and the neurological status in survivors were compared as the main outcomes. The difference in the risk of death between the HT3 and RC groups was calculated.

RESULTS

A total of 124 patients were included into the study: 45 in the HT3 group and 79 in the RC group. The matched cohorts consisted of 45 HT3 patients and 45 RC patients. The mortality rate in both groups was 24% and 49% (p = 0.02) respectively; the relative risk of death was 2.0 (p = 0.02). ICU length of stay was significantly longer in the RC group (p < 0.001). Factors associated with survival in the HT3 group included patient age, rewarming rate, and blood BE; while in the RC group, patient age and lactate concentration.

CONCLUSIONS

The occurrence of rescue collapse is linked to a doubling of the risk of death in severely hypothermic patients. Procedures which are known as potential triggers of rescue collapse should be performed with special attention, including in conscious patients.

Cardiac Arrest Secondary to Accidental Hypothermia: Rewarming Strategies in the Field

Hypothermic cardiac arrest is rare and poses a challenge to prehospital responders. Standard cardiac arrest protocols advise treating reversible causes of arrest; however, rewarming the cold casualty is not easily achieved in the field. This article aimed to review the literature on hypothermia in order to produce evidence-based recommendations on rewarming that could realistically be applied to hypothermic cardiac arrest patients.

The prehospital management of hypothermia - An up-to-date overview

BACKGROUND

Accidental hypothermia concerns a body core temperature of less than 35°C without a primary defect in the thermoregulatory system. It is a serious threat to prehospital patients and especially injured patients, since it can induce a vicious cycle of the synergistic effects of hypothermia, acidosis and coagulopathy; referred to as the trauma triad of death. To prevent or manage deterioration of a cold patient, treatment of hypothermia should ideally begin prehospital. Little effort has been made to integrate existent literature about prehospital temperature management. The aim of this study is to provide an up-to-date systematic overview of the currently available treatment modalities and their effectiveness for prehospital hypothermia management.

DATA SOURCES

Databases PubMed, EMbase and MEDLINE were searched using the terms: "hypothermia", "accidental hypothermia", "Emergency Medical Services" and "prehospital". Articles with publications dates up to October 2017 were included and selected by the authors based on relevance.

RESULTS

The literature search produced 903 articles, out of which 51 focused on passive insulation and/or active heating. The most effective insulation systems combined insulation with a vapor barrier. Active external rewarming interventions include chemical, electrical and charcoal-burning heat packs; chemical or electrical heated blankets; and forced air warming. Mildly hypothermic patients, with significant endogenous heat production from shivering, will likely be able to rewarm themselves with only insulation and a vapor barrier, although active warming will still provide comfort and an energy-saving benefit. For colder, non-shivering patients, the addition of active warming is indicated as a non-shivering patient will not rewarm spontaneously. All intravenous fluids must be reliably warmed before infusion.

CONCLUSION

Although it is now accepted that prehospital warming is safe and advantageous, especially for a non-shivering hypothermic patient, this review reveals that no insulation/heating combinations stand significantly above all the others. However, modern designs of hypothermia wraps have shown promise and battery-powered inline fluid warmers are practical devices to warm intravenous fluids prior to infusion. Future research in this field is necessary to assess the effectiveness expressed in patient outcomes.

Measurements of rates of cooling of a manikin insulated with different mountain rescue casualty bags

Background

Accidental hypothermia is common in those who sustain injuries in remote environments. This is unpleasant and associated with adverse effects on subsequent patient outcomes. To minimise further heat loss, a range of insulating systems are available to mountain rescue teams although the most effective and cost-efficient have yet to be determined.

Methods

Under ambient, still, dry, air conditions, a thermal manikin was filled with water at a temperature of 42 °C and then placed into a given insulation system. Water temperature was then continuously observed via an in-dwelling temperature sensor linked to a PROPAQ 100 series monitor and recorded every 10 min for 130 min. This method was repeated for each insulating package.

