Ver el código de «Accidental hypothermia»

==Background==
[[File:Windchill21.gif|thumb|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.<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>  
*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>
*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>
*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===
*Increased heat loss
**Environmental exposure
***Avalanche victims
***Homeless population
***Elderly patients → particularly low income during winter months
***[[Submersion injuries]]
**Induced vasodilation
***Drugs
***[[Carbon monoxide]]
***[[Alcohol intoxication]]
*Decreased heat production
**Endocrine
***[[Hypopituitarism]]
***[[Hypothyroidism]]
***[[adrenal insufficiency|Hypoadrenalism]]
***[[Hypoglycemia]]
**Neuromuscular inefficiency
***Extremes of age
***Impaired shivering
**Erythrodermas
***[[Psoriasis]]
***[[exfoliative erythroderma|Exfoliative dermatitis]]
***Ichthyosis
***[[Eczema]]
***[[Burns]]
**Impaired Thermoregulation
**Other
***[[Sepsis]]
***[[Trauma]]

==Clinical Features==
[[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.]]
[[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.]]
{{Swiss staging system}}

===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}}

==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

===[[ECG]]===
[[File:Osborn wave.gif|thumb]]
[[File:HypothermiaECG.jpg|thumb|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
**[[PVC]]s

==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

===[[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<ref name=Hoek>Hoek T. 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010. 122:5829-5861</ref>
**Reasonable to perform further defibrillation attempts concurrent with rewarming<ref name=Hoek />

===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
|}

===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<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

===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||
|}

==[[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:
**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''

==Disposition==
*ICU for severe cases

==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]

==See Also==
*[[Cold injuries]]
*[[Therapeutic hypothermia]]
*[[Water-related injuries]]

==References==
<references/>

[[Category:Environmental]]