Clinical Reasoning-Hyponatremia Flashcards
Why would you want to occasionally pass up on water while running a marathon?
When you are running, you are volume depleted and your urine will be hyper concentrating while trying to dilute the blood. Ingesting more water than you excrete while running will cause hyponatremia and decrease performance.
What is the definition of hyponatremia?
Serum Na < 135 mEq/L
What three ways can we develop hyponatremia?
Hypovolemia (loss of Na & H2O), Euvolemia (increased H2O), Hypervolemia (increase in Na & H2O)
How can a patient’s body induce euvolemia when it already has edema?
The extra fluid in the third spaces is not sensed. The body only senses the fluid in the vasculature and will adjust according to what it senses there.
How do you fix a patient with hyponatremia due to hypovolemia?
Hypovolemic hyponatremia is a result of ADH action to reabsorb Na and H2O in response to decreased ECV. It so happens that H2O is reabsorbed faster than Na and causes hyponatremia. This is corrected by adding volume.
How do you fix a patient with hyponatremia due to hypervolemia?
Hypervolemic hyponatremia is a result of inappropriate ADH action because the body perceives hypovolemia when ECV is actually overloaded. To correct this you need to find the underlying drug or volume abnormality.
How do you fix a patient with hyponatremia due to euvoemia?
Euvolemic hyponatremia is a result of inappropriate ADH secretion, ADH sensitivity or limitation in the nephron’s ability to dilute the urine. To correct this you need to find the underlying drug or volume abnormality.
What is the equation for plasma osmolality?
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A patient comes to see you with a plasma [Na+] of 120 mEq/L and a urine osmolality is 120. What could be contributing to this condition?
The patient is hyponatremic, but retaining water. This could be caused by excess glucose pulling more water out in a diabetic or a patient with renal failure who has excess BUN.
A 55 year old male comes to the hospital with a history of pituitary gland removal. When he got to the hospital his serum sodium levels were normal. After being in the hospital for four days his serum sodium is 124. Why is this patient hyponatremic?
He was likely given DDAVP (ADH) because his pituitary gland was taken out and wasn’t taking it regularly before coming to the hospital. Once he got there, he started taking his meds regularly and increased ADH caused increased fluid retention which caused hyponatremia.
What are normal plasma and urine osmolalities?
Plasma < 280. Urine < 100 in max dilute urine
What are the four simple lab values that can provide significant clues to why someone is hyponatremic?
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When patients are hyponatremic, the final diagnosis by exclusion is inappropriate ADH. What are some sources of inappropriate ADH?
Hypoaldosteronism, Thiazides, GI loss, Sweating and Burns
A 55 year old male status post large anterior MI with pulmonary and peripheral edema would have what levels of ADH?
High, he just had an MI and will likely have inadequate ECV.
A 45 year old male with alcoholic cirrhosis, presenting with ascites, peripheral edema and pleural effusions would have what levels of ADH?
High, he has all of his fluid in third spaces which will reveal inadequate ECV.
A 22 year old female who is 25 weeks pregnant with 1+ pitting ankle edema will be hyper or hypovolemic?
Hypervolemic from fluid overload and flooding out of the vascular space.
A 65 year old woman with a urinary tract infection and sepsis will be hyper or hypovolemic?
Sepsis changes the permeability of the capillary walls, fluid leaves the vasculature and the patient will be hypovolemic.
