Update: Efficacy of Military Fluid Intake Guidance

Military Medicine, Sep 2018

Fluid intake during military training is prescribed based on the interactions among work rates, environmental conditions, and uniform configurations. The efficacy of this guidance has not been empirically assessed in over a decade. To determine the acceptability of the fluid intake guidance, sweat losses were measured in a variety of conditions with modern uniform/body armor configurations and were then compared to prescribed fluid intakes for each condition (workload, environment, clothing).

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Update: Efficacy of Military Fluid Intake Guidance

Abstract Background Fluid intake during military training is prescribed based on the interactions among work rates, environmental conditions, and uniform configurations. The efficacy of this guidance has not been empirically assessed in over a decade. To determine the acceptability of the fluid intake guidance, sweat losses were measured in a variety of conditions with modern uniform/body armor configurations and were then compared to prescribed fluid intakes for each condition (workload, environment, clothing). Methods Whole body sweat losses of 324 Soldiers and 14 model simulations were measured under a variety of work intensities ((Watts) easy, moderate, hard), work durations (2–25 h), environmental conditions (White-Black flag), and uniform configurations (including Army Combat Uniform and body armor). Whole body sweat losses were then calculated relative to 4 h drinking guidance and in accordance with TB MED 507 recommended work/rest ratios. The differences between the prescribed fluid intake and sweat loss were calculated and expressed as a percent loss or gain of body weight. Values within a threshold of ±2% body water flux (BWF) were deemed an acceptable conservative starting point for performance and health concerns. Findings Values within ±2% BWF numbered 309/338; 25 of 338 observations exceeded the +2% BWF while 4 of 338 observations exceeded the −2% BWF. When total fluid restriction was simulated, all experienced body weight loss with 151 of 338 observations exceeding the −2% BWF. Discussion When calculated using actual measured sweating rates from the laboratory and model simulations, current fluid intake guidance appears to predict with 91.4% accuracy the volume of fluid required to maintain a proper euhydrated state (±2%) during 4 h of exercise. Simulations of total fluid restriction support the necessity for fluid intake guidance so that the Warfighter’s performance does not degrade. It is recommended that the current military fluid intake guidance focuses on methods for accurately tracking fluid intakes. INTRODUCTION In 2003, the military fluid intake guidance published in Military Medicine in 19991 was incorporated into Technical Medical Bulletin 507, Heat Stress Control and Heat Casualty Management, TB MED 507,2 which is a multi-service bulletin that provides guidance to military and civilian health care providers, Allied medical personnel, and military leadership. The guidance halted the swing of the pendulum from the performance debilitating practice of water restriction to the potential health hazards of a command emphasis on drinking.3 Significant improvements have been made to the precision and usability of water needs models such as the Soldier Water Estimation Tool (SWET)4–6 that better sustain Warfighter performance and health, while also improving the logistics and safety of water supply convoys in hostile environments. Despite the availability of knowledge2 and materiel4 products aimed at providing the Warfighter with accurate potable water estimates, fluid and electrolyte imbalances remain formidable and enduring military challenges.7 For example, incidences of hyponatremia have recently increased in some service branches.8 Given that under- and over-drinking of water are the primary risk factors for hyper- and hyponatremia, respectively,7,9 it is worth determining if the published fluid intake guidance2 is still sufficiently accurate to avoid serious fluid and electrolyte imbalances. This