Case of the Quarter: Hypothermia-Induced Cardiac Arrest

EMS World’s new Case of the Quarter feature is developed by Texas’ Montgomery County Hospital District EMS to share lessons learned with the wider EMS community. For further discussion of this case, visit www.emsworld.com/podcasts. 

Hypothermia is a complex medical condition caused by prolonged exposure to cold temperatures that can disrupt multiple organ systems and even induce cardiac arrest. There is no universally accepted treatment guideline for hypothermia-induced cardiac arrest, but many suggested guidelines have fundamental similarities.¹ There are case reports of intact neurologic survival with prolonged resuscitations of more than 3 hours,² supporting a fundamental principle in emergency medicine education regarding resuscitation of severely hypothermic patients: “You are not dead until you are warm and dead.” 

Although hypothermia can be relatively common in some parts of the world, Houston, Texas, is not one of them. This case illustrates the necessity of emergency medical responders practicing in all environments to appropriately identify and initiate proper resuscitation of critically ill hypothermic patients. 

Staffed by around 250 paramedics and supported by 12 regional first-responder organizations, Montgomery County Hospital District (MCHD) EMS is a publicly funded 9-1-1 provider for Montgomery County, Texas, covering 1100 square miles just north of Houston. MCHD answers more than 80,000 calls a year. This article follows an MCHD crew responding to a call for hypothermia-induced cardiac arrest. 

The Call

A 35-year-old female was found unresponsive outside a residence, and a third-party caller alerted 9-1-1. 

En Route

Paramedics attempted to gather pertinent information regarding the patient. However, little was known to the crew. The call occurred at night with the temperature around 32ºF.

Scene Findings

The patient was found on the ground outside a residence wearing minimal clothing. Her airway and breathing were intact on primary examination, and pulses were palpable. The patient was moaning incomprehensibly and withdrawing and opening her eyes to pain, which resulted in a GCS of 8. 

On secondary examination it was noted the patient was extremely cold to the touch and had vomited on herself, and there were abrasions and contusions on the right upper quadrant of her abdomen, bilateral elbows, and bilateral knees. A brief inspection of the surrounding scene found ground markings that led to the back door of a nearby residence. Inside the house a first responder found a note and empty bottles of promethazine, gabapentin, and hydrocortisone, among other medications, including chlorpromazine, naproxen, and eszopiclone. 

Pathophysiology

Hypothermia occurs when the body loses heat faster than it can produce it. Heat retention is achieved in a cold external environment through increased metabolic rate and muscle tone, peripheral vasoconstriction, and shivering. When the temperature drops below 35ºC, progressive multisystem impairment begins to occur. Central nervous system symptoms start to emerge, consisting of poor judgment, amnesia, ataxia, apathy, and ultimately loss of consciousness. In 30% of fatal cases, a common behavioral finding is paradoxical undressing, where individuals take off their clothes in the later stages.¹

The cardiovascular response to decreasing internal body temperature includes profound peripheral vasoconstriction accompanied by tachycardia and hypertension, followed by progressive bradycardia and hypotension. Body temperatures below 32ºC increase the risk of cardiac collapse. Anecdotally there is a phenomenon called rescue collapse, where cardiac arrest occurs during the transport and treatment of profoundly hypothermic patients due to myocardial irritability. Like the cardiovascular response, respiratory changes consist of initial tachypnea followed by a progressive bradypnea and eventual respiratory arrest. The renal system responds to hypothermia through cold diuresis, where peripheral vasoconstriction induces central hypervolemia, which results in significant renal fluid losses.¹

It is important to note that hypothermia of increasing severity decreases metabolic demands, resulting in neuroprotective and cardioprotective effects that allow patients to survive prolonged periods of cardiorespiratory arrest without significant hypoxic brain injury.³

Interventions

The crew carefully moved this patient to the ambulance to begin rewarming; however, once there she was found to be pulseless and in cardiac arrest. Cardiac arrest was likely due to movement of the patient resulting in rescue collapse. 

In cases like this it is essential to take 30–45 seconds to ensure the patient is in cardiac arrest before initiating CPR. Patients can be bradycardic and in low-flow states, resulting in pulses that can be difficult to palpate. If the patient is mistaken to be in cardiac arrest and CPR is initiated, the patient can degenerate into cardiac arrest via rescue collapse due to mechanical irritation. 

Once our patient was confirmed in cardiac arrest, providers began CPR immediately. The crew provided respiratory support via bag-valve mask ventilation until an i-gel was placed and endotracheal intubation eventually performed. Medics established parenteral access via peripheral intravenous and intraosseous lines. The patient was administered naloxone due to the possibility of an unknown overdose. Other pharmacologic interventions included epinephrine, amiodarone, magnesium sulfate, and a 1.5-L warm fluid bolus of normal saline. 

