Overview of Presentation
Exertional heat stroke (EHS) is one of the top three causes of sudden death in sports (1,9,15). Unlike other life-threatening conditions, EHS is most successfully treated on-site with cold water immersion (2–8,10,12,13,17–19). This has resulted in over 500 documented cases being successfully treated (8,9). Complications from EHS arise when effective treatment is not available, not utilized or when EHS is not recognized (14,16). Despite these observations, an ongoing controversy is balancing treatment “on-site” with rapid cooling versus rapid transportation to definitive care. This case study provides a unique examination of two individual recoveries from EHS associated with two dichotomous treatments received while participating in the same marathon.
The 2008 Marine Corps Marathon on October 26th started at 8 a.m. Two military men running the marathon collapsed in separate incidences, one around mile 24 and the other at the finish. One was immediately taken to the finish line medical tent (MT) and the other was sent directly to the hospital emergency room (ER). Both men signed a consent form approved by our institutional review board to have their data published anonymously.
Both MT and ER were questioned regarding their training preparation. Neither had a history of heat illness. Fourteen days prior to the race, MT was training in California, with an average high temperature of 34.2°C (range: 28.3 to 37.8°C), and ER was training in Maryland, with an average high temperature of 20°C (range: 13.4 to 29.1°C). Both locations were warmer than during the race day (temperature at collapse = 14.4°C, 64% relative humidity). MT and ER both reported training for 4 months and had many similar demographics (25 vs 23 years, 82 vs 77 kg, and 185 vs 170 cm tall, respectively). The day of the marathon, MT and ER did not report feeling sick, did not take any supplements, medications or ergogenic aids, had an average of 8 h of sleep per night 72 h prior, and had a goal of finishing the marathon within ∼3:30 to 3:40 h:min. MT did report having two to three cups of coffee, while ER had none. Lastly, MT had a friend pacing him during the race, while ER did not. When questioned regarding their hydration strategies for the race, MT reported that he helped a friend move the day before the race and noticed that his urine was dark so he drank a lot of water the night before to help rehydrate. ER reported drinking a mix of electrolyte drinks and water at the water stations.
When asked what symptom was the strongest upon their collapse, MT replied “anger/irritability,” while ER reported “fatigue.” In terms of their memory of their collapse, MT reported, “I remember running up the final hill towards the finish … and falling over …. The last thing I remember was looking down as my buddy … helped me walk across the finish line.” ER reported, “Except for small blocks of memory, [I remember] nothing until two days later.”
Diagnosis
MT finished the marathon in just under 4 h and was taken directly to the medical tent. Other emergency medical conditions were ruled out, his rectal temperature was assessed (41.1°C), and he was diagnosed with EHS. When ER collapsed (around mile 24, but on pace to finish in 3.5 h), an ambulance was called and he was transported directly to the hospital (admitted at 11:57 a.m.). His initial rectal temperature was taken (41.2°C at 12:27 p.m.), and he was diagnosed with EHS.
Treatment
MT was rapidly cooled via aggressive ice water dousing, which was described previously (14). MT’s peak temperature was 42.2°C at minute 8 of cooling; however, after 30 min of cooling, MT’s rectal temperature had returned to 38.9°C, at which point cooling was ceased. MT’s peak temperature was likely recorded at 8 min of cooling because of two factors: 1) Rectal temperature reflects deep body temperature, which has an established delay in temperature response during cooling; 2) MT’s rectal thermometer was reinserted at minute 7 because of suspicious temperature readings, and this adjustment may have allowed for a deeper placement of the probe, obtaining a higher temperature. From peak rectal temperature to final rectal temperature, the resulting cooling rate was 0.15°C·min (see Fig. 1). MT was sent to the hospital for blood work but was released and returned home within 4 h.
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Figure 1: Cooling curves for two EHS cases occurring during the same marathon in separate incidences. MT = treated onsite at the medical tent. ER = treated at the emergency room. The overlay contains ACSM’s guidelines from the heat illness position statement regarding an early intervention cooling initiated at 10 min curve versus late intervention cooling (initiated at 50 min) curve (Shaded area between the late and early intervention cooling curves represents EHS victims that are exposed to more than 60°C·min above 40.5°C, and risk for morbidity and mortality is greatly elevated). ACSM early intervention = ACSM-calculated heat exposure limit (120°F under the cooling curve). ACSM late intervention = ACSM-calculated heat exposure that has an increased risk of morbidity and mortality. ACSM critical level = critical body temperature at which time above this body temperature increases risk for morbidity and mortality.
ER was initially treated with ice packs on his neck and armpits until a cooling blanket was applied (at 12:35 p.m.). At 12:45 p.m. (∼1 h postcollapse), his rectal temperature was 40.6°C; by 1:15 p.m., it was 39.7°C. By 1:40 p.m. (∼133 min postcollapse), ER’s temperature was 39.2°C. This equated to a cooling rate of 0.021°C·min (from the first temperature taken at the hospital to the final temperature). However, this does not account for the passive cooling from the point of collapse and likely overestimates his cooling rate (see Fig. 1). ER was transferred to another hospital on day 3 (10/29/2008) for a possible liver transplant due to elevating liver enzymes. It was decided that he would not need the transplant, and he was discharged on day 7.
