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==Background==
==Background==
#Definition: Core Temp <35C (95F)
[[File:Windchill21.gif|thumb|Whid chill chart]]
#Severity:
===Definition: Core Temperature <35°C (95°F)===
##Mild hypothermia: 32-35C (90-95F)
*Unintentional hypothermia (core cooling <35°C) is associated with significant morbidity and mortality.  Roughly 1500 persons die of accidental hypothermia in the US annually.<ref>Baumgartner EA, Belson M, Rubin C, Patel M. [[Hypothermia]]and other cold-related morbidity emergency department visits: United States, 1995-2004. Wilderness Environ Med 2008;19:233-237</ref> 
##Moderate hypothermia: 28-32C (82-90F)
*Despite the high mortality associated with pre-hospital arrest, well-directed treatment can result in complete neurologic recovery in the hypothermic patient.<ref>Friberg H, Rundgren. Submersion, accidental hypothermia, and cardiac arrest, mechanical chest compressions as a bridge to final treatment: a case report. Scand J Trauma Resusc Emerg Med. 2009; 17: 7</ref>
##Severe hypothermia: <28C (82F)
*50% who die of hypothermia are >65 years old<ref>Centers for Disease Control and Prevention: Hypothermia-related deaths—United States, 2003–2004. MMWR Morb Mortal Wkly Rep 54: 173, 2005</ref>
#Immersion in any water colder than 16-21C (60.8-69.8F) can lead to severe hypothermia
*Risk of cardiac arrest increased with temperature <32°C, as stable cardiac rhythms can quickly degenerate into unstable rhythms.  Hypothermic patient without a pulse must be managed differently due to physiology changes that occur at low temperatures. Defibrillation and many medications may be ineffective until the core temperature is above 30.0°C. If defibrillation is warranted but unsuccessful, active rewarming should be initiated while CPR is continued.


==DDx==
===Causes===
#Accidental (environmental) exposure
*Increased heat loss
#Metabolic disorders
**Environmental exposure
##Hypoglycemia
***Avalanche victims
##Hypothyroidism
***Homeless population
##Hypoadrenalism
***Elderly patients → particularly low income during winter months
##Hypopituitarism
***[[Submersion injuries]]
#Hypothalamic and CNS
**Induced vasodilation
##Head trauma
***Drugs
##Tumor
***[[Carbon monoxide]]
##Stroke
***[[Alcohol intoxication]]
##Wernicke encephalopathy
*Decreased heat production
#Drugs
**Endocrine
##Ethanol
***[[Hypopituitarism]]
##Sedatives-hypnotics
***[[Hypothyroidism]]
#Sepsis
***[[adrenal insufficiency|Hypoadrenalism]]
#Dermal disease
***[[Hypoglycemia]]
##Burns
**Neuromuscular inefficiency
##Exfoliative dermatitis
***Extremes of age
#Acute incapacitating illness
***Impaired shivering
#Massive fluid or blood resuscitation
**Erythrodermas
***[[Psoriasis]]
***[[exfoliative erythroderma|Exfoliative dermatitis]]
***Ichthyosis
***[[Eczema]]
***[[Burns]]
**Impaired Thermoregulation
**Other
***[[Sepsis]]
***[[Trauma]]


==Diagnosis==
==Clinical Features==
===ECG===
[[File:1024px-Medical students take to the water to learn about hypothermia 150407-G-NW142-051.jpg|thumb|Medical students learning about the effects of hypothermia on the body.]]
#Dysrhythmias a/w temp <30C (86F)
[[File:US Navy 090408-N-3714M-289 A SEAL Qualification Training candidate looks out from a two-man tent during a re-warming exercise in which he spent five minutes in near freezing water.jpg|thumb|Man being rewarmed after spending five-minutes in near freezing water.]]
#Typical sequence is sinus brady > a fib w/ slow ventricular response > v-fib > asystole
{{Swiss staging system}}
#Other ECG findings:
##Osborn (J) wave
##T-wave inversions
##PR, QRS, QT prolongation
##Muscle tremor artifact
#AV block
##PVCs


