'''Rewarming shock''' (also known as '''rewarming collapse''') has been described as a drop in blood pressure following the warming of a person who is very cold.<ref name="Tveita 260–266">{{Cite journal|title = Rewarming from hypothermia. Newer aspects on the pathophysiology of rewarming shock|journal = International Journal of Circumpolar Health|date = 2000-10-01|issn = 1239-9736|pmid = 11209678|pages = 260–266|volume = 59|issue = 3–4|first = T.|last = Tveita}}</ref> The real cause of this rewarming shock is unknown.<ref name="Tveita 260–266"/>
There was a theoretical concern that external rewarming rather than internal rewarming may increase the risk.<ref name=NEJM2012>{{cite journal|last1=Brown|first1=DJ|last2=Brugger|first2=H|last3=Boyd|first3=J|last4=Paal|first4=P|title=Accidental hypothermia.|journal=The New England Journal of Medicine|date=Nov 15, 2012|volume=367|issue=20|pages=1930–8|pmid=23150960|doi=10.1056/NEJMra1114208}}</ref> These concerns were partly believed to be due to afterdrop, a situation detected during laboratory experiments where there is a continued decrease in core temperature after rewarming has been started.<ref name=NEJM2012/> Recent studies have not supported these concerns, and problems are not found with active external rewarming.<ref name=NEJM2012/><ref name=ACLS05>{{cite journal | author = ECC Committee, Subcommittees and Task Forces of the American Heart Association | title = 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care | journal = Circulation | volume = 112 | issue = 24 Suppl | pages = IV–136 | date = December 2005 | pmid = 16314375 | doi = 10.1161/CIRCULATIONAHA.105.166550 | url = http://circ.ahajournals.org/cgi/content/full/112/24_suppl/IV-136 | doi-access = | url-access = subscription }}</ref>
== Clinical features == Patients show signs of respiratory and cardiovascular compromise due to a mismatch between oxygen supply and demand. Specific signs and symptoms include:<ref name=":0">{{Cite journal |last=Davies|first=Anthony|last2=Wassink|first2=Guido|last3=Bennet|first3=Laura|last4=Gunn|first4=AlistairJ|last5=Davidson|first5=JoanneO|date=2019|title=Can we further optimize therapeutic hypothermia for hypoxic-ischemic encephalopathy?|url=https://journals.lww.com/10.4103/1673-5374.257512|journal=Neural Regeneration Research|language=en|volume=14|issue=10|pages=1678|doi=10.4103/1673-5374.257512|doi-access=free|issn=1673-5374|pmc=6585539|pmid=31169174}}</ref>
* Hypotension * Bradycardia * Heart failure * Respiratory compromise * Acidosis
Overall, the patient is unable to regulate their body temperature resulting in a distributive shock.<ref name=":0" />
== Pathophysiology == There is no consensus for the mechanism. In essence, rewarming shock is a failure of the body to hemodynamically and metabolically meet the needs to maintain homeostasis. Proposed mechanisms are detailed below.
=== Vasodilation and Venous Pooling === The process of active rewarming at a fast pace forces the body compensate by dilating its blood vessels. At a fast rate of expansion, it causes pooling in the extremities therefore releasing vast amounts of heat.<ref name=":1">{{Cite journal |last=Connolly|first=E.|last2=Worthley|first2=L. I. G.|date=2000-03-01|title=Induced and Accidental Hypothermia|url=https://www.sciencedirect.com/science/article/pii/S144127722302118X|journal=Critical Care and Resuscitation|volume=2|issue=1|pages=22–29|doi=10.1016/S1441-2772(23)02118-X|issn=1441-2772|doi-access=free}}</ref>
=== Heart failure === Since the cardiovascular system is already weak due to hypothermia, the rapid dilation of blood vessels results in a significant decrease in cardiac output. This leads to a sudden decrease in blood pressure and a state of shock.<ref>{{Cite journal |last=Mydske |first=Sigurd |last2=Thomassen |first2=Øyvind |date=2020-08-10 |title=Is prehospital use of active external warming dangerous for patients with accidental hypothermia: a systematic review |url=https://doi.org/10.1186/s13049-020-00773-2 |journal=Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine |language=en |volume=28 |issue=1 |pages=77 |doi=10.1186/s13049-020-00773-2 |doi-access=free|issn=1757-7241 |pmc=7419182 |pmid=32778153}}</ref>