question is particularly warranted when Warfighters don modern military protective equipment10 while working in mild flag categories (Wet Bulb Globe Temperature Index (WBGT): White (78–81.9 °F) and Green (82–84.9 °F) flags). This scenario may be more likely to produce a potential risk for hyponatremia than a scenario where Warfighters are working in greater thermal load flag categories (Yellow (85–87.9 °F), Red (88–89.9 °F), and Black (>90 °F) flags), since over-drinking is easier when relative to lower sweating rates. Fluid and electrolyte imbalances not only threaten the health7,8 of Warfighters but they can significantly impair performance2,11 and reduce combat effectiveness. For example, one leadership-generated after action report found as many as 40% of the fighting force was evacuated and treated for dehydration-heat exhaustion during the first 72 h of combat operations. Between two and four Warfighters were required to render aid and assist in evacuation of each victim, effectively reducing squad combat fighting power by 22–44%. The purposes of this paper are to: (1) evaluate the efficacy of the current fluid intake guidance in TB MED 5072 with the goal of updating or revising the bulletin based on the results; and (2) document the procedures and outcome of the evaluation in a widely read, military-relevant journal for maximal tri-service visibility and dissemination. Given that the Office of the Surgeon General has recently directed the Army to update TB MED 5072, this evaluation is a germane and important undertaking. METHODS Table I shows the recommended rate of drinking for a matrix of 15 conditions (3 work rates × 5 flag categories).2 Adjustments for protective clothing are provided in the table legend. Whole body sweating rates (losses/time) were measured with precision in a series of published studies.4–6,10,12,13 The majority of the published studies (with the exception of a night-executed field study5) took place in thermal chambers where participants exercised at a walking pace of 2.75–3.5 miles per hour wearing either the Army Combat Uniform (ACU) or ACU with Interceptor Body Armor in environmental conditions of WBGT ranging from 53.4 to 90.5 °F. Exercise duration ranged from 2 to 8 h while following various work: rest ratios.4–6,10,12 These published studies yielded 240 individual Soldier observations who wore the ACU and 46 individual Soldier observations who wore ACU with Interceptor Body Armor, fulfilling 5 and 6 of the 15 matrix conditions, respectively. Table I. Fluid Replacement and Work/Rest Guidance for Warm Weather Training Conditions2  Easy Work (250 W) Moderate Work (425 W) Hard Work (600 W) Heat Category WBGT Index (oF)6,7 Work: Rest (min)1,3 Water Intake (qt/h)4,5 Work: Rest (min) Water Intake (qt/h) Work:Rest (min) Water Intake (qt/h) 1 (White) 78–81.9 NL2 1/2 NL 3/4 40:20 3/4 2 (Green) 82–84.9 NL 1/2 50:10 3/4 30:30 1 3 (Yellow) 85–87.9 NL 3/4 40:20 3/4 30:30 1 4 (Red) 88–89.9 NL 3/4 30:30 3/4 20:40 1 5 (Black) >90 50:10 min 1 20:40 1 10:50 1   Easy Work (250 W) Moderate Work (425 W) Hard Work (600 W) Heat Category WBGT Index (oF)6,7 Work: Rest (min)1,3 Water Intake (qt/h)4,5 Work: Rest (min) Water Intake (qt/h) Work:Rest (min) Water Intake (qt/h) 1 (White) 78–81.9 NL2 1/2 NL 3/4 40:20 3/4 2 (Green) 82–84.9 NL 1/2 50:10 3/4 30:30 1 3 (Yellow) 85–87.9 NL 3/4 40:20 3/4 30:30 1 4 (Red) 88–89.9 NL 3/4 30:30 3/4 20:40 1 5 (Black) >90 50:10 min 1 20:40 1 10:50 1  Easy Work Moderate Work Hard Work  Weapon maintenance Walking hard surface at 2.5 mph, <30 pound (lb) load Manual of arms Marksmanship training Drill and ceremony   Walking loose sand at 2.5 mph, no load Walking hard surface at 3.5 mph, <40 lb load Calisthenics Patrolling Individual movement techniques, that is low crawl, high crawl Defensive position construction   Walking hard surface at 3.5 mph, > or equal to 40 lb load Walking loose sand at 2.5 mph with load Field assaults   Easy Work Moderate Work Hard Work  Weapon maintenance Walking hard surface at 2.5 mph, <30 pound (lb) load Manual of arms Marksmanship training Drill and ceremony   Walking loose sand at 2.5 mph, no load Walking hard surface at 3.5 mph, <40 lb load Calisthenics Patrolling Individual movement techniques, that is low crawl, high crawl Defensive position construction   Walking hard surface at 3.5 mph, > or equal to 40 lb load Walking loose sand at 2.5 mph with load Field assaults   Notes: 1. The work: rest times and fluid replacement volumes will sustain performance and hydration for at least 4 h of work in the specified heat category. Fluid needs can vary based on individual differences (±1/4.qt/h) and exposure to full sun or full shade (±1/4 qt/h). 