An evaluation of the Swiss staging model for hypothermia using case reports from the literature

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.

Prehospital body temperature measurement in trauma patients: A literature review

OBJECTIVES

Accidental hypothermia in trauma patients can contribute to cardiorespiratory dysfunction, acidosis, and coagulopathy, causing increased morbidity and mortality. The early recognition of the clinical signs of hypothermia and the accurate measurement of body temperature by prehospital care providers are essential to avoid deterioration. This review provides an overview of studies that examine the reliability of different core temperature measurement options, with a focus on the prehospital setting.

METHODS

A search was performed in PubMed, Embase, Cochrane Library, and CINAHL using combinations of the Medical Subject Headings terms "ambulances," "emergency medical services," "thermometers," "body temperature," "hypothermia," and "body temperature regulation." Studies up to October 2021 were included, and different measurement options were listed and discussed. Eligible studies included those that identified the specific type of thermometer and focused on the out-of-hospital environment.

RESULTS

The search strategy yielded 521 studies, five of which met the eligibility criteria. Four studies focused on tympanic temperature measurement, and one focused on temporal artery temperature measurement. Among the noninvasive options, tympanic temperature measurement was most frequently identified as a reliable option for out-of-hospital use.

CONCLUSION

A thermistor-based tympanic thermometer that features insulation of the ear and a temperature probe with a cap is likely the most suitable option for prehospital body temperature measurement in trauma patients. These results are based on outdated literature with currently more novel temperature measurement devices available. Future studies are necessary to provide strong recommendations regarding temperature measurement due to emerging technology, the lack of studies, and the heterogeneity of existing studies.

Clinical relevance of impaired consciousness in accidental hypothermia: a Japanese multicenter retrospective study

Aim

This study aimed to investigate the association between level of impaired consciousness and severe hypothermia (<28°C) and to evaluate the association between level of impaired consciousness and inhospital mortality among accidental hypothermia patients.

Methods

This was a multicenter retrospective study using the J‐Point registry database, which includes data regarding patients whose core body temperature was 35.0°C or less and who were treated as accidental hypothermia in emergency departments between April 1, 2011 and March 31, 2016. We estimated adjusted odds ratios of the level of impaired consciousness for severe hypothermia less than 28°C and inhospital mortality using a logistic regression model.

Results

The study included 505 of 572 patients in the J‐Point registry. Relative to mildly impaired consciousness (Glasgow Coma Scale [GCS] 13–15), the adjusted odds ratios for severe hypothermia less than 28°C were: moderate (GCS 9–12), 3.26 (95% confidence interval [CI], 1.69–6.25); and severe (GCS < 9), 4.68 (95% CI, 2.40–9.14). Relative to mildly impaired consciousness (GCS 13–15), the adjusted odds ratios for inhospital mortality were: moderate (GCS9–12), 1.65 (95% CI, 0.95–2.88); and severe (GCS < 9), 2.10 (95% CI, 1.17–3.78).

Conclusion

The level of impaired consciousness in patients with accidental hypothermia was associated with severe hypothermia and inhospital mortality.

Clinical staging of accidental hypothermia: The Revised Swiss System: Recommendation of the International Commission for Mountain Emergency Medicine (ICAR MedCom)

Clinical staging of accidental hypothermia is used to guide out-of-hospital treatment and transport decisions. Most clinical systems utilize core temperature, by measurement or estimation, to stage hypothermia, despite the challenge of obtaining accurate field measurements. Recent studies have demonstrated that field estimation of core temperature is imprecise. We propose a revision of the original Swiss Staging system. The revised system uses the risk of cardiac arrest, instead of core temperature, to determine the staging level. Our revised system simplifies assessment by using the level of responsiveness, based on the AVPU scale, and by removing shivering as a stage-defining sign.