Cold-induced bronchorrhea, along with a depression of cough and gag reflexes, makes aspiration pneumonia a common complication
===Associated Problems===
*[[Cold injuries]]
*Cardiac dysfunction
**[[Dysrhythmias]]
***May occur spontaneously if temperature <30°C (86°F)
**Afterdrop: Initial drop in temperature and MAP as rewarming is started due to loss of vasoconstriction/AV shunting colder peripheral tissues
*[[Coagulopathy]]
**Decreased clotting function
***platelet function and inhibition of coagulation cascade
***Part of the [[Trauma_(main)#Lethal_Triad_of_Major_Trauma|lethal triad of trauma]]
**[[Thromboembolism]]
***Secondary to hemoconcentration, increased blood viscosity, and poor circulation
***[[Disseminated intravascular coagulation]]
*Ineffective Drugs
**Protein binding increases as body temperature drops, and most drugs become ineffective
**Pharmacologic manipulation of the pulse and blood pressure generally should be avoided
**Oral meds poorly absorbed because of decreased gastrointestinal motility
**Intramuscular route avoided due to poor absorption from vasoconstricted sites
*Other
**[[Acid-base disorders]]
**[[Aspiration pneumonia and pneumonitis|Aspiration pneumonia]]
**[[Pancreatitis]]
**[[Rhabdomyolysis]]


==Differential Diagnosis==
{{Cold injuries DDX}}


The combination of hemoconcentration, cold-induced increase in blood viscosity, and poor circulation may lead to intravascular thrombosis and embolic complications. Disseminated intravascular coagulation may occur because of the release of tissue thromboplastins into the blood stream, especially when circulation is restored during rewarming. Because cold inhibits both platelet function and the enzymatic reactions of the coagulation cascade, hypothermic patients are prone to bleeding.
==Evaluation==
*'''Use low-reading thermometer'''
**Some standard thermometers record only to 34°C
**Measure core temperature with esophageal probe if intubated (most accurate)
*Check blood glucose as can be very high in [[DM]] or [[CVA]] or low when metabolized to keep warm
*Potassium >10-12 mEq/L not compatible with life
*Coagulopathy:  clotting factor activity and platelet function significantly reduced at temperature < 34°C
**Blood is rewarmed for lab testing so results may appear normal
*If ABG is rewarmed before analysis, results will be different from patient's actual acid/base state
**Refer to [[therapeutic hypothermia]] for over and underestimations


==Treatment==
===[[ECG]]===
===General===
[[File:Osborn wave.gif|thumb]]
#Handle pt gently
[[File:HypothermiaECG.jpg|thumb|Atrial fibrillation and Osborn J waves in a person with hypothermia.]]
##V-fib may be induced by rough handling of pt due to irritable myocardium
*Typical sequence is sinus bradycardia → atrial fibrillation with slow ventricular response → ventricular fibrillation → asystole
#O2
*Other ECG findings:
##Hypothermia causes leftward shift of oxyhemoglobin dissociation curve
**Osborn (J) wave - Size of wave correlates with degree of hypothermia. No prognostic value.  
#IVF
**Muscle tremor artifact
##Reasons:
**T-wave inversions
###Hypothermia > impaired renal concentrating ability > cold diuresis
**PR, QRS, [[QT prolongation]]
###Pts are prone to rhabdo
**[[ST segment elevation]] or depression
###Intravascular volume is lost due to extravascular shift
**AV block
#CPR
**[[PVC]]s
##Only perform if pt truly does not have a pulse (unnecessary CRP may lead to V-fib)
##Spend 30-45s attempting to detect respiratory activity and pulse before starting CPR
#Dysrhythmias
##Rewarming is treatment of choice
###Most dysrhythmias (e.g. sinus brady, a-fib/flutter) require no other therapy
###Activity of antiarrhythmics is unpredictable in hypothermia
###Hypothermic heart is relatively resistant to atropine, pacing, and countershock
##V-fib
###May be refractory to therapy until pt is rewarmed
###Attempt a single defibrillation attempt
####If unsuccessful continue CPR and attempt defibrillation again once temp >30C (86F)


