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Hypothermia

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Other Names

  • Hypothermia
  • Cold Injury
  • Accidental hypothermia
  • Primary accidental hypothermia
  • Secondary hypothermia
  • Environmental hypothermia

Background

  • This page refers to hypothermia, a condition defined as core body temperature below 35°C (95°F)
    • Occurs when total body heat loss exceeds physiologic heat production
    • Note this page refers to primary environmental or accidental hypothermia and not secondary hypothermia

History
Epidemiology

  • Prevalence
    • In the united states, responsible for approximately 1500 deaths per year[1]
  • Incidence
    • Ranges from 0.13 to 6.9 cases per 100,000 per year in Europe, New Zealand[2][3]
    • Responsible for 2 deaths per 100,000 per year in Scotland[4]
    • Responsible for 5 deaths per 100,000 per year in Poland[5]
  • Prevalence
    • 50% of deaths occur in patients > 65 years old[6]

Introduction

Differential diagnosis of secondary hypothermia (click to enlarge)[7]

General

  • Core temperature drops below 35°C (95°F)
  • Occurs when total body heat loss exceeds physiologic heat production
  • As hypothermia worsens, vitals signs decrease slowly until cardiac arrest occurs
  • Organs affected: heart, brain, kidney, blood coagulation, and, possibly, the immune system

Normal temperature regulation

  • Humans are homeothermic, normal temperature is 37 ± 0.5 °C
  • Core temperature is regulated by central and peripheral processes
  • Centrally, the hypothalamus controls temperature
  • Peripherally, vasoconstriction and dilation, shivering, and sweating help

Terminology

  • Thermoregulation impaired by external source
    • Conduction
    • Convection
    • Evaporation
    • Radiation (primary hypothermia)
  • Impaired thermoregulation due to other pathology
    • Due to things like trauma, stroke, shock, etc
    • Termed secondary hypothermia

Natural History

  • Environmental cooling
    • Windy and wet environment will speed cooling
    • Wind chill index: ambient air temperature + wind speed on the skin surface temperature[8]
    • Avalanches: cooling rate of buried victims may reach 9 °C/h
    • Water immersion: at temp of 1–2 °C, can reach 5 °C/10 min[9]
    • Cooling rate in cold water immersion is highly variable and depends on conditions, slower but still significant
    • During avalanche burial, hypercapnia can also lead to rapid cooling (need citation)
  • Cardiac Arrest
    • A person immersed in cold water (<15 °C) can arrest after 30 min[10]
    • In a young healthy individual, cardiac arrest may occur below 30 °C
    • In elderly patients with comorbidities, this can occur when core temperature drops below 32 °C
    • Vital signs can be present with core temperature below 24 °C[11]
    • Lowest documented survival from accidental hypothermia is 13.7 °C (need citation)
    • Note hypothermic cardiac arrest is fundamentally different from normthermic cardiac arrest
  • Following Extrication
    • Cooling continues as warm central blood is redistributed to the cold periphery by a countercurrent heat exchange
    • Cooling may also continue from conduction of heat from the core to cooler surface tissues
    • Shivering may or may not be present. The absence of shivering suggests spontaneous rewarming may not be possible
    • Normal level of consciousness correlates with a low risk of hypothermic cardiac arrest[12]
  • Rescue collapse/ arrest
    • A term applied when cardiocirculatory collapse occurs during extrication or transfer of a hypothermic patient
    • Stated different, this may be a witnessed cardiac arrest[13]
    • Pathophysiology of a "rescue arrest" is not well understood
    • Likely some combination of hypovolemia, cardiac dysrhythmias triggered by interventions, mechanical stimuli such as sudden movement
    • Cardiac arrest may also be caused by afterdrop (further cooling, even after rewarming has started)
    • One study found the core temp in witnessed hypothermic cardiac arrest was 23.9 °C +/- 2.7 °C.
    • Rescue collapse appears to double the risk of death in severely hypothermic patients[14]