Vital Signs in Accidental Hypothermia

Pasquier, Mathieu, Evelien Cools, Ken Zafren, Pierre-Nicolas Carron, Vincent Frochaux, and Valentin Rousson. Vital signs in accidental hypothermia. High Alt Med Biol. 22: 142-147, 2021. Background: Clinical indicators are used to stage hypothermia and to guide management of hypothermic patients. We sought to better characterize the influence of hypothermia on vital signs, including level of consciousness, by studying cases of patients suffering from accidental hypothermia. Materials and Methods: We retrospectively included patients aged ≥18 years admitted to the hospital with a core temperature below 35°C. We identified the cases from a literature review and from a retrospective case series of hypothermic patients admitted to the hospital between 1994 and 2016. Patients who experienced cardiac arrest, as well as those with potential confounders such as concomitant diseases or intoxications, were excluded. Relationships between core temperature and heart rate, systolic blood pressure, respiratory rate, and level of consciousness were explored via correlations and regression. Results: Of the 305 cases reviewed, 216 met the criteria for inclusion. The mean temperature was 29.7°C ± 4.2°C (range 19.3°C-34.9°C). The relationships between temperature and each of the four vital signs were generally linear and significantly positive, with Spearman correlations for respiratory rate, heart rate, systolic blood pressure, and Glasgow Coma Score (GCS) of 0.29 (p = 0.024), 0.44 (p < 0.001), 0.47 (p < 0.001), and 0.78 (p < 0.001), respectively. Based on linear regression, the mean decrease of a vital sign associated with a 1°C decrease of temperature was estimated to be 0.50 minute^-1 for respiratory rate, 2.54 minutes^-1 for heart rate, 4.36 mmHg for systolic blood pressure, and 0.88 for GCS. Conclusions: There is a significant positive correlation between core temperature and heart rate, systolic blood pressure, respiratory rate, and GCS. The relationship between vital signs and temperature is generally linear. This knowledge might help clinicians make appropriate decisions when determining whether the clinical condition of a patient should be attributed to hypothermia. This could enhance clinical care and help to guide future research.

Predictive accuracy of biomarkers for survival among cardiac arrest patients with hypothermia: a prospective observational cohort study in Japan

Background

There is limited information on the predictive accuracy of commonly used predictors, such as lactate, pH or serum potassium for the survival among out-of-hospital cardiac arrest (OHCA) patients with hypothermia. This study aimed to identify the predictive accuracy of these biomarkers for survival among OHCA patients with hypothermia.

Methods

In this retrospective analysis, we analyzed the data from a multicenter, prospective nationwide registry among OHCA patients transported to emergency departments in Japan (the JAAM-OHCA Registry). We included all adult (≥18 years) OHCA patients with hypothermia (≤32.0 °C) who were registered from June 2014 to December 2017 and whose blood test results on hospital arrival were recorded. We calculated the predictive accuracy of pH, lactate, and potassium for 1-month survival.

Results

Of the 34,754 patients in the JAAM-OHCA database, we included 754 patients from 66 hospitals. The 1-month survival was 5.8% (44/754). The areas under the curve of the predictors and 95% confidence interval were as follows: pH 0.829 [0.767–0.877] and lactate 0.843 [0.793–0.882]. On setting the cutoff points of 6.9 in pH and 120 mg/dL (13.3 mmol/L) in lactate, the predictors had a high sensitivity (lactate: 0.91; pH 0.91) and a low negative likelihood ratio (lactate: 0.14; pH 0.13), which are suitable to exclude survival to 1 month. Furthermore, in additional analysis that included only the patients with potassium values available, a cutoff point of 7.0 (mmol/L) for serum potassium had high sensitivity (0.96) and a low negative likelihood ratio (0.09).

Conclusion

This study indicated the predictive accuracy of serum lactate, pH, and potassium for 1-month survival among adult OHCA patients with hypothermia. These biomarkers may help define a more appropriate resuscitation strategy.

Cardiac Arrest Secondary to Accidental Hypothermia: The Physiology Leading to Hypothermic Arrest

Cardiac arrest secondary to accidental hypothermia is rare in the United Kingdom. However, some evidence suggests that it is under-reported; furthermore, recognizing hypothermia as the cause of death is difficult in the postmortem setting. Urban and rural residents are exposed to cold winter conditions both at home and while undertaking recreational activities. Understanding the physiology underpinning hypothermic cardiac arrest is crucial in order to make informed clinical decisions in regard to triage and management by air ambulance services and in prevention of this rare presentation. This article discusses the epidemiology and pathophysiology of accidental hypothermic to explain how personnel can survive after 8 hours 40 minutes of cardiac arrest.

Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update

To provide guidance to clinicians, the Wilderness Medical Society convened an expert panel to develop evidence-based guidelines for the out-of-hospital evaluation and treatment of victims of accidental hypothermia. The guidelines present the main diagnostic and therapeutic modalities and provide recommendations for the management of hypothermic patients. The panel graded the recommendations based on the quality of supporting evidence and a balance between benefits and risks/burdens according to the criteria published by the American College of Chest Physicians. The guidelines also provide suggested general approaches to the evaluation and treatment of accidental hypothermia that incorporate specific recommendations. This is the 2019 update of the Wilderness Medical Society Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2014 Update.

Hypothermie accidentelle

L’hypothermie accidentelle est définie comme une baisse non intentionnelle de la température centrale du corps en dessous de 35 °C. La prévention de l’hypothermie est essentielle. La mesure de la température centrale est nécessaire au diagnostic d’hypothermie et permet d’en juger la sévérité. En présence de signes de vie, et en présence d’une hypothermie pure, l’instabilité hémodynamique apparente ne devrait en principe pas faire l’objet d’une prise en charge spécifique. Un risque d’arrêt cardiaque (AC) est présent si la température chute en dessous de 30–32 °C. En raison du risque d’AC, un patient hypotherme devrait bénéficier de l’application d’un monitoring avant toute mobilisation, laquelle devra être prudente. En cas d’AC, seule la mesure de la température oesophagienne est fiable. Si l’hypothermie est suspectée comme étant potentiellement responsable de l’AC du patient, celui-ci doit être transporté sous réanimation cardiopulmonaire vers un hôpital disposant d’une méthode de réchauffement par circulation extracorporelle (CEC). La valeur de la kaliémie ainsi que les autres paramètres à disposition (âge, sexe, valeur de la température corporelle, durée du low flow, présence d’une asphyxie) permettront de décider de l’indication d’une CEC de réchauffement. Le pronostic des patients victimes d’un AC sur hypothermie est potentiellement excellent, y compris sur le plan neurologique.

Body temperature measurement in ambulance: a challenge of 21-st century?

Background

Some crucial decisions in treatment of hypothermic patients are closely linked to core body temperature. They concern modification of resuscitation algorithms and choosing the target hospital. Under- as well as over-estimation of a patient’s temperature may limit his chances for survival. Only thermometers designed for core temperature measurement can serve as a guide in such decision making. The aim of the study was to assess whether ambulance teams are equipped properly to measure core temperature.

Methods

A survey study was conducted in collaboration with the Health Ministry in April 2018. Questionnaires regarding the model, number, and year of production of thermometers were sent to each pre-hospital unit of the National Emergency Medical System in Poland.

Results

A total of 1523 ground ambulances are equipped with 1582 thermometers. 53.57% are infrared-based ear thermometers, 23.02% are infrared-based surface thermometers, and 20.13% are conventional medical thermometers. Only 3.28% of devices are able to measure core body temperature. Most of analyzed thermometers (91.4%) are not allowed to operate in ambient temperature below 10 °C.

Conclusions

There are only 3.28% of ground ambulances that are able to follow precisely international guidelines regarding a patient’s core body temperature. A light, reliable thermometer designed to measure core temperature in pre-hospital conditions is needed.

An evaluation of the Swiss staging model for hypothermia using hospital cases and case reports from the literature

BACKGROUND

The Swiss staging model for hypothermia uses clinical indicators to stage hypothermia and guide the management of hypothermic patients. The proposed temperature range for clinical stage 1 is < 35-32 °C, for stage 2 is < 32-28 °C, for stage 3 is < 28-24 °C, and for stage 4 is below 24 °C. Our previous study using 183 case reports from the literature showed that the measured temperature only corresponded to the clinical stage in the Swiss staging model in approximately 50% of cases. This study, however, included few patients with moderate hypothermia. We aimed to expand this database by adding cases of hypothermic patients admitted to hospital to perform a more comprehensive evaluation of the staging model.

METHODS

We retrospectively included patients aged ≥18 y admitted to hospital between 1.1.1994 and 15.7.2016 with a core temperature below 35 °C. We added the cases identified through our previously published literature review to estimate the percentage of those patients who were correctly classified and compare the theoretical with the observed temperature ranges for each clinical stage.

