ADH is normally used to regulate osmolality We start with an increase in the plasma osmolality This is detected by the brain The brain releases ADH ADH acts on the kidney The kidney reacts by retaining water and producing a small amount of concentrated urine. The retained water goes here not here
What Studies Are Needed?
Tests to send...
UA, Urine: Na and Osmolality
Serum osmolality, TSH, uric acid, BNP, cortisol
What is the Volume Status?
Volume expansion with SALINE
Excess intake in Free Water
Defect in Free Water Clearance
ADH Should NOT Be Present When...
Euvolemic / Hypervolemic states
Serum Osmolality is low - normal range
If ADH is elevated... that would be INAPPROPRIATE
Diagnostic Criteria for SIADH
Urine Na >25
Urine Osmolality elevated
>200 higher than Serum Osmolality
Causes of SIADH
First generation sulfonylureas
Conservative vs. Aggressive
Who should get treated and why?
Mental status changes
Hypoxia / respiratory failure
Symptomatic vs. Asymptomatic
Conservative approach is best
Acute symptomatic hyponatremia
In patients with neurologic symptoms due to hyponatremia: 3%.
Increase sodium until symptoms abate or 6 mmol/L, which ever comes first.
Increase Na < 24 mEq/L in the first 24 hours.
Goal is not more than 0.5 mEq/L/hour
The problem with compensation The starting point is after compensation has reduced the amount of intracellular solute and the ICP Now, an over-eager intern sees the low sodium and starts an infusion of 3% NaCl to raise the sodium to normal. Sodium 108 Sodium 134 The sodium draws water from the inside of the cells causing the brain to shrivel.
C entral P ontine M yelinolysis
Mental status changes
Usually fatal within three to five weeks
Hyponatremia for > 24 hours
Over-correction of hyponatremia (> 24 mEq/L/day)
Rapid correction (greater than 1–2 meq/hr)
Damned if you do. Damned if you don’t
Without treatment patients have cerebral edema.
With mistreatment patients are at risk of CPM.
TAKE HOME POINTS
Hyponatremia is a WATER problem, not sodium problem
In general best strategy in ER if not symptomatic... DO NOTHING (Primum non nocere) ... including holding NS unless dehydrated
Repeat blood tests to confirm and watch for psuedohyponatremia, send off urine studies