Results

The vacuum mattress/Pertex©/fibrepile blanket system, either on its own or coupled with the Wiggy bag, was the most efficient with water temperatures only decreasing by 3.2 °C over 130 min. This was followed by the heavy-weight casualty bags without the vacuum mattress/Pertex©/fibrepile blanket system, decreasing by 4.2–4.3 °C. With the Blizzard bag, a decline in water temperature of 5.4 °C was seen over the study duration while a decrease of 9.5 °C was noted when the plastic survival bag was employed.

Conclusions

Under the still-air conditions of the study, the vacuum mattress/Pertex©/fibrepile blanket was seen to offer comparable insulation effectiveness compared to be both heavy-weight casualty bags. In turn, these three systems appeared more efficient at insulating the manikin than the Blizzard bag or plastic survival bag.

Electronic supplementary material

The online version of this article (doi:10.1186/s13728-017-0055-7) contains supplementary material, which is available to authorised users.

A Novel Cooling Method and Comparison of Active Rewarming of Mildly Hypothermic Subjects

OBJECTIVE

To compare the effectiveness of arteriovenous anastomosis (AVA) vs heated intravenous fluid (IVF) rewarming in hypothermic subjects. Additionally, we sought to develop a novel method of hypothermia induction.

METHODS

Eight subjects underwent 3 cooling trials each to a core temperature of 34.8±0.6 (32.7 to 36.3°C [mean±SD with range]) by 14°C water immersion for 30 minutes, followed by walking on a treadmill for 5 minutes. Core temperatures (Δtes) and rates of cooling (°C/h) were measured. Participants were then rewarmed by 1) control: shivering only in a sleeping bag; 2) IVF: shivering in sleeping bag and infusion of 2 L normal saline warmed to 42°C at 77 mL/min; and 3) AVA: shivering in sleeping bag and circulation of 45°C warmed fluid through neoprene pads affixed to the palms and soles of the feet.

RESULTS

Cold water immersion resulted in a decrease of 0.5±0.5°C Δtes and 1±0.3°C with exercise (P < .01); with an immersion cooling rate of 0.9±0.8°C/h vs 12.6±3.2°C/h with exercise (P < .001). Temperature nadir reached 35.0±0.5°C. There were no significant differences in rewarming rates between the 3 conditions (shivering: 1.3±0.7°C/h, R² = 0.683; IVF 1.3±0.7°C/h, R² = 0.863; and AVA 1.4±0.6°C/h, R² = 0.853; P = .58). Shivering inhibition was greater with AVA but was not significantly different (P = .07).

CONCLUSIONS

This study developed a novel and efficient model of hypothermia induction through exercise-induced convective afterdrop. Although there was not a clear benefit in either of the 2 active rewarming methods, AVA rewarming showed a nonsignificant trend toward greater shivering inhibition, which may be optimized by an improved interface.

Wilderness medicine

BACKGROUND

Human activity in wilderness areas has increased globally in recent decades, leading to increased risk of injury and illness. Wilderness medicine has developed in response to both need and interest.

METHODS

The field of wilderness medicine encompasses many areas of interest. Some focus on special circumstances (such as avalanches) while others have a broader scope (such as trauma care). Several core areas of key interest within wilderness medicine are discussed in this study.

RESULTS

Wilderness medicine is characterized by remote and improvised care of patients with routine or exotic illnesses or trauma, limited resources and manpower, and delayed evacuation to definitive care. Wilderness medicine is developing rapidly and draws from the breadth of medical and surgical subspecialties as well as the technical fields of mountaineering, climbing, and diving. Research, epidemiology, and evidence-based guidelines are evolving. A hallmark of this field is injury prevention and risk mitigation. The range of topics encompasses high-altitude cerebral edema, decompression sickness, snake envenomation, lightning injury, extremity trauma, and gastroenteritis. Several professional societies, academic fellowships, and training organizations offer education and resources for laypeople and health care professionals.

CONCLUSIONS

THE FUTURE OF WILDERNESS MEDICINE IS UNFOLDING ON MULTIPLE FRONTS: education, research, training, technology, communications, and environment. Although wilderness medicine research is technically difficult to perform, it is essential to deepening our understanding of the contribution of specific techniques in achieving improvements in clinical outcomes.

