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Hyponatremia• Definition: – Commonly defined as a serum sodium concentration< 135 meq/L – Hyponatremia represents a relative excess of water in relation to sodium. – occur due to: 1)Water retention dt impaired free water excretion 2) Less: Na loss>water loss (thiazide induced hyponatremia)
Hyponatremia Epidemiology: Frequency ocw.jhsph.edu Hyponatremia is the most common electrolyte disorder prevalence of approximately 7% 30% of patients treated in the intensive care unit 50% of NHR had atleast one episode of hyponatremia.
Hyponatremia Epidemiology Cont. Mortality/Morbidity Acute hyponatremia (developing over 48 h or less) are subject to more severe degrees of cerebral edema sodium level is less than 105 mEq/L, the mortality is over 50% Chronic hyponatremia (developing over more than 48 h) experience milder degrees of cerebral edema Brainstem herniation has not been observed in patients with chronic hyponatremia
Hyponatremia Physiology Serum sodium concentration regulation: stimulation of thirst secretion of ADH feedback mechanisms of the renin- angiotensin-aldosterone system renal handling of filtered sodium www.daviddarling.info
1- Stimulation of thirst: Thirst center is located in the anteriolateral center of the hypothalamus Osmolality increases Main driving force Only requires an increase of 2% - 3% Blood volume or pressure is reduced Requires a decrease of 10% - 15%2- Secretion of ADH Synthesized by the neuroendocrine cells in the supraoptic and paraventricular nuclei of the hypothalamus Triggers: Osmolality of body fluids A change of about 1% Volume and pressure of the vascular system Increases the permeability of the collecting duct to water and urea
ADH No ADH: ADH Present:
Age related changes of water metabolism: The elderly have a delayed and less intense thirst response than do younger person total body water decreases because of an increase in fat and a decrease in lean body mass (from about 60% of body weight in healthy young adults to about 45% of body weight in the elderly The ability to concentrate urine decreases with age in part because of tubular senescence. Many elderly persons also have resistance to the renal action of ADH, ie, a form of acquired partial nephrogenic diabetes insipidus. Decreased renal conservation of Na dt: Nephron loss Decreased renin and aldosterone Increased ANP An age-related decrease in serum sodium concentration of 1 mEq/L/decade occurs after age 40
Pathophysiology hyponatremia occur when some condition impairs normal free water excretion or Na loss exceed water loss acute drop in the serum osmolality: neuronal cell swelling occurs due to the water shift from the extracellular space to the intracellular space Swelling of the brain cells elicits 2 responses for osmoregulation, as follows: It inhibits ADH secretion and hypothalamic thirst center immediate cellular adaptation
Clinical Manifestations most patients with a serum sodium concentration exceeding 125 mEq/L are asymptomatic Patients with acutely developing hyponatremia are typically symptomatic at a level of approximately 120 mEq/L Most abnormal findings on physical examination are characteristically neurologic in origin patients may exhibit signs of hypovolemia or hypervolemia
Manifestations In acute hyponatremia, osmotic forces cause water movement into brain cells leading to cerebral edema Mild Sx: anorexia, nausea, lethargy Mod Sx: disoriented, agitated, neuro deficit Sev Sx: seizures, coma, death
Classification According to Plasma Osmolality: 1. Hypotonic hyponatremia 2.Hypertonic hyponatremia: (Redistributive hyponatremia) excess of another effective osmole (glc, mannitol) that draws water intravenously. hyperglycemia (1.6/100) 3. Isotonic hyponatremia: *Pseudohyponatremia ; hyperlipidemia or hyperprotienemia results in low measured Na⁺ concentration (but osmolality is normal) it is a rare lab artifact *Artefactual hyponatremia; taking blood from a drip arm into which a low sodium fluid is being infused.
Labs Osm: 275-290 mosm/kg Plasma Urine Osm Volume Status Urine Na Concentration
Treatment four issues must be addressed Asymptomatic vs. symptomatic acute (within 48 hours) chronic (>48 hours) Volume status 1st step is to calculate the total body water total body water (TBW) = 0.6 × body weight
Treatment Cont next decide what our desired correction rate should be Symptomatic immediate increase in serum Na level by 8 to 10 meq/L in 4 to 6 hours with hypertonic saline is recommended acute hyponatremia more rapid correction may be possible 8 to 10 meq/L in 4 to 8 hours chronic hyponatremia slower rates of correction 12 meq/L in 24 hours
IV Fluids One liter of Lactated Ringers Solution contains: 130 mEq of sodium ion = 130 mmol/L 109 mEq of chloride ion = 109 mmol/L 28 mEq of lactate = 28 mmol/L 4 mEq of potassium ion = 4 mmol/L 3 mEq of calcium ion = 1.5 mmol/L One liter of Normal Saline contains: 154 mEq/L of Na+ and Cl− One liter of 3% saline contains: 514 mEq/L of Na+ and Cl−
Na+deficit= Target Na - Current Na e.g. 120-115 Total body Na+ deficit= Na+deficit x total body water = 5 x 0.6x body wt (50kgs) = 125meq Amount of 3% NaClneeded (Na=513meq/L)= 125/513= 240ml Rate of infusion=0.5meq/hour=10 hours =24ml/hour
SIADH response to isotonic saline is different in the SIADH In hypovolemia both the sodium and water are retained sodium handling is intact in SIADH administered sodium will be excreted in the urine, while some of the water may be retained possible worsening the hyponatremia
SIADH Water restriction 0.5-1 liter/day Salt tablets Demeclocycline Inhibits the effects of ADH Onset of action may require up to one week
Volume depletion: Isotonic saline: raises plasma sodium by 1-2 meq/L for every liter of fluid infused since saline has higher Na concentration (154 meq/L) than hyponatremic plasma volume repletion removes stimulation of ADH
CHF, Cirrhosis, Nephrotic syndrome Patients have increased total body sodium stores. Treatment consists of sodium and water restriction and attention to the underlying cause. The vasopressin receptor antagonists conivaptan (Vaprisol) and tolvaptan (Samsca) are now approved for use in hospitalized patients with hypervolemic hyponatremia, though clinical experience is scant
Indications for 3% NaCl Symptomatic hyponatremia (SZ, coma) Acute severe hyponatremia (<24h, < 120 mEq/L) SAH with hyponatremia worsening on 0.9% NaCl
Why don’t we correct the hyponatremiarapidly?? It results in a severe neurological syndrome due tolocal areas of demyelination called “CentralPontine Myelinosis” or “Osmotic DemyelinationSyndrome”. Symptoms include dysarthia, dysphagia, spasticquadriplegia, psuedobulbar palsy, and respiratoryarrest. Occurs in the pons mostly, but also in the basalganglia, internal capsule, and cerebral cortex.