HyponatremiaBy

James Yost, MD, MS, MBA

Emory Family Medicine

Hyponatremia• Definition• Epidemiology• Physiology• Pathophysiology• Types• Clinical Manifestations• Diagnosis • Treatment

Hyponatremia

• Definition:– Commonly defined as a serum sodium concentration

135 meq/L

– Hyponatremia represents a relative excess of water in relation to sodium.

Hyponatremia

• Epidemiology:– Frequency

• Hyponatremia is the most common electrolyte disorder• incidence of approximately 1%• prevalence of approximately 2.5%• surgical ward, approximately 4.4%• 30% of patients treated in the intensive care unit

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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

• Epidemiology Cont.– Age

• Infants – fed tap water in an effort to treat symptoms of gastroenteritis – Infants fed dilute formula in attempt to ration

• Elderly patients with diminished sense of thirst, especially when physical infirmity limits independent access to food and drink

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

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Hyponatremia

• Physiology Cont.– Stimulation of thirst

• Osmolality increases– Main driving force– Only requires an increase of 2% - 3%

• Blood volume or pressure is reduced– Requires a decrease of 10% - 15%

• Thirst center is located in the anteriolateral center of the hypothalamus

– Respond to NaCL and angiotensin II

Hyponatremia

• Physiology Cont.– Secretion of ADH

• Synthesized by the neuroendocrine cells in the supraoptic and paraventricular nuclei of the hypothalamus

• Triggeres:– 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

Hyponatremia

• Physiology Cont– renin-angiotensin-aldosterone

• Renin– Stemuli are perfusion pressure, sympathetic activity, and NaCl

delivery to the macula densa– Increase in NaCl delivery to the macula decreases the GFR by

decrease in the renin secretion• Aldosterone

– Reduces NaCl excretion by stimulating it’s resorption » Ascending loop of Henle» Distal tubule» Collecting duct

Hyponatremia

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Hyponatremia

• Physiology Cont.– extracellular-fluid and intracellular-fluid

compartments make up 40 percent and 60 percent of total body water

– renal handling of water is sufficient to excrete as much as 15-20 L of free water per day

– sodium is the predominant osmole in the extracellular fluid (ECF) compartment and serum

Hyponatremia

• Pathophysiology– hyponatremia can only occur when some

condition impairs normal free water excretion– 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

Hyponatremia

• Types– Hypovolemic hyponatremia– Euvolemic hyponatremia– Hypervolemic hyponatremia– Redistributive hyponatremia– Pseudohyponatremia

Hypovolemic hyponatremia

• develops as sodium and free water are lost and/or replaced by inappropriately hypotonic fluids

• Sodium can be lost through renal or non-renal routes

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Hypovolemic hyponatremia

• Nonrenal loss– GI losses

• Vomiting, Diarrhea, fistulas, pancreatitis

– Excessive sweating– Third spacing of fluids

• ascites, peritonitis, pancreatitis, and burns

– Cerebral salt-wasting syndrome• traumatic brain injury, aneurysmal subarachnoid

hemorrhage, and intracranial surgery• Must distinguish from SIADH

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Hypovolemic hyponatremia

• Renal Loss– Acute or chronic renal insufficiency– Diuretics

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Euvolemic hyponatremia

• Normal sodium stores and a total body excess of free water– Psychogenic polydipsia, often in psychiatric

patients – Administration of hypotonic intravenous or

irrigation fluids in the immediate postoperative period

Euvolemic hyponatremia

– administration of hypotonic maintenance intravenous fluids

– Infants who may have been given inappropriate amounts of free water

– bowel preparation before colonoscopy or colorectal surgery

Euvolemic hyponatremia

• SIADH– downward resetting of the osmostat – Pulmonary Disease

• Small cell, pneumonia, TB, sarcoidosis

– Cerebral Diseases• CVA, Temporal arteritis, meningitis, encephalitis

– Medications• SSRI, Antipsychotics, Opiates, Depakote, Tegratol

Hypervolemic hyponatremia

• Total body sodium increases, and TBW increases to a greater extent.

• Can be renal or non-renal– acute or chronic renal failure

• dysfunctional kidneys are unable to excrete the ingested sodium load

– cirrhosis, congestive heart failure, or nephrotic syndrome

Redistributive hyponatremia– Water shifts from the intracellular to the

extracellular compartment, with a resultant dilution of sodium. The TBW and total body sodium are unchanged.

• This condition occurs with hyperglycemia• Administration of mannitol

Hyponatremia

• Pseudohyponatremia– The aqueous phase is diluted by excessive

proteins or lipids. The TBW and total body sodium are unchanged.

