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HYPONATREMIA
Dr. M. A. SOFI MD; FRCP
(London); FRCPEdin; FRCSEdin
HYPONATREMIA
 Hyponatremia is commonly defined as a serum sodium
concentration below 135 meq/L but can vary to a small
degree in different clinical laboratories.

The dilutional fall in serum sodium is in most patients
associated with a proportional reduction in the serum
osmolality (i.e., to a level below 275 mosmol/kg), but there
are some exceptions

Hyponatremia represents a relative excess of water in
relation to sodium. It can be induced:
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Marked increase in water intake (primary polydipsia)
Impaired water excretion from advanced renal failure
Persistent release of antidiuretic hormone (ADH).
Acute hyponatremia:
Developed within the previous 24 hours
Hyperacute hyponatremia
Developed over just a few hours due to a marked increase in water
intake (self-induced water intoxication, as may be seen in
marathon runners, psychotic patients, and users of ecstasy)
Sub-acute :
Developed within the previous 24 to 48 hours.
Chronic hyponatremia:
Present for more than 48 hours, or if the duration is unknown
(such as in patients who develop hyponatremia at home).
Mild to moderate and sever hyponatremia:
Mild:
Serum Na concentration 130 - 135 meq/L;
Moderate:
Serum Na concentration 121 - 129 meq/L.
Severe:
Serum sodium of 120 meq/L or less.
EVALUATION — The diagnostic approach consists of a
directed history and physical examination, appropriate
laboratory tests.
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A history of fluid loss (e.g., vomiting, diarrhea, diuretic
therapy) and, on examination, signs of volume depletion,
such as decreased skin turgor, a low jugular venous
pressure or orthostatic or persistent hypotension.
A history of low protein intake and/or high fluid intake.
A history consistent with one of the causes of SIADH.
Use of medications associated with hyponatremia.
Signs of peripheral edema and/or ascites, which can be due
to heart failure, cirrhosis, or renal failure.
Symptoms and signs suggestive of adrenal insufficiency or
hypothyroidism.
Signs & Symptoms
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More profound when the decrease in sodium is very
large or occurs rapidly (i.e. over hours)
Generally asymptomatic if Na+ level >125
Symptoms include:
 Headache
 Nausea, vomiting
 Muscle cramps
 Disorientation, depressed reflexes, lethargy,
restlessness
 Seizure, coma, permanent brain damage,
respiratory arrest, brainstem herniation & death
Symptoms : Hyponatremia
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Absent symptoms –
Asymptomatic, if the
hyponatremia is chronic
and of mild or moderate
severity (i.e., serum
sodium >120 meq/L).
Patients may have
subclinical impairments in
mentation and gait.
Mild to moderate
symptoms –Relatively
nonspecific and include:
 Headache
 Nausea, vomiting
 Fatigue
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Gait disturbances
Confusion in patients with
chronic hyponatremia (i.e.,
>48 hours duration).
In patients with more acute
hyponatremia, such symptoms
should be considered ominous
and may evolve without warning
to seizures, respiratory arrest,
and herniation.
Severe symptoms – Severe
symptoms of hyponatremia
include:
Seizures
 Obtundation
 Coma
 Respiratory arrest
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Approach to Hyponatremia
 1st assess volume status
Is the patient volume overloaded, depleted, or euvolemic?
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2nd assess osmolality (hyper, iso, or hypo)
Is the blood concentrated? For hypotonic hyponatremia,
continue to 3rd step:
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3rd assess urinary sodium excretion and FeNa %
Is the urine concentrated?
*Remember VOU – volume status, osmolality, and urine
studies
Laboratory tests :
Three laboratory tests provide
important initial
information in the
differential diagnosis of
hyponatremia :
 Serum osmolality
 Urine osmolality
 Urine Na+, K+, and
Chloride concentrations
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Serum osmolality (Sosm),
(NR 275 to 290 mosmol/kg)
is reduced in most
hyponatremic patients.
In some patients Sosm is
high or normal.
The three most common
causes of hyponatremia
with a high or normal Sosm
 Marked hyperglycemia
 Severe azotemia
 Alcohol intoxication
STEP 1 – (V) Volume Status
• 1st assess volume status (extracellular fluid volume)
• Hypotonic hyponatremia has 3 main etiologies:
– Hypovolemic – both H2O and Na decreased (H20 < Na)
• Consider obvious losses from diarrhea, vomiting,
dehydration, malnutrition, etc.
– Euvolemic – H20 increased and Na stable
• Consider SIADH, thyroid disease, primary polydipsia
– Hypervolemic – H20 increased and Na increased (H2O >
Na)
• Consider obvious CHF, cirrhosis, renal failure
STEP 2 - (O) Osmolality
• 2nd assess osmolality hyper, iso, or hypo
– Hypotonic hyponatremia = warrants further workup, when
there is no obvious fluid overload or depletion
• Serum Osmolality: Calculated serum osmolality
(2 X serum [Na]) + [glucose, in mmol/L] + [urea, in
mmol/L]
– Hypertonic - >295
• hyperglycemia, mannitol, glycerol
– Isotonic - 280-295
• pseudo-hyponatremia from elevated lipids or protein
– Hypotonic - <280
• excess fluid intake, low solute intake, renal disease,
SIADH, hypothyroidism, adrenal insufficiency, CHF,
cirrhosis, etc.
