Hyponatremia By Ehealthguide.info

By Author: Ibrahim Machiwala
Total Articles: 396
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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 FNa 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 (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