• hypertriglyceridemia• multiple myeloma

Hyponatremia

• 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

Hyponatremia• Diagnosis

– CT head, EKG, CXR if symptomatic– Repeat Na level– Correct for hyperglycemia– Laboratory tests provide important initial

information in the differential diagnosis of hyponatremia

• Plasma osmolality • Urine osmolality • Urine sodium concentration • Uric acid level• FeNa

Hyponatremia

• Laboratory tests Cont.– Plasma osmolality

• normally ranges from 275 to 290 mosmol/kg• If >290 mosmol/kg :

– Hyperglycemia or administration of mannitol

• If 275 – 290 mosmol/kg :– hyperlipidemia or hyperproteinemia

• If <275 mosmol/kg :– Eval volume status

Hyponatremia

• Laboratory tests Cont.– Plasma osmolality < 275 mosmol/kg

• Increased volume:– CHF, cirrhosis, nephrotic syndrome

• Euvolemic – SIADH, hypothyroidism, psychogenic polydipsia, beer

potomania, postoperative states

• Decreased volume– GI loss, skin, 3rd spacing, diuretics

Hyponatremia

• Laboratory tests Cont.– Urine osmolality

• Normal value is > 100 mosmol/kg• Normal to high:

– Hyperlipidemia, hyperproteinemia, hyperglycemia, SIADH

• < 100 mosmol/kg– hypoosmolar hyponatremia

» Excessive sweating» Burns» Vomiting» Diarrhea» Urinary loss

Hyponatremia• Laboratory tests Cont.

– Urine Sodium• >20 mEq/L

– SIADH, diuretics

• <20 mEq/L– cirrhosis, nephrosis, congestive heart failure, GI loss, skin, 3rd

spacing, psychogenic polydipsya

– Uric Acid Level• < 4 mg/dl consider SIADH

– FeNa• Help to determine pre-renal from renal causes

Hyponatremia

• Treatment– four issues must be addressed

• Asyptomatic 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

Hyponatremia• 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

Hyponatremia• Symptomatic or Acute

– Treatment Cont. - Here comes the Math!!!• estimate SNa change on the basis of the amount of Na

in the infusate• ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)

– ΔSNa is a change in SNa– [Na + K]inf is infusate Na and K concentration in 1 liter of

solution

– OH MY GOD, what did he just say!!!!!!!!!!!!!!!!!!

Hyponatremia• IV Fluids

– One liter of Lactated Ringer's 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−

Hyponatremia• Example:

– a 60 kg women with a plasma sodium of 110 meq/L– Formula:

• ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)

– What is the TBW?– How high will 1 liter of normal saline raise the

plasma sodium?

• Answer:– TBW is 30 L– Serum sodium will increase by approximately 1.4

meq/L for a total SNa of 111.4 meq/L

Hyponatremia• Example:

– a 90 kg man with a plasma sodium of 110 meq/L– Formula:

• ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)

– What is the TBW?– How high will 1 liter of 3% saline raise the plasma

sodium?

• Answer:– TBW is 54 L– Serum sodium will increase by approximately 7.3

meq/L for a total SNa of 117.3 meq/L

Hyponatremia

• Asymptomatic or Chronic– 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

Hyponatremia

• Asypmtomatic or Chronic– 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

Hyponatremia• Example:

– 85 y/o male with weakness and head ache– SNa is 118 mEq/L– Plasma osmolality is 254 mosmol/kg– Urine osmolality is 130 mosmol/kg– Urine sodium >20 mEq/L– Uric acid is 3mg/dl

• What type of hyponatremia does this patient have?

• What additional labs/studies would you want?

Hyponatremia

• Example Cont.:– Noncontrast CT Head:

• Tx– Call Neurology and

neurosurgery– Free water restriction

Ouch!!!!!

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Hyponatremia• Example:

– 63 y/o female at 75 Kg with N/V/D for 4 days– SNa is 108 mEq/L– She has had one seizure in the ambulance

• Plasma osmolality is 251 mosmol/kg• Urine osmolality is 47 mosmol/kg• Uric acid is 6mg/dl

• What type of hyponatremia does this patient have?

• What additional labs/studies would you want?

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Hyponatremia• How will you Tx her?

– Calculate the total body water• 0.5 x weight = 37.5 L

– What rate of correction do you want?• 8 to 10 mEq/L in 6 to 8 hours

– What fluid will you use?• 3% Saline

– How will you calculate the amount of sodium to give her?

• ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)

– How will her sodium increase after 1 liter of 3% saline?

• By 10.8 mEq/L to 118.8 mEq/L

Hyponatremia

• What other medication will she need?– Lasix and a foley

• Her sodium increases to 118.8 mEq/L over the next 8-10 hours. How will you continue to correct her hyponatremia?– ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)

– ΔSNa = 154mEq/L – 118.8mEq/L ÷ 38.5L = 0.9 mEq/L

• So 2 liters of normal saline over the next 14 hours

Hyponatremia

• Congrats!!!!!!!! You saved her!

• Questions????