Etiology

  • Modern countries
    • Primarily affects people who live, work or recreate outside
  • Less developed country
    • More significant impacts from homelessness, mass accidents, natural disasters

Risk Factors

  • Temperature
    • Risk increases as temperature drops
    • However many cases occur during low/moderate cold stress with prolonged exposure
  • Socioeconomic
    • Homelessness
    • Alcohol or drug use
  • Environmental
    • Cold or temperate, wet climates
    • Mountains
    • Natural Disasters
  • Demographic
    • Children, low BMI adults due to large surface area to weight ratio[15]
    • Geriatric patients living alone with multiple comorbidities[16]
  • Sports
    • Mountaineering
    • Diving

Differential Diagnosis


Clinical Features

History

  • History of cold exposure
  • Symptoms can vary wildly depending on duration of exposure, core temperature
  • Range from shivering to cardiac arrest (see classification)

Physical Exam

  • Patients with mild symptoms may be shivering, be cold peripherally
  • Sicker patients may be altered, bradycardic
  • As core temperature drops, vital signs become unstable and cardiac arrest can occur
  • Vital signs tend to decrease linearly with core temperature[17]
  • Presence or absence of shivering can not be used to diagnose hypothermia
  • Level of consciousness is the best way to measure severity in the absence of a core temperature

Evaluation

Example of epitympanic thermomemter. A thermoster based device is designed for outdoor use.[18]

Diagnosis is primarily clinical

  • Out of hospital diagnosis can be challenging
  • Core temperature can help guide management decisions
  • If thermometer not available, treat based on clinical presentation and suspicion of hypothermia
  • Imaging is not generally needed

Temperature Measurement

  • General Points
    • Out of hospital
      • Can touch patients chest and use the revised Swiss system if no thermometer
      • Thermistor based epitympanic probe in non-intubated patients
      • Esophageal probe or deep nasopharyngeal probe if intubated
    • In hospital
      • Urinary bladder temperature is widely used and accepted
    • Infrared epitympanic devices useful for screening, not for monitoring
  • Optimal thermometer
    • Minimally invasive, easy to use, hygienic, independent of environmental conditions, measures core temperature with high accuracy, and has a short response time
    • No such device exists
  • Not practical, influence by environmental conditions
    • Skin
    • Temporal artery
    • Oral
    • Axillary temperatures
    • Infrared tympanic
  • Thermistor based epitympanic temperature measurement[19]
    • Device intended for outdoor use, well insulated
  • Nonvascular central thermometers
    • Designed to correlate with pulmonary artery catheter measurement (most accurate method of core temp measurement)
    • Includes esophageal, urinary bladder, rectal, and nasopharyngeal thermometers
    • Can lag behind true core temp, have thermal inertia due to surrounding tissue and bodily contents[20]
    • Esophageal or epitympanic give the best estimate of true brain temperature
  • Future technology
    • Not yet ready for clinical use
    • Includes microwave and zero-heat-flux thermometers

Classification

Classical Staging of Accidental Hypothermia

Stage Core Findings Estimated Core Temperature °C (°F)
Hypothermia I (mild) Conscious, shivering, social withdrawal, minor behavior changes[21] 32°C to 35°C (89.6°F-95°F)
Hypothermia II (moderate) Impaired consciousness; may or may not be shivering, pupils dilate, cardiac arrythmias can occur 28°C to 32°C (82.4°F-89.6°F)
Hypothermia III (severe) Unconscious*; vital signs present, severe bradycardia, ventricular fibrillation, loss of DTR, loss of volitional motion <28°C (86°F)
Hypothermia IV (severe) Cardiac arrest, Apparent death, vital signs absent <24°C (75°F)**
  • **Cardiac arrest can occur at earlier or later stages of hypothermia. Some patients may have vital signs with core temperatures < 24 °C.

