Transcript Hyponatremia and Hypernatremia

Hyponatremia and
Hypernatremia
Conor Gough
HO – III
2008-2009
Hyponatremia
• Defined as sodium concentration < 135 mEq/L
• Generally considered a disorder of water as
opposed to disorder of salt
• Results from increased water retention
• Normal physiologic measures allow a person to
excrete up to 10 liters of water per day which
protects against hyponatremia
• Thus, in most cases, some impairment of renal
excretion of water is present
Causes
• Normal ADH response to low sodium is to be
suppressed to allow maximally dilute urine to be
excreted thereby raising serum sodium level
• Psuedohyponatremia – High blood sugar (DKA) or
protein level (multiple myeloma) can cause falsely
depressed sodium levels
• Causes of Hyponatremia can be classified based
on either volume status or ADH level
– Hypovolemic, Euvolemic or Hypervolemic
– ADH inappropriately elevated or appropriately
suppressed
ADH suppresion
• Conditions which ADH is suppressed
– Primary Polydipsia
– Low dietary solute intake “Tea and Toast
syndrome” or “Beer Potomania”
– Advanced Renal Failure
ADH elevation
• Conditions which ADH is elevated
– Volume Depletion
• True volume depletion (i.e. bleeding)
• Effective circulating volume depletion (i.e. heart failure
and cirrhosis)
– Exercised induced hyponatremia
– Thiazide Diuretics
– Adrenal insufficiency
– SIADH
First step in Assessment: Are
symptoms present?
• Hyponatremia can be asymptomatic and
found by routine lab testing
• It may present with mild symptoms such as
nausea and malaise (earliest) or headache and
lethargy
• Or it may present with more severe symptoms
such as seizures, coma or respiratory arrest
Presentation determines if immediate
action is needed
• If severe symptoms are present, hypertonic saline
needs to be administered to prevent further
decline
• If severe symptoms are not present, can start by
initiating fluid restriction and determining cause
of hyponatremia
• Oral fluid restriction is good first step as it will
prevent further drop in sodium
• NOTE: This does not mean that you can’t give
isotonic fluids to someone who is truly volume
depleted
WHAT NEXT?
• With no severe symptoms and fluid restriction
started, next step is to assess volume status to
help determine cause
• Hypovolemic – urine output, dry mucous
membranes, sunken eyes
• Euvolemic – normal appearing
• Hypervolemic – Edema, past medical history,
Jaundice (cirrhosis), S3 (CHF)
Volume status helps predict cause
• Hypovolemia
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True Volume Depletion
Adrenal insufficiency
Thiazide overdose
Exercised induced hyponatremia
• Euvolemia
– SIADH
– Primary Polydipsia
• Hypervolemia
– Cirrhosis and CHF
Workup for Hyponatremia
• 3 mandatory lab tests
– Serum Osmolality
– Urine Osmolality
– Urine Sodium Concentration
• Additional labs depending on clinical suspicion
– TSH, cortisol (Hypothryoidism or Adrenal
insufficiency)
– Albumin, BMP, triglycerides and SPEP
(psuedohyponatremia, cirrhosis, MM)
How to interpret the tests?
• Serum Osmolality
– Can differentiate between true hyponatremia,
pseudohyponatremia and hypertonic hyponatremia
• Urine Osmolality
– Can differentiate between primary polydipsia and
impaired free water excretion
• Urine Sodium concentration
– Can differentiate between hypovolemia hyponatremia
and SIADH
Additional Tests
• TSH – high in hypothyroidism
• Cortisol – low in adrenal insufficiency, though
may be inappropriately normal in
infection/stressful state, therefore should get
Corti-Stim test to confirm
• Head CT and Chest Xray – May see evidence of
cerebral salt wasting or small cell carcinoma
which can both cause hyponatremia
And of course…the not so common
• Iatrogenic infusion of hypotonic fluids (“Surgeon sign”)
• Ecstasy use – increased water intake with inappropriate
ADH secretion
• Underlying infections
• NSIAD – Nephrogenic syndrome of inappropriate
antidiuresis – Hereditary disorder that presents with
low sodium levels in newborn males with undetectable
ADH levels
• Reset Osmostat – Occurs in elderly and pregnancy
where regulated sodium set point is lowered
SIADH: Important concept to
understand
• Caused by various etiologies
• CNS disease – tumor, infection, CVA, SAH, DTs
• Pulmonary disease – TB, pneumonia, positive
pressure ventilation
• Cancer – Lung, pancreas, thymoma, ovary,
lymphoma
• Drugs – NSAIDs, SSRIs, diuretics, TCAs
• Surgery - Postoperative
• Idopathic – most common
Main diagnostic criteria for SIADH
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Clinical Euvolemia
Hypotonic Hyponatremia
Normal hepatic, renal and cardiac function
Normal thyroid and adrenal function
Urine osmolality greater than 100 mOsm/kg
though generally greater than 400-500 mOsm/kg
in setting of low serum osmolality (AKA
inappropriate)
• Urine sodium level greater than 20 mEq/L
Treatment is based on symptoms
• Patients with serum sodium above 120 are
generally asymptomatic
• Symptoms tend to occur at serum sodium
levels lower than 120 or when a rapid decline
in sodium levels occur
• Patients can have mild symptoms at sodium
concentrations of 110-115 mEq/L when this
level is reached gradually
Severe symptoms present
• As stated earlier, symptoms dictate treatment
• If severe symptoms are present, starting bolus of
100 ml of 3% hypertonic saline which generally
raise serum sodium level by 2-3 mEq/L
• Goals for correction:
– 1.5 to 2 mEq/L per hour for first 3-4 hours until
symptoms resolve
– Increase by no more than 10 mEq/L in first 24 hrs
– Increase by no more than 18 mEq/L in first 48 hrs
What if little to no symptoms are
present?
