Baby It’s Cold Outside: Review of Current Literature and Protocols of Resuscitation of the Accidental Hypothermic Patient
By M. Subramanian, MD and J. Haber, MD
With Punxsutawney Phil predicting another 6 weeks of winter, it’s time for a review of literature on resuscitation of the hypothermic patient. Hypothermia can be a source of anxiety for the emergency physician. The risk of malignant arrest or arrhythmia is very high (and should be expected to occur) in any patient with a core body temperature under 32 degrees Celsius, despite rewarming and resuscitation; this is due to a phenomenon called Rescue Collapse or Afterdrop. Morbidity and mortality are very high in these patients, with less than 50-60% of patients survive neurologically intact after experiencing hypothermic arrest. While there are very few studies on hypothermia resuscitation, there exists some interesting opinions on protocols.
Let’s start at the beginning….
Many of the protocols start with recognizing hypothermia, either by measuring core temperature (which is difficult to do in the field) or by feeling a cold trunk. Hypothermia is defined as a core temperature of less than 35 degrees Celsius. A few studies show that esophageal measurement of core body temperature is equivocal to rectal and bladder temperature, but rectal and bladders temperatures may lag behind core temperatures during the process of rewarming.
The next step should be assessment of vital signs. Hypothermic patients may have cardiac instability or irritability, which places them at a very high risk of developing a malignant arrhythmia. Initiation of CPR in an altered hypothermic patient with a bradycardic pulse may actually cause cardiac arrest. Many of the protocols recommend gentle handling of the altered hypothermic patient, and one even recommends checking for a plus for 60 seconds before initiating CPR. Staging the degree of hypothermia is important to determine management; the standard scale used is the Swiss Hypothermia Scale.
Classification depends more on clinical symptoms rather than core temperature. A patient with a core temperature less than 35 degrees Celsius who is alert (Stage 1) can be treated with passive rewarming measures, such as blankets, heat lamp, and active movement. It is important that the patient have a shivering response as this is key to recovery.
For the altered hypothermic patient with a pulse (Stage 2 or 3), many protocols recommend passive and minimally invasive rewarming. These include blankets/Bair huggers and warm lights. It is generally not recommended to attempt bladder lavage, peritoneal lavage or thoracic lavage in these patients as such practices may aggravate the cardiac membrane and initiate malignant arrhythmia. Warm IV fluids does not substantially contribute to rewarming, but may be used for volume resuscitation as hypothermia may cause cold-diuresis. One protocol recommends normal saline boluses of 500 ml. Other protocols, however, recommend using crystalloids other than normal saline as patients may require massive amounts of fluids and large boluses of normal saline may worsen acidosis. Warmed humidified air has been seen in multiple studies to improve rewarming rates and is recommended by most protocols. Early airway management was also generally recommended as endotracheal intubation had low rates of instigating arrhythmias in hypothermic patients. As providers should expect a fatal arrhythmia to occur, securing the airway, placing of defibrillating pads and adequate IV access is recommended. Different protocols recommended rewarming the patient to 32-34 degrees Celsius, and then following therapeutic hypothermia rewarming protocols over the next 24 hours. Sinus bradycardia is a normal physiological process in the setting of hypothermia. It is not necessary to use atropine or cardiac pacing, as this will resolve with rewarming. Hypotension or ventricular arrhythmias reflect cardiac irritability, and while supportive management is the mainstay, providers must prepare for a probable malignant arrhythmia.
The hypothermic arrest patient provides a challenge to the typical ACLS resuscitation. The physiology of medication metabolism and the cardiac myocyte response to electricity in hypothermia decreases success of current practices. European guidelines recommend trying 3 rounds of epinephrine and cardiac defibrillation before core body temperature is rewarmed to 32 degrees Celsius. Other sources say to only give one round of epinephrine and one defibrillation attempt before core temperature reaches 32 degrees Celsius. Dr. Doug Brown recommends a combination of the two; one dose of epinephrine and one defibrillation attempt (in the setting of a shockable rhythm) at first, then continuous CPR with rewarming. With every 5 degree Celsius increase in core body temperature, he recommends checking for pulse and shockable rhythm, and if pulseless with shockable rhythm, giving another round of epinephrine and defibrillation. If that does not work, continue CPR and rewarming until core body temperature is 32 degrees Celsius, and a last round of epinephrine and defibrillation. If at that point the arrest is not reversed, the patient is presumed dead and CPR may be terminated. As the emergency medicine adage goes- “the patient is not dead, until warm and dead”. This alteration to the typical ACLS process allows for fewer interruptions of CPR and defined end point. Unfortunately, there is no solid evidence defining what is “warm enough”, but consensus appears to settle around 30-32 degree Celsius.
It is in the setting of Stage 3-4 that invasive rewarming techniques is found to be most beneficial. Multiple case reports and series have shown an advantage to patients who received extracorporeal warming. Techniques include continuous venovenous, continuous arteriovenous (which can be done in the ED), hemodialysis and cardiac bypass. Other techniques of invasive rewarming include lavages of the bladder, peritoneum (similar to a DPL) and thoracic cavities. While these latter techniques are recommended by a few protocols, Dr. Weingart of EMCrit discourages against bladder and peritoneal lavage. He states the risk of complications with peritoneal lavage is not worth the benefit of rewarming. Also, bladder lavage rewarming rates are not aggressive enough to justify the intervention. However, given the high mortality of stage 3 and stage 4, it may be reasonable for clinicians to decide to perform these procedures, as a last resort if all else has failed. Almost all protocols agree that extracorporeal warming is the best for rapid rewarming. Mortality rates improve from below 37% survival to 50-60% survival. Unfortunately many community practices do not have facilities to achieve this, and transfer to such facilities may be difficult to ensure. Hemodialysis is more readily available and has rewarming rates of 1.5 degrees Celsius/hour. Dr. Gentilello created a machine that took blood from an arterial line to a level 1 infuser, warming the blood and connecting it to a venous catheter. However it is difficult to find this adapter anymore.
If a patient does not rewarm at the established rates (given the rewarming interventions), providers should consider other causes preventing an increase in core body temperature. Most common causes of failure to rewarm include hypoglycemia, alcohol intoxication, infection/sepsis, Addison’s, malnutrition and myxedema coma. It is important to check a fingerstick glucose as well as labs for CBC, metabolic panel, thyroid function tests and blood cultures.
While there are many case reports of successful return of spontaneous circulation in hypothermic arrest patients, slow or stagnant neurologic recovery is a significant part of morbidity. Stage 1 patients have the best chances of survival with rates up to 100% neurologically intact. Organ failure is common within the first 24 hours of Stage 4 hypothermic patients, with pulmonary edema as the leading cause of death. Resuscitated hypothermic patients have an in-hospital mortality of 40%. However, given the existence of case reports highlighting the rare patient with full neurologic recovery from Stage 3 or 4 hypothermia, it is difficult to counsel family on withdrawing care. One study found that patients with hypothermia that were found indoors had worse outcomes. Other prognostic factors include serum potassium. A significantly elevated serum potassium is indicative of hypoxia and traumatic cell death. One protocol suggested termination if serum potassium was greater than 12 mmol/liter. Another factor is hypothermia from avalanche burial; indications that hypoxia preceded hypothermia (and therefore not likely to respond to CPR) include snow in the airway, asystole and burial time greater than 35 minutes.
While there are multiple protocols addressing the management of the hypothermic patient, there is little evidence to support one protocol versus another. More research is needed to determine the best evidence based approach to hypothermic patients. Therefore, consider contributing your hypothermia cases to the International Hypothermia Registry, and increase available data to help establish a standard of practice.
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