[Management of severe accidental hypothermia]

Accidental hypothermia is an environmental condition with basic principles of classification and resuscitation that apply to mountain, sea or urban scenarios. Along with coagulopathy and acidosis, hypothermia belongs to the lethal triad of trauma victims requiring critical care. A customized healthcare chain is involved in its management, extending from on site assistance to intensive care, cardiac surgery and/or the extracorporeal circulation protocols. A good classification of the degree of hypothermia preceding admission contributes to improve management and avoids inappropriate referrals between hospitals. The most important issue is to admit hypothermia victims in asystolia or ventricular fibrillation to those hospitals equipped with the medical technology which these special clinical scenarios require. This study attempts to establish the foundations for optimum management of accidental hypothermia from first emergency care on site to treatment in hospital including, resuscitation and rewarming with extracorporeal circulation.

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.

Detection and management of hypothermia at a large outdoor endurance event in the United kingdom

OBJECTIVE

Optimum detection of hypothermia in athletes during outdoor exposure events remains controversial. The aims of this study were firstly to assess whether temperature readings affected competitor discharge from the treatment station and secondly to assess agreement between oral and tympanic thermometer measurements.

METHODS

All competitors treated for symptomatic hypothermia at an outdoor endurance event in the United Kingdom during January 2009 were included. Temperature readings were taken using oral (Digitemp digital oral thermometer) and tympanic (Braun Thermoscan IRT 4520 ExacTemp) thermometers, with a temperature <35 degrees C classifying hypothermia.

RESULTS

From 4700 competitors, 64 (1.4%) were treated for symptomatic hypothermia. Of these, 92% were male, the mean age was 26 years, and the mean treatment time was 25 minutes. There was no severe/life-threatening hypothermia, and no competitors required transport to a hospital for hypothermia. At discharge, 19% of competitors were still classed as hypothermic in the oral group and 28% in the tympanic group, despite competitors only being discharged when no longer symptomatic. Oral readings at discharge were significantly lower than tympanic readings (33.8 degrees C [95% CI, 33.2 degrees C to 34.5 degrees C] vs 35.0 degrees C [95% CI, 34.6 degrees C to 35.3 degrees C], respectively, P = .003).

CONCLUSIONS

The use of thermometers had a limited role in discharging competitors at this event, who were apparently safely discharged when no longer symptomatic. Treating clinicians and the thermometers did not always agree on whether a patient was hypothermic or not. Oral and tympanic thermometers had poor agreement. Routine thermometer readings at future events may be unnecessary, although screening competitors of concern will remain useful.

[Water rescue. A unique area of emergency medicine with many facets]

Emergencies on or in water are relatively rare in the rescue service. For this reason, water accident treatment and management does not receive much attention in the training of emergency medicine physicians. Consequently doctors working in emergency medicine often have minimal knowledge in this area. On the other hand, the number of fatal accidents on and in water has increased in recent years. In Germany the number of non-swimmers is also increasing, so it can be assumed that the number of water-related accidents will continue to rise. Drowning accidents and near drowning are important in this context and will be discussed in detail in this review as well as hypothermia (a frequent problem), accompanying injuries and diving accidents.

[Management of accidental hypothermia]

Patients with hypothermia are frequently encountered in emergency medicine. Particularly trauma patients, but also other predisposed persons, can be expected to suffer from hypothermia at any time of the year. Therapy focuses not only on symptom-oriented intensive care to stabilize and secure vital functions, but also on rewarming. Even in cases of severe hypothermia with circulatory arrest, therapy can produce excellent results. This paper first gives a brief overview of the typical clinical symptoms of hypothermia, before giving a detailed description of the preclinical and in-hospital management of the hypothermia patient. The various rewarming strategies are the subject of special attention and critical evaluation.

Accidental Hypothermia

Hypothermia is a multi-system disorder that significantly increases morbidity and mortality in the injured patient. It is an environmental hazard that can kill in its own right. The most difficult differentiation and management decisions are likely to be with victims in Stage II or Stage III hypothermia. Following successful rescue in these cases, arresting any further cooling of the core temperature, instituting rewarming strategies and careful patient handling will be the key factors in reducing morbidity and mortality.