During EMS care the patient was primarily in ventricular fibrillation and was defibrillated 4 times in the field and transit. The EMS team rewarmed the patient during transport with heat packs and blankets while she received continuous compressions via automatic CPR device. Despite multiple attempts a core temperature was not established, likely due to the patient being colder than the low range of the EMS electronic thermometer. 

Treatment for hypothermic cardiac arrest is significantly different from more common arrest causes. The mainstay of treatment for these patients is active and passive rewarming. Increased core temperature allows cardiac contractility to return as physiologic enzymatic processes resume. The American Heart Association (AHA) recommends 3 attempts at defibrillation and 3 doses of cardiac medication, then deferral of any further intervention until the patient’s core body temperature is above 30ºC. Termination of ALCS should only be considered when the patient has not achieved ROSC and core temperature is greater than 32ºC.⁴ The most effective methods to monitor the patient’s core temperature are via esophageal and rectal temperature probes.

Rewarming can be achieved through various interventions and should be based on the patient’s level of hypothermia. The EMS crew was able to use heat packs and blankets to begin the process; however, there are multiple additional avenues for rewarming if available. Warm fluids (40–42ºC) administered through the IV is an option that may be accessible in the field. Recent evidence even suggests ambulance cabin heaters can be used to adequately warm fluids.⁵ 

Once in the emergency department, more invasive warming interventions include warmed and humidified oxygen, thoracic lavage, peritoneal lavage, and bladder lavage. In larger institutions ECMO may be an option in critical hypothermia. It is crucial to rewarm the patient’s core before rewarming extremities due to the risk of afterdrop, when peripheral vasodilation causes the return of peripheral cold blood centrally, further decreasing the core body temperature.⁶

Clinical Course and Outcome

After arrival at the hospital, the patient received escalated rewarming measures, continued CPR, and multiple rounds of defibrillation before ROSC was achieved over 3 hours from when initial resuscitation efforts began. The patient was admitted to the intensive care unit. She had numerous complications from prolonged severe hypothermia and cardiac arrest, including aspiration pneumonia, necrotizing pancreatitis, and acute kidney injury requiring hemodialysis. Despite the exceedingly difficult clinical course, she had a remarkable neurological recovery and essentially returned to her prearrest baseline.   

Take-home Points

1. Use great care when moving hypothermic patients, as mechanical agitation can induce fatal arrhythmias. 
2. Take 30–45 seconds to ensure the patient is in cardiac arrest before starting CPR. 
3. Rewarming is the mainstay of treatment in hypothermia-induced cardiac arrest. The AHA recommends 3 rounds of defibrillation and cardiac medications and then deferring further interventions until the patient’s temperature is >30ºC. 
4. Rewarm the patient’s core before the periphery to avoid afterdrop.  
5. Termination of resuscitative efforts should not be considered with a core temperature <32ºC. 

References

1. Tintinalli, JE, Stapczynski, JS, Ma OJ, et al. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8th ed. McGraw-Hill Education; 2016.

2. Forti A, Brugnaro P, Rauch S, et al. Hypothermic Cardiac Arrest With Full Neurologic Recovery After Approximately Nine Hours of Cardiopulmonary Resuscitation: Management and Possible Complications. Ann Emerg Med. 2019; 73(1): 52–7. doi: 10.1016/j.annemergmed.2018.09.018

3. Frei C, Darocha T, Debaty G, et al. Clinical Characteristics and Outcomes of Witnessed Hypothermic Cardiac Arrest: A Systematic Review on Rescue Collapse. Resuscitation. 2019; 137: 41–8. https://doi.org/10.1016/j.resuscitation.2019.02.001

4. Part 8: Advanced Challenges in Resuscitation. Circulation. 2000; 102(1): 229–52. https://doi.org/10.1016/s0300-9572(00)00288-4

5. Lyng JW, Perlmutter MC, West MA. A simple improvised prehospital method to warm intravenous fluid. JACEP Open. 2021; 2(5): e12536. doi:10.1002/emp2.12536

6. Brown D, Ellerton J, Paal P, Boyd J. Hypothermia Evidence, Afterdrop, and Practical Experience. Wilderness Environ Med. 2015; 26(3): 437–9. https://doi.org/10.1016/j.wem.2015.01.008

Sean O’Leary, MD, is a resident at HCA Houston Healthcare in Kingwood, Texas.

Marlee Laures, DO, is a resident at HCA Houston Healthcare in Kingwood, Texas.

Kevin Mifflin, LP, is a district chief with Montgomery County Hospital District EMS in Conroe, Texas. 

Payden Seals, EMT-P, is an in-charge paramedic with Montgomery County Hospital District EMS in Conroe, Texas. 

James Seek, LP, is division chief of Montgomery County Hospital District EMS’s clinical department. 

Robert Dickson, MD, is EMS medical director at Montgomery County Hospital District EMS and faculty at HCA Houston Healthcare in Kingwood, Texas. 

Casey Patrick, MD, is medical director for Harris County ESD 11 Mobile Healthcare and assistant medical director for the Montgomery County Hospital District EMS in Conroe, Texas.