2. NL equals no limit to work time per hour (up to 4 continuous hours). 3. Rest means minimal physical activity (sitting or standing), accomplished in shade if possible. 4. CAUTION: Hourly fluid intake should not exceed 1 1/2 qt. 5. Daily fluid intake should not exceed 12 quarts. 6. If wearing body armor, add 5 °F to WBGT index in humid climates. 7. If wearing NBC clothing (mission-oriented protective posture (MOPP 4)), add 10 °F to WBGT index for easy work, and 20 °F to WBGT index for moderate and hard work. Applies to average size and heat-acclimatized Warfighter wearing ACU in hot weather. Table I. Fluid Replacement and Work/Rest Guidance for Warm Weather Training Conditions2  Easy Work (250 W) Moderate Work (425 W) Hard Work (600 W) Heat Category WBGT Index (oF)6,7 Work: Rest (min)1,3 Water Intake (qt/h)4,5 Work: Rest (min) Water Intake (qt/h) Work:Rest (min) Water Intake (qt/h) 1 (White) 78–81.9 NL2 1/2 NL 3/4 40:20 3/4 2 (Green) 82–84.9 NL 1/2 50:10 3/4 30:30 1 3 (Yellow) 85–87.9 NL 3/4 40:20 3/4 30:30 1 4 (Red) 88–89.9 NL 3/4 30:30 3/4 20:40 1 5 (Black) >90 50:10 min 1 20:40 1 10:50 1   Easy Work (250 W) Moderate Work (425 W) Hard Work (600 W) Heat Category WBGT Index (oF)6,7 Work: Rest (min)1,3 Water Intake (qt/h)4,5 Work: Rest (min) Water Intake (qt/h) Work:Rest (min) Water Intake (qt/h) 1 (White) 78–81.9 NL2 1/2 NL 3/4 40:20 3/4 2 (Green) 82–84.9 NL 1/2 50:10 3/4 30:30 1 3 (Yellow) 85–87.9 NL 3/4 40:20 3/4 30:30 1 4 (Red) 88–89.9 NL 3/4 30:30 3/4 20:40 1 5 (Black) >90 50:10 min 1 20:40 1 10:50 1  Easy Work Moderate Work Hard Work  Weapon maintenance Walking hard surface at 2.5 mph, <30 pound (lb) load Manual of arms Marksmanship training Drill and ceremony   Walking loose sand at 2.5 mph, no load Walking hard surface at 3.5 mph, <40 lb load Calisthenics Patrolling Individual movement techniques, that is low crawl, high crawl Defensive position construction   Walking hard surface at 3.5 mph, > or equal to 40 lb load Walking loose sand at 2.5 mph with load Field assaults   Easy Work Moderate Work Hard Work  Weapon maintenance Walking hard surface at 2.5 mph, <30 pound (lb) load Manual of arms Marksmanship training Drill and ceremony   Walking loose sand at 2.5 mph, no load Walking hard surface at 3.5 mph, <40 lb load Calisthenics Patrolling Individual movement techniques, that is low crawl, high crawl Defensive position construction   Walking hard surface at 3.5 mph, > or equal to 40 lb load Walking loose sand at 2.5 mph with load Field assaults   Notes: 1. The work: rest times and fluid replacement volumes will sustain performance and hydration for at least 4 h of work in the specified heat category. Fluid needs can vary based on individual differences (±1/4.qt/h) and exposure to full sun or full shade (±1/4 qt/h). 2. NL equals no limit to work time per hour (up to 4 continuous hours). 3. Rest means minimal physical activity (sitting or standing), accomplished in shade if possible. 4. CAUTION: Hourly fluid intake should not exceed 1 1/2 qt. 5. Daily fluid intake should not exceed 12 quarts. 6. If wearing body armor, add 5 °F to WBGT index in humid climates. 