==General Management==
===Basic Measures===
*Handling
**Handle patient gently
**[[V-fib]] may be induced by rough handling of patient due to irritable myocardium (anecdotal)
*[[Oxygen therapy]]
**[[Hypothermia]] causes leftward shift of oxyhemoglobin dissociation curve
**[[Intubation]]
**Intubate gently
**If [[RSI]] is given medications may act at a slower rate
*[[IVF]]
**Patients are also hypovolemic since [[hypothermia]] causes impaired renal concentrating ability, in turn causing cold diuresis
**Patients are prone to [[Rhabdomyolysis|rhabdomyolysis]] and will need hydration
**Intravascular volume is lost due to extravascular shift
**[[Normal saline]] preferred over [[Lactated Ringers]], as cold liver poorly metabolizes LR


===Rewarming===
===[[Dysrhythmias]]===
#Passive
*Rewarming is treatment of choice
##Techniques
*Most dysrhythmias (e.g. sinus brady, [[a-fib]]/[[flutter]]) require no other therapy
###Removal from cold environment
*If the patient requires central venous access, femoral is recommended to avoid irritating the myocardium
###Insulation
*Activity of antiarrhythmics is unpredictable in hypothermia
##Consider in pt w/ mild hypothermia who is able to generate intrinsic heat
*Hypothermic heart is relatively resistant to atropine, pacing, and countershock
#Active External
*[[Ventricular tachycardia]] or [[Ventricular fibrillation]] are most common
##Techniques
**May be refractory to therapy until patient is rewarmed
###Warm water immersion
**Attempt defibrillation
###Heating blankets
**Value of deferring repeat defibrillation until a target temperature is reached is uncertain<ref name=Hoek>Hoek T. 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010. 122:5829-5861</ref>
###Radiant heat
**Reasonable to perform further defibrillation attempts concurrent with rewarming<ref name=Hoek />
###Forced air
##Rewarm trunk BEFORE the extremities
###Otherwise may lead to hypotension, core temperature afterdrop
##May be ineffective in pts w/ poor perfusion or in cardiac arrest
##Consider in:
###Moderate-severe hypothermia
###Mild hypothermia in pt who is unstable or cannot generate intrinsic heat
###Failure to respond to passive external rewarming
#Active Internal
##Techniques
###Heated IV fluids
####If central line is placed avoid irritating the heart
###GI tract lavage
###Bladder lavage
###Pleural lavage
###Peritoneal lavage
##Consider alone or along with active external warming in:
###Severe hypothermia
###Moderate hypothermia which fails to respond to less aggressive measures


===Medications for Unexplained Hypothermia in Specific Patient Populations===
*[[Antibiotics]]
**Give if suspect [[sepsis]] (e.g. hypothermia fails to correct with rewarming measures)
*[[Thiamine]]
**Consider if [[Wernicke disease]] is possible cause of hypothermia (e.g. alcoholic patient)
*[[Hydrocortisone]]
**Consider if patient has history of adrenal suppression or insufficiency
***100mg hydrocortisone
*[[Levothyroxine]]
**Consider if any suspicion for [[hypothyroidism]]/[[myxedema coma]]
**Could cause dysrhythmia or cardiac ischemia if not in myxedema coma
*[[Hyperglycemia]]
**Hyperglycemia common in hypothermia:
***Stimulates catecholamine induced glycogenolysis
***Inhibits insulin release and uptake by cell membranes
**Rebound hypoglycemia during rewarming can occur if clinicians too aggressively deliver exogenous insulin


==Rewarming==
'''Recommendations on Rewarming Modality based on Temperature and Clinical picture'''
{| class="wikitable"
|-
| '''Stage of Hypothermia''' || '''Recommended rewarming modality'''
|-
| I/ Mild: 32-35°C (90-95°F) || Passive external
|-
| II/ Moderate: 28-32°C (82-90°F) || Active external
|-
| III/ Severe: 20-28°C (68-82°F) || Active internal
|-
| IV/ Profound: <20°C (68°F) || As severe + modified ACLS
|}