Management
Creatine phosphokinase (CPK), a marker of muscle damage and indicator of rhabdomyolysis, as well as markers of liver function, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) were evaluated for both MT and ER (see Fig. 2).
Figure 2: Liver enzyme levels the day of two EHS cases and 5 d after. MT = treated onsite at the MT. ER = treated at the ER.
Both ER and MT recalled symptoms experienced during recovery (Table). MT was cleared to return to activities of normal living 3 d following his EHS and began running 2 to 3 wk after his EHS (MT reported performing 3- to 4-mile runs at a “slow pace,” ∼8 to 9 min per mile); he reported no complications with exercise. Alternatively, ER reported taking between 60 and 90 d before he was back to normal daily living and was unable to begin exercising again until 34 d after his EHS. ER reported taking precautions; he started slow and gradually increased his workouts.
Table: Subject signs and symptoms throughout recovery from exertional heat stroke.
ER and MT both had heat tolerance tests performed in 40°C and 40% humidity for 120 min (in separate laboratories). ER had his test on 2/5/2009 (102 d post-EHS) where he performed the established Israeli protocol of walking at 3.1 mph with a 2% grade. MT had his test on 8/10/2009 (288 d post-EHS) where he walked at 3.3 mph with a 4% grade. The authors are not able to speak to the increased exercise demands applied in this test but considered these within the interpretation of the results. The standards for a negative test were as follows: a heart rate <160 bpm and a rectal temperature <38.6°C (see Fig. 3). During the test, ER drank 2.6 L of fluid while MT drank 2.8 L.
Figure 3: Heart rate and rectal temperature responses during two separate heat tolerance tests following Exertional Heat Stroke (EHS) cases occurring during the same marathon in separate incidences. (A) Heart rate response from EHS treated in the ER. (B) Heart rate response from EHS treated at the finish line MT. (C) Rectal temperature response from EHS treated in the ER. (D) Rectal temperature response from EHS treated at the finish line MT. Both heat tolerance tests were performed in 40% humidity and 40°C; however, ER walked at 3.1 mph at a 2% grade while MT walked at 3.3 mph at a 4% grade. The bold horizontal lines represent passing criteria that values should not exceed.
Currently, MT has returned to full military duty, while ER decided not to return. The drastic dichotomy in outcomes for these men started with the initial treatment provided. MT’s cooling treatment was successful in reducing his temperature quickly (within 30 min), while ER took approximately 2 h. MT spent 20 min over 40.5°C while ER spent ∼80 min over this temperature. This is the temperature defined as the “critical threshold” for EHS by the American College of Sports Medicine (ACSM), and the literature demonstrates that survival rate drastically drops the longer the body temperature remains over 40.5°C (see Fig. 1) (7,11). It is clear from Figure 1 that ER’s cooling curve starts and remains above the ACSM-recommended cooling curve. One last but very important note is that the cooling curve for ER is based on the delayed rectal temperature recorded in the hospital and likely drastically underestimates the peak temperature achieved (and therefore thermal load experienced). Based on published passive cooling rates, ER’s temperature may have been elevated as high as 42.82°C.
The liver function tests demonstrated that MT’s ALT and AST did not spike or elevate greatly, especially when compared with the spike observed in ER 1 d postrace. MT’s CPK had a much larger elevation earlier on (peaked 1 d postrace) but recovered very quickly thereafter, while ER’s CPK gradually increased during the 4 d following the race (though not to the same level as MT’s peak CPK level). These observations also point to the importance of monitoring patient’s organ function 24 h following the event to determine whether organ function is improving and within safe levels.
Interestingly, MT and ER’s impressions of their recoveries did not mirror these comparative results as expected. MT reported his symptoms lasting longer than ER’s, but MT was able to return to activity and work quicker with few to no complications, perhaps indicating a differing interpretation of his recovery or simply differing personal impressions of their recoveries (see Table).
The heat tolerance test results demonstrated that MT clearly tolerated the imposed exercise load and stress as indicated by his heart rate and rectal temperature plateau. ER did not have a distinct plateau in heart rate or rectal temperature, and his rectal temperature approached the cut-off temperature (despite a lower exercise load than MT). While ER had a more severe outcome from his EHS, his test was performed sooner, 102 d after the EHS case, at which point MT was already running and exercising without complications.
This comparative analysis supports current EHS sports medicine recommendations (supported by ACSM [1] and the National Athletic Trainers’ Association [NATA] [2,7]) for on-site cooling prior to transport for definitive hospital emergency room care. The timing for discharge (same day versus 7 d), return to physical activity (∼21 d with no complications vs 34 d with activity restriction), and ability to return to their pre-EHS life (return to duty versus no return to duty) is drastically different. The emotional and financial implication for such recoveries is great for those in athletics, the military, or the laborers who risk losing their career if not cared for properly. Currently, the standard of care for EHS victims includes immediate rectal temperature assessment, cooling on-site first (with aggressive ice water immersion), and transporting second, when appropriate medical care is available (13). Providers who have responsibility for the provision of on-site medical care should have access to appropriate equipment and emergency action plans to treat EHS to minimize morbidity and mortality.
The authors would like to thank the two case study individuals for allowing the authors to share this manuscript.
The authors declare no conflict of interest and do not have any financial disclosures. The assertions and opinions herein represent those of the authors and do not represent those of the Uniformed Services University, the United States Army, or the Department of Defense.
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