Investigation and management of hyponatraemia in patients presenting for urgent medical assessment
Dr James Ahlquist Endocrinologist Southend Hospital Hyponatraemia
common
worrying
badly managed Hyponatraemia
Confident diagnosis Effective treatment
Prevent disasters Hyponatraemia: a common electrolyte disorder
Electrolyte disorder Prevalence
Hyponatraemia
Mild 15–22% of hospitalised patients1 (Serum [Na+] < 135 mmol/L) Approximately 7% of ambulatory patients1 Moderate1 Up to 7% of hospitalised patients1 (Serum [Na+] < 130 mmol/L) Severe2 Around 3% of patients2 (Serum [Na+] ≤ 125 mmol/L) Hyperkalaemia 2–5% of patients3
Hypercalcaemia < 1%; 15 cases per 100,000 person-year4
1. Ellison DH, Berl T. N Engl J Med. 2007;356(20):2064-2072. 2. Hoorn EJ, et al. Nephrol Dial Transplant. 2006;21(1):70-76. 3. Weir MR, Rolfe M. Clin J Am Soc Nephrol. 2010;5(3):531-548. 4. Lumachi F, et al. Curr Med Chem. 2008;15(4):415-421. Hyponatraemia: treatment options
Fix cause
Restrict Normal Give fluids saline more salt Sequence of assessment
• Confirm hyponatraemia, additional tests • Likely causes from history: wet or dry? • Hypervolaemic: – heart failure, liver failure, renal failure • Euvolaemic: – SIADH, glucocorticoid deficiency • Hypovolaemic: – Diarrhoea, vomiting, burns, Addison’s disease Hyponatraemia: caused by different underlying conditions
Aetiology of hyponatraemia (serum Na+ <130 mmol/L)
7% 2% 4% (n=121)
20% Primary polydipsia Hypervolaemia Hypovolaemia SIADH 35% Diuretic-induced Adrenal insufficiency
32%
1. Fenske W, et al. Am J Med. 2010;123(7):652-657. A three dimensional approach
• Clinical assessment doesn’t give the diagnosis
• Urine osmolality doesn’t give the diagnosis
• Urine sodium doesn’t give the diagnosis
All three together gives the diagnosis. Lab tests in hyponatraemia
• Serum electrolytes & osmolality • Urine electrolytes & osmolality
• Cortisol (9 am or stressed) to detect adrenal insufficiency • Thyroid function test to exclude hypothyroidism
Lab tests: interpretation
• Serum electrolytes: for detection • Serum osmolality: to exclude ‘hidden’ osmolality: glucose, urea, triglycerides • Urine osmolality: low (<100) or high (>100) • Low in polyuria (excess intake, renal failure) • High (heart failure, SIADH, dehydration) • Urine Na: low (<30) or high (>30) • Low in heart failure, also in dehydration • High in SIADH (also in adrenal insufficiency) Clinical assessment of volume status is important in the differential diagnosis of hyponatraemia
Urine [Na+] Urine [Na+] < 20 mmol/L > 40 mmol/L Hypovolaemia Vomiting, diarrhoea, Diuretics, Addison’s, Dry tongue, CVP, skin losses, burns CSW, Na+ losing urea, pulse, nephropathy BP
Euvolaemia Hypothyroidism SIADH Any cause + hypotonic Glucocorticoid fluids deficiency
Hypervolaemia CCF, Cirrhosis, Renal failure, any Oedema, ascites, Nephrotic syndrome cause + diuretics LVF, JVP, CVP
CVP = central venous pressure; BP = blood pressure; CSW = cerebral wasting; LVF = left ventricular failure; JVP = jugular venous pressure; CCF = congestive cardiac failure; SIADH = syndrome of inappropriate secretion of antidiuretic hormone Figure provided by Prof C. Thompson Hypotonic hyponatraemia
Excess water intake Impaired renal dilution Urine osmolality < 100 > 100 mOsm/kg mOsm/kg Urine sodium Frequent causes: • Primary polydipsia < 30 > 30 Clinical status • Low solute intake mOsm/kg mOsm/kg
ECF volume ECF volume Decision making
Hypovolaemia Hypervolaemia Hypovolaemia Euvolaemia [Total body water ] [Total body water ] [Total body water ] [Total body water ] [Total body sodium ] [Total body sodium ] [Total body sodium ] [Total body sodium ] Action required
Extrarenal solute Oedematous Renal solute loss: • Glucocorticoid loss: disorders: • Diuretic excess deficiency • Gastrointestinal loss • Heart failure (diarrhoea, vomiting) • Liver cirrhosis • Third space burns • Nephrotic syndrome • Salt losing nephritis • Hypothyroidism • Pancreatitis • Osmotic diuresis • Pain • Traumatised muscle (mannitol, glucose) • Nausea • SIADH • Glucocorticoid deficiency
Adapted from Fenske W, et al. Am J Med. 2010;123(7):652-657. Schrier R.W. J Curr Opin Crit Care. 2008;14(6):627-634. Verbalis J. Best Pract Res Clin Endocrinol Metab. 2003;17(4):471-503. … Diagnosis of SIADH
• Decreased serum osmolality: serum osmolality <275 mOsmol/kg • Inappropriate urinary concentration: urine osmolality >100 mOsmol/kg • Clinically euvolemic • Elevated urinary sodium excretion (>20-30 mmol/L) with normal salt and water intake. • Exclude other causes of euvolemic hypo-osmolality: severe hypothyroidism, glucocorticoid insufficiency • Normal renal function, no diuretic use. Treatment of SIADH
• Fix underlying cause • Fluid restrict: realistic? effective? • Modest fluid intake • Urine osmolality >500 mosmol/kg • Check Furst ratio: urine Na+K / serum Na ratio <0.5: fluid restrict to 1000 mL/day ratio 0.5-1: fluid restrict to 500 mL/day ratio >1: fluid restriction not likely to succeed Medical therapy for SIADH
• Loop diuretics (+ salt)
• Tolvaptan tablets (Samsca) 15 mg or 30 mg NHS cost £74.68/tablet Osmotic demyelination syndrome
• Severe hyponatraemia (Na <120 mmol/L) • Chronic: cerebral adaptation has occurred • Correction of low Na by >10 mmol/L per day • High risk: alcohol, malnutrition, liver disease • Neurological changes at day 2-6: • dysarthria, paraparesis, lethargy, confusion • Avoid osmotic demyelination: – cautious correction of hyponatraemia – re-lower Na if necessary Acute symptomatic hyponatraemia
• Post-op or acute severe illness • Acute hyponatraemia (<48 hours) • Headache, nausea, vomiting confusion, seizures, respiratory arrest • Acute cerebral oedema • Level 2 care, IV hypertonic saline: 100 mL 3% saline IV over 10 minutes and repeat until Na rises by 5 mmol/L.
Summary
• Hyponatraemia: challenge, worth getting right
• Correct diagnosis: – clinical, tests and good understanding
• SIADH: treatment options
• Acute hyponatraemia: rare, serious, important Am J Med 2013; 126 S1-S42
Eur J Endocrinol 170 (3) G1-G47 UK consensus advice
Eur J Clin Invest 2015; 45 (8): 888–894