Hyponatremia

Hyponatremia
By :
James Yost, MD, MS, MBA
Emory Family Medicine

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

Hyponatremia
* Definition:
o Commonly defined as a serum sodium concentration 135 meq/L
o Hyponatremia represents a relative excess of water in relation to sodium.
* Epidemiology:
o 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
o 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
o 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
* Physiology
o Serum sodium concentration regulation:
+ stimulation of thirst
+ secretion of ADH
+ feedback mechanisms of the renin-angiotensin-aldosterone system
+ renal handling of filtered sodium
o 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
o 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
o 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
o extracellular-fluid and intracellular-fluid compartments make up 40 percent and 60 percent of total body water
o renal handling of water is sufficient to excrete as much as 15-20 L of free water per day
o sodium is the predominant osmole in the extracellular fluid (ECF) compartment and serum

* Pathophysiology
o hyponatremia can only occur when some condition impairs normal free water excretion
o 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
* Types
o Hypovolemic hyponatremia
o Euvolemic hyponatremia
o Hypervolemic hyponatremia
o Redistributive hyponatremia
o 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
* Nonrenal loss
o GI losses
+ Vomiting, Diarrhea, fistulas, pancreatitis
o Excessive sweating
o Third spacing of fluids
+ ascites, peritonitis, pancreatitis, and burns
o Cerebral salt-wasting syndrome
+ traumatic brain injury, aneurysmal subarachnoid hemorrhage, and intracranial surgery
+ Must distinguish from SIADH
* Renal Loss
o Acute or chronic renal insufficiency
o Diuretics

Euvolemic hyponatremia
* Normal sodium stores and a total body excess of free water
o Psychogenic polydipsia, often in psychiatric patients
o Administration of hypotonic intravenous or irrigation fluids in the immediate postoperative period
o administration of hypotonic maintenance intravenous fluids
o Infants who may have been given inappropriate amounts of free water
o bowel preparation before colonoscopy or colorectal surgery
* SIADH
o downward resetting of the osmostat
o Pulmonary Disease
+ Small cell, pneumonia, TB, sarcoidosis
o Cerebral Diseases
+ CVA, Temporal arteritis, meningitis, encephalitis
o Medications
+ SSRI, Antipsychotics, Opiates, Depakote, Tegratol

* Total body sodium increases, and TBW increases to a greater extent.
* Can be renal or non-renal
o acute or chronic renal failure
+ dysfunctional kidneys are unable to excrete the ingested sodium load
o cirrhosis, congestive heart failure, or nephrotic syndrome

Redistributive hyponatremia
o 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
* Pseudohyponatremia
o The aqueous phase is diluted by excessive proteins or lipids. The TBW and total body sodium are unchanged.
+ hypertriglyceridemia
+ multiple myeloma
* Clinical Manifestations
o most patients with a serum sodium concentration exceeding 125 mEq/L are asymptomatic
o Patients with acutely developing hyponatremia are typically symptomatic at a level of approximately 120 mEq/L
o Most abnormal findings on physical examination are characteristically neurologic in origin
o patients may exhibit signs of hypovolemia or hypervolemia
* Diagnosis
o CT head, EKG, CXR if symptomatic
o Repeat Na level
o Correct for hyperglycemia
o Laboratory tests provide important initial information in the differential diagnosis of hyponatremia
+ Plasma osmolality
+ Urine osmolality
+ Urine sodium concentration
+ Uric acid level
+ FeNa
o 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
o 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
o 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
o Urine Sodium
+ >20 mEq/L
# SIADH, diuretics
+ <20 mEq/L
# cirrhosis, nephrosis, congestive heart failure, GI loss, skin, 3rd spacing, psychogenic polydipsya
o Uric Acid Level
+ < 4 mg/dl consider SIADH
o FeNa
+ Help to determine pre-renal from renal causes
* Treatment
o four issues must be addressed
+ Asyptomatic vs. symptomatic
+ acute (within 48 hours)
+ chronic (>48 hours)
+ Volume status
o 1st step is to calculate the total body water
+ total body water (TBW) = 0.6 × body weight
o next decide what our desired correction rate should be
o Symptomatic
+ immediate increase in serum Na level by 8 to 10 meq/L in 4 to 6 hours with hypertonic saline is recommended
o acute hyponatremia
+ more rapid correction may be possible
# 8 to 10 meq/L in 4 to 8 hours
o chronic hyponatremia
+ slower rates of correction
# 12 meq/L in 24 hours

* Symptomatic or Acute
o 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
o OH MY GOD, what did he just say!!!!!!!!!!!!!!!!!!

* IV Fluids
o 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
o One liter of Normal Saline contains:
+ 154 mEq/L of Na+ and Cl−
o One liter of 3% saline contains:
+ 514 mEq/L of Na+ and Cl−

* Example:
o a 60 kg women with a plasma sodium of 110 meq/L
o Formula:
+ ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)
o What is the TBW?
o How high will 1 liter of normal saline raise the plasma sodium?
* Answer:
o TBW is 30 L
o Serum sodium will increase by approximately 1.4 meq/L for a total SNa of 111.4 meq/L

* Example:
o a 90 kg man with a plasma sodium of 110 meq/L
o Formula:
+ ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)
o What is the TBW?
o How high will 1 liter of 3% saline raise the plasma sodium?
* Answer:
o TBW is 54 L
o Serum sodium will increase by approximately 7.3 meq/L for a total SNa of 117.3 meq/L

* Asymptomatic or Chronic
o 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
o 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

* 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
o What type of hyponatremia does this patient have?
o What additional labs/studies would you want?

* Example Cont.:
o Noncontrast CT Head:
* Tx
o Call Neurology and neurosurgery
o Free water restriction

* Example:
o 63 y/o female at 75 Kg with N/V/D for 4 days
o SNa is 108 mEq/L
o 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
o What type of hyponatremia does this patient have?
o What additional labs/studies would you want?
* How will you Tx her?
o Calculate the total body water
+ 0.5 x weight = 37.5 L
o What rate of correction do you want?
+ 8 to 10 mEq/L in 6 to 8 hours
o What fluid will you use?
+ 3% Saline
o How will you calculate the amount of sodium to give her?
+ ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)
o How will her sodium increase after 1 liter of 3% saline?
+ By 10.8 mEq/L to 118.8 mEq/L

* What other medication will she need?
o 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?
o ΔSNa = {[Na + K]inf − SNa} ÷ (TBW + 1)
o ΔSNa = 154mEq/L – 118.8mEq/L ÷ 38.5L = 0.9 mEq/L
* So 2 liters of normal saline over the next 14 hours

Hyponatremia.ppt