Sodium Balance:
?The human body contains 1 g Na / Kg of BW
?Sodium is located:95% extracellularly
5% intracellularly.
?Daily balance of sodium is 6 gr (150 meq)
?Daily losses = 150 meq = 100 meq in urine + 35 meq in sweat + 15 meq in feces
Sodium reabsorption
?Sodium is reabsorbed almost completely
(~ 99% ) esp. in proximal tubule.
?The percent amount of sodium that is excreted in the urine is called F'Na and is calculated by the formula:

FENa (%) = Urinesodium/Plasmasodium X 100
Urinecreatinine/Plasmacreatinine

Hyponatremia:
Plasma Na < 135meq /L
?Almost always due to ?ADH Secretion
?Appropriate
?Inappropriat
?One Exception: Primary Polydipsia ? supression of ADH Secretion BUT still overwhelms kidney's diluting ability ? Free water retention & Hyponatremia

Epidemiology of Hyponatremia:
Hyponatremia is among the most common electrolyte disorders encountered in clinical medicine, with an incidence of 0.97% and a prevalence of 2.48% in hospitalized adult patients when plasma [Na+ ] concentration below 130 mEq/L is the diagnostic criterion.

Clinical Manifestations:
?< 125 mEq/l ?
?Malaise - Muscle cramps
?Nausea, Vomiting, Headache
?Hypotension ? Tachycardia

?< 110 mEq/L ?
?Confusion, convulsions, coma

Type of Hyponatremias:
1) Hypotonic hyponatremias:
?Hypervolumic
?Euvolumic
?Hypovolumic

2) Hypertonic hyponatremia
3) Isotonic hyponatremia

Hypovolemic Hypotonic Hyponatremia:
?Primary Na loss ? Secondary Water gain

Renal Losses (FENA > 1%)
?Diuretics
?Hypoaldosteronism
?Salt-wasting Nephropathy

Extra-renal Losses (FENA < 1%)
?GI losses
?Third Spacing
?Insensible losses

Euvolemic Hypotonic Hyponatremia:

?Psychogenic Polydipsia:
?Requires intake of >10 L/day
?Uosm < 100 mosm/kg
?Low Uric Acid

?Reset Osmostat:
?ADH physiology reset to secrete at subnormal serum osmolality threshold (<280 mosm/kg)
?Seen in: Elderly, Pulmonary processes (e.g. TB), Malnutrition

Euvolemic Hypotonic Hyponatremia:
?SIADH

?Diagnostic Criteria:
?Euvolemic state
?Normal renal, thyroid and adrenal function
?Hypoosmolar serum (<270 mosm/Kg)
?Inappropriately concentrated urine (>100 mosm/Kg)
?High urinary Na (>40 meq/L) with normal salt and water intake

?Etiologies:
?Endocrinopathies: Hypothyroidism, Adrenal Insufficiency
?Pulmonary Pathology: Pneumonia, Asthma, COPD, PTX
?Intracranial Pathology: Trauma, Infection, Hemorrhage
?Malignancies: Small Cell Lung ca. Intracranial Tumors
?Drugs: Antipsychotic, Antidepressants, Thiazides

Hypervolemic Hypotonic Hyponatremia:
?Decreased Effective Arterial Volume
?Congestive Heart Failure
?Cirrhosis
?Nephrotic Syndrome
?Advanced Renal Failure

Workup:
?Determine Tonicity?
?Osmolality = 2 (Na meq/L) + Glucose(mg/dl) + BUN(mg/dl)
18 2.8
For Hypotonic Hyponatremia:
?Determine Volume Status?

Treatment:
?Hypovolemic Hyponatremia:
?Volume replacement with 0.9% NaCl
?Na Deficit =
0.6 X Body Wt. X (140 ? Measured Na) (X 0.85 in women)

?Hypervolemic Hyponatremia:
?Sodium Restriction to 1-3 g/day
?Water Restriction: 1.0-1.5 L/day
?Diuretics
?Na <110 meq/l + CNS symptoms: judicious administration 3% saline with diuretics
?Emergency dialysis

?Euvolemic hyponatremia :
?Free Water Restriction
?Careful Na correction
?Asymptomatic but Na <120 meq/l : 0.9% saline + frusemide maybe used
?In case of Neurological Emergencies
?Loop Diuretics + Fluid Replacement with Hypertonic Saline ( 3% )
?If Chronic ? Demeclocycline 300-600 mg twice daily
?Fludrocortisone
?Selective vasopressin V2 antagonist