CASE

An unknown age male, estimated 30 years old, is brought into the emergency department by emergency medical services in cardiac arrest.  He was found unresponsive on a park bench outside on a cold night.  When EMS arrived he was noted to be very cold with no palpable pulse, spontaneous respirations, or response to sternal rub.  A supraglottic airway was placed but they were unable to establish IV access. They performed 30 minutes of chest compressions and brought him to the emergency department on a LUCAS device.

On arrival, the patient continued to be pulseless and apneic.  His jaw was barely mobile so he was unable to be intubated, but he had bilateral breath sounds so he was ventilated via his LMA. Compressions continued by LUCAS device. His rectal temperature was 66°F (18.9°C). IV access was established with one peripheral IV, an IO line, and a femoral CVC.  He was fully exposed and no obvious injuries were noted.  He was cold, mottled, and partially frozen.  Rewarming was begun with warmed IV fluid infusion, bladder irrigation, and a Bair Hugger.  He received 105 minutes total of CPR.  ECMO team was consulted and declined due to patient being frozen. Time of death was ultimately called due to him being frozen with rigor mortis and a very poor chance of a good neurologic outcome even if ROSC was achieved.

DIAGNOSIS

Hypothermic cardiac arrest

DISCUSSION

Clinical features:

Hypothermia is defined as a core body temperature <35°C.  It is divided into 3 classes based on temperature and clinical features: mild, moderate, and severe.  The clinical effects and treatments for each class are organized in this table from EmCrit:

Hypothermia can be classified as primary or secondary. Primary hypothermia is the result when heat production is overcome by cold exposure, while secondary hypothermia occurs as a result of another medical condition.  Some common causes of secondary hypothermia include sepsis, metabolic/endocrine disorders such as hypothyroidism or hypoadrenalism, and neurologic conditions such as hypothalamic strokes.

The main organ systems affected by hypothermia are the central nervous system and cardiovascular systems, demonstrated by altered mental status and abnormal cardiac conduction and rhythms.  The most severe manifestations of hypothermia result in coma, malignant cardiac dysrhythmias (especially ventricular fibrillation), and asystole.  Other organ systems may be involved as well, particularly after the initial rewarming phase as patients develop potential renal failure, liver failure, or clotting issues such as DIC.

Management:

Rewarming is the treatment for hypothermia.  Methods can be divided into passive and active measures.  Passive measures are usually sufficient for patients with mild hypothermia, and include removing wet clothing, drying the patient, warming the patient’s room, and providing insulation with blankets. 

Active rewarming is divided into external and internal measures. Patient’s with moderate to severe hypothermia usually warrant some active measures be taken.  External rewarming is performed by providing circulating heated air with devices such as a Bair Hugger.  Internal rewarming methods exist on a spectrum of invasiveness.  As patients become more hypothermic and more unstable, more invasive measures are indicated.

On the less invasive side, warmed IV fluids at 40°C can be infused. Warmed humidified oxygen can be administered via nonrebreather or ET tube in intubated patients. Bladder and gastric lavage are the next measures you can take.  They involve placing a Foley or NG/OG tube and instilling 300-500cc of warmed fluids, allowing it to swell for 5-10 minutes, and then draining and replacing the fluid.  If these measures are not enough, you can move on to thoracic and peritoneal lavage.  Thoracic lavage involves placing chest tubes bilaterally and instilling 500cc of warmed fluids for 5-10 minutes at a time, similar to bladder or gastric lavage.  Notably this will decrease lung capacity which is an important consideration in for trauma patients, especially those that are intubated. Alternatively, an anterior and lateral/posterior chest tube can be placed to allow constant infusion and drainage of warmed fluids.  Peritoneal lavage can be considered in conjunction with surgery, and is performed similarly to a diagnostic peritoneal lavage (DPL).

One of the unique aspects of hypothermia is how differently cardiac arrest should be treated from normal ACLS protocol. Patients can have good neurologic outcomes despite prolonged resuscitative times, as demonstrated by several case reports and reviews. [1,5,8]  Some patients have survived to a full neurologic recovery with 9 hours of no flow time. [8]

ACLS protocol should be modified, as the goal is not to get the patient to the catheterization lab but to focus on rewarming. The most common cardiac rhythms in patients with severe hypothermia are ventricular fibrillation and asystole, with the latter predominating at lower temperature.  The European Resuscitation Counsel recommends performing up to 3 defibrillations for shockable rhythms and withholding epinephrine until the core temperature is 30°C.  They then recommend doubling the time between epinephrine doses until 35°C. [2] Generally speaking, rewarming should continue and the patient should not be pronounced until they are a normal temperature. Although new data is changing this, we view the old mantra of “you’re not dead until you’re warm and dead.” Some exceptions to this rule include patients with a history of full submersion in water or burial in an avalanche, as these patients likely went into cardiac arrest due to hypoxia first.

