Fluid Replacement in the Endurance Athlete

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Fluid Replacement in the Endurance Athlete

• Joseph N. Chorley, M.D.
• Assistant Professor in Pediatrics
• Section of Sports Medicine
• Baylor College of Medicine
• Texas Childrens Hospital

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FOOD FLUIDS
METABOLIC WATER
Gastric emptying Intestinal Absorption
GI
Vomit, Stool
FLUID SHIFTS
INSENSIBLES
ICF
ECF PLASMA BLOOD INTERSTITIUM
Skin, Respiratory
Gender, Rate Acclimitazation Fitness
GFR, ADH Aldosterone ANF
Glycogen Fat metabolism
UOP
SWEAT
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Goals and Objectives

• To be able to counsel endurance athletes about
  hyponatremia and dehydration
• To understand the sodium balance
• To understand the risk groups
• To individualize fluid recommendations

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THE FLUID SPECTRUM
DEHYDRATION
FLUID OVERLOAD
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Big Picture

• We are Americans!!!
• We wanted to go farther, faster, under extreme
  conditions NOW.

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Big Picture

• We are Americans!!!
• We are obese.
• We are out of shape.
• We are hypertensive and diabetic.

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We need some good advice

• This is not a simple problem
• There are no sound bites that tell the whole
  story
• Experts are arguing

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Present Recommendations

• American College of Sports Medicine
• Nutritionally balanced diet and drink adequate
  fluids during the 24-h period before an event
• Drink about 500 ml (about 17 ounces) of fluid
  about 2 h before exercise

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Present Recommendations

• Ingested fluids be cool and flavored
• For exercise events of duration greater than 1 h
• carbohydrates and/or electrolytes to a fluid
  replacement solution is recommended
• For exercise lasting less than 1 h
• there is little evidence of physiological or
  physical performance differences between
  consuming a carbohydrate-electrolyte drink and
  plain water.

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Present Recommendations

• During exercise, athletes should start drinking
  early and at regular intervals in an attempt to
  consume fluids at a rate sufficient to replace
  all the water lost through sweating (i.e., body
  weight loss), or consume the maximal amount that
  can be tolerated.   NO NUMBERS GIVEN

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Present Recommendations

• Rate of carbohydrate intake
• 30-60 g h-1
• can be achieved without compromising fluid
  delivery by drinking 600-1200 ml h-1 of
  solutions containing 4-8 carbohydrates (g 100
  ml-1)
• Actually 375ml of 8 to 1500ml of 4
• Inclusion of sodium (0.5-0.7 g l-1 of water or
  20-30mEq/L)

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Balance-Fluids
Urine, Stool, Vomit
Metabolic Water
Insensibles
Fluids
Food
Sweat
INPUT
OUTPUT
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Input Fluids Food

• Fluids
• Behavior and Rate
• correlation between total fluid and change in
  Na and final Na
• Gastric emptying
• May be the rate limiting factor for fluid
  tolerance
• Fluid absorption

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Fluids

• Type
• Water versus CHO/lyte versus rehydration
  fluid
• Baseline hydration status

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Food

• Relatively minimal weight change from food
  ingested.
• Can help with carbohydrate and electrolyte
  requirements
• Ie. 30-60 grams of CHO to gel packets

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Metabolic Water

• 1.0-1.5 kilograms of water released from the
  burning of glycogen in ICF (total body 800 grams
  when carbo loaded)
• Fluid shift from ECF to ICF (but how much
  re-equilibrates)
• 2/3 ICF 700-1000 ml
• 1/3 ECF 300-500 ml

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Input

• Fluid MOST IMPORTANT
• Food minimal
• Metabolic Water 300-500 ml

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Outputs

• Insensible
• Skin
• Respiratory
• GI
• Urine output
• Fuel consumed
• Sweat

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Insensibles

• Skin
• Should remain constant as at rest 350ml/day
• 15ml/hr (about 50-75 ml)
• Respiratory
• Should increase from 350 to 650 ml/day
• 25-30ml/hr (about 75-100ml)

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Gastrointestinal

• Emesis
• Stool

(hopefully none)
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Sweat (0.25 to 2.5L/h)

• Gender
• Rate
• women sweat rate is lower
• Composition
• Acclimatization
• Fitness
• Temperature

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Urine Output

• The average adult will have a UOP rate of 1
  ml/min
• With exercise, urine production can decrease by
  20-60
• Should yield 0.4-0.8 ml/minute