Management

Principles of Pre-hospital Management (Revised Swiss System)

Stage I Stage II Stage III Stage IV
Clinical findings** Alert Verbal Painful or Unconscious, vital signs present Unconscious, vital signs absent
Risk of cardiac arrest Low Moderate High Hypothermic Cardiac Arrest
Oxygen administration Y Y Y Y
Carbohydrates Warm sweet tea, sweet bars Glucose IV/IO Glucose IV/IO N/A
Active movement Y N N N
Passive rewarming Y Y Y Y
Active rewarming Consider Y Y Y
Cautious mobilization/ horizontal transport N Y Y N
Defibrillation pads N Y Y Y
Intubation N N Consider Y
CPR N N N Y
Defibrillation N N N Y
Drugs (ACLS) N N N Y
Hospitalization with ECMO N N Y Y
  • **In the revised Swiss system, “Alert” corresponds to a GCS score of 15. “Verbal” corresponds to GCS scores of 9–14, including confused patients. “Painful” and “Unconscious” correspond to GCS scores < 9.

Prehospital

Example of a commercial hypothermia bag
  • Primary objectives
    • Early recognition is critical
    • Remove from cold environment
    • Prevent/ slow further heat loss
    • Initiate rewarming as soon as possible
    • Note: core temperature can decrease during medical care, exposure, analgesia, anesthesia, infusion of fluids[22]
  • Critical actions
    • Rewarming often not feasible due limited equipment, short transport times
    • Emphasis on preventing further heat loss
    • Essential measures: extricate from cold, limit heat loss, rapid transportation
  • Mild hypothermia (stage I)
    • Typically fully alert, making diagnosis straight forward
    • Can often be managed on site without transport
    • Passive rewarming by removing from cold, increase insulation, warm drinks, active movements
  • Moderate or severe hypothermia (stage II, III)
    • Prevent further heat loss
      • Require active rewarming. The entire body should be insulated.
      • If horizontal, place on a stretcher with insulation from the ground
      • Wet clothing should be removed in a protected environment, dry clothing or layers applied
      • Chemical or electrical heat packs should be placed on trunk (avoid directly on the skin, prevent burns)
      • Vapour barrier should be added, can be packed with dry clothing or blankets
    • If supine, leave supine for at least 30 minutes before allowing to walk
      • Allows for shivering, calorie consumption
      • Walking can increase heat production, also increases after drop
    • Rewarming out of hospital is challenging
      • Attempts to rewarm should not delay transport
      • Apply oxygen, place on monitor, apply defibrillation pads
      • Obtaining IV access can be difficult due to vasoconstriction, consider IO as needed
      • Warm IV fluids (38 to 42 C) should be given in boluses, guided by vital signs
    • Most dysrhythmias will improve with rewarming
      • This includes supraventricular rhythms such as atrial fibrillation
    • Avoid endotracheal intubation unless necessary
      • Defer until the patient is in a warm environment if possible
      • Most drugs are not effective in hypothermia, tubes are less pliable, IV lines can freeze
      • Rigidity, trismus can make intubation difficult
      • End tidal CO2 is not reliable in hypothermia[23]
  • Hypothermia without vital signs (stage IV)
    • Diagnosis is hypothermic cardiac arrest
      • Note that this can be difficult to assess in an unconsious, hypothermic patient
      • Vital signs can be minimal, difficult to detect or palpate
      • Recommend spending 60 seconds looking for vital signs before beginning CPR/ ACLS
      • Can augment exam with electrocardiogram, ultrasound and capnography to identify presence of vital signs
    • Cardiopulmonary Resuscitation
      • CPR is performed the same as a euthermic patient
      • Can attempt up to 3 shocks for ventricular fibrillation with core temperature <30 °C
      • If 3 unsuccessful, refrain from further shocks until core temperature above 30 °C
      • Epinephrine, amiodarone are not indicated for temperature <30 °C
      • The administration interval for epinephrine is 6 to 10 minutes (instead of 3 to 5)
      • Once normothermia is achieved, standard ACLS protocols should be followed
    • Prehospital triage
      • Do not start CPR if valid DNR, clear signs of irreversible death (livor mortis), danger or exhaustion to resucers, avalanche burial more than 60 minutes with asystole, completely obstructed airway
      • Hypothermic rigidity (pseudo rigor mortis) is not a reliable sign of death[24]
      • The following are not contraindications to rewarming a hypothermic patient in cardiac arrest: asystole, unwitnessed CA, low core temperature, long no-flow or low-flow time, fixed, dilated pupils, hypocapnia (ETCO2 <10 mmHg), old age, or trauma (even major trauma
    • Patient referral and transport
      • The patient should be transferred to an ECMO center for the following: cardiac arrest, core temperature < 30 C, systolic blood pressure < 90 mmHg, or ventricular dysrhythmia
      • Consider stopping at a non ACLS hospital for hospital triage
      • HOPE score can estimate survival probability: https://hypothermiascore.org/
      • Perform continuous CPR if possible during transport
Table of rewarming techniques for hypothermia (click to enlarge)[25]