=== Metabolic demand === At a hypothermic baseline, the cells metabolic needs are lowered yet they are still deprived from oxygen and nutrients. <ref>{{Cite journal |last=Polderman |first=Kees H |date=June 2008 |title=Induced hypothermia and fever control for prevention and treatment of neurological injuries |url=https://linkinghub.elsevier.com/retrieve/pii/S0140673608608375 |journal=The Lancet |volume=371 |issue=9628 |pages=1955–1969 |doi=10.1016/s0140-6736(08)60837-5 |issn=0140-6736|url-access=subscription }}</ref> As the rewarming process begins, the cells start increasing its metabolic needs further causing an increase in oxygen demand. Because the cardiovascular system is already weakened, it cannot keep up with the demand of the cells. <ref name=":3">{{Cite journal |last=Avellanas Chavala |first=M. L. |last2=Ayala Gallardo |first2=M. |last3=Soteras Martínez |first3=Í. |last4=Subirats Bayego |first4=E. |date=2019-12-01 |title=Management of accidental hypothermia: A narrative review |url=https://www.sciencedirect.com/science/article/pii/S2173572719302292 |journal=Medicina Intensiva (English Edition) |volume=43 |issue=9 |pages=556–568 |doi=10.1016/j.medine.2018.11.006 |issn=2173-5727|url-access=subscription }}</ref>
== Management and treatment == The goal of managing rewarming shock is to increase the core body temperature, maintain cardiac output and blood pressure through hemodynamic support.<ref name=":02">{{Cite journal |last=Mydske|first=Sigurd|last2=Thomassen|first2=Øyvind|date=2020-08-10|title=Is prehospital use of active external warming dangerous for patients with accidental hypothermia: a systematic review|url=https://doi.org/10.1186/s13049-020-00773-2|journal=Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine|language=en|volume=28|issue=1|pages=77|doi=10.1186/s13049-020-00773-2|doi-access=free|issn=1757-7241|pmc=7419182|pmid=32778153}}</ref> Fluid therapy and electrolyte replacement are an important part of treatment since patients with prolonged exposure may experience cold diuresis. <ref name=":02" />
=== Prehospital interventions === On initial assessment of the patient, it is important to move the patient as little as possible.<ref name=":3" /> Doing so could result in a phenomenon called 'afterdrop' where the toxic metabolites from the extremities travel back to the heart causing arrhythmias. <ref name=":3" /> Limit the patient to staying still for at least 30 minutes.<ref name=":3" /> Remove any wet clothes and apply external heat packs to the trunk of the patient to mitigate any peripheral vasodilation. Some external heat sources include chemical pads, heated blankets, etc. <ref name=":2">{{Cite journal |last=Paal|first=Peter|last2=Gordon|first2=Les|last3=Strapazzon|first3=Giacomo|last4=Brodmann Maeder|first4=Monika|last5=Putzer|first5=Gabriel|last6=Walpoth|first6=Beat|last7=Wanscher|first7=Michael|last8=Brown|first8=Doug|last9=Holzer|first9=Michael|last10=Broessner|first10=Gregor|last11=Brugger|first11=Hermann|date=2016-09-15|title=Accidental hypothermia–an update|url=https://doi.org/10.1186/s13049-016-0303-7|journal=Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine|language=en|volume=24|issue=1|pages=111|doi=10.1186/s13049-016-0303-7|doi-access=free|issn=1757-7241|pmc=5025630|pmid=27633781}}</ref>
=== Fluid resuscitation === It is important to keep patients hydrated as hypothermic patients suffer from cold diuresis where the body attempts to maintain core body temperature by urinating resulting in dehydration. <ref name=":2" /> To counteract this, warmed intravenous solution is given in boluses. It is recommended to warm IV fluids to 41-42 degrees celsius.<ref name=":1" /> Also consider potassium shifts as potassium shifts from extracellular to intracellular when core body temperature drops.<ref name=":1" /> It is recommended to wait until the body temperature is 35 degrees celsius as treating prematurely will cause hyperkalemia. <ref name=":1" />
=== Active internal rewarming === For moderate to severe hypothermia, more invasive measures are used to further prevent cardiovascular collapse and peripheral vasodilation. One of the measures is providing humidifed oxygen at 41-42 degrees celsius.<ref name=":1" /> Patients can also undergo body cavity lavage where warm fluid is circulated into different cavities of the body such as bladder, gastric, or pleural.<ref name=":2" /> Peritoneal dialysis at 44 degrees celsius at a rate of 4-6 degrees celsius per hour is highly recommended if the modality is available for treatment. <ref name=":1" />
==References== <references />
Category:Medical emergencies
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