Hyponatremia and Sodium Handling By Brent Lee Lechner, DO MAJ, MC, USA

Basic Concepts in Urine Evaluation U Na+ reflects renal perfusion independent of S Na+: Low U Na+ (<10 to 20 mEq/L) Renal Perfusion is decreased Possible Tubular defect High U Na+ (>20 mEq/L) Renal Perfusion is increased or normal Defect in tubule reabsorption So: If U Na+ elevated in clinical circumstance when renal blood flow is expected : Identify renal reabsorption defective.

Basic Concepts in Urine Evaluation U OSM reflects H20 removal from tubule fluid: Normal U OSM (200-1200 mOsm/L) SG in urine 1.010 = U OSM 300mOm/L U OSM > 1.5 X S OSM: ADH must be acting on collecting duct – irrespective of S OSM Physiologic stimuli for ADH release Increase S OSM/ S Na+ Decrease intravascular volume If U OSM/S OSM > 1.5 without increased S OSM or decreased intravascular volume – ADH secretion is non-physiologic – irrespective of urine volume.

Clinical Utilization of U Na and U OSM Increased Weight U Na U OSM Decreased Weight Hypoalbuminema <10 >500 Dehydration/Volume Depletion Nephrosis/Cirrhosis Cystic Fibrosis AGN Acute Volume expansion <10 <300 Diabetes Insipidus Water Intoxication Excess IV Fluid Acute Renal Failure >50 <= 300 Adrenal Insufficiency Sepsis,Shock, Nephrotoxin Salt-losing Nephropathy Interstitial Npehritis/Cystic Dz/ Urinary Tract Obstruction Non-Physiologic ADH >50 >500 DKA Osmotic Diuretics

Case Series Serum Urine Change in Weight Na K Osm Glucose BUN/Cr Na Osm Decreased 125 4.5 255 90 40/0.5 <10 750 Decreased 125 7.5 255 40 40/1.2 60 550 Increased 125 5.0 250 90 40/1.0 <10 400 Decreased 125 6.2 285 450 40/1.0 50 450 Increased 125 4.5 250 90 5/0.5 60 800 Decreased 125 6.1 285 90 90/4.5 60 260