Because a number of hypothermic patients are thiamine-depleted alcoholics (and because Wernicke disease may cause hypothermia), consider giving IV thiamine, 100 milligrams. Between 50 and 100 mL of 50% glucose should be administered if a test-strip serum glucose measurement is low or if a rapid glucose test is unavailable
===Passive External===
*Prevent additional heat loss → Remove wet clothes
*Heated room
*Blankets - If patient still shivering, capable of rewarming 0.5°C/hr
*Hypothermia cap


thorough search for infection is indicated.  
===Active External===
*Rewarm trunk BEFORE the extremities, otherwise you cause further hypotension ("core temperature afterdrop")
**Afterdrop: warmed vasodilated peripheral tissue allows cooler blood in extremities to circulate back to core
*Options:
**Warm water immersion (Capable of 2-4°C/Hr rewarming)
**Heating blankets
**Radiant heat
**Forced air - e.g. Bair hugger or Arctic Sun (Up to 1-2.5°C/Hr rewarming)
**Warm humidified air via facemask or endotracheal tube


Hydrocortisone (100 milligrams) should be given to the patient who has a history of adrenal suppression or insufficiency or is in myxedema coma. Routine corticosteroid therapy is not necessary.
===Active Internal===
Options:
*Heated IV fluids: 38-42°C.
**Two animal studies have showed 65°C IVF via central line warmed subjects faster without side effects, but this has not been tested in humans<ref>Fildes J, Sheaff C, and Barrett J. Very hot intravenous fluid in the treatment of hypothermia. J Trauma. 1993; 35(5):683-686.</ref><ref>Sheaff CM, Fildes JJ, Keogh P, et al. Safety of 65 degrees C intravenous fluid for the treatment of hypothermia. Am J Surg. 1996; 172(1):52-55.</ref>
**If central line is placed, avoid irritating the heart
*GI tract lavage
**Can cause fluid and electrolyte fluctuations, also risk of pulmonary aspiration
*[[Bladder lavage]]
**Small surface area available for heat exchange
*[[Thoracic lavage]]
*[[Peritoneal lavage]]
*Bypass/[[ECMO]]<ref>Ginty C, et al. Extracorporeal membrane oxygenation rewarming in the ED: an opportunity for success. American Journal of Emergency Medicine. 2014 December 3 (ahead of print).</ref>/AV Dialysis
**[https://www.hypothermiascore.org/ HOPE score] can predict probability of survival with ECMO


In severe hypothermia or hypothermia secondary to an underlying illness, patients may fail to rewarm passively; active rewarming is then indicated. Active rewarming is also indicated for patients with cardiovascular compromise.
===Rewarming Rates===
{| {{table}}
| align="center" style="background:#f0f0f0;"|'''Mode'''
| align="center" style="background:#f0f0f0;"|'''°C/Hr'''
| align="center" style="background:#f0f0f0;"|'''Comments'''
|-
| '''Passive External'''||||
|-
| Shivering<ref name=Kempainen>Kempainen, R. R. and Brunette, D. D. The Evaluation and Management of Accidental Hypothermia. Respir.Care 2004;49(2):192-205 </ref>||1.5||
|-
| Warming Blanket<ref name=Kempainen />||2||
|-
| '''Active External'''||||
|-
| Warm IV fluids (47°C)||1-3||Highly variable; Limited by tubing distance, requires large volumes with risk of volume overload
|-
| Forced air  (Bair hugger)||1-2.5||
|-
| Warm water immersion ||2-4||
|-
| '''Active Internal'''||||
|-
| Warm Humidified Air (intubated)||0.5-1.2||Low heat transport capacity
|-
| Peritoneal Lavage<ref name=Kempainen />||3||
|-
| Thoracic Lavage<ref name=Kempainen />|| 3-6||
|-
| Hemodialysis<ref name=Kempainen />||3-4||
|-
| Open thoracotomy lavage||Up to 8 (median 3)||Highly invasive. 71% survival in 1 study
|-
| Cardiac Bypass<ref name=Kempainen />||7-10||
|}


