So Take Off All Yo’ Clothes: Exertional Heat Stroke Part 2

Author: Esteban Davila

Peer Editor: Alec Feuerbach

Illustrations: Vincent Xiao 

This is a continuation of Part 1.

Key Initial Steps

ABCs and Supportive Care

Like any other resuscitation, attention should be primarily towards assessing the ABCs. Patients with impaired awareness, airway secretions, aspiration, worsening respiratory distress, or status epilepticus may require intubation.[1] However, attempts to aggressively treat the hyperthermia may resolve some of these indications and should be performed concurrently while preparing for intubation.[2] Rocuronium may be preferable to succinylcholine given the concern for worsening hyperkalemia.[3] 

IV fluids may be beneficial if there is evidence of dehydration, though attention should be paid to avoid over-resuscitation and pulmonary edema.[4] Use of vasopressors may be necessary to treat hypotension.[5] Exposure, through removal of any clothing, is an important initial step towards cooling and should be addressed early. Cardiac defibrillator pads should be placed before cold water immersion.[2] Bladder catheterization may be useful in monitoring urine output. 

Rapid Cooling

After the initial ABCs, all attention needs to be paid to rapid cooling and temperature monitoring. The target appears to be initiation of cooling within 30 minutes of collapse [6,7] with early resolution of hyperthermia associated with decreased mortality,[8] though this target time was extrapolated from retrospective reviews. There does not appear to be a consistent temperature cut-off to stop cooling,[9,10] and direct evidence is scarce. One prior study by Proulx et al that included seven patients who exercised themselves to a core temperature of 40 degrees celsius who then were placed into cold water baths recommended an exit temperature of 38.6 degrees celsius to avoid hypothermia.[11] Continuous temperature monitoring should include either esophageal or rectal thermometer. 

So, we know that we need to rapidly cool this patient, but that requires some serious logistics and resource allocation, not to mention considering the evidence behind available cooling strategies. We’ll discuss each feasible option. 

Figure 1: Comparison of different cooling modalities.[12]

Cold Water Immersion (CWI)

Evidence: Prior studies on CWI included different temperatures of water (14 to 17, 9 to 12, and 1 to 5 degrees celsius). A 2020 systematic review by Douma et al showed faster cooling rates using all water temperatures compared to passive cooling. This study had significant limitations including inclusion of healthy patients with induced, exertional hyperthermia as well as a lack of randomized controlled trials.[12] Application of CWI varied and included use of tarps, commercial circulating water tubs, inflatable pools, and large containers or tubs. Depth of immersion included either just the posterior surface of the whole body, from hip joints to the shoulders, up to chin with all extremities submerged, or lower extremities up to iliac crest. Prior case reports also demonstrated success using a body bag and sheets soaked in ice-cold water.[13,14,15] 

Logistics: In many hospitals the use of a body bag to facilitate CWI will be the most easily accessible and rapid method. First place the body bag on a new stretcher. After initial stabilizing steps and insertion of a temperature probe, the patient should be transferred into the body bag. Large amounts of ice can then be poured into the body bag around the patient. Here, the use of any available personnel is paramount, as ice in large amounts will need to be transported from the closest available source (cafeteria, ice machine, corner store across the street), ideally ahead of time if pre-notification is given. A patient belonging bag is easily accessible and could work well for transport of ice. The bag is filled until the patient’s body is submerged excluding the face, then the bag is zipped up to the neck. The patient will remain here until a rectal temperature of 38.6 celsius is attained. 

Figure 2: Body bag cold water immersion.[14]

Evaporative Cooling (Misting and Fanning) 

Evidence: Evaporative cooling demonstrated marginally faster cooling rates compared to passive cooling.[12] However, when compared to CWI, evaporative cooling appeared to have lower cooling rates.[12,16] If used with warmed air in a variation called a body cooling unit, this method is purported to decrease the shivering response by theoretically reducing peripheral vasoconstriction.[9,17] In this method, the water sprayed is at a temperature of 15 degrees celsius, and the air fanned on the patient is 32 to 33 degrees celsius, though this method did not show a difference in cooling times when compared to traditional evaporative cooling.[17] Other options include draping the patient with a damp sheet. 

Logistics: Remove the patient’s clothing, then spray the patient with tepid water while circulating air onto the patient with a fan. This requires the availability of both a spray bottle/atomizer and a large fan that can both adjust the temperature of the blown air and fit in the patient’s room. This method should be continued until the clinical picture improves. 

Figure 3: Evaporative Cooling. Source: https://www.emdocs.net/heat-related-illness-how-to-cool-em-and-what-to-do-after/#gallery-3

Commercial Ice Packs

Evidence: No statistical difference was found between commercial ice packs applied to the neck, axilla, and groin compared to passive cooling.[12] However, Lissoway et al showed significantly steeper decline in temperature when applying chemical cold packs to skin surfaces of cheeks, palms, and soles of feet.[18] Ice packs may provide additional benefit when used in combination with other definitive cooling methods. Commercial ice packs include frozen water in resealable bags, pre-frozen phase-change gel, and instant chemical ice packs. 

