Fluids, Electrolytes and Hydrationforms.acsm.org/TPC/PDFs/12 Heiman.pdf · Fluids, Electrolytes and...
Transcript of Fluids, Electrolytes and Hydrationforms.acsm.org/TPC/PDFs/12 Heiman.pdf · Fluids, Electrolytes and...
Fluids, Electrolytes and
Hydration
Diana Heiman, MD
Associate Professor, Family Medicine Residency Director
East Tennessee State University
Objectives
Discuss optimum hydration and effects of
dehydration on exercise
Discuss the best methods for fluid replacement
Review the electrolyte composition of sports
drinks
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
* increased losses with increased sweat
rate and dehydration
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
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
Hourly Sweat Rates
Sweat
1L of sweat loss
= 1 kg body weight loss
= ~580 kcal loss
ACSM Position Stand on Exercise and
Fluid Replacement 2007
Sweat Rates in Different Sports
ACSM Position Stand on Exercise and
Fluid Replacement 2007
Measures of Hydration Status
Urine measures not accurate during rehydration.
Measures of Hydration Status
Can’t rely on thirst, dizziness, headache,
tachycardia, dry mouth, skin turgor to predict
dehydration
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
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
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
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
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
Exercise-Associated
Hyponatremia
Treatment:
Get a sodium level immediately!
Hypertonic fluid replacement immediately and
transport to the ED with clear diagnosis
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
Fluid Replacement – During
Exercise
Goal is to prevent excessive dehydration (>2% BW)
Fluid replacement should mirror losses (0.4 - 1.8 L/hr)
and not be excessive, especially in exercise >3 hours
Periodically drink, don’t drink at every water station
Marathoners safe to drink 0.4 – 0.8 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
Marathon Hydration Levels and
Body Weight Loss
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
Sports Drinks
Institute of Medicine-recommended composition of sports drinks for prolonged physical activity in hot weather:
20-30 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)
1mEq Na = 23 mg, 1mEq K = 39 mg
Sports Drinks
8 oz ≈ ¼ L goal is 115-173 mg Na and 20-48 mg K per 8 oz
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.
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
Caffeine Content
Red Bull 80 mg/8.3 oz Fixx Extreme Ultra Shot 400mg/0.17 oz
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