Electrolyte Disturbances in Endurance Exercise

Question 1

ADH controls…

Aldosterone controls…

Answer 1

ADH: controls water and therefore Na concentration
Aldosterone: controls total body Na content and therefore volume

Question 2

Why is endurance exercise a challenge to homeostasis?

Answer 2

Loss of electrolytes and water (sweat and insensible losses)
Shift of water from intravascular to extravascular space (increased osmolality around muscles because of by products of energy production)
The decrease in intravascular volume causes ADH and aldosterone release

Question 3

Is sweat iso, hypo, or hypertonic?

Answer 3

Hypotonic

Question 4

Are sports drinks iso, hypo, or hypertonic?

Answer 4

Hypotonic

Most contain very little salt, but some can be iso-osmolar

Question 5

Why does exercise-associated hyponatremia occur?

Answer 5

When the advice to athletes was to drink as much water as possible
Its severe and potentially life-threatening hyponatremia that can occur during or following exercise

Question 6

Pathophys of EAH

Answer 6

Increased fluid intake (hypotonic fluids)
ADH secretion (prolonged or inappropriate - leads to impaired renal water excretion)
Loss of Na in sweat (minor role)
Inability to mobilize Na stores

Question 7

Risk factors for EAH

Answer 7

Exercise duration >4 hours
Female gender (lower body weight)
Low body weight
Excessive drinking during the event
Pre-exercise overhydration
Abundant availability of drinking fluids at the event
NSAIDs
Extreme hot or cold environment

Question 8

Symptoms of hyponatremia

Answer 8

Majority have mild, asymptomatic hyponatremia

Symptoms range from nausea, headache, confusion to seizures, coma and death (cerebral edema)

Question 9

Symptoms severity of EAH depends on what 3 factors

Answer 9

Rate of onset
Severity of hyponatremia
Patient factors (ex: young people more predisposed to cerebral edema)

Question 10

Treatment for EAH

Answer 10

Most med tents have onsite blood analyzers to determine electrolyte profile quickly
Hypertonic saline should be used to treat EAH (rapid improvement in symptoms)

Question 11

How to prevent EAH

Answer 11

Drink to thirst
Drink fluids with solutes (Na and glucose)
Decrease availability of fluids along race courses
For events over 24 hours, use monitoring of body weight (gaining weight = gaining water)

Question 12

Exercise induced hypernatremia

Answer 12

More common than EAH in ultramarathon races but is less deadly
Sign of dehydration
Symptoms may be similar: lethargy, weakness, irritability, and can progress to twitching, seizures, and coma (due to subarachnoid hemorrhage or demyelinating brain lesions)

Question 13

Difference between hypovolemia and dehydration

Answer 13

Hypovolemia: decreased effective circulating volume (volume depletion)
Dehydration: isolated loss of water (implies hypernatremia or hypertonicity)

Question 14

Hypernatremia

Answer 14

Occurs due to a loss of hypotonic fluid (dehydration - GI, renal, insensible) and impaired access to free water
Powerful stimuli for thirst so usually only occurs in those without access to free water or impaired thirst sensation
Treatment: replace free water deficit

Question 15

Signs of dehydration vs volume depletion

Answer 15

Clinical findings may be very similar, differentiation is based on lab findings
Signs: lethargy, irritability, increased thirst, dry MM, flat JVP, tachycardia, orthostatic hypotension, decreased capillary refill, decreased skin turgor, decreased urine output

Question 16

Factors that influence rate of dehydration and electrolyte imbalance during exercise

Answer 16

Intensity and duration of activity
Participant fitness
Climate (hot, humid)
Heat acclimatization
Intake
Always a balance between risk of dehydration/hyperNa and EAH