STEP 3 – (U) Urine Studies
• For euvolemic hyponatremia, check urine osmolality
– Urine osmolality <100 - excess water intake
• Primary polydipsia, tap water enemas, post-TURP
– Urine osmolality >100 - impaired renal concentration
• SIADH, hypothyroidism, cortisol deficiency
• Check urine sodium & calculate FeNa %
– A low urine sodium (<10) and low FeNa (<1%) implies
the kidneys are appropriately reabsorbing sodium
– A high urine sodium (>20) and high FeNa (>1%) implies
the kidneys are not functioning properly
Diagnosis of the underlying aetiology of the hyponatraemia using
this system relies on an accurate assessment of the patient's volume
status and measurement of urinary [Na+].
Urine [Na+] <20 mmol/L
Urine [Na+] >40 mmol/L
Hypovolaemia
(dry tongue, decreased CVP,
increased urea, increased
pulse, decreased BP)
Vomiting, diarrhoea, skin
losses, burns
Diuretics, Addison's,
cerebral salt-wasting
syndrome, salt-losing
nephropathy
Euvolaemia
Hypothyroidism
SIADH
Any cause + hypotonic fluids Glucocorticoid deficiency
Drugs
Hypervolaemia
(oedema, ascites, LVF,
increased JVP, increased
CVP)
CCF, cirrhosis Nephrotic
syndrome
Renal failure, any cause +
diuretics
BP = blood pressure; CCF = congestive cardiac failure; CVP = central venous pressure; LVF
= left ventricular failure; JVP = jugular venous pressure; SIADH = syndrome of
inappropriate secretion of antidiuretic hormone.
Treatment Hyponatremia
Hyponatremia:
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•
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Hyper-acute
Acute
Severe
Moderate symptomatic
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All admitted
to hospital
• Severe symptoms: 100 mL
of 3% NaCl infused
intravenously over 10
minutes × 3 as needed
• Mild to moderate
symptoms, Patients at low
risk for herniation: 3% NaCl
infused at 0.5–2 mL/kg/h
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In all hyponatremia
patients the serum sodium
initially be increased by 4
to 6 mEq/L during the first
24 hours and by less than
9 meq/L over any given 24hour period.
Patients receiving
emergency therapy their
serum sodium measured
every two hours to ensure
increase at the desired rate
Treatment Hyponatremia
Chronic hyponatremia:
(known duration >48 hours)
 To avoid osmotic
demyelination syndrome
(ODS) the treatment
includes:
 Minimum correction of
serum Na by 4-8 mmol/L
per day, with a lower goal
of 4-6 mmol/L per day if
the risk of ODS is high
 For patients at high risk of
ODS: maximum
correction of 8 mmol/L in
any 24-hour period
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For patients at normal risk
of ODS: maximum
correction of 10-12 mmol/L
in any 24-hour period; 18
mmol/L in any 48-hour
period
Patients should have their
serum sodium measured
often enough to ensure an
appropriate rate of
correction
Chronic hyponatremia is
more at risk from rapid
correction of hyponatremia
The urine output should
also be monitored
Treatment Hyponatremia
Hypervolemic
Hyponatremia (SIADH)
• First-line treatment for
patients with SIADH and
moderate or profound
hyponatremia should be
fluid restriction. (500
mL/d below the 24-hour
urine volume)
• Second-line treatments
include increasing solute
intake with 0.25–0.50 g/kg
per day of urea or combined
treatment with low-dose
loop diuretics and oral
sodium chloride
Hypovolemic
Hyponatremia:
• For patients with reduced
circulating volume,
extracellular volume should
be restored with an
intravenous infusion of
0.9% saline or a balanced
crystalloid solution at 0.5
to 1.0 mL/kg per hour
• Lithium, demeclocycline,
and vaptans are not
recommended for patients
with moderate or profound
hyponatremia
Treatment Hyponatremia
• Normovolemic
Hponatremia:
• For normovolemic
(euvolemic), asymptomatic
hyponatremic patients, free
water restriction (<1 L/d) is
generally the treatment of
choice.
Pharmacologic treatment:
• Demeclocycline is a drug of
choice to increase the diluting
capacity of the kidneys, by
achieving vasopressin
antagonism and a functional
diabetes insipidus.
• Demeclocycline is
contraindicated in cirrhotic
patients.
Aquaretics (Vaptns):
• AVP receptor antagonists,
designed specifically to
promote aquaresis (ie,
electrolyte-sparing
excretion of free water)
• The use of these vaptans is
limited and exact benefits
have yet to be determined.