7. If wearing NBC clothing (mission-oriented protective posture (MOPP 4)), add 10 °F to WBGT index for easy work, and 20 °F to WBGT index for moderate and hard work. Applies to average size and heat-acclimatized Warfighter wearing ACU in hot weather. In an effort to fairly assess all conditions of the matrix, remaining conditions of the matrix were modeled using the Soldier Water Estimation Tool (SWET).4–6 SWET utilizes manual ambient temperature and relative humidity inputs in conjunction with selected options of cloud cover (solar radiation), activity level, and clothing ensemble to accurately predict the amount of fluid required for the duration of a selected mission. SWET is also capable of predicting fluid requirements for various group sizes, fulfilling potential situations military leadership could face.4 Using SWET, 5 of the remaining 10 ACU conditions and the remaining 9 ACU with Interceptor Body Armor conditions of the matrix were modeled. Data were further supplemented with an additional 38 Soldiers wearing ACU with Interceptor Body Armor while performing a ruck march of 72 km over the course of 25 hours.13 These 38 Soldiers were natives to warm, humid conditions. In total, 324 individual Soldier sweating rate measurements were observed and 14 SWET models were used (n = 338 total observations) to evaluate the efficacy of the fluid intake guidance across a matrix of 15 conditions. Table II provides the distribution of sample sizes by activity level and weather condition. Table II. Ratio of Soldier Observations to Model Simulations During Each Environmental Condition Flag Category Easy Work Moderate Work Hard Work Sum White 5:1 133:0 96:1 236 Green 1:1 41:0 22:1 66 Yellow 0:1 5:0 2:1 9 Red 3:1 10:1 0:2 17 Black 0:1 6:1 0:2 10 Sum 14 197 127 338  Flag Category Easy Work Moderate Work Hard Work Sum White 5:1 133:0 96:1 236 Green 1:1 41:0 22:1 66 Yellow 0:1 5:0 2:1 9 Red 3:1 10:1 0:2 17 Black 0:1 6:1 0:2 10 Sum 14 197 127 338  The ratio of human observations and model simulations of sweating rates wearing ACUs or ACU and body armor configuration. Value: value is ratio of Soldier observations to modeling simulations. Table II. Ratio of Soldier Observations to Model Simulations During Each Environmental Condition Flag Category Easy Work Moderate Work Hard Work Sum White 5:1 133:0 96:1 236 Green 1:1 41:0 22:1 66 Yellow 0:1 5:0 2:1 9 Red 3:1 10:1 0:2 17 Black 0:1 6:1 0:2 10 Sum 14 197 127 338  Flag Category Easy Work Moderate Work Hard Work Sum White 5:1 133:0 96:1 236 Green 1:1 41:0 22:1 66 Yellow 0:1 5:0 2:1 9 Red 3:1 10:1 0:2 17 Black 0:1 6:1 0:2 10 Sum 14 197 127 338  The ratio of human observations and model simulations of sweating rates wearing ACUs or ACU and body armor configuration. Value: value is ratio of Soldier observations to modeling simulations. In order to compare the fluid intake guidance to the total observed sweat rate estimates, hourly sweat rates were calculated and summed to a 4 h standard duration regardless of the actual duration of testing (2–25 h). The calculated 4 h sweat rates were then used to determine the relative balance between over- or under-drinking when adhering to the recommended drinking rates. The impact of total fluid restriction on hydration status was also calculated by simulation depicting the worst-case scenario (fluid non-availability) that could be experienced by the 338 observed Soldiers/model simulations during the adjusted 4 h work durations. The efficacy of the guidance was evaluated specifically by the time-accumulated difference between recommended drinking rates and total observed sweating rates, expressed as a percentage loss or gain in body weight over the 4 h observation period. The formula used was: ((drink volume – sweat volume)/body weight) ×100, computed for each of the 338 paired differences. A difference of ±2% loss or gain in body weight over the observation period was considered acceptable body water flux error11 and would not produce clinical hypernatremia or hyponatremia (hypernatremia: blood sodium ≥ 145 mmol/L;14 hyponatremia: blood sodium < 135 mmol/L7 (local laboratory values may be slightly different based on norms)). It is important to acknowledge that these thresholds of ±2% are conservative starting points for performance (under-drinking) or health (over-drinking) problems.11,15,16 While SWET does not require a Warfighter’s individual body weight to calculate a sweating rate, randomized body weights ranging from 50 to 90 kg were used to simulate the expected variances in Warfighters using a manual SWET template input file (Excel®) to evaluate the ±2% body water flux threshold in the 14 model observations. RESULTS Table II shows the