Hypernatremia Flashcards
hypernatremia is a problem w/
WATER deficit
clinical shortcut to calculate free water deficit
pt [Na+] minus 140 divided by 3
free water clearance calculation
urine volume - ((urine osm/plasma osm) x urine volume)
electrolyte free water clearance calculation
urine volume - ((urine Na+ + K+/plasma Na+) x urine volume)
polyuria from water diuresis
> 3 l/day d/t;
- polydipsia
- hypotonic solution
- impaired urinary concentration (central or nephrogenic DI)
polyuria from solute diuresis
> 3 l/day d/t;
- isotonic solution
- osmotic diuresis (DM, mannitol)
- solute diuresis (diuretics)
if polyuria (UOP > 3 l/day) next step
check urine Osm
if polyuria and urine Osm < 100 mosm/kg, ML diagnosis
- primary polydipsia
- central or nephrogenic DI
if polyuria and urine Osm < 100 mosm/kg (water diuresis), next step
water deprivation test
if polyuria and urine Osm 100-300 mosm/kg (mixed polyuria), ML diagnosis
- partial DI (central and nephrogenic)
- simultaneous water and solute intake
- CKD
if polyuria and urine Osm 100-300 mosm/kg (mixed polyuria), next step
water deprivation test or 24-hour urine collection (urine Na+, K+, glucose, and urea)
if polyuria and urine Osm > 300 mosm/kg (solute diuresis), ML diagnosis
- hyperglycemia
- azotemia
- high solute intake
if polyuria and urine Osm > 300 mosm/kg (solute diuresis), next step
water deprivation test or 24-hour urine collection (urine Na+, K+, glucose, and urea)
if primary polydipsia water deprivation test (WDT) result
will be able to concentrate urine
if DI WDT result
still have water diuresis; unable to concentrate urine
after WDT, DDAVP response test; expected response if central DI
urine concentrates
after WDT, DDAVP response test; expected response if nephrogenic DI
NO response; unable to concentrate urine
causes of nephrogenic DI
- congenital = V2 receptor mutation
- medications = Li+, amphotericin, etc
- electrolyte abnormalities = hypokalemia, hypercalcemia
- intrinsic renal diseases = polycystic kidney disease, medullary cystic disease, SCD, obstruction
gestational DI
- placenta produces vasopressinase usually in 3rd trimester
causes of central DI
- congenital (Wolfram syndrome)
- head trauma
- suprasellar tumors (either primary or metastatic)
- granulomatous disease (TB, sarcoid, etc)
- Histiocytosis
- vascular (cerebral thrombosis, Sheehan syndrome, etc)
