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