distribution and sums of the total observations made for each flag condition and work rate combination. The ratios of human measured observations and model observations are also listed in each of the 15 combinations. Moderate and hard work intensities made up the majority of total observations (95.9%), while White and Green flag conditions represented 89.3%, and Yellow, Red, and Black flag conditions represented the remaining 10.7% of total observations (n = 338). The majority of total observations (72.5% (245/338)) were for ACUs while 27.5% (93/338) were for ACU and body armor (ACU + BA) configuration. The absolute loss or gain in body weight (y-axis) was plotted as a function of absolute body weight (x-axis) in Figure 1A in order to visualize the performance of fluid intake recommendations. The distribution of percentage losses (22.5%) and gains (77.5%) of respective body weight indicate a tendency for drinking rates to be higher than sweating rates in an absolute sense (above zero difference), with 7.4% of the total observations (25/338) reaching or exceeding the +2% gain in body weight threshold. Of the observations that exceeded the +2% gain in body weight, 56.0% (14/25) wore ACUs while 44.0% (11/25) wore ACU + BA. A very small percentage (1.2%; 4/338) of observations exceeded the −2% loss in body weight threshold with 2 observations wearing ACUs while working at a hard intensity and 2 observations wearing ACU + BA while working at an easy intensity. Importantly, 91.4% (309/338) of total observations fell within the ±2% loss or gain of body weight threshold, indicating highly acceptable performance of the fluid intake guidance. FIGURE 1. View largeDownload slide (A and B) Fluid loss/gain (L) during 4 h work duration adhering to current fluid intake guidance (Fig. 1A). Simulated fluid loss/gain (L) during 4 h work duration while restricted of fluid intake (Fig. 1B). FIGURE 1. View largeDownload slide (A and B) Fluid loss/gain (L) during 4 h work duration adhering to current fluid intake guidance (Fig. 1A). Simulated fluid loss/gain (L) during 4 h work duration while restricted of fluid intake (Fig. 1B). A simulation of the potential impact that total fluid restriction would have on the Warfighter provided a “snapshot” of the worst-possible scenario. Figure 1B (same figure axis orientation was applied as in Fig. 1A) depicts the potential outcome if fluid was not available during the 4 h duration. While all total observations experienced a loss of body weight, the magnitude of that loss varied with 44.7% (151/338) of total observations exceeded the −2% body weight loss. Of the observations that exceeded the −2% body weight loss, 58.3% (88/151) of observations wore ACUs while 41.7% (63/151) wore ACU + BA. DISCUSSION The results of this investigation indicate the existing military fluid intake guidance published in TB MED 5072 remains valid for preventing both excessive dehydration and over-hydration. The continued accuracy of the guidance provides sufficient evidence that it can be utilized by military health professionals and leadership to adequately maintain a euhydrated state in Soldiers working in the five designated flag conditions while wearing modern uniform configurations across a range of metabolic rates. The agreement between past17 and current assessments of the fluid intake guidance provides strong confidence that the guidance is still viable for use with modern uniform configurations in primarily mild flag conditions (White and Green flag conditions (89.3% of total observations)). This agreement confirms that following the current guidance will appropriately re-hydrate Soldiers in scenarios where over-drinking is most at risk to occur. A fair assessment of the fluid intake guidance was of the utmost priority during the current assessment. To ensure this was achieved, we simulated Soldiers following the fluid intake guidance for the condition to which they were exposed. Since the majority of observed Soldiers (with the exception of a night-executed field study5 and a group of Soldiers natives to the tropics13) exercised in a thermal chamber4,6,10,12 where solar radiation was not