IV fluids and blood should also be warmed to 40°C (104°F) before administration, especially in patients receiving massive volume resuscitation. Commercial fluid warmers allow the temperature of infused fluids to be precisely controlled.
==[[Cardiac Arrest]]==
*Only perform if patient truly does not have a pulse (unnecessary CPR may lead to [[V-fib]])
*Spend 30-45s attempting to detect respiratory activity and pulse before starting CPR
*Rhythms can quickly degenerate into unstable rhythms
*Be careful when inserting guidewires, persistent shocks can degenerate fib into asystole
*Standard [[ACLS]] guidelines may not apply:
**Any organized rhythm should be assumed to be perfusing the patient adequately
**Starting [[CPR]] may precipitate fatal ventricular rhythms
*Modified vs. Standard ACLS:
**ERC recommends up to 3 defibrillations with [[epi]] held until temperature >30°C, then [[epinephrine]] interval of 6 min until temperature >35°C
**AHA recommends 3 defibrillations and 3 rounds of [[epinephrine]] with further dosing guided by clinical response
**Recent consensus suggest only one [[defibrillation]] and round of ACLS meds → rewarm 5°C → one defib/meds → Repeat


Both inhalation rewarming and administration of heated fluids should be used in all patients, because these are simple techniques without complications, as long as the temperature is controlled.
===Termination of [[CPR]]===
*Should be considered if:
**K > 12 mmol<ref>Schaller M, Fischer AP, Perret CH. Hyperkalemia: A Prognostic Factor During Acute Severe Hypothermia. JAMA. 1990;264(14):1842–1845. doi:10.1001/jama.1990.03450140064035</ref><ref name="Paal">Paal P, Gordon L, Strapazzon 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(1):111. Published 2016 Sep 15. doi:10.1186/s13049-016-0303-7</ref>
**[[Asystole]] persists beyond >32°C
*''Lactate and pH have less consistent prognostic significance in hypothermia''


lavage with warmed saline is simple, and patients can be lavaged with large volumes of warm fluid over a short time. However, the obtunded hypothermic patient may develop pulmonary aspiration if lavaged with an unprotected airway. The urinary bladder can also be lavaged with warm saline solution through a urinary drainage catheter.
==Disposition==
*ICU for severe cases


Pleural lavage using thoracostomy tubes has provided effective rewarming in animal studies and a few human cases.15 Lavaging the left thoracic cavity delivers heated fluid in close proximity to the heart, which potentially allows rapid cardiac warming. Two thoracostomy tubes (for fluid inflow and outflow) generally have been employed. If this technique is chosen, care must be taken to monitor the net fluid infusion, because increased intrathoracic pressure and tension hydrothorax may complicate the procedure. The risk of precipitating dysrhythmias during chest tube insertion is unknown.
==External Links==
*[http://lifeinthefastlane.com/ecg-library/basics/hypothermia/ LITFL Hypothermia]
*[http://dhss.alaska.gov/dph/Emergency/Documents/ems/documents/Alaska%20DHSS%20EMS%20Cold%20Injuries%20Guidelines%20June%202014.pdf Alaska Cold Injury Guidelines]
*[https://emcrit.org/ibcc/hypothermia/ IBCC Hypothermia]


Approach to Rewarming
==See Also==
Patients with mild hypothermia, who are still in the excitation stage, generally improve spontaneously, as long as endogenous heat production mechanisms are functional. At temperatures of >30°C (>86°F), the incidence of dysrhythmias is low, and rapid rewarming is rarely necessary.
*[[Cold injuries]]
*[[Therapeutic hypothermia]]
*[[Water-related injuries]]