Logistics: These are generally easily available. Evidence suggests preferential application of ice packs to cheeks, palms, and soles of the feet first, then groin, axilla, and neck. Attention should be paid to wrapping the ice pack in a thin cloth to avoid iatrogenic burn.[19] 

Cooling Vests, Jackets, and Arctic Sun

Evidence: Cooling vests and jackets did not show statistically significant decreases in body temperature compared to passive cooling, and there was significant heterogeneity in individual vests and jackets used among the studies included in a meta-analysis.[12] The use of non-invasive cooling devices such as the Arctic Sun was not included in this meta-analysis.[12] The Arctic Sun device utilizes energy transfer pads with temperature-controlled water circulating at high flow rates inside the pads, a manner described as similar to cold water immersion.[20] Case reports of its use for heat stroke and neuroleptic malignant syndrome demonstrated decreased reduction in core temperature to below 38.5 degrees celsius within 2 hours.[20,21,22] 

Logistics: Given cooling vests/jackets are not readily available in most EDs, we will focus on the Arctic Sun, which is more widely available. Pads are placed over 40% of the patient’s total body surface, the temperature probe is attached and then you select normothermia as your target temperature. More on the setup can be found here. Cardiac monitor and IV access can be easily maintained. 

Figure 4: Arctic Sun. Source: https://www.bd.com/en-us/products-and-solutions/products/product-families/arcticgel-pads

Fanning, Reflective Blankets, Hand Cooling Devices, and Cold Shower

Evidence: Only cold showers resulted in faster mean core cooling than passive cooling alone and should only be used in combination with other treatments.[12] 

Logistics: Pretty self explanatory. If the patient can ambulate, they are unlikely to have true heat stroke.   

Cold IV Fluids and Endovascular Cooling

Evidence: For cold IV fluids, a randomized controlled crossover trial by McDermott et al showed that cold IV fluids had faster rates of whole body cooling rates compared to passive cooling, though there was no significant difference in rectal temperatures between study arms and neither achieved the goal temperature of 39.17 degrees celsius in less than 40 minutes.[23] This study utilized 1L of normal saline with crushed ice stored in a cooler for at least one hour. The use of endovascular cooling in conjunction with evaporative cooling compared to only evaporative cooling was prospectively studied by Yokobori et al, showing a statistical increase in the percentage of patients achieving target temperature of 37 degrees celsius at 24 hours. Limitations of the study include only 21 patients among ten sites over two years, lack of randomization, and comparison to evaporative cooling instead of CWI.[24] Other case reports demonstrate similar improvements in temperature in patients with heat stroke through the use of endovascular cooling,[25,26,27] though common criticisms include the lack of CWI before initiating these measures.[28] 

Logistics: If given pre-notification, IV fluids may be cooled prior to patient arrival. Otherwise, this requires planning to keep cooled IV fluids available at all times. The use of endovascular cooling requires both the time to insert a cooling catheter and the availability of that catheter. 

Back to the Patient

You order 2 g of calcium gluconate for suspected hyperkalemia as well as fentanyl and propofol for post-intubation analgosedation and decide to utilize the Arctic Sun. While this is arranged, a rectal temperature probe is placed, ice packs are placed on the cheeks, palms, soles, groin, axilla, and neck, and cold IV fluids are infused. The potassium is 6.3 mmol/L, bicarbonate 14 mmol/L, BUN/creatinine of 31/2.96 mg/dL, glucose 80 mg/dL,  platelets 78 x109/L, and a creatinine phosphokinase 1,561 mcg/L. As you begin treating the hyperkalemia, acute kidney injury, and rhabdomyolysis, you wonder what other complications may occur. 

Complications

Shivering: Shivering theoretically does not occur in exertional heat stroke patients with ice water immersion unless cooled for too long.[16] If shivering occurs, IV diazepam or chlorpromazine may resolve the shivering.[29]. 

Electrolyte abnormalities: Common electrolyte abnormalities include hyper- and hypokalemia, hyper- and hyponatremia, hypochloremia, hypocalcemia, and hyperphosphatemia. Correct potassium and calcium accordingly. 

Rhabdomyolysis: Secondary to exercise and muscle injury, CPK levels begin to rise within 2-12 hours after injury and peak within 1-5 days, so the testing should be continued until downtrending. Treatment goals include adequate fluid resuscitation titrated to a urine output of 200 to 300 mL/h.[30] A retrospective cohort study by Mok et al demonstrated that the use of cold IV saline for fluid resuscitation may reduce peak creatinine and length of stay, though they noted no changes in CPK levels.[31]

Arrhythmias: Common arrhythmias include sinus tachycardia, atrial fibrillation, and supraventricular tachycardia, with more severe cases including ventricular tachyarrhythmias, stress-induced cardiomyopathy, and cardiac arrest.The AHA recommends removal from water before CPR and cardioversion,[32,33] although this may not be preferable in heat stroke where rapid cooling is paramount. One case report demonstrated effective cardioversion of a ventricular tachycardia and CPR in a patient still submerged in ice water.[2] 

Back to the Patient

Two hours after arrival, the patient’s temperature is 101 degrees Fahrenheit, at which time the patient began to have purposeful movements. He was admitted to the ICU where his course was complicated by DIC. He developed acute liver injury with peak ALT of 2,816 U/L and AST of 2,213 U/L along with elevated INR. His CPK peaked at 22,075 mcg/L, though he never became anuric. He eventually clinically improved and was discharged 6 days later ambulatory with normal neurologic function. 

Take Home Points: 

- Though there are no head-to-head comparisons, cold water immersion appears to be the most effective method of rapid cooling 

- Consider placing defibrillator pads before water immersion 

- Consider the use of a body bag for rapid initiation of cold water immersion 

- Employ an ‘all hands on deck’ strategy to obtain ice from the nearest source