• Oral fluid restriction is the first step
– No more than 1500 mL per day
– NOTE: This only pertains to oral fluid, isotonic IV
fluids do not count towards fluid intake
• If volume depletion is present, isotonic (0.9%)
saline can be given intravenously
• Careful monitoring should be used whether
symptoms are present or not
– Serum sodium levels should be drawn every 4-6 hours
or more frequently if hypertonic saline is used
Formulas that may help: How much
sodium does the patient need?
• Sodium deficit = Total body water x (desired
Na – actual Na)
• Total body water is estimated as lean body
weight x 0.5 for women or 0.6 for men
How about an example:
• 60 kg woman with sodium level of 116
• How much sodium will bring him up to 124 in
the next 24 hours?
• Sodium needed = 0.5 x 60 x (124-116) = 240
• Hypertonic saline contains 500 mEq/L of
sodium
• Normal saline contains 154 mEq/L of sodium
Example (continued)
• The patient needs 240 mEq in next 24 hours
• That averages to 10 mEq per hour or 20 mL of
hypertonic saline per hour
• However, this will only raise the serum sodium
by 0.33 per hour therefore, increasing the rate
60 mL to 90 mL will produce the desired rate
of serum sodium increase of 1.0 to 1.5 mEq
per hour until symptoms resolve
What if the sodium increases too fast?
• The dreaded complication of increasing
sodium too fast is Central Pontine Myelinolysis
which is a form of osmotic demyelination
• Symptoms generally occur 2-6 days after
elevation of sodium and usually either
irreversible or only partially reversible
• Symptoms include: dysarthria, dysphagia,
paraparesis, quadriparesis, lethargy, coma or
even seizures
Risk Factors for demyelination
• Rate of correction over 24 hours more important
than rate of correction in any one particular hour
• More common if sodium increases by more than
20 mEq/L in 24 hours
• Very uncommon if sodium increases by 12 mEq/L
or less in 24 hours
• CT but preferably MRI to diagnose demyelination
if suspected, though imaging studies may not be
positive for up to 4 weeks after initial correction
Treatment Options
• CPM is associated with poor prognosis
• Prevention is key
• Small studies have shown that plasmapharesis
done immediately after diagnosis may
improve clinical outcomes
Summary of Hyponatremia
• Hyponatremia has variety of causes
• Treatment is based on symptoms
– Severe symptoms = Hypertonic Saline
– Mild or no symptoms = Fluid restriction
• Overcorrection, more than 12 mEq increase in
24 hours must be avoided with monitoring
• Serum Osmolality, Urine Osmolality and Urine
sodium concentration are initial tests to order
Moving on to Hypernatremia
• Produced by either administration of hypertonic
fluids or much more frequently, loss of thirst
• Because of extremely efficient regulatory
mechanisms such as ADH and thirst,
hypernatremia generally occurs only in people
with prolonged lack of thirst mechanism
• Patients with loss of ADH (Diabetes Insipidus)
usually can compensate with increased fluid
intake
Causes of Hypernatremia
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Insensible and sweat losses
GI losses
Diabetes Insipidus (both central and nephrogenic)
Osmotic Diuresis – DKA or HHNK
Hypothalamic lesions which affect thirst function
– Causes include tumors, granulomatous diseases
or vascular disease
• Sodium Overload – Infusion of Hypertonic sodium
bicarbonate for metabolic acidosis
Symptoms of Hypernatremia
• Initial symptoms include lethargy, weakness and
irritability
• Can progress to twitching, seizures, obtundation
or coma
• Resulting decrease in brain volume can lead to
rupture of cerebral veins leading to hemorrhage
• Severe symptoms usually occur with rapid
increase to sodium concentration of 158 mEq or
more
• Sodium concentration greater than 180 mEq are
associated with high mortality
Diagnosis of Hypernatremia
• Same labs as workup for hyponatremia: Serum
osmolality, urine osmolality and urine sodium
• Urine sodium should be lower than 25 mEq/L if
and water and volume loss are cause. It can be
greater than 100 mEq/L when hypertonic
solutions are infused or ingested
• If urine osmolality is lower than serum osmolality
then DI is present
– Administration of DDAVP (Desmopressin ) will
differentiate
• Urine osmolality will increase in central DI, no response in
nephrogenic DI
Treatment of Hypernatremia
• First, calculate water deficit
• Water deficit = CBW x ((plasma Na/desired Na
level)-1)
• CBW = current body water assumed to be 50%
of body weight in men and 40% in women
• So let’s do a sample calculation:
– 60 kg woman with 168 mEq/L
– How much water will it take to reduce her sodium
to 140 mEq/L
Calculation continued
• Water deficit = 0.4 x 60 ([168/140]-1) = 4.8 L
• But how fast should I correct it?
• Same as hyponatremia, sodium should not be
lowered by more than 12 mEq/L in 24 hours
– Overcorrection can lead to cerebral edema which can
lead to encephalopathy, seizures or death
• So what does that mean for our patient?
– The 4.8 L which will lower the sodium level by 28
should be given over 56-60 hours, or at a rate of 75-80
mL/hr
– Typical fluids given in form of D5 water
Summary of Hypernatremia
• Loss of thirst usually has to occur to produce
hypernatremia
• Rate of correction same as hyponatremia
• D5 water infusion is typically used to lower
sodium level
• Same diagnostic labs used: Serum osmolality,
Urine osmolality and Urine sodium
• Beware of overcorrection as cerebral edema
may develop
Questions?