28 yo male patient had been out with friends and was last seen leaving the bar around midnight. A roommate noted patient was not at home when he awoke at noon. EMS was activated after the roommate found the patient unresponsive, sitting in his car outside the bar. Roommate reports no known recent illness, no chronic medical problems.
EMS calls to medical control with report: BP unable, HR 32 with weak femoral pulse, O2 sat unable, RR 6, GCS 3. EMS requests instructions for initial management. As you are running through the differential diagnosis with them—Tox, trauma, tox, cardiac, tox, PE, tox—the paramedic adds “hurry up, we’re freezing our ***s off out here!” Oh yeah, it’s -22°F outside.
On arrival to the ED the patient is placed in the trauma room under warming lights. His clothing is removed and warm blankets are placed over him and around his head and neck. Paramedics have placed 2 IVs and warm saline bolus is initiated. Primary survey is as follows
A-endotracheal tube in place, placement confirmed with lung sounds, ETCO2 low but has waveform with ventilation
B-bilateral rales, on vent with warm, humidified O2. Sat monitor does not read
C-weak femoral pulse, sinus bradycardia 30s on monitor, skin is cold and mottled, BP does not read
D-GCS 3, pupils nonreactive 5mm
E-no visible trauma, T 82°F (27.8°C) rectally
2. How would you classify the degree of hypothermia in this patient and why does it matter?
3. What are the priorities of resuscitation and what is the preferred method of rewarming this patient? Options?
Labs are drawn and pending, EKG shown below.
4. What do you anticipate as laboratory abnormalities in this patient?
As you are preparing to institute your rewarming therapy of choice, the monitor alarms and you see the rhythm has changed to V fib.
5. How is the management of cardiac arrest different in hypothermia? When do you stop?
The patient receives CPR and defibrillation x3 but continues in V fib. The decision is made to continue CPR without medications or further shocks and to continue warming with external methods and warm IV/oxygen until cardiopulmonary bypass can begin. The perfusion team arrives and the patient is transferred to wherever it is they do that. He does fine and has a full neurologic recovery. Now he’s a rocket scientist. Good job.
Discussion:
My review here is limited to primary or accidental hypothermia, not that related to sepsis or other disease states. Environmental exposure is primarily responsible for hypothermia and is exacerbated by alcohol, homelessness, impaired cognition, extremes of age, etc. Don’t forget that extreme cold is not required for hypothermia; it can happen in all climates and all times of the year.
As presented, there is not much of a diagnostic dilemma for this patient. Severe hypothermia (less than 28 degrees Celsius / 82.4 degrees Farenheit) has a fairly uniform presentation with coma, decreased respirations or apnea, decreased blood pressure/HR and risk for ventricular arrhythmias. More subtle presentations may exist with mild (Less than 35 degrees C / 95 degrees F) and moderate (less than 32 degrees C/89.6 degrees F) hypothermia. Mental status changes progressing from confusion to hallucination or paradoxical undressing can be observed. Cardiopulmonary response may be elevation of HR/BP/RR as initial compensation progressing to global decrease in cardiac output and respiratory rate. Shivering as a method of heat generation disappears with moderate hypothermia. EKG classically demonstrates J or Osborn waves with moderate to severe hypothermia though this may be present only 30 percentish of the time. The waves can be greater amplitude with lower temperature. Diuresis occurs, probably related to ADH dysfunction. Lab abnormalities are confusing.
Discussion of questions
1. Initial management is not really different from general ABCs of resuscitation. Protecting from the cold environment, removing wet or cold clothing and instituting rewarming are all key. There is dogmatic concern about precipitating ventricular arrhythmia by interventions such as intubation, CPR, patient movement or invasive lines. In practice, the arrhythmia may happen anyway and the patient won’t survive without things like ventilation and circulation so you need to do what you have to do. Authors recommend “gentle treatment” of patients without unnecessary movement or jostling so I guess my typical two-handed shoulder shake and screaming “walk away from the light!” is out. Intubation is safe and necessary but don’t root around in there any more than you have to. Consider femoral lines to avoid cardiac stimulation with wires. No transvenous pacers.
