Exertional Heat Illness (EHI) fundamentally negatively impacts warfighter performance.
This paper references independent scientific and military research to summarize the impact of conductive cooling in preventing exertional heat illness and providing an operational advantage to the individual warfighter.
Exertional Heat Illness: A Significant Threat
According to the March 2017 Department of Defense Medical Surveillance Monthly Report, “heat-related illness remains a significant threat to the health and operational effectiveness of military members and their units and accounts for considerable morbidity, particularly during recruit training in the U.S. military .” In 2016, there were 2,536 documented cases of heat illness, 406 of which were a severe form of heat illness known as heat stroke . The effects of heat stroke go beyond the immediate time lost. Heat stroke “may have lasting effects, including damage to the nervous system and other vital organs and decreased heat tolerance, making an individual more susceptible to subsequent episodes of heat illness .” Among all branches of the U.S. military, the Army is disproportionately affected by heat illness with three Army Installations accounting for over 30% of the 2016 documented cases of heat illness: Fort Benning, GA; Fort Bragg, NC; and Fort Jackson, SC . In 2017, the U.S. Army Training and Doctrine Command (TRADOC) had “a 9 percent increase in reported heat incidents compared to the previous year .”
The Body Armor Cooling Problem
The warfighter body armor cooling problem is well understood and has been extensively studied by the military. Soldiers are weighed down by dozens of pounds of necessary protective gear. This gear impacts military personnel’s work performance , “significantly increasing thermal and cardiovascular strain .” Heat strain is exacerbated by limiting air circulation to and increasing insulation around the torso .
The body of medical and scientific literature on topics related to exertional heat illness and cooling within the military and performance communities is tremendous.
Studies have focused on two primary cooling categories :
Active Cooling: direct heat offload through conduction and convection.
Passive Cooling: promoting the body’s natural heat offload through evaporation.
Due to the high heat loads warfighters encounter wearing Individual Body Armor (IBA), passive measures have not been effective , however active measures have shown promise. A 2014 study in Military Medicine noted that “active cooling devices may decrease the physiological strain associated with wearing IBA in hot environments.” The study also noted that “further development of optimal cooling strategies to reduce physiological strain during operations where IBA is required is warranted .”
Preventing EHI: Heat Offloading Techniques
Heat illness refers to “a spectrum of disorders that occur when the body is unable to dissipate heat absorbed from the external environment and the heat generated by internal metabolic processes .” EHI risk is exacerbated by cumulative heat exposure. As a result, leaders are encouraged to monitor a soldier’s previous three days of heat exposure when assessing risk. Effective heat offloading remains a key component of prevention and treatment. 
Scientists have studied a number of different heat off-loading techniques:
- Arm Immersion Cooling Systems (AICS)
- Full-body Immersion,
- Ice Sheets
- Ice Packs and Vests,
- Cooling Vests,
- Cold IV saline treatments,
- Cold Water and Ice Slurry Ingestion.
Each of these techniques use the principles of conduction and/or convection to draw heat out of the body, aimed at reducing core body temperature (Tc).
Research has also been done to look at the effectiveness of when cooling techniques are applied: prior to (pre-cooling), during (per-cooling), and after (post-cooling) exertion. A comprehensive overview of current scientific knowledge showed that “using a mixed method pre-cooling strategy is most effective in improving exercise performance of athletes, whereas cold water/ice slurry ingestion is most favorable per-cooling strategy .” The same review said that although, “per-cooling is effective in improving exercise performance” per-cooling methods such as wearing an ice vest is generally “not practical during competitive, field-based, settings .”
AICS and Full Body Immersion
AICS involves immersing hands and forearms (up to the elbow) in cool water to accelerate body cooling after strenuous activity. A June 2007 Aviation, Space, and Environmental Medicine article affirmed that full forearm immersion (as opposed to simple hand immersion) was significant in reducing Tc after intermittent bouts of exercise with protective gear . A retrospective study by the US Army Public Health Command showed that, although AICS did not reduce the overall incidence of EHI, AICS did reduce the severity, “as indicated by hospitalization status .” AICS was associated with a medical cost savings of $1,719 per casualty according to a November 2017 issue of Military Medicine .
Full body immersion also results in a dramatic reduction in core temperature in acute situations. According to a 2009 article in the Journal of Athletic Training, “ice-water immersion and cold-water immersion are the methods proven to have the fastest cooling rates .”
One rapid cooling method is Ice-Sheet Cooling (ISC). ISC involves wrapping an overheated soldier’s body in sheets soaked in ice water with the goal of lowering Tc. A study published in the September 2017 issue of Military Medicine challenges the effectiveness of ISC in lowering Tc: “ISC does not provide effective reduction in Tre [rectal temperature] following exertional hyperthermia compared to no treatment. However, perceptual benefits may warrant the use of ISC in settings where rapid reductions in core temperature are not a concern (i.e., recovery from exercise). Thus, clinicians should continue to utilize validated techniques (i.e., cold-water immersion) for the treatment of exertional heat illnesses .”
