Cold Water Immersion: The Gold Standard for Exertional Heatstroke Treatment

Douglas J. Casa; Brendon P. McDermott; Elaine C. Lee; Susan W. Yeargin; Lawrence E. Armstrong; Carl M. Maresh

Disclosures

Exerc Sport Sci Rev. 2007;35(3):141-149. 

In This Article

Treatment of EHS

Overwhelming evidence indicates that the amount of time that rectal temperature exceeds a critical threshold temperature for cell damage dictates the severity of EHS injury.[4,13,17,24,28] Lowering the core body temperature to less than 40°C (104°C) within 30 min should be the primary goal of EHS treatment.[1,7] Optimal treatment begins with rapid and accurate assessment because minimal time will be lost in the process of initiating cooling.[1,3,7,8,9,28] This explains why rectal temperature must be done on-site and why the medical provider cannot rely on inaccurate modes of assessing core temperature (i.e., tympanic/aural, oral, temporal, axillary sites).[1,3,7,8,9,28]

The window of opportunity to provide immediate cooling postcollapse is narrow and must be done with a modality that has sufficient cooling potential.[8] The clinician also must consider which cooling modalities are feasible and optimal for each particular circumstance. The literature indicates that the care provider should use CWI unless a reason exists to use another cooling technique. The clinician also should consider the logistics of moving an athlete into and out of a tub; maintenance of the airway, breathing and circulation; and monitoring of temperature measurements.

Physiological Issues Related to Hyperthermia and EHS

Gaffin and Hubbard[13] eloquently describe a cascade of events that may occur when homeostasis is impaired because of sustained and severe hyperthermia during EHS. An examination of their model for the physiology and pathophysiology of heat stress and heatstroke provides rationale for the multisystem organ damage that commonly afflicts those who are not rapidly cooled. After the onset of cell destruction extensive enough to cause organ damage or failure, the prognosis worsens. This cascade of events causes most EHS deaths to occur during the 12-h to 1-wk period after EHS. It is quite rare for an EHS patient to succumb in the few hours after the incident, but the action taken in this period will dictate the degree of cell damage that will either lead to recovery or spiral toward catastrophic organ deterioration.[1,3,7,8,9,13]

Effectiveness of Different Cooling Modalities (Cooling Rates)

Extensive evaluations of cooling rates associated with various cooling modalities have been previously published.[9,17,26] Not all studies are truly comparable because of methodological differences that influence the cooling rates. These differences include questions such as:

  • Was the patients experiencing EHS or acute hyperthermia?

  • Was the condition classic heatstroke or EHS?

  • Specifics regarding the cooling process (What were the core body temperature starting and ending points? What was the specific technique? Was the entire body immersed or only the torso? Was the water circulated? What was the water temperature? Was the subject exercising? What are the subjects' body fat percent?, etc.).

The effectiveness of a wide variety of cooling modalities are compared in Figure 1.[9] This figure shows the superior cooling rates documented in water immersion studies. Other modes of cooling also may be effective, including that used by the Israeli military: a combination of spraying moderate-temperature water plus rapid air movement provided by a fan. This form of cooling encourages evaporative and convective cooling with good results.[16] In addition, medical staffs at the Twin Cities Marathon, Marine Corps Marathon, and Quantico Marine Base have placed cold, wet towels over the entire body and/or continuously doused with cold water and placed ice packs on peripheral arteries (and massaging the limbs with ice bags in some situations). This method results in cooling rates that are 2/3 to 3/4 as fast as CWI, and because medical care begins immediately, survival rates are excellent.[20] Medical staff should also consider cold showers or dousing athletes with cold water from a hose when CWI is not possible.

Figure 1.

Cooling rates associated with various modalities. Figure depicts experiments with healthy hyperthermic athletes and heatstroke victims. Reference's are associated with original article. (Reprinted with permission from Casa, D.J., L.E. Armstrong, M.S. Ganio, and S.W. Yeargin. Exertional heat stroke in competitive athletes. Curr. Sports Med. Rep. 4:309-317, 2005. Copyright © 2005 Current Medicine Group, LLC. Used with permission.)

The cooling rate of ice bags on the peripheral arteries (about 0.03°C/min [0.05°F/min]), one example of an inferior cooling method (see Fig. 1), causes the area under the curve (i.e., time vs rectal temperature) to be large and increases the likelihood of tissue and organ injury (Fig. 2). We do not recommend a modality that provides cooling of less than 0.1°C/min (0.18°F/min) when cooling begins immediately, and not less than 0.15°C/min (0.27°F/min) if cooling is delayed longer than 20-30 min after collapse (i.e., only CWI).

Figure 2.

Area under the curve for three cooling rates. The graph is a representation of expected core temperature decrease of an exertional heatstroke (EHS) victim who exhibits a characteristic starting temperature of 43°C (109°F). The end point has been standardized here as a body temperature of 40°C (104°F), which is just below a likely threshold for reduced risk of cell damage. Cooling rates from the typical starting temperature to the set hypothetical standard of 40°C are in units of °C per minute. The area under each curve represents cumulative time a patient may spend above the threshold temperature of 40°C during cooling. The assumptions in assembling this theoretical image include: (1) constant cooling rate (cooling rates are known to fluctuate, but average cooling rate is used here, may represent the best estimate of a relative °C per minute comparison); (2) initial temperature (43°C) is the same in all conditions; (3) initiation of treatment relative to diagnosis and onset is the same for all conditions; and (4) conditions represent average individual with similar thermal response capacities.

The key element is that cooling is initiated as soon as possible after the onset of the condition. Many modes can accomplish this goal. Ultimately though, the best cooling rates reported in the literature are with CWI, which consistently provides outstanding cooling rates in both controlled studies and clinical interventions of EHS patients.[2,10,11,17,22,26] Proulx et al.[22] probably offered the single greatest this field as the first to combine certain techniques in a controlled setting, producing the fastest known cooling rate in the scientific literature. They immersed subjects in various water temperatures under controlled conditions (the only thing different was the temperature of the water bath), including immersing the entire body (except the head), stirring the water, and previous exercise to heat up to 40°C (104°F). The four water temperatures between 2°C (36°F) and 20°C (68°F) all provided excellent cooling rates (greater than 0.2°C/min for the decline from 40°C to 38°C), but the cooling rate of the 2°C bath (0.39°C/min for the decline from 40°C to 38°C) was nearly twice that of the other temperatures.[22] This rate translates into approximately a 4°F drop in 5-6 min, a staggering testament to the cooling potential of immersion in moving water! Although the subjects did not experience EHS but induced hyperthermia, the physiological influence of cold water as a cooling modality remains relevant. Others have provided additional evidence of the powerful influence of cold water on cooling of actual EHS patients.[2,6,11,20]

The goal is not to criticize or even question non-CWI cooling modalities that are effective in rapidly cooling EHS patients. Many are suitable and successful.[16,20] Our goal is to refute the myth that CWI hinders cooling and to show that CWI actually has outstanding cooling and survival rates. Because of its negligible cost and the relative ease and availability in controlled athletic and many military training (i.e., basic training) settings, and superior cooling effectiveness, CWI should be the preferred cooling method in most circumstances. Some wartime situations, remote athletic events, and other specific circumstances may preclude its use, but these are the exceptions rather than the rule. In addition, the survival rates resulting from the above mentioned alternatives are impressive, but CWI initiated right after the onset of symptoms is believed to have a survival rate that is nearly (or perhaps actually) 100%.[6,11]

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