Review articleThe prehospital management of hypothermia — An up-to-date overview☆
Introduction
Accidental hypothermia is defined as an unintentional decrease in body temperature to below 35 °C, without the presence of a primary defect in the patient’s thermoregulatory mechanism. It can be subdivided into mild (35–32 °C), moderate (32–28 °C) and severe ( <28 °C) hypothermia; a temperature below which cardiac arrest or low flow state can occur [1]. Hypothermia negatively affects multiple organ systems [2], [3], [4], [5], [6], and is associated with poor outcomes including death [7], [8], [9], [10], [11], [12], [13]. In the United States, approximately 1500 people die of primary hypothermia each year [14]. The etiology of hypothermia is multifactorial and the assumed main causes of accidental hypothermia in injured patients are heat loss due to environmental exposure, the administration of cold intravenous fluids, hemorrhagic shock and the effects of anesthesia or sedation on thermoregulation [15], [16], [17].
All prehospital patients could become hypothermic due to their sickness or injury. Especially in the severely injured trauma patients its incidence ranges from 13.3% to 43% in various prehospital environments worldwide [11], [13], [18], [19], [20]. In studies of trauma patients who were hypothermic on arrival at the emergency department, the average core temperature was 33.5 °C [13], [18], [19], [21], [22]. Hypothermia is one of the components of the trauma triad of death, which is a vicious cycle caused by the synergistic effects that hypothermia, coagulopathy and acidosis have on each other [18], [25], [26], [27].
One of the effects of hypothermia is poor tissue oxygenation throughout the body caused by peripheral vasoconstriction, decreased myocardial contractility and decreased oxygen release from hemoglobin to tissue [16], [23], [24], [25]. This effect on tissue oxygenation causes an increase in the cell metabolism’s proportion of anaerobic metabolism. Normally, during aerobic metabolism, heat is produced by the hydrolysis of adenosine triphosphate (ATP) to adenosine diphosphate (ADP); in contrast, the anaerobic metabolism results in decreased ATP synthesis and consequently decreased heat production. Anaerobic metabolism also produces higher lactate levels and causes metabolic acidosis [24].
The activity of coagulation enzymes decreases with acidosis [15] and lower body temperatures. In addition, hypothermia causes a defect in the aggregation and adhesion of platelets and a decrease of fibrinogen availability, resulting in prolonged bleeding times [26], [27]. These abnormalities can be reversed by rewarming [26].
Early recognition and treatment of hypothermia is essential to oppose the deterioration of a patient’s condition. Treatment ideally begins in the prehospital setting and should focus on reducing heat loss, promoting cardiovascular stability, restoring fluid volumes and reversing core cooling. Regarding core temperature maintenance, there is considerable laboratory-based literature specifically regarding properties of insulation materials and heat sources, as well as randomized controlled trials on rewarming methods for cold subjects, but little effort has been made to integrate all of this information. The most recent reviews, which focused primarily on the prehospital treatment of hypothermia, were performed 16 years ago [28], [29]. As well, there is a shortage of large randomized controlled trials conducted in the pre-hospital setting.
The aim of this review article is to provide an up-to-date systematic overview of the available treatment modalities relating to insulation and/or application of heat for the prehospital management of hypothermic patients and to present the best available evidence for their effectiveness to improve patient care.
Section snippets
Methods
The databases PubMed, EMbase (OvidSP) and MEDLINE (OvidSP) were searched using various keywords and strategies; which are listed in Table 1. Articles with publication dates up to October 2017 were reviewed. The relevance of the articles was judged by their title; abstract and full-text; which were all screened by two authors (FH; ET) and discussed with the third author (GG). Articles were included if they contained information about treatment modalities for hypothermia that could be applied
Results
The literature search returned 903 potential inclusions for consideration, of which 51 focused on insulation only (with or without a vapor barrier) (to decrease heat loss) and/or active heating (Fig. 1). An overview of these studies is displayed in Table 2. The interventions are categorized into insulation/vapor barrier materials, external heat sources and heat sources with internal heat transfer. The term ‘hypothermia wrap’ refers to insulation with or without vapor barrier and a heat source.
Discussion
The current practice of prehospital hypothermia management is based on considerable laboratory research but minimal controlled studies on actual patients in the field. In contrast, in-hospital management of cold patients has been studied more thoroughly; effective rewarming methods are available for in-hospital use, such as warm fluid lavage of body cavities or extracorporeal rewarming [81]. Extracorporeal rewarming can be accomplished by hemodialysis, continuous arteriovenous rewarming,
Limitations and strengths
This article provides an up-to-date systematic overview of interventions used for the management of hypothermia in the prehospital setting, after the last review on this topic was performed 16 years ago. A broad literature search was performed by searching multiple databases, using broad search terms without limitations on publication dates.
It is hard to combine the available data and consequently make recommendations about the usefulness of each treatment modality because of the differences in
Conclusion
On the basis of our literature review it can be stated that the best way to manage hypothermia in a prehospital setting is to reduce further heat loss by placing the patient in a warm and dry environment and applying insulation in combination with a vapor barrier. The addition of an active rewarming method such as heat packs or blankets is not compulsory in vigorously shivering patients who will likely warm up eventually, but must be considered when treating severe hypothermic patients who will
Funding
No funding was received for the performance of this study.
Author contributions
Literature search: F.H., E.T.
Study design F.H., E.T.
Data collection: F.H., E.T.
Data analysis: F.H., E.T., G.G.
Data interpretation: F.H., E.T., G.G.
Drafting the manuscript: F.H.
Critical revision of the manuscript: E.T., G.G.
Approval of the version of the manuscript to be published: F.H., E.T., G.G.
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A previous version of the abstract of this article was presented as a poster at the European Congress of Trauma and Emergency Surgery from May 7th to May 9th 2017, Boekarest, Romania.