Fluids, Electrolytes and Hydration. Diana Heiman, MD Associate Professor, Family Medicine Residency Director East Tennessee State University

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1 Fluids, Electrolytes and Hydration Diana Heiman, MD Associate Professor, Family Medicine Residency Director East Tennessee State University

2 Objectives Discuss optimum hydration and effects of dehydration on exercise Discuss the best methods for fluid replacement Review the electrolyte composition of sports drinks

3 Optimum Hydration Performance decreases with water loss of 2% or more of body weight Prehydration prior to exercise helps avoid excessive losses during exercise (goal to be euvolemic) Measuring body weight prior to and after exercise can estimate sweat rates Electrolytes also need to be replaced more or less depending on sweat rate and salt content

4 Sweat Major means of cooling the exercising body Losses vary greatly person to person and with different types of activities Contains: Water Electrolytes Sodium * Potassium Calcium Magnesium Chloride * Electrolytes must be replaced Excessive salty sweating can lead to hyponatremia * increased losses with increased sweat rate and dehydration

5 Sweat Water loss (sweat) during exercise is dependent on: Exercise intensity Ambient temperature and humidity Clothing Body surface area/body weight Acclimatization Metabolic efficiency in the exercise

6 Hourly Sweat Rates

7 Sweat 1L of sweat loss = 1 kg body weight loss = ~580 kcal loss

8 Sweat Rates in Different Sports ACSM Position Stand on Exercise and Fluid Replacement 2007

9 Measures of Hydration Status Urine measures not accurate during rehydration. ACSM Position Stand on Exercise and Fluid Replacement 2007

10 Measures of Hydration Status Can t rely on thirst, dizziness, headache, tachycardia, dry mouth, skin turgor to predict dehydration

11 Effects of Dehydration on Performance With dehydration: increased strain and perceived exertion for the same task Exaggerated in warm-hot conditions and with greater degree of dehydration Less effect of dehydration seen in cold conditions Dehydration (>2% BW) decreases aerobic performance, especially in warm-hot conditions Dehydration (>2% BW) may decrease mental/cognitive performance Dehydration (3-5% BW) doesn t decrease anaerobic performance or muscle strength

12 Dangers of Impaired Fluid Balance Dehydration Increases risk for exertional heat illness Muscle cramps (salty sweaters) Increases risk for renal damage with rhabdomyolysis Hyperhydration Hyponatremia free water intake greater than sweat loss or large sweat sodium losses

13 Exercise-Associated Hyponatremia First recognized in the comrades marathon (South Africa, reported in 1971) Associated with overdrinking of hypotonic fluids and/or excessive salt loss Athletes at higher risk: women and older adults, smaller athletes who run slowly, sweat less and drink hypotonic fluids before, during and after the race; CF gene carriers; football and tennis players who overhydrate to prevent cramps or get hypotonic IV hydration

14 Exercise-Associated Hyponatremia Beware of diagnosing the endurance athlete with dehydration and encouraging hypotonic fluid replacement Symptoms occur with rapid decline in levels below 130 mmol/l Symptoms increase with the rapidity of decline, the longer it remains low and the lower it goes

15 Exercise-Associated Hyponatremia Symptoms at levels of 125 mmol/l or less: headache, vomiting, swollen hands and feet, restlessness, fatigue, confusion and disorientation (cerebral edema), wheezing (pulmonary edema) Progression of symptoms with levels below 120mmol/L: cerebral edema with seizure, coma, brainstem herniation, respiratory arrest and death

16 Treatment: Exercise-Associated Hyponatremia Get a sodium level immediately! Hypertonic fluid replacement immediately and transport to the ED with clear diagnosis

17 Fluid Replacement Pre-Exercise Goal is to start euhydrated If not euhydrated from prior exercise (<12 hour interval between activities), drink slowly at least 4 hours prior to exercise If urine is dark or no urine output, drink more 2 hours prior to exercise Add salt to beverages or eat salty food to assist in fluid retention

18 Fluid Replacement During Exercise Goal is to prevent excessive dehydration (>2% BW) Fluid replacement should mirror losses ( L/hr) and not be excessive, especially in exercise >3 hours Periodically drink, don t drink at every water station Marathoners safe to drink L/hr Slower, thinner athletes most at risk of overhydration in activity >3 hours Salty sweaters need to replace electrolytes during exercise to avoid hyponatremia

19 Marathon Hydration Levels and Body Weight Loss

20 Fluid Replacement After Exercise Goal is to fully replace fluid and electrolyte deficits If mild deficits, normal eating and drinking will replace losses with time (12+ hours) If more moderate deficits, more aggressive replacement is warranted 1.5 L fluid/kg weight lost Replacing fluid without sodium leads to excessive urine production and delayed euhydration IVF should be used only when losses exceed >7% BW with inability to ingest oral fluids No benefit vs. oral rehydration

21 Sports Drinks Institute of Medicine-recommended composition of sports drinks for prolonged physical activity in hot weather: meq/l sodium 2-5 meq/l potassium 5-10% carb Concentrations >8% delay gastric emptying Ranges are variable to account for different exercise conditions, durations and intensity Carb intake is important only for extended periods of exercise (>1 hour)

22 Sports Drinks Gatorlytes add 700 mg Na and 200 mg K; also 70 mg Ca and 40 mg Mg only really want to use in salty sweaters or bad crampers. 8 oz ¼ L goal is mg Na and mg K per 8 oz 1mEq Na = 23 mg, 1mEq K = 39 mg

23 Caffeine and Alcohol Caffeine, in small amounts (< 180 mg/d), does not lead to dehydration Alcohol does increase urine output, especially in higher doses, use in the rehydration period can delay full rehydration

24 Caffeine Content Red Bull 80 mg/8.3 oz Fixx Extreme Ultra Shot 400mg/0.17 oz

25 Summary Proper hydration is important to good performance Dehydration negatively impacts performance Rehydration should be performed orally when possible Salty sweaters are at risk of hyponatremia if not replacing electrolyte losses Sports drinks are a good way of replacing losses, but often don t contain the recommended electrolyte concentrations