Hyponatraemia
NICE CKS guideline hyponatraemia
Definition
Hyponatraemia is defined as a serum sodium concentration <135 mmol/L
Hyponatraemia results from a relative excess of body water to sodium
Normal 135-145 mmol/L
Mild 130–135 mmol/L
Moderate 125–129 mmol/L
Severe <125 mmol/L
Acute < 48 hours
Chronic ≥ 48 hours
Pseudo-hyponatraemia:
Hyponatraemia can also be artefactual due to high serum protein or lipid levels, or hyper-osmolar due to severe hyperglycaemia.
Common causes
Drugs
Syndrome of Inappropriate antidiuretic hormone (SIADH)
Heart failure
Addison’s disease
Thyroid disease
Drug causes:
Diuretics (especially thiazides), SSRis, carbamazepine, PPIs, antipsychotics, TCAs, opiates, NSAIDs, ACEi/ARBs, vasopressin analogues (terlipressin), MDMA (‘ecstasy’)
Symptoms: hyponatraemia is an adverse prognostic indicator
Usually asymptomatic
Symptoms: nausea, vomiting, headache, drowsiness, muscle cramps, lethargy, gait instability, falls, cognitive decline and delirium.
Medical emergency indicated by:
severe symptoms: seizures, coma, altered GCS, encephalopathy, cerebral oedema and cardio-respiratory arrest
severe (<125 mmol/L) hyponatraemia that is often acute onset (< 48 hours)Hyponatraemia in hospitalized people is associated with an increased mortality
Diagnostic algorithm
Asses fluid volume status
Measure serum osmolality
Stop interfering drugs
Specialist investigations:
Serum osmolality AND urine sodium + urine osmolality
9am cortisol (if low or borderline consider short Synacthen test)
Thyroid function tests
Glucose
Lipids
U&E and LFTs
Abbreviations
SIADH: Syndrome of Inappropriate Antidiuretic Hormone
PPI: Proton Pump Inhibitor
1. Check serum osmolality to confirm if ‘true’ hypotonic hyponatraemia vs. pseudo-hyponatraemia
LOW serum osmolality
(<275 mOsmol/kg)
hypotonic
most common
hypotonic hyponatraemia
NORMAL serum osmolality
(275–295 mOsmol/kg)
normotonic
—> measure serum lipids and total protein concentrations (consider myeloma screen)
HIGH serum osmolality
(> 295 mOsmol/kg)
hypertonic
—> measure serum glucose to exclude hyperglycaemia
—> causes osmotic diuresis (urinary sodium>30 mmol/L)
2. Clinical fluid volume status
Hypovolaemic hyponatraemia
Renal loss
Osmotic diuresis*
Diuretic therapy*
Addison’s (primary adrenal insufficiency)*
Salt-losing nephropathy*
Cerebral salt-wasting*
Extra-renal losses
diarrhoea, vomiting, burns, fistulae, pancreatitis, bowel obstruction, sepsis
Treat cause
Fluid replacement (0.9% saline)
Euvolaemic hyponatraemia
SIADH*
Drugs and diuretics*
Thyroid, adrenal, pituitary disease
Hypothyroidism*
Addison’s disease (+secondary ADH response)*
Hypopituitarism—>secondary adrenal insufficiency *
High water low solute intake
primary polydipsia
anorexia nervosa
beer potomania (excess beer consumption with a low solute diet)
Treat cause
Fluid restriction (<1L/day)
Salt restriction
Hypervolaemic hyponatraemia
Raised JVP, pulmonary oedema, oedema, ascites
Congestive cardiac failure
Diuretic therapy for heart failure*
Chronic Kidney Disease*
Nephrotic syndrome
Liver failure
Treat cause
Fluid restriction (<1L/day)
Salt restriction
Key:
Asterix * means urinary sodium>30 mmol/L
Urine osmolality ≤100 mOsm/kg
Primary polydipsia
Low solute intake (for example 'tea and toast diets')
Urine osmolality >100 mOsm/kg
AND urine sodium concentration> 30 mmol/L:
If hypovolaemic: excess Na loss: osmotic diuresis, diuretic therapy, Addison’s disease, salt-losing nephropathy, cerebral salt-wasting
If euvolaemic: SIADH, hypopituitarism (—>secondary adrenal insufficiency), Addison’s disease (+ secondary ADH response), hypothyroidism, diuretic therapy, drugs
If hypervolaemic: chronic kidney disease, diuretic therapy for heart failure, pregnancy
AND urine sodium concentration ≤ 30 mmol/L:
If hypervolaemia: nephrotic syndrome, cirrhosis, cardiac failure
If hypovolaemia: extra-renal losses (diarrhoea, vomiting, burns, fistulae, pancreatitis, bowel obstruction, sepsis)
Diagnostic Criteria for SIADH
Clinically euvolaemic
Serum osmolality < 275 mOsm/Kg
Inappropriately concentrated urine > 100 mOsm/Kg, usually > 300 mOsm/Kg
Increased urine Na+ (> 30 mmol/L)
Absence of adrenal, thyroid, pituitary, renal insufficiency or diuretic therapy
Primary care treatment
Management strategies depend on the rate of onset of hyponatraemia, the person's symptoms, and volume status.
Aim to identify the underlying cause of hyponatraemia
A combination of hyponatraemia and hyperkalaemia is suggestive of Addison's disease.
If acute illness is contributory, recheck serum sodium after 2 weeks
Drugs that may be contributing to the hyponatraemia should be modified and the serum sodium concentration rechecked after 2 weeks.
Reset osmostat syndrome: chronic stable hyponatraemia in pregnancy and chronic conditions arising from secretion of antidiuretic hormone (ADH) at a lower plasma osmolality threshold resulting in persistent and stable euvolaemic hyponatraemia.
Secondary care treatment
ADMIT if hyponatraemia is severe, symptomatic, significant hypovolaemia or Addison disease is suspected
ENDOCRINOLOGY advice If asymptomatic AND moderate hyponatraemia
SIADH
SIADH is associated with: pulmonary causes (pneumonia, lung abscess, TB), neoplastic causes (small cell lung cancer, lymphoma) or CNS disease (meningitis, stroke, tumours)
Arrange tests to find underlying cause (e.g. CT chest/abdo/pelvis/head)
Commence fluid restriction: 1 litre, if no response, 0.5 litres, assess response at 24-48hr
If poor response to fluid restriction, consider short trial of V2 receptor antagonist (tolvaptan) or demeclocyclineAcute onset symptomatic hyponatraemia (severe symptoms: seizures, coma, altered GCS, encephalopathy)
iv bolus of 100mls of hypertonic sodium chloride solution (1.8%), over 30 mins and HDU care.
Check serum Na concentration
May need to repeat iv bolus
Consider slow iv infusion 0.9% salineInappropriate rapid correction of hyponatraemia can cause osmotic demyelination syndrome
Therefore, rate of correction of hyponatremia should be 6-9mmol/L/24 hours (never exceed 12mmol/L/24 hours)