==References==
<references/>


By far the most important consideration in the selection of rewarming techniques is the patient's cardiovascular status; a secondary consideration is the presenting temperature. Some feel that patients with a stable cardiac rhythm (including sinus bradycardia and atrial fibrillation) and stable vital signs do not need rapid rewarming, even if the temperature is very low. They recommend passive rewarming and noninvasive rewarming modalities (e.g., forced-air rewarming, administration of warm moist oxygen, and use of warm IV fluids) in this setting. Others argue that profoundly hypothermic patients, even if currently in "stable" condition, are at risk of developing life-threatening dysrhythmias. They recommend rapid rewarming until the temperature has reached 30°C to 32°C (86.0°F to 89.6°F) to minimize the time period during which dysrhythmias may develop. The relative merits of each approach have not been studied.
[[Category:Environmental]]
 
Patients with cardiovascular insufficiency or instability, including persistent hypotension and life-threatening dysrhythmias, need to be rewarmed rapidly.
 
Unless there is strong evidence that the patient is incapable of survival, resuscitative efforts should be continued until core temperature is at least 30°C to 32°C (86.0°F to 89.6°F).
 
 
 
 
 
 
 
 
 
 
==Work-Up==
 
 
 
 
 
 
 
 
 
 
 
==Source==
Tintinalli
 
[[Category:Environ]]

Latest revision as of 01:56, 28 April 2024

Background

Whid chill chart

Definition: Core Temperature <35°C (95°F)

  • Unintentional hypothermia (core cooling <35°C) is associated with significant morbidity and mortality. Roughly 1500 persons die of accidental hypothermia in the US annually.[1]
  • Despite the high mortality associated with pre-hospital arrest, well-directed treatment can result in complete neurologic recovery in the hypothermic patient.[2]
  • 50% who die of hypothermia are >65 years old[3]
  • Risk of cardiac arrest increased with temperature <32°C, as stable cardiac rhythms can quickly degenerate into unstable rhythms. Hypothermic patient without a pulse must be managed differently due to physiology changes that occur at low temperatures. Defibrillation and many medications may be ineffective until the core temperature is above 30.0°C. If defibrillation is warranted but unsuccessful, active rewarming should be initiated while CPR is continued.

Causes

Clinical Features

Medical students learning about the effects of hypothermia on the body.
Man being rewarmed after spending five-minutes in near freezing water.

Swiss Hypothermia Staging System[4]

Classification Temperature Signs/Symptoms
I / Mild 32-35°C (90-95°F) Shivering, awake
II / Moderate 28-32°C (82-90°F) Shivering, depressed mental status
III / Severe 20-28°C (68-82°F) unconscious/severely depressed mental status, shivering ceases
IV / Profound <20°C (68°F) unobtainable VS

Associated Problems

  • Cold injuries
  • Cardiac dysfunction
    • Dysrhythmias
      • May occur spontaneously if temperature <30°C (86°F)
    • Afterdrop: Initial drop in temperature and MAP as rewarming is started due to loss of vasoconstriction/AV shunting colder peripheral tissues
  • Coagulopathy
  • Ineffective Drugs
    • Protein binding increases as body temperature drops, and most drugs become ineffective
    • Pharmacologic manipulation of the pulse and blood pressure generally should be avoided
    • Oral meds poorly absorbed because of decreased gastrointestinal motility
    • Intramuscular route avoided due to poor absorption from vasoconstricted sites
  • Other

Differential Diagnosis

Cold injuries

Evaluation

  • Use low-reading thermometer
    • Some standard thermometers record only to 34°C
    • Measure core temperature with esophageal probe if intubated (most accurate)
  • Check blood glucose as can be very high in DM or CVA or low when metabolized to keep warm
  • Potassium >10-12 mEq/L not compatible with life
  • Coagulopathy: clotting factor activity and platelet function significantly reduced at temperature < 34°C
    • Blood is rewarmed for lab testing so results may appear normal
  • If ABG is rewarmed before analysis, results will be different from patient's actual acid/base state