RESULTS

We included 305 cases (122 patients from the hospital sampling and the 183 previously published). Using the theoretically derived temperature ranges for clinical stages resulted in 185/305 (61%) patients being assigned to the correct temperature range. Temperature was overestimated using the clinical stage in 55/305 cases (18%) and underestimated in 65/305 cases (21%); important overlaps in temperature existed among the four stage groups. The optimal temperature thresholds for discriminating between the four stages (32.1 °C, 27.5 °C, and 24.1 °C) were close to those proposed historically (32 °C, 28 °C, and 24 °C).

CONCLUSIONS

Our results provide further evidence of the relationship between the clinical state of patients and their temperature. The historical proposed temperature thresholds were almost optimal for discriminating between the different stages. Adding overlapping temperature ranges for each clinical stage might help clinicians to make appropriate decisions when using clinical signs to infer temperature. An update of the Swiss staging model for hypothermia including our methodology and findings could positively impact clinical care and future research.

Management of accidental hypothermia: A narrative review

A narrative review is presented on the diagnosis, treatment and management of accidental hypothermia. Although all these processes form a continuum, for descriptive purposes in this manuscript the recommendations are organized into the prehospital and in-hospital settings. At prehospital level, it is advised to: a) perform high-quality cardiopulmonary resuscitation for cardiac arrest patients, regardless of body temperature; b) establish measures to minimize further cooling; c) initiate rewarming; d) prevent rescue collapse and continued cooling (afterdrop); and (e) select the appropriate hospital based on the clinical and hemodynamic situation of the patient. Extracorporeal life support has revolutionized rewarming of the hemodynamically unstable victim or patients suffering cardiac arrest, with survival rates of up to 100%. The new evidences indicate that the management of accidental hypothermia has evolved favorably, with substantial improvement of the final outcomes.

Moderate brain hypothermia started before resuscitation improves survival and neurobehavioral outcomes after CA/CPR in mice

AIM OF THE STUDY

No definitive experimental or clinical evidence exists whether brain hypothermia before, rather than during or after, resuscitation can reduce hypoxic-ischemic brain injury following cardiac arrest/cardiopulmonary resuscitation (CA/CPR) and improve outcomes. We examined the effects of moderate brain hypothermia before resuscitation on survival and histopathological and neurobehavioral outcomes in a mouse model.

METHODS

Adult C57BL/6 male mice (age: 8-12 weeks) were subjected to 8-min CA followed by CPR. The animals were randomly divided into sham, normothermia (NT; brain temperature 37.5 °C), and extracranial hypothermia (HT; brain temperature 28-32 °C) groups. The hippocampal CA1 was assessed 7 day after resuscitation by histochemical staining. Neurobehavioral outcomes were evaluated by the Barnes maze (BMT), openfield (OFT), rotarod, and light/dark (LDT) tests. Cleaved caspase-3 and heat shock protein 60 (HSP70) levels were investigated by western blotting.

RESULTS

The HT group exhibited higher survival and lower CA1 neuronal injury than did the NT group. HT mice showed improved spatial memory in the BMT compared with NT mice. NT mice travelled a shorter distance in the OFT and tended to spend more time in the light compartment in the LDT than did sham and HT mice. The levels of cleaved caspase-3 and HSP70 were non-significantly higher in the NT than in the sham and HT groups.

CONCLUSIONS

Moderate brain hypothermia before resuscitation improved survival and reduced histological neuronal injury, spatial memory impairment, and anxiety-like behaviours after CA/CPR in mice.

Measuring core temperature using the proprietary application and thermo-smartphone adapter

Fast and accurate measurement of core body temperature is crucial for accidental hypothermia treatment. We have developed a novel light and small adapter to the headset jack of a mobile phone based on Android. It has been applied to measure temperature and set up automatic notifications (e.g. Global Positioning System coordinates to emergency services dispatcher, ECMO coordinator). Its validity was confirmed in comparison with Vital Signs Monitor Spacelabs Healthcare Elance 93300 as a reference method, in a series of 260 measurements in the temperature range of 10-42 °C. Measurement repeatability was verified in a battery of 600 measurements (i.e. 100 readings at three points of 10, 25, 42 °C for both esophageal and tympanic catheters). Inter-method difference of ≤0.5 °C was found for 98.5% for esophageal catheter and 100% for tympanic catheter measurements, with concordance correlation coefficient of 0.99 for both. The readings were almost completely repeatable with water bath measurements (difference of ≤0.5 °C in 10 °C: 100% for both catheters; in 25 °C: 99% for esophageal catheter and 100% tympanic catheter; in 42 °C: 100% for both catheters). This lightweight adapter attached to smartphone and standard disposable probes is a promising tool to be applied on-site for temperature measurement in patients at risk of hypothermia.