2. This is addressed above. Definitions use the 35°/32°/28°C cutoffs but clinical presentation is of course a spectrum. There are survival reports down to 13-14°C. The treatment of the patient will be based on clinical parameters more so than the absolute temperature but generally severe hypothermia will require active internal rewarming methods where more mild or moderate cases can be handled less invasively. Core temperature monitoring is challenging as different sites can cool/warm at different rates. Monitoring multiple sites (rectal, bladder, esophageal, bloodstream) might be a good idea.
3. Priority for resuscitation is ABCs and rewarming. The rewarming should be as fast as possible and starting it shouldn’t be delayed for other stuff. Patients will almost universally need volume replacement but there is such a thing as too much, especially in severely decreased cardiac output. Methods for rewarming are plentiful, authors recommend using whatever you have experience with. That said, hypothermic cardiac arrest is not that common and there may not be much experience around. All patients should receive passive external warming, which is really preventing further environmental losses. Blankets (especially covering the head and neck), warm environment, removal of wet clothes and humidified air are all appropriate. Active external methods are also safe and can be added to most patients, especially heat lights and forced-air blankets. Warm water immersion works but adds to the challenge of caring for the patient who is now underwater. Dogmatists will bring up the concern of afterdrop with external warming—the decline of core temp seen with warming the extremities. Studies seem to see variable but probably unimportant amounts of afterdrop with active external methods. Adding some warm IV fluids is a good way to combat it. Active internal methods are many and range from warm IV fluids and air to bypass. There doesn’t seem to be much head-to-head comparison of methods out there, hence the recommendation to use what you have experience with. For fully arrested patients, cardiopulmonary bypass will probably be the option as it can provide oxygenation and circulation. Continuous AV rewarming, dialysis and even the innercool are options for patients with their own circulation. Warm fluid lavage of various body cavities seems to be one of those “only if you don’t have a better idea” sort of things. HCMC has a paper on ED thoracotomy with mediastinal lavage but I’m not trying that.
4. I intentionally didn’t get too specific with labs as I don’t really understand that sort of thing. For those interested, there are fascinating acid-base changes with hypothermia and a great number of people would love to write papers about it for you. Importantly, “neutral” pH rises with decreasing temperature so interpretation of ABGs needs some care and attention to the temperature at which the test is performed. Hemoconcentration will elevate hemoglobin/hematocrit. Glucose is probably high initially but can be low or high as hypothermia becomes more severe. Electrolytes are “unpredictable” and renal function will decline due to decreased renal perfusion and intravascular volume depletion. Coagulation studies may or may not be abnormal as heating blood for the test may normalize things. In vivo, cold patients will have a coagulopathy related both to platelets and the clotting cascade.
5. Ventricular arrhythmias are most common below 28°C. The recommendation is a trial of defibrillation but it probably won’t work until the patient is above 30°C. Lidocaine won’t work and epinephrine will have decreased clearance so should be given at longer intervals. Below 30°C the recommendation is no meds at all, unless you have some bretylium lying around which might help. CPR should continue while warming and you can give sparky another chance once the temperature is over 30°. There are reports of survival with good neurologic function after many hours of CPR and I suspect the Lucas can keep things going for a long time. In general, people who survive hypothermic cardiac arrest have surprisingly good neurologic outcomes, especially if they start out young and healthy. There is not clear evidence on which cold patients are actually dead. Some have looked at a K+ greater than 10 as a non-survivable level but I don’t think this is generally accepted as absolute. If patients have significant comorbidities, especially major trauma, they are much less likely to recover and may not need warming to terminate resuscitation. When in doubt, get them to 35°C and see what happens.
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References:
Kempainen and Brunette, The Evaluation and Management of Accidental Hypothermia. Respiratory Care Feb 2004; 49:192-205.
Brunette, Hypothermic cardiac arrest: An 11 year review of ED management and outcome. Am J Emerg Med 2000; 18:418-422.
Dufresne, Powerpoint presentation. www.mcgill.ca/files/emergency/Hypothermia.ppt
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