ECG

Osborn wave.gif
Atrial fibrillation and Osborn J waves in a person with hypothermia.
  • Typical sequence is sinus bradycardia → atrial fibrillation with slow ventricular response → ventricular fibrillation → asystole
  • Other ECG findings:
    • Osborn (J) wave - Size of wave correlates with degree of hypothermia. No prognostic value.
    • Muscle tremor artifact
    • T-wave inversions
    • PR, QRS, QT prolongation
    • ST segment elevation or depression
    • AV block
    • PVCs

General Management

Basic Measures

  • Handling
    • Handle patient gently
    • V-fib may be induced by rough handling of patient due to irritable myocardium (anecdotal)
  • Oxygen therapy
    • Hypothermia causes leftward shift of oxyhemoglobin dissociation curve
    • Intubation
    • Intubate gently
    • If RSI is given medications may act at a slower rate
  • IVF
    • Patients are also hypovolemic since hypothermia causes impaired renal concentrating ability, in turn causing cold diuresis
    • Patients are prone to rhabdomyolysis and will need hydration
    • Intravascular volume is lost due to extravascular shift
    • Normal saline preferred over Lactated Ringers, as cold liver poorly metabolizes LR

Dysrhythmias

  • Rewarming is treatment of choice
  • Most dysrhythmias (e.g. sinus brady, a-fib/flutter) require no other therapy
  • If the patient requires central venous access, femoral is recommended to avoid irritating the myocardium
  • Activity of antiarrhythmics is unpredictable in hypothermia
  • Hypothermic heart is relatively resistant to atropine, pacing, and countershock
  • Ventricular tachycardia or Ventricular fibrillation are most common
    • May be refractory to therapy until patient is rewarmed
    • Attempt defibrillation
    • Value of deferring repeat defibrillation until a target temperature is reached is uncertain[5]
    • Reasonable to perform further defibrillation attempts concurrent with rewarming[5]

Medications for Unexplained Hypothermia in Specific Patient Populations

  • Antibiotics
    • Give if suspect sepsis (e.g. hypothermia fails to correct with rewarming measures)
  • Thiamine
    • Consider if Wernicke disease is possible cause of hypothermia (e.g. alcoholic patient)
  • Hydrocortisone
    • Consider if patient has history of adrenal suppression or insufficiency
      • 100mg hydrocortisone
  • Levothyroxine
  • Hyperglycemia
    • Hyperglycemia common in hypothermia:
      • Stimulates catecholamine induced glycogenolysis
      • Inhibits insulin release and uptake by cell membranes
    • Rebound hypoglycemia during rewarming can occur if clinicians too aggressively deliver exogenous insulin

Rewarming

Recommendations on Rewarming Modality based on Temperature and Clinical picture

Stage of Hypothermia Recommended rewarming modality
I/ Mild: 32-35°C (90-95°F) Passive external
II/ Moderate: 28-32°C (82-90°F) Active external
III/ Severe: 20-28°C (68-82°F) Active internal
IV/ Profound: <20°C (68°F) As severe + modified ACLS

Passive External

  • Prevent additional heat loss → Remove wet clothes
  • Heated room
  • Blankets - If patient still shivering, capable of rewarming 0.5°C/hr
  • Hypothermia cap

Active External

  • Rewarm trunk BEFORE the extremities, otherwise you cause further hypotension ("core temperature afterdrop")
    • Afterdrop: warmed vasodilated peripheral tissue allows cooler blood in extremities to circulate back to core
  • Options:
    • Warm water immersion (Capable of 2-4°C/Hr rewarming)
    • Heating blankets
    • Radiant heat
    • Forced air - e.g. Bair hugger or Arctic Sun (Up to 1-2.5°C/Hr rewarming)
    • Warm humidified air via facemask or endotracheal tube

Active Internal

Options:

  • Heated IV fluids: 38-42°C.
    • Two animal studies have showed 65°C IVF via central line warmed subjects faster without side effects, but this has not been tested in humans[6][7]
    • If central line is placed, avoid irritating the heart
  • GI tract lavage
    • Can cause fluid and electrolyte fluctuations, also risk of pulmonary aspiration
  • Bladder lavage
    • Small surface area available for heat exchange
  • Thoracic lavage
  • Peritoneal lavage
  • Bypass/ECMO[8]/AV Dialysis
    • HOPE score can predict probability of survival with ECMO

