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

Misconceptions About Using CWI for the Treatment of EHS

Numerous reasons have been cited for not using CWI to treat EHS. Table 1 provides examples from the medical literature of explanations/reasons why CWI should not be used for the rapid cooling of hyperthermic individuals. Our goal in this section is to refute these misconceptions.

Peripheral Vasoconstriction

This assertion states that CWI induces PVC in hyperthermic athletes, which shunts warm blood away from the surface of the body and impedes cooling via convection and conduction. The speculation continues that the hyperthermic athlete may even "heat up" because the heat has nowhere to go. Wyndham et al.[30] are likely one of the sources of this assertion. The results of their classic study indicated inferior cooling rates for CWI. The reasons are not completely understood, however, because no subsequent study reported similar results. We do not dispute that PVC occurs during CWI. Cold water immersion, despite PVC, provides great conductive and convective thermal transfer so that body organs cool rapidly.[15]

We do not argue against PVC occuring in a normothermic person immersed in cold water or even the possibility that some PVC occurs when a severely hyperthermic athlete is placed in cold water.[15,29] The most relevant point has to do with the notion that the PVC somehow prevents rapid cooling from occurring. We are not aware of any severely hyperthermic athlete who has been placed in CWI and not demonstrated rapid cooling.

In great measure, the thermoregulatory response to heat is dictated by the hypothalamus and the temperature it perceives from the core, whereas a lesser portion is influenced by the skin temperature. The evidence supports this notion: cooling rates of hyperthermic individuals during CWI are consistently reported to be about 0.16-0.2°C/min (0.29-0.36°F/min) or upward of 0.35°C/min (0.63°F/min) when multiple elements that influence cooling rates are in place: circulating the water, immersing the entire body except the head, previous exercise, thin stature).[2,10,11,22] Conversely, a normothermic person who is placed in cold water shows no change or a slight (0.1-0.2°C [0.18-0.36°F]) increase in core body temperature (the Currie response; see (Fig. 3) during the first 8 to 10 min because of the combination of PVC and shivering.[12,15,23] For most normothermic individuals, core body temperature can be preserved for about 15-20 min from the beginning of CWI, but then the temperature begins to fall rapidly as the body can no longer provide enough stimulus to offset the powerful cooling capacity of water.[15,23] The rapid cooling is why survivors of capsized boats, downed planes, or people who fall through the ice experience miserably debilitating hypothermia in less than an hour in most cold water situations (assuming no wet suits, average body fat). These individuals have a typical physiological response that provides short-term protection of body temperature and then an inevitable succumbing to the elements.[15] The Currie response was noted in 1798,[12] when some of the first experiments with humans and water (both cold and hot) immersion were conducted. The misinterpretation of this physiological response (the lack of body temperature drop when initially placed in cold water and maybe even a very slight paradoxical increase in core temperature Fig. 3) has been largely caused by the notion that this information was assumed to be true for all humans in cold water ( Table 1 ). This is simply not the case. The typical response for those who have collected data on cooling rates of severely hyperthermic individuals during CWI immediately postexercise is a rapid cooling rate. This finding speaks to the difference in the thermoregulatory response for normothermic and hyperthermic individuals when subjected to CWI. This is the crux of the argument in favor of CWI for the acute treatment of EHS. In addition, it is also at the core of debunking the principal reason provided to not use CWI ( Table 1 ).

Figure 3.

Comparison of responses to cold water immersion for hyperthermic (left panel) and normothermic (right panel) individuals. This figure represents the hypothetical differences in initial response to cold water immersion. Note that the scales are the same, representing 4°C to show the proposed increase in temperature is short-lived and insignificant in a normothermic individual. This figure shows a typical cooling rate of CWI (0.2°C/min) and is not based on actual data points, but is hypothetical based on research studies of exertional heatstroke victims and hyperthermic athletes involving CWI. The temperature of the normothermic individual would begin a precipitous drop beyond approximately 20 min.

The misinterpretation of the Currie response (see Fig. 3) has caused many medical professionals to worry about the consequences of no change or a slight increase in body temperature when initially placed in cold water. However, this increase is quite transient, the influence is quite minor (only 0.1-0.2°C [0.18-0.36°F]), and most importantly, it is a normothermic response. When medical professionals see the rising temperatures plotted against time, they may become leery of CWI as a cooling modality for EHS ( Table 1 , Fig. 3). The message for educational sessions is that the human body in cold water cools rapidly, more quickly in a hyperthermic individual than a normothermic individual, but in both cases the drop is precipitous and powerful.