present, prescribed fluid intake adhered to the recommended guidance when working in the absence of solar radiation (refer to Table I, note 1). This non-bias methodology provided validation of the guidance for both indoor and outdoor work/exercise.2 Fluid restriction while exercising was also simulated during the current investigation to gain insight into the necessity of fluid replacement to avoid excess dehydration (>2% body weight) and the potentially degraded physical and cognitive performance associated with deficits exceeding this threshold.18,19 The results of this simulation indicate that 44.7% of Soldiers would have exceeded −2% dehydration over the 4 h observation period if no drinking was permitted or water was not available (Figure 1B). While this level of dehydration does not pose serious long-term health risks to the Warfighter, this level of dehydration coupled with the thermal load of Yellow, Red, and Black flag conditions can potentially degrade a Warfighter’s physical work capability by 20-30%2 thereby jeopardizing mission/ training success. Few Soldiers (7.4%) during this investigation gained >2% of their respective body weights and no Soldier exhibited any gross signs or symptoms of hyponatremia. Recall that gaining 2% of body mass from over-drinking represents a conservative risk of clinical hyponatremia (blood sodium <135 mmol/L) requiring, in addition to water retention, significant solute losses. Food consumption (solute gain) and urination (water loss) also make hyponatremia less likely to occur in practice even in the presence of over-drinking. However, the occurrence of hyponatremia continues to be a recurring military problem with more serious potential health consequences than dehydration. Military fluid and electrolyte problems have fluctuated greatly over a decade in which fluid intake guidance has not changed.8 Given the adequacy of the fluid intake guidance and SWET application for fluid prescription, education and improved volume tracking methods are of paramount importance2,3 to avoid gross under- and over- drinking (Fig. 1A). The publication of papers like this one, read by preventive medicine officers, military medical consultants, advisors, and surgeons assigned to operational units should help improve the visibility of the problem and adequacy of the guidance. The development of the handheld SWET application allows accurate water volume planning for groups “on the fly” via a “Mission Calculator.” This feature of SWET allows leadership to input the number of Warfighters and hours the mission/ training activity will require of a team and receive a real-time estimate of fluid requirements which align with static TB MED tabled doctrine. Until such time that a non-invasive, real time or point of care hydration monitor is available to alert Warfighters or medics of under- or over-drinking, knowledge2 and materiel products4 guiding behavior provide the best solution to combat under- and over- drinking. Table III is an example of how valid guidance may be re-introduced to solve under- or over-drinking problems related to difficulty with volume tracking. A standard refill policy based on the volumes of fluids currently expressed as hourly canteen volumes was developed in conjunction with the modern use of 3 L collapsible drink systems, thus obviating the need for hourly volume tracking by a standard refill policy that prevents under-/over-drinking. Table III. Refill Frequency for 3 L Collapsible Drink Systems While Working in Hot Environments Flag Condition Easy Work Refill Frequency Moderate Work Refill Frequency Hard Work Refill Frequency White NL 4 h NL 4 h 40:20 4 h Green NL 4 h 50:10 4 h 30:30 3 h Yellow NL 4 h 40:20 4 h 30:30 3 h Red NL 4 h 30:30 4 h 20:40 3 h Black 50:10 3 h 20:40 3 h 10:50 3 h  Flag Condition Easy Work Refill Frequency Moderate Work Refill Frequency Hard Work Refill Frequency White NL 4 h NL 4 h 40:20 4 h Green NL 4 h 50:10 4 h 30:30 3 h Yellow NL 4 h 40:20 4 h 30:30 3 h Red NL 4 h 30:30 4 h 20:40 3 h Black 50:10 3 h 20:40 3 h 10:50 3 h  NL equals no limit to work time per hour (up to 4 continuous hours). Refill frequency applies to average size