Ice Packs and Vests
The use of simple ice packs applied to key points on the body has also been shown to reduce Tc. In an article titled “Efficacy of Field Treatments to Reduce Body Core Temperature in Hyperthermic Subjects” applying ice packs to the neck, axillae, and groin reduced Tc at a rate of 0.07 +/- 0.02°C/min .
Upper body pre-cooling using an ice vest did not improve intermittent sprint exercise in a moderately warm environment, although ice- or cooling- vests were second only to ice cold water/ice slurry in per-cooling performance enhancing effectiveness .
Studies exploring the effects of cooling vests “perfused with chilled water” reported “lower max core and skin temperatures when vests continuously perfused with chilled water were worn as compared to the control condition .” One study looking at body temperature recovery in a thermoneutral environment stated that “ice-water immersion should remain the standard of care for rapidly cooling severely hyperthermic individuals,” due to the fact that “the cooling rate for the vest group was not significantly different from the cooling rate for the no-vest group .”
Cold IV Saline Treatments
Adding cold intravenous saline treatments to ice-sheeting as a protocol has been shown to reduce the length of heat casualty related hospitalizations . One study in Experimental Physiology though showed that the administration of an intravenous cold saline solution, compared to ice pack treatments and fan treatments, following post exercise-induced hyperthermia, resulted in a significantly higher heart rate, indicating reduced vagal modulation, that may require further examination .
Cold Water & Ice Slurry Ingestion
One study out of Medicine and Science in Sports and Exercise found that the drinking of cold water increased endurance capacity: “Compared with a drink at 37 degrees C, the ingestion of a cold drink before and during exercise in the heat reduced physiological strain (reduced heat accumulation) during exercise, leading to an improved endurance capacity (23 +/- 6%) .”
An ice slurry is a drink that contains liquid in addition to ice particles. Since ice absorbs a larger amount of energy than just water, ice slurries “absorb more heat energy and provide a greater cooling effect than cold fluids alone .” The same article suggests that benefits of ice slurry ingestion, “may be limited by the lack of simultaneous skin cooling .” Compared to cold water, “ice slurry ingestion lowered preexercise rectal temperature, increased submaximal endurance running time in the heat (+19% ± 6%) .”
A variety of methodologies and procedures have been studied to off-load heat before, during, and after intense physical exertion. An effective EHI mitigation strategy will continue to take into account individual heat load over time, pre-cooling, per-cooling, and post-cooling strategies, as well as creative innovations that combine modalities.
Targeted Torso Cooling
Water torso-immersion has been shown to be particularly effective in reducing rectal temperature (Tr) . Researchers studied how immersing the torso in cold water compared to hands and feet immersion influenced Tc in joggers experiencing heat strain. The difference in cooling techniques was evident after 10 minutes, concluding “that rectal temperatures can be reduced rapidly through the use of a cool water torso-immersion technique .”
Per-Cooling: A Gap in Heat Mitigation Strategy
Per-cooling is defined as “any opportunity to reduce thermal stress during an exercise performance trial .” There is a significant gap in per-cooling during high risk events in the current heat mitigation strategies. One study’s meta-analyses “concluded that ice vest cooling appeared to be the most effective [per-cooling] method followed by cold water ingestion and cooling packs .” This same study though, acknowledges the traditional limitation of wearing an ice vest in high performance scenarios .
Individual Warfighter Overmatch and IcePlate
IcePlate’s design has a number of important features that bridge that gap. Identical in size to a medium SAPI plate, IcePlate, a block of frozen ice that doubles as a hydration vessel, can be worn directly between the user’s base layer and IBA, conductively cooling the body at a rate of 70 Watts per plate over a two hour period. IcePlates can also be worn in tandem, doubling heat off-loading. Each IcePlate provides 50 oz. of drinkable water maintaining a 32°F (0°C) temperature throughout the melting process . Although outside of the scope of this discussion, IcePlate, replacing traditional hydration bladders, more ideally distributes water-carrying load, thus decreasing rotational strain on the body . IcePlate does not attempt to replace post-cooling best-practices, including cold-water immersion for severely hyperthermic soldiers.
Integrating seamlessly into pre-existing kit, IcePlate is a portable microclimate cooling station that travels with the soldier, allowing him to transcend his environment and increase physical and mental performance capabilities. Individually issued and adopted on a larger scale, IcePlate could efficiently minimize EHI at high risk events, reducing long-term use of more invasive and costly interventions.
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