CC 1 - Exercise Associated Hyponatremia Flashcards
Normal plasma [Na+] range?
135-145 mEq/L
Effect of prolonged endurance on the body?
Creates a state of dynamic and continous homeostatic imbalance and the body struggles to maintain homeostasis under that kind of stress
Definition of exercise associated hyponatremia (EAH)?
Occurrence of hyponatremia in individuals engaged in prolonged physical activity and is defined by a plasma [Na+] below the normal reference range of the lab performing the test (for most labs, this is <135 mmol/L)
Can EHA occur both during and after physical activity?
YUP
Common length of exercise for EAH to occur?
Longer than 4 hours
Physiology of hyponatremia?
Drop of [Na+] outside the brain due to dilution from retained water or due to increased losses in urine and/or sweat => water moves into the brain due to osmosis => cerebral edema where brain occupies the space with the cerebrospinal fluid was => compression of cerebral blood vessels => cerebral ischemia => death
What happens during cerebral edema once the brain has reached the limits of the skull? Consequence?
Herniation through cerebellum and spinal cord => compression of respiratory centers => respiratory arrest
2 potential causes of death due to EAH?
- Cerebral ischemia
2. Respiratory arrest
Can’t the brain just adapt to cerebral edema with water/Na+ moving out of it?
Yes, but that takes 24-48 hours so not fast enough to adapt to the edema
Effect of hyponatremia on lungs?
Pulmonary edema
What % of marathon runners become hyponatremic? More males or females?
15%
More females
Why is EAH a modern disease?
Because marathons become popular
Is EAH the most common life threatening manifestation of fluid dysregulation during prolonged endurance exercise?
YUP
2 types of hyponatremia? Which is more common?
- Dilution (2/3rds)
2. Depletion (1/3rd)
Treatment for depletion hyponatremia?
Saline IV
How do we know EAH is due to water intoxication and not excessive sweat loss?
Studies done measuring body weight and hyponatremia is associated with overhydration and high body weight + normalizing sodium after endurance makes patients excrete water
If your water homeostasis in normal during endurance, are you supposed to gain or lose weight?
Loose 2kg in lean body mass due to muscle metabolism
Is there also sodium depletion in EAH?
A little, but that is not the source of the issue
When does thirst begin? Describe it. What to note?
When AVP is causing maximal urine concentration, thirst starts and increases in linear proportion to increases in plasma osmolarity
Note: PERCEPTIBLE thirst does not begin until a higher plasma osmolarity is reached
What is the osmotic threshold for thirst?
5-10 mOsm/kg H2O higher than that of AVP secretion
In what way was EAH mismanaged?
Marathon runners were advised to drink as much as possible, even when they were not thirsty
Max volume of kidney excretion a day?
18-24 L = 700 mL-1L/hour = 14.2 mL/min
What is the most important hormone in the body? Why?
AVP - it controls body water, which is the largest component of our body
Why does maximal urine excretion decrease during exercise?
Because AVP secretion is stimulated by many factors that occur during exercise:
- Hypovolemia due to sweating
- Nausea
- Hypoxia
- Hypoglycemia
- Stress
- Physical activity
Describe the relationship between AVP and urine concentration.
Linear relationship
Describe the relationship between urine osmolarity and urine volume.
Exponential and inverse, meaning that a low levels of AVP there are greater effects on the amount of water you excrete
Describe how exercise increases AVP secretion?
AVP increases in relation to work intensity
Based on EAH findings, what are the new recommendations regarding endurance exercise and hydration?
- Drink only to thirst, no forced hydration
OR
- Take USATF sweat test to gauge true fluid requirements
- Decrease water/sport drink stops at endurance events
- Point of care electrolyte testing at medical tent
Should you drink ahead of your thirst to prevent dehydration? Explain.
NOOO
Thirst is there to prevent dehydration, that is how mammals have evolved
6 risk factors for EAH?
- Weight gain
- Race time >4h
- Low or high BMI
Univariate:
- Female
- Consumption of over 3L of fluids
- Consumption of fluids every mile
Why does increased race time increase EAH risk?
Because more opportunities to drink more water
What is the myth around sports drinks?
They replete electrolytes - which they BARELY do. They barely protect from hyponatremia because they do not have that much Na+
What is the best drink to avoid EAH after a race?
Bloody mary: Na+ rich to replete osmolarity and alcohol to increase urine output by inhibiting AVP secretion
Normal sweat osmolarity?
30-60 mmol/L
How does alcohol affect urine output?
It increases it independently of the volume ingested because it inhibits AVP secretion by the posterior pituitary