Hospital

  • General
    • Treatment depends on circulatory status, stage of hypothermia, available resources
  • Types of rewarming (see table)
    • Passive: increases core temperature without exogenous heat
    • Active: exogenous heat is delivered
    • Active rewarming can be external or internal
    • Most patients require passive and active external rewarming
    • Hemodynamic instability and cardiac arrest are indications for active internal rewarming
  • Mild hypothermia (stage I)
    • Passive rewarming, active external rewarming
    • Can consider minimally invasive internal rewarming such as warm oral fluids
    • Shivering, active movement will speed rewarming
    • Temperature goal: normothermia with a core temperature about 37 °C
  • Moderate/ severe hypothermia (stage II, III)
    • Includes patients at risk of cardiac arrest
    • Active rewarming is necessary
    • External is often effective, if it is not, internal rewarming should be initiated
    • Signs of failure of external rewarming: core temperature unchanged or decreasing, elevated lactate, worsening mental status, decreased blood pressure, ventricular dysrhthmias
    • Active internal methods to consider include catheters and continuous renal replacement therapy (CRRT)
  • Cardiac arrest (Stage IV)
    • These patients are pulseless, require active CPR
    • Extracorporeal life support (ECLS) are the preferred method of rewarming, includes cardiopulmonary bypass and Extracorporeal Membrane Oxygenation (ECMO)[26]
    • If not available, additional other forms of active, internal rewarming should be employed during resuscitation including:
      • Bladder Lavage
      • Gastric Lavage
      • Thoracic Lavage
      • Peritoneal Lavage
      • Move the patient to a warm room
    • Continuous Renal Replacement Therapy and Hemodialysis should be reserved for patients with a pulse
    • Target rewarming rate is <5 °C/h[27]
      • However, a slower rate of rewarming (approximately 2 °C/h) may be associated with improved survival with good neurologic outcome[28]
    • Etracorporeal Membrane Oxygenation (ECMO)
      • Preferred method, can be maintained post-ROSC
      • Helps manage other common complications including ARDS (adult respiratory disress syndrome)
    • Volume replacement
      • IV fluids should be warmed to 40 °C to avoid cooling, however not effective in rewarming
      • Patients may require generous IV fluid resuscitation due to hypothermia induced plasma shifts and cold-induced diuresis
    • HOPE score can be used to predict outcomes[29]
    • Termination of CPR
      • Consider if potassium > 12 or persistent asystole with temperature > 32 °C

