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Third stage
Medicine
Lec-2
د
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عبدالحق
1/1/2014
Hyponatremia and Hypernatremia
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
Volume status helps predict cause
Deplesional Hyponat
• Hypovolemic Hyponatremia
– Diarrhea ,Vomiting
– Adrenal insufficiency(Addison disease(
– Thiazide overdose..loss of Na.
– Decrease intake of Na, Excessive sweating→ increased thirst → intake of
excessive amounts of pure water only without Na
Delusional Hyponat
• Euvolemic
– SIADH
– Primary Polydipsia
• Hypervolemia
– Cirrhosis and CHF, Nephrotic Synd
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Clinical manifestations of Hyponatremia
• Neurological symptoms
– Lethargy, headache, confusion, apprehension, depressed reflexes, seizures and
coma
• Muscle symptoms
– Cramps, weakness, fatigue
• Gastrointestinal symptoms
– Nausea, vomiting, abdominal cramps, and diarrhea
Psuedohyponatremia
High blood sugar (DKA) or protein level (multiple myeloma) can cause falsely depressed
sodium levels
Normal ADH response to low sodium is to be suppressed to allow maximally dilute
urine to be excreted thereby raising serum sodium level
Causes of Hyponatremia can be classified based on ADH level
_ Hyponatremia with ADH inappropriately elevated (SIADH)
_appropriately suppressed eg. Primary polydypsia
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)
– Increase plasma Osmolality(NR..275-290 mOsm/kg)
– SIADH
Main diagnostic criteria for SIADH
• Clinical Euvolemia
• Hyponatremia below 130 mmol/l
• Urine osmolality isnot minimally low(as one expect
(
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Usually more than 150 mOmol/kg,though generally greater than 400-500 mOsm/kg in
setting of low serum osmolality (below 270 mOsm/kg)
• Urine sodium is not minimally low ie greater than 30 mEq/L
• Normal hepatic, renal and cardiac function
• Normal thyroid and adrenal function
SIADH
Caused by
• CNS disease – tumor, infection, CVA, SAH,
• Pulmonary disease – TB, pneumonia, positive pressure ventilation
• Cancer – Lung, pancreas, thymoma, ovary, lymphoma
• Drugs – NSAIDs, SSRIs, diuretics, TCAs
• Surgery - Postoperative
• Idopathic – most common
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
WHAT NEXT?
• With no severe symptoms : 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)
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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, LFTs, B.glucose ,Keton in urine,and S.Protein electrphoresis
(psuedohyponatremia…..DKA,MM) Chest Xray (small cell carcinoma ؟
Treatment is based on symptoms &type of Hyponatremia
• 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
• If Hyponat. Develops over hours or days..morbidity high due to cerebral oedema
relatively rapid correction with starting bolus of 100 ml of 3% hypertonic saline which
generally raise serum sodium level by 2-3 mEq/L
• Goals for correction : gradual correction
• 2 mEq/L per hour for first 3-4 hours until symptoms resolve
• Increase by no more than 10-12 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
:
• For Delusional Hyponatremia
Oral fluid restriction is the first step
– No more than 600-1000 mL per day
– Removal of cause of SIADH,
– Demeclocycline 600-900 mg
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• If volume depletion (Deplesional Hypovolemic) is present, isotonic (0.9%) saline can
be given intravenously
• Hypervolemic Hyponatremia : treat underlying cause ,Causious Duiretics with fluid
restriction. K sparing duiretics are especially benificial in states of Secondary
Hyperaldoseronism
*Serum sodium levels should be drawn every 4-6 hours or more frequently if hypertonic
saline is used
Hypertonic saline contains 500 mEq/L of sodium
Normal saline contains 154 mEq/L of sodium
What if the sodium increases too fast?
The serious complication of replacing 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 death
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
Hypernatremia
– Produced by either administration of hypertonic fluids or much more
frequently, loss of thirst or failure of ADH mechanisms
– Water moves from ICF → ECF
&Cells dehydrate
Because of extremely efficient regulatory mechanisms such as ADH and thirst,
hypernatremia generally occurs only in people with prolonged lack of thirst
mechanism
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Patients with loss of ADH -
Diabetes Insipidus(DI(usually can compensate with
increased fluid intake
Causes of Hypernatremia
sweat losses in prolonged fever…..loss of pure water.
Insufficient intake of water (hypodipsia(
GIT losses
Diabetes Insipidus (both central and nephrogenic(
Osmotic Diuresis – DKA
Hypothalamic lesions which affect thirst function – Causes include tumors,
granulomatous diseases or vascular disease
Sodium Overload – Infusion of Hypertonic sodium bicarbonate for metabolic acidosis
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
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
If urine osmolality is lower than serum osmolality then DI is suspected
Administration of Desmopressin-DDAVP will differentiate types of DI
* Urine osmolality will increase in central DI, no response in nephrogenic DI
Treatment of hypernatremia
Typical fluids given in form of Dextrose 5%
• 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