Severe Hypothermia Management in Mountain Rescue: A Survey Study

Podsiadło, Paweł, Tomasz Darocha, Sylweriusz Kosiński, Kinga Sałapa, Mirosław Ziętkiewicz, Tomasz Sanak, Rachel Turner, and Hermann Brugger. Severe hypothermia management in mountain rescue: A survey study. High Alt Med Biol 18:411–416, 2017.

Introduction: Severe hypothermia is a rare but demanding medical emergency. Although mortality is high, if well managed, the neurological outcome of survivors can be excellent. The aim of the study was to assess whether mountain rescue teams (MRTs) are able to meet the guidelines in the management of severe hypothermia, regarding their equipment and procedures.

Methods: Between August and December 2016, an online questionnaire, with 24 questions to be completed using Google Forms, was sent to 123 MRTs in 27 countries.

Results: Twenty-eight MRTs from 10 countries returned the completed questionnaire. Seventy-five percent of MRTs reportedly provide advanced life support (ALS) on-site and 89% are regularly trained in hypothermia management. Thirty-two percent of MRTs transport hypothermic patients in cardiac arrest to the nearest hospital instead of an Extracorporeal Life Support facility; 39% are equipped with mechanical chest compression devices; 36% measure core body temperature on-site and no MRT is equipped with a device to measure serum potassium concentration on-site in avalanche victims.

Conclusions: Most MRTs are regularly trained in the treatment of severe hypothermia and provide ALS. The majority are not equipped to follow standard procedural guidelines for the treatment of severely hypothermic patients, especially with cardiac arrest. However, the low response rate—23% (28/123)—could have induced a bias.

Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia

Accidental hypothermia is an unintentional drop in core temperature to 35°C or below. Core temperature is best measured by esophageal probe. If core temperature cannot be measured, the degree should be estimated using clinical signs. Treatment is to protect from further heat loss, minimize afterdrop, and prevent cardiovascular collapse during rescue and resuscitation. The patient should be handled gently, kept horizontal, insulated, and actively rewarmed. Active rewarming is also beneficial in mild hypothermia but passive rewarming usually suffices. Cardiopulmonary resuscitation should be performed if there are no contraindications to resuscitation. CPR may be delayed or intermittent.

Accidental hypothermia-an update : The content of this review is endorsed by the International Commission for Mountain Emergency Medicine (ICAR MEDCOM)

BACKGROUND

This paper provides an up-to-date review of the management and outcome of accidental hypothermia patients with and without cardiac arrest.

METHODS

The authors reviewed the relevant literature in their specialist field. Summaries were merged, discussed and approved to produce this narrative review.

RESULTS

The hospital use of minimally-invasive rewarming for non-arrested, otherwise healthy, patients with primary hypothermia and stable vital signs has the potential to substantially decrease morbidity and mortality for these patients. Extracorporeal life support (ECLS) has revolutionised the management of hypothermic cardiac arrest, with survival rates approaching 100 % in some cases. Hypothermic patients with risk factors for imminent cardiac arrest (temperature <28 °C, ventricular arrhythmia, systolic blood pressure <90 mmHg), and those who have already arrested, should be transferred directly to an ECLS-centre. Cardiac arrest patients should receive continuous cardiopulmonary resuscitation (CPR) during transfer. If prolonged transport is required or terrain is difficult, mechanical CPR can be helpful. Delayed or intermittent CPR may be appropriate in hypothermic arrest when continuous CPR is impossible. Modern post-resuscitation care should be implemented following hypothermic arrest. Structured protocols should be in place to optimise pre-hospital triage, transport and treatment as well as in-hospital management, including detailed criteria and protocols for the use of ECLS and post-resuscitation care.

CONCLUSIONS

Based on new evidence, additional clinical experience and clearer management guidelines and documentation, the treatment of accidental hypothermia has been refined. ECLS has substantially improved survival and is the treatment of choice in the patient with unstable circulation or cardiac arrest.