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Fuel consumed

• Useful concepts
• VO2 is the volume of O2 consumed by working
  muscles.
• 1L O2 5 kilocalories of fuel
• 7700 kilocalories 1 Kilogram of fuel (35001lb)
• MET metabolic equivalents the energy it takes
  to sit quietly
• 1 MET 1 kilocalorie/ pound/ hour

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METS
155 pound runner 26.2 miles

• Walking 2 mph(13h) 2.5kc/lb/h 1.45lb .65kg
• Walking 3 mph(845) 3.3 1.27 .57
• Walking 4 mph(633) 4.5 1.30 .59
• Walking 5 mph(515) 8.0 1.85 .83
• Jogging 6 mph (422) 10.2 1.97 .90

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VDOT
70 kilogram runner 26.2 miles

• 330 45ml/k/min 661L .42kg
• 400 38 638 .41
• 430 33 624 .40
• 500 29 609 .40

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Outputs

• Insensible 100-200 mg
• Skin
• Respiratory
• GI 0
• Urine output 150-200 ml
• Fuel consumed 500-750 mg
• Sweat 1000-6000mg

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Where is balance?

• Fluid in equals
• Sweat out resulting in a net loss of about
  0.75-1.0 kilograms

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Measure sweat rate under different temperatures

• Urinate
• Weigh yourself naked
• Get dressed and go run for 1 hour while drinking
  a precise amount of water
• Towel off
• Urinate if necessary
• Reweigh your self
• PRE POST FLUID INGESTED SWEAT LOST IN 1 HOUR

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Dehydration is a Clinical Diagnosis

• Dry mucous membranes, sunken eyes
• Poor cap refill
• Hypotensive, tachycardic
• Fatigue
• Decreased body weight
• Increased sodium, bicarb, hematocrit, BUN/Cr
• May lead to heat injury

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Hyponatremia is a hard diagnosis

• Fatigue and just not feeling right
• Confusion
• Nauseated and vomiting
• Shortness of breath
• May be puffy
• Normal vital signs
• Abnormally low sodium

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Exercise Induced Hyponatremia

• Hyperhydration
• Inappropriate Fluid retention

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ADH secretion is stimulated by

• Osmotic
• Na x2
• Glucose /18
• BUN/2.8

• Non-osmotic
• Heat
• Exercise
• Psychological stress
• Blood Pressure
• ANF
• Angiotensin II
• Medications
• Altered clearance

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Plasma Osmolality
Psychological PAIN, STRESS NAUSEA THIRST
Heat
Renal Liver
ADH activity
Exercise INTENSITY DURATION CONDITIONING
Medications TCA, MAO,SSRI NICOTINE NSAIDS
Angiotensin II
Atrial Naturetic Factor
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Who is our patient?
NSAIDs
Luteal phase?
Longer finish times
Femalesgt Males
Less experience
Middle Aged
Stressed Physically and Mentally
Drinking more OCD?
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Syndrome of Inappropriate ADH

• Hyponatremia with hypo-osmolality
• Increased urine concentration
• gt40 mEq/L of Na
• gt100 mosm/kg
• Normal acid base relationship
• Primarily seen in cancer patients with ectopic
  ADH production

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Exercise Induced SIADHNeeds both Hyperhydration
and SIADH, some sodium losses
I was told to drink this much
Abnormal Drinking Patterns
I not feeling good. I must be dehydrated, so I
need to drink more
Hyperhydration
Low sweat rate
Water stops frequency
SIADH
Fluids
Water versus CHO/electrolyte
Sodium losses
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Exercise Induced SIADHNeeds both Hyperhydration
and SIADH, some sodium losses
Luteal phase
Osmotic Factors
Hyponatremia
Age
SIADH
Pain, nausea thirst, stress
Hypertonic Urine
Non osmotic Factors
Prolonged exercise
Hyperhydration
Heat stress
Sodium losses
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Exercise Induced SIADHNeeds both Hyperhydration
and SIADH, some sodium losses
High Sweat rate
Poorly acclimated to heat
High sweat sodium concentration
Sodium losses
Cystic fibrosis
ANF stimulation
Hyperhydration
Renal naturesis
SIADH
Aldosterone suppression
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Chorleys Take Home Points

• Individualize to your patient/client
• Sweat is hypotonic but most electrolyte drinks
  are even more hypotonic.
• Sweat rate measurements in different conditions
  can be helpful.
• Slower, lighter, more out of shape,
  inexperienced, females are at highest risk.
• You should lose 0.75-1.0 kg during a marathon.

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Who will end up in the Medical Tent?