Prevention

  • General
    • Important to understand weather conditions, air temperatures, wind chill, water temperatures, and the planned exercise
    • Need to determine if it is safe to continue with planned event
    • Event coordinators and medical directors should consider having an ambient and wind-chill temperature guideline
  • Temperature thresholds
    • Many governing bodies cancel events or modify training for temperatures below −20°C (–4°F)[30]
    • No practice or training at ambient temperatures of −23°C (–10°F) or wind chill of −40°C (–40°F)
    • For swimming, USA triathalon recommends shortening swims for temperatures of 53°F to 56°F (11.7°C-13.3°C), cancelling events for water temperatures of less than 53°F (11.7°C)[31]
  • Clothing layers
    • Proper clothing layering, ability to respond to changing weather conditions
    • Athletes should individualize layering based on past cold weather experiences and training
    • Innermost layer should wick sweat away from the body to reduce cold injury risk
      • Should transfer the water/sweat to outer layers of clothing
      • Note wool can retain heat even when wet
      • Good base layers include polypropylene, polyester, and synthetic wool
      • Avoid cotton, which traps moisture
    • Middle layers are for insulation
      • Often made from fleece or wool
    • Outer layer should allow moisture transfer, ventilation, protection against wind and rain
      • Should be worn as needed, especially in wet conditions to maintain dry internal layers
    • Hats, balaclavas should be worn to protect heat loss from the head
    • Mittens protect the hands better than gloves
  • Clohing factors
    • Waterproof cothing
      • Often advertised as "breathable"
      • Exercise sweat rates may exceed the breathability of these materials
      • Assume the more waterproof clothing is, the less it will breath
    • Fitt
      • Clothing should be well fitting, not too tight or too loose
      • If it is too tight, it can constrict peripheral blood flow and increase risk
      • If more than one pair of socks is worn, increase shoe size
    • Chemical warmers
      • Can be used to maintain peripheral warmth
    • Avoid skin protecting emollients which increase the risk of frostbite[32]
    • Avoid vasoconstricting substances (alcohol, caffeine, medications)
  • Caloric intake
    • Shivering, heavy clothing and increased workload can increase energy expenditure by up to 40%
    • Increased calories must be obtained through frequent snacks
    • Carbohydrate rich foods are recommended
    • Maintain good hydration
  • Training
    • Important to train for cold weather exercise
    • Collapse from fatigue or exhaustion greatly increases risk of hypothermia, frost bite
  • Recognition
    • Important for individuals and team to recognize early signs and symptoms of frostbite and hypothermia
    • This can prevent worsening of the conditions and corrective actions by the individual
    • Frequent cold checks with a buddy are recommended