Patients in cardiac arrest or with unstable cardiac rhythms should be considered for extracorporeal assisted rewarming (ECAR).  Venoarterial ECMO is the most studied and utilized method of ECAR, but all forms of bypass have been used and can provide fast rewarming including venovenous ECMO, hemodialysis, or cardiopulmonary bypass.  ECMO has been proven to improve the likelihood of survival in patients with and without cardiac arrest. [4,7] A study by Dunne et al in 2014 showed 67.7% survival to discharge and a 61.5% rate of good neurological recovery for patients presenting with pure hypothermic cardiac arrest, compared to a 23.4% survival and a 9.4% rate of good neurological outcome in patients with combined hypoxia and hypothermia.

Prognostication:

Hypoxia is one of the main factors associated with poor outcomes and failure of rewarming.  Patients who suffer cardiac arrest purely from hypothermia do better as cooling has a neuro-protective effect, and slows metabolism down enough to protect cells from damage.  A serum potassium level greater than 12 is an indicator of hypoxia and significant cellular death, and is therefore an indication to cease rewarming efforts.

Rewarming takes a considerable amount of resources and thus, the correct patients need to be chosen.  This has historically been a challenge as there are not many clear indicators other than mechanism or a high potassium for which patients may do well and in which a patient’s rewarming would be futile.  Some studies in the past few years have sought to answer that question, and have looked at scoring systems such as the SOFA and qSOFA scores. [6] The most promising prognostic tool being developed seems to be the HOPE score. This was developed in a study from 2018 called “Hypothermia outcome prediction after extracorporeal life support for hypothermic cardiac arrest patients: The HOPE score.” [9]  The HOPE score uses patient age, sex, mechanism (with or without asphyxia), CPR duration, serum potassium, and starting temperature to predict the survival probability for patients undergoing ECAR.  Demonstrated in the figure below from this study, the HOPE score has a higher sensitivity than serum potassium alone for predicting which patients will be non-survivors despite rewarming.  It can help rule out a larger number of patients to undergo such intensive measures.  Ongoing studies are occurring to externally validate this score.

AUTHOR: Frederick Varone, MD is a PGY4 at Brown University/Rhode Island Hospital.

FACULTY REVIEWER: Katelyn Moretti, MD is an attending physician at Rhode Island Hospital.

References:

1.Bolte RG, Black PG, Bowers RS, Thorne JK, Corneli HM. The use of extracorporeal rewarming in a child submerged for 66 minutes. JAMA. Jul 15 1988;260(3):377-379. 

2. Brown et al. Accidental Hypothermia. NEJM 2012;367: 1930-8.

3. Dow J et al. Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update. Wilderness Environ Med. 2019 Dec;30(4S):S47-S69. doi: 10.1016/j.wem.2019.10.002. Epub 2019 Nov 15. PMID: 31740369.

4. Dunne et al. Extracorporeal-Assisted Rewarming in the management of deep hypothermic cardiac arrest. A systematic review of the literature. Heart, Lung, and Circulation 2014;23: 1029-1035.

5. Forti A et al. Hypothermic Cardiac Arrest With Full Neurologic Recovery After Approximately Nine Hours of Cardiopulmonary Resuscitation: Management and Possible Complications. Ann Emerg Med. 2019 Jan;73(1):52-57. doi: 10.1016/j.annemergmed.2018.09.018. Epub 2018 Nov 9. PMID: 30420231.

6. Kandori et al. Prognostic ability of the sequential organ failure assessment score in accidental hypothermia: a multi-institutional retrospective cohort study. Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine (2019) 27:103. https://doi.org/10.1186/s13049-019-0681-8

7. Ohbe H, Isogai S, Jo T, Matsui H, Fushimi K, Yasunaga H. Extracorporeal membrane oxygenation improves outcomes of accidental hypothermia without vital signs: A nationwide observational study. Resuscitation. 2019 Nov;144:27-32. doi: 10.1016/j.resuscitation.2019.08.041. Epub 2019 Sep 9. PMID: 31513865.

8. Paal P, Brown D. Cardiac arrest from accidental hypothermia, a rare condition with potentially excellent neurological outcome, if you treat it right. Resuscitation. 2014 Jun;85(6):707-8. doi: 10.1016/j.resuscitation.2014.03.045. Epub 2014 Mar 29. PMID: 24686021.

9. Pasquier et al. Hypothermia outcome prediction after extracorporeal life support for hypothermic cardiac arrest patients: The HOPE score. Resuscitation 2018; 126: 568-64. https://doi.org/10.1016/j.resuscitation.2018.02.026.

10. van der Ploeg GJ, Goslings JC, Walpoth BH, Bierens JJ. Accidental hypothermia: rewarming treatments, complications and outcomes from one university medical centre. Resuscitation. 2010 Nov;81(11):1550-5. doi: 10.1016/j.resuscitation.2010.05.023. Epub 2010 Aug 11. PMID: 20702016. 

11. Yohei et al. Prognostic factors for patients with accidental hypothermia: A multi-institutional retrospective cohort study. The American Journal of Emergency Medicine. 2019; 37(4): 565-570. https://doi.org/10.1016/j.ajem.2018.06.025.

12. Zafren K et al. State of Alaska Cold Inju