and heat-acclimatized Warfighter wearing ACU in hot weather. Table III. Refill Frequency for 3 L Collapsible Drink Systems While Working in Hot Environments Flag Condition Easy Work Refill Frequency Moderate Work Refill Frequency Hard Work Refill Frequency White NL 4 h NL 4 h 40:20 4 h Green NL 4 h 50:10 4 h 30:30 3 h Yellow NL 4 h 40:20 4 h 30:30 3 h Red NL 4 h 30:30 4 h 20:40 3 h Black 50:10 3 h 20:40 3 h 10:50 3 h  Flag Condition Easy Work Refill Frequency Moderate Work Refill Frequency Hard Work Refill Frequency White NL 4 h NL 4 h 40:20 4 h Green NL 4 h 50:10 4 h 30:30 3 h Yellow NL 4 h 40:20 4 h 30:30 3 h Red NL 4 h 30:30 4 h 20:40 3 h Black 50:10 3 h 20:40 3 h 10:50 3 h  NL equals no limit to work time per hour (up to 4 continuous hours). Refill frequency applies to average size and heat-acclimatized Warfighter wearing ACU in hot weather. A potential limitation to our data interpretation was the use of modeling (SWET) to simulate matrix conditions for which no human data were available. In this context, the model used in this study4 was developed solely for the purpose of predicting sweat losses; it was not developed with any intake guidance in mind. The model was, however, developed using both laboratory and field data with outdoor solar exposures.5,6 The large number of human volunteers tested in the studies used to retrospectively investigate this research question (n = 324) makes necessary the use of valid models when time, money, resources, and the risks associated with testing more volunteers outweigh the benefits. SWET4 is based on the most accurate sweat prediction equation in the world5,6 and its use in this case is consistent with the principles and philosophy of modeling in biomedical research.20 CONCLUSION The U.S Department of Defense is sensitive to problems of under- and over-hydration of the Warfighter.7,8 Actions have been taken to revise fluid intake guidance1 and improve prediction models4–6 as a consequence, and to periodically validate that guidance to optimize Warfighter health and performance. The unchanging nature of the fluid intake guidance throughout multiple validation efforts, when viewed in conjunction with erratic incidence rates of over-/ under- hydration during the same time period,8 implicates education or guidance implementation difficulties and the need for improvements in practice. The validation of the current fluid intake guidance as well as the potential integration of innovative fluid intake techniques such as a standard refill policy (Table III) will provide leadership with additional resources to ensure Warfighter compliance is achieved and military readiness is sustained. References 1 Montain SJ , Latzka WA , Sawka MN : Fluid replacement recommendations for training in hot weather . Mil Med   1999 ; 164 : 502 – 8 . Google Scholar Crossref Search ADS PubMed   2 Force DotAaA : Heat stress control and heat casualty management. Departments of the Army and Air Force Technical Bulletin Medical 507 . Air Force Pam  , 48 – 152 (I). 2003 . 3 Montain SJ , Ely M : Water requirements and soldier hydration. In: Military Quantitative Physiology: Problems and Concepts in Military Operational Medicine Fort Detrick  , pp 181 – 204 . Edited by Friedl K. E. , Santee W. R. 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Author notes The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Army or the Department of Defense. Citations of commercial organizations and trade names in this report do not constitute an official Department of the Army endorsement or approval of the products or services of these organizations. Approved for public release; distribution unlimited. Published by Oxford University Press on behalf of Association of Military Surgeons of the United States 2018. This work is written by (a) US Government employee(s) and is in the public domain in the US.


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Luippold, Adam J, Charkoudian, Nisha, Kenefick, Robert W, Montain, Scott J, Lee, Jason K W, Teo, Ya Shi, Cheuvront, Samuel N. Update: Efficacy of Military Fluid Intake Guidance, Military Medicine, 2018, e338-e342, DOI: 10.1093/milmed/usy066