Shivering

Shivering is an inevitable consequence of falling temperature or the potential for decreasing temperature (i.e., especially skin temperature). An interesting note here is that nearly all normothermic individuals begin to shiver when placed in cold water, yet EHS victims generally do not shiver (unless cooled too long). This emphasizes the integrative role of hypothalamic and skin temperature in regulating shivering ( Table 1 ). In addition, the work of Proulx et al.[22] shows the powerful cooling that can occur in hyperthermic individuals (but not EHS), despite the presence of a shivering response.

Discomfort for Patient or Staff

Some authors have noted that cold water is extremely uncomfortable for the EHS victim and the staff providing care. The physical comfort of the patient or the staff should not be a primary concern during the acute treatment of EHS. Rapid cooling maximizes the likelihood that cell destruction will not occur during this period of extreme hyperthermia. Comfort, although a consideration, should be secondary to delivery of optimal treatment. In addition, we have never received serious complaints from an athlete with EHS about the water temperature (cold water and ice may be quite refreshing for a person who has a body temperature of 43.3°C [110°F]).

Access to Supplemental Treatments

Access to supplemental treatments is the most legitimate concern about CWI, but this is an emergency in which the risks of EHS far outweigh the risks or inconveniences of foregoing supplemental treatments. Administration of oxygen and intravenous fluids is quite feasible during immersion; the mouth and arms are easily accessed. Potential use of an automated external defibrillator (AED) is a greater concern. Fortunately, athletes with EHS who are treated rapidly via aggressive cooling rarely have cardiovascular problems requiring an AED. Cardiac events may be associated with EHS, but these likely occur in individuals who were not recognized or treated rapidly, and who have organ damage at some point after the initial condition. If AED treatment is required, the athlete should be removed from the tub, the contact points dried, and the process begun (similar to an individual who is pulled from a swimming pool). Some authors speculate that CWI can induce cardiac arrhythmia and have recommended using warmer water with older heatstroke patients.[14,16] Our clinical experiences and the existing literature both support the notion that the risk of not cooling aggressively far outweighs the potential risk of cardiac events.

Risk of Drowning

Any athlete who is immersed during the treatment of EHS could be a potential drowning victim. A few precautions should be in place to assure this does not occur:

  1. Supervise the athlete continuously.

  2. Recruit teammates and colleagues to assist.

  3. Use tubs that are designed with ease of entry and exit in mind.

  4. To ensure that the head does not go underwater, place a sheet under the armpits of the athlete, and have an assistant stand behind the athlete while holding both ends of the sheet.

Unsanitary Conditions

Some people claim that CWI can cause sanitation issues because of the potential for vomiting or diarrhea. Although this is a distinct possibility during cooling, we believe that a dirty tub is an acceptable tradeoff to a permanently disabled athlete. We recommend buying cleaning products and cleaning the tub after each use in which it becomes apparent this is necessary. A tub with quick drainage, an area for the water to drain, and the ability to quickly refill the tub for the next use are all important considerations.

Hypothermic Afterdrop

Hypothermic afterdrop occurs when an athlete with EHS is cooled excessively and experiences a below normal core body temperature that requires rewarming. This may be of greater concern if hypothalamic control of body temperature is blunted. Such hypothermia (i.e., <36°C [96.8°F]) can be avoided if simple precautions are taken. A flexible rectal thermistor should remain in place during CWI[7]. This allows the temperature to be monitored and signals when the patient can be removed from the water bath (i.e., when a rectal temperature of 39°C [102°F] is reached). When using a common inflexible rectal thermometer, a typical CWI cooling rate (i.e., 0.2°C/min [0.36°F/min]) should be used to calculate when the temperature will reach approximately 39°C (102°F). This reduces the number of times that the rectal thermometer needs to be inserted. If rectal temperature cannot be assessed on-site, yet the medical provider is confident of the EHS diagnosis, cooling should be instituted for approximately 15-20 min, using the best clinical judgment as to when to cease cooling therapy.

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