Rewarming Rates

Mode °C/Hr Comments
Passive External
Shivering[9] 1.5
Warming Blanket[9] 2
Active External
Warm IV fluids (47°C) 1-3 Highly variable; Limited by tubing distance, requires large volumes with risk of volume overload
Forced air (Bair hugger) 1-2.5
Warm water immersion 2-4
Active Internal
Warm Humidified Air (intubated) 0.5-1.2 Low heat transport capacity
Peritoneal Lavage[9] 3
Thoracic Lavage[9] 3-6
Hemodialysis[9] 3-4
Open thoracotomy lavage Up to 8 (median 3) Highly invasive. 71% survival in 1 study
Cardiac Bypass[9] 7-10

Cardiac Arrest

  • Only perform if patient truly does not have a pulse (unnecessary CPR may lead to V-fib)
  • Spend 30-45s attempting to detect respiratory activity and pulse before starting CPR
  • Rhythms can quickly degenerate into unstable rhythms
  • Be careful when inserting guidewires, persistent shocks can degenerate fib into asystole
  • Standard ACLS guidelines may not apply:
    • Any organized rhythm should be assumed to be perfusing the patient adequately
    • Starting CPR may precipitate fatal ventricular rhythms
  • Modified vs. Standard ACLS:
    • ERC recommends up to 3 defibrillations with epi held until temperature >30°C, then epinephrine interval of 6 min until temperature >35°C
    • AHA recommends 3 defibrillations and 3 rounds of epinephrine with further dosing guided by clinical response
    • Recent consensus suggest only one defibrillation and round of ACLS meds → rewarm 5°C → one defib/meds → Repeat

Termination of CPR

  • Should be considered if:
  • Lactate and pH have less consistent prognostic significance in hypothermia

Disposition

  • ICU for severe cases

External Links

See Also

References

  1. ↑ Baumgartner EA, Belson M, Rubin C, Patel M. Hypothermiaand other cold-related morbidity emergency department visits: United States, 1995-2004. Wilderness Environ Med 2008;19:233-237
  2. ↑ Friberg H, Rundgren. Submersion, accidental hypothermia, and cardiac arrest, mechanical chest compressions as a bridge to final treatment: a case report. Scand J Trauma Resusc Emerg Med. 2009; 17: 7
  3. ↑ Centers for Disease Control and Prevention: Hypothermia-related deaths—United States, 2003–2004. MMWR Morb Mortal Wkly Rep 54: 173, 2005
  4. ↑ Brown et al., Accidental Hypothermia. N Engl J Med 2012; 367:1930-1938
  5. ↑ 5.0 5.1 Hoek T. 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010. 122:5829-5861
  6. ↑ Fildes J, Sheaff C, and Barrett J. Very hot intravenous fluid in the treatment of hypothermia. J Trauma. 1993; 35(5):683-686.
  7. ↑ Sheaff CM, Fildes JJ, Keogh P, et al. Safety of 65 degrees C intravenous fluid for the treatment of hypothermia. Am J Surg. 1996; 172(1):52-55.
  8. ↑ Ginty C, et al. Extracorporeal membrane oxygenation rewarming in the ED: an opportunity for success. American Journal of Emergency Medicine. 2014 December 3 (ahead of print).
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 Kempainen, R. R. and Brunette, D. D. The Evaluation and Management of Accidental Hypothermia. Respir.Care 2004;49(2):192-205
  10. ↑ Schaller M, Fischer AP, Perret CH. Hyperkalemia: A Prognostic Factor During Acute Severe Hypothermia. JAMA. 1990;264(14):1842–1845. doi:10.1001/jama.1990.03450140064035
  11. ↑ Paal P, Gordon L, Strapazzon 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(1):111. Published 2016 Sep 15. doi:10.1186/s13049-016-0303-7
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