Rehab and Return to Play

Rehabilitation

  • Needs to be updated

Return to Play/ Work

  • Needs to be updated

Complications and Prognosis

Prognosis
Complications


See Also


References

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  2. Herity, B.; Daly, L.; Bourke, G.J.; Horgan, J.M. Hypothermia and mortality and morbidity. An epidemiological analysis. J. Epidemiol. Commun. Health 1991, 45, 19–23.
  3. Taylor, N.A.; Griffiths, R.F.; Cotter, J.D. Epidemiology of hypothermia: Fatalities and hospitalisations in New Zealand. Aust. N. Z. J. Med. 1994, 24, 705–710.
  4. Hislop, L.J.; Wyatt, J.P.; McNaughton, G.W.; Ireland, A.J.; Rainer, T.H.; Olverman, G.; Laughton, L.M. Urban hypothermia in the west of Scotland. West of Scotland Accident and Emergency Trainees Research Group. BMJ 1995, 311, 725.
  5. Kosinski, S.; Darocha, T.; Galazkowski, R.; Drwila, R. Accidental hypothermia in Poland—Estimation of prevalence, diagnostic methods and treatment. Scand. J. Trauma Resusc. Emerg. Med. 2015, 23, 13.
  6. Centers for Disease Control and Prevention: Hypothermia-related deaths—United States, 2003 2004. MMWR Morb Mortal Wkly Rep 54: 173, 2005
  7. Paal, P.; Gordon, L.; Strapazzon, G.; Brodmann Maeder, M.; Putzer, G.; Walpoth, B.; Wanscher, M.; Brown, D.; Holzer, M.; Broessner, G.; et al. Accidental hypothermia-an update: The content of this review is endorsed by the International Commission for Mountain Emergency Medicine (ICAR MEDCOM). Scand. J. Trauma Resusc. Emerg. Med. 2016, 24, 111.
  8. Lankford, H.V.; Fox, L.R. TheWind-Chill Index. Wilderness Environ. Med. 2021, 32, 392–399.
  9. Proulx, C.I.; Ducharme, M.B.; Kenny, G.P. Effect of water temperature on cooling efficiency during hyperthermia in humans. J. Appl. Physiol. 2003, 94, 1317–1323.
  10. Tipton, M.J.; Collier, N.; Massey, H.; Corbett, J.; Harper, M. Cold water immersion: Kill or cure? Exp. Physiol. 2017, 102, 1335–1355.
  11. Pasquier, M.; Zurron, N.; Weith, B.; Turini, P.; Dami, F.; Carron, P.N.; Paal, P. Deep accidental hypothermia with core temperature below 24 degrees c presenting with vital signs. High Alt. Med. Biol. 2014, 15, 58–6
  12. Musi, M.E.; Sheets, A.; Zafren, K.; Brugger, H.; Paal, P.; Holzl, N.; Pasquier, M. Clinical staging of accidental hypothermia: The Revised Swiss System: Recommendation of the International Commission for Mountain Emergency Medicine (ICAR MedCom). Resuscitation 2021, 162, 182–187.
  13. Frei, C.; Darocha, T.; Debaty, G.; Dami, F.; Blancher, M.; Carron, P.N.; Oddo, M.; Pasquier, M. Clinical characteristics and outcomes of witnessed hypothermic cardiac arrest: A systematic review on rescue collapse. Resuscitation 2019, 137, 41–48
  14. Podsiadlo, P.; Smolen, A.; Kosinski, S.; Hymczak, H.;Waligorski, S.;Witt-Majchrzak, A.; Drobinski, D.; Nowak, E.; Barteczko- Grajek, B.; Toczek, K.; et al. Impact of rescue collapse on mortality rate in severe accidental hypothermia: A matched-pair analysis. Resuscitation 2021, 164, 108–113.
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  18. Lapostolle, Frédéric, et al. "Hypothermia in trauma victims at first arrival of ambulance personnel: an observational study with assessment of risk factors." Scandinavian journal of trauma, resuscitation and emergency medicine 25.1 (2017): 1-6.
  19. Walpoth, B.H.; Galdikas, J.; Leupi, F.; Muehlemann, W.; Schlaepfer, P.; Althaus, U. Assessment of hypothermia with a new “tympanic” thermometer. J. Clin. Monit. 1994, 10, 91–96.
  20. Stone, J.G.; Young,W.L.; Smith, C.R.; Solomon, R.A.;Wald, A.; Ostapkovich, N.; Shrebnick, D.B. Do standard monitoring sites reflect true brain temperature when profound hypothermia is rapidly induced and reversed? Anesthesiology 1995, 82, 344–351.
  21. McMahon JA, Howe A. Cold weather issues in sideline and event management. Curr Sports Med Rep. 2012;11:135-141.
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  23. Darocha, T.; Kosinski, S.; Jarosz, A.; Podsiadlo, P.; Zietkiewicz, M.; Sanak, T.; Galazkowski, R.; Piatek, J.; Konstanty-Kalandyk, J.; Drwila, R. Should capnography be used as a guide for choosing a ventilation strategy in circulatory shock caused by severe hypothermia? Observational case-series study. Scand. J. Trauma Resusc. Emerg. Med. 2017, 25, 15.
  24. Pasquier, M.; Zurron, N.; Weith, B.; Turini, P.; Dami, F.; Carron, P.N.; Paal, P. Deep accidental hypothermia with core temperature below 24 degrees c presenting with vital signs. High Alt. Med. Biol. 2014, 15, 58–63.
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Created by:
John Kiel on 30 June 2019 22:53:47
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Last edited:
19 April 2024 15:29:57
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