Management of patients with fluid and electrolyte disturbances

Question 1

Where are Na and K primarily concentrated (intracellularly or extracellularly)?

Answer 1

Na+ - extracellularly

K+ - intracellularly

Question 2

Which cation is the most important determinant of extracellular osmotic pressure and volume

Answer 2

Na+

Question 3

What is normal plasma osmolality

Answer 3

280-290mOsm/L

Question 4

In what circumstances would you see a large osmolar gap?

Answer 4

High concentration of osmotically active substances in plasma such as: ethanol, mannitol, methanol, ethylene glycol, isopropyl alcohol
Patients with CKD, ketoacidosis, and those receiving large amounts of glycine (as during TURP)

Question 5

Which is the primary hormone for regulating osmolality?

Answer 5

ADH

Question 6

What is the mechanism for ADH?

Answer 6

Increases water reabsorption in renal collecting tubules (reducing plasma osmolality)

Question 7

What happens when ADH is blocked/suppressed?

Answer 7

Diuresis and increased plasma osmolality

Question 8

What is diabetes insipidus? What is renal vs nephrogenic DI?

Answer 8

Impairment in renal concentrating ability.
Neurogenic: due to decreased ADH secretion
Nephrogenic: failure of renal tubules to respond to ADH

Question 9

What would urine and plasma osmolality be relative to each other in DI?

Answer 9

Urine osmolality lower than plasma osmolality

Question 10

What is the treatment for central DI?

Answer 10

Vasopressin or desmospressin (DDAVP)

Question 11

How do you confirm a diagnosis of nephrogenic DI (as opposed to central)?

Answer 11

Urine osmolality does not increase despite exogenous vasopressin

Question 12

How fast should hypernatremia be corrected? What can happen if corrected too rapidly

Answer 12

0.5mEq/L/h

seizures, brain edema, neurological damage