Hyponatraemia

Dr Ali Chakera

alichakera@nhs.net

Classifying hyponatraemia to guide management

Sodium Value

• Mild 130-135

• Moderate 125-129

• Profound <125

Speed of Onset

• Acute <48 hrs

• Chronic >48 hours

Symptoms

• Mod severe

• Severe

Moderately severe Nausea without vomitingConfusionHeadache

Severe VomitingCardiorespiratory distressAbnormal and deep somnolenceSeizuresComa (Glasgow Coma Scale <8)

Hyponatraemia is common

• Occurs in up to 30% of hospitalised patients

• Rotterdam population:

– 7.7% aged >55 years exhibited hyponatremia

– higher in subjects >75 years of age (11.6%)

• All of us see it commonly

• We often ignore it (and it gets better)

Filippatos et al. Clinical Interventions in Aging. 2017

1) Acute on chronic hyponatraemia

2) Recurrent hyponatraemia and confusion

3) Hyponatraemia, shortness of breath and diabetes

Regulation of water

Osmoreceptors –detect serum concentration

Baroreceptors –detect pressure/ stretch/ circulating volume

Thirst

Thirst

Vasopressin

Causes of hyponatraemia -pseudohyponatraemia

• Laboratory artefact of diluting samples

– High lipids

– High protein

• Sodium will be normal on blood gas

• No symptoms

Normal Pseudohyponatraemia

Causes of hyponatraemia - hyperglycaemia

• Hyperglycaemia leads to water retention

• Overall effective osmolarity is the same

• Beware (particularly in children and HHS) of reducing the glucose too quickly – brain oedema

Normal Hyperglycaemia

• Corrected Na+ = Na+ + 2.4 x (glucose-5.5)/5.5

Causes of hyponatraemia – decreased ECF volume (clinically dry)

• Vomiting

• Diarrhoea

• Burns

• Primary adrenal insufficiency

• ‘Third spacing’ of fluidNormal Hypovolaemia

Causes of hyponatraemia – increased total body water (clinically euvolaemic)

• SIADH

• Secondary adrenal insufficiency

• Hypothyroidism

• Primary polydipsia

Normal Increased total body water

Causes of hyponatraemia – increased ECF (clinically oedematous)

• Heart Failure

• Nephrotic syndrome

• Cirrhosis

Normal Increased Extracellular Fluid

Flowchart for diagnosing hyponatraemia

Rule out other causes – check glucose (cortisol, thyroid, lipids)

Hypotonic hyponatraemia – Osm <275

Check urinary Osmolality and sodium

Oedematous: Heart failure; cirrhosis; nephrotic synd

Dry: D&V; Third spacing; burns

Clinical Euvolaemia: SIADH; 2o adrenal insufficiency

Dry: Vomiting; 1o adrenal insufficiency; Salt-wasting

< 100 mOsm/kg > 100 mOsm/kg

Urine Na+ < 30 Urine Na+ >30

Primary polydipsiaiv fluidsLow solutes

Sodium Value

• Mild 130-135

• Mod 125-129

• Profound <125

Speed of Onset

• Acute <48 hrs

• Chronic >48 hours

Symptoms

• Mod

• Severe

Emergency management of hyponatraemia

• Severe symptoms:

– vomiting

– cardiorespiratory arrest

– seizures

– reduced consciousness

– coma (GCS ≤8)

Emergency Rx of severe hyponatraemia

Treatment in the first hour

If no improvement in symptoms

Further iv 150ml 3% hypertonic saline over 20 mins

Aim for 1mmol/L increase in Na+ per infusion

Stop if: symptoms resolve; 10mmol/L increase in Na+

Aim for 5mmol/L increase in Na+ in first hour

Repeated iv 150ml 3% hypertonic saline over 20 mins

Sodium Value

• Mild 130-135

• Mod 125-129

• Profound <125

Speed of Onset

• Acute <48 hrs

• Chronic >48 hours

Symptoms

• Mod severe

• Severe

Emergency management of hyponatraemia

• Moderate severe symptoms

– Nausea without vomiting

– Confusion

– Headache

Rx of moderately severe hyponatraemia

Initial Treatment

Ongoing Treatment

Stop offending drugs/treat underlying causeCheck Na+ at 1, 6 and 12 hours

Limit increase to 10mmol/L in the first 24 hoursLimit increase to 8 mmol/L in subsequent 24 hours

Consider iv 150ml 3% hypertonic saline over 20 mins

Aim for 5mmol/L increase in Na+ in 24 hours

Rx of hyponatraemia with minimal symptoms

Acute < 48 hours

Consider iv 150ml 3% hypertonic saline

Chronic > 48 hours

Investigate

Ongoing Treatment

Stop offending RxDiagnostic algorithm

Treat underlying cause

Ongoing Treatment

Stop offending RxDiagnostic algorithm

Treat underlying cause

SIAD(H)

Essential criteria• Effective serum osmolality <275 mOsm/kg

• Urine osmolality >100 mOsm/kg

• Clinical euvolaemia

• Urine sodium concentration >30 mmol/l

• Absence of adrenal, thyroid, pituitary or renal insufficiency

• No recent use of diuretic agents

Causes of SIAD

Malignancy Neurological Pulmonary Drugs Other

Lung Meningitis Malignancy Antidepressant Pain

GI Encephalitis Infections Antipsychotic Stress

GU AIDS Asthma Anticonvulsant Genetic

Sarcoma Tumours Cystic Fibrosis Opiates Idiopathic

Bleeds PPIs

Thrombosis NSAIDs

Methotrexate

Treatment of SIAD(H)

• Fluid restriction

• Demeclocycline - risk of AKI

• Alternatives (as per European guidance)

– 0.25–0.50 g/kg per day of urea or

– low-dose loop diuretics & oral sodium chloride

Spasovski G et al. Eur J Endocrinol; Nephrol Dial Transplant;Intensive Care Med 2014Verbalis JG et al. Am J Med 2013

Case 1

• Chronic hyponatraemia

– Since 2011 (Na+ 127 – 130)

– Admitted with IECOPD & confusion

– Na+ - 120 mmol/L

Rule out other causes – check glucose (cortisol, thyroid, lipids)

Hypotonic hyponatraemia – Osm <275

Check urinary Osmolality and sodium

Oedematous: Heart failure; cirrhosis; nephrotic synd

Dry: D&V; Third spacing; burns

Euvolaemic: SIADH; 2o adrenal insufficiency

Dry: Vomiting; 1o adrenal insufficiency; Salt-wasting

> 100 mOsm/kg

Urine Na+ < 30 Urine Na+ >30

Rule out other causes – check glucose (cortisol, thyroid, lipids)

Hypotonic hyponatraemia – Osm <275

Check urinary Osmolality and sodium

Oedematous: Heart failure; cirrhosis; nephrotic synd

Dry: D&V; Third spacing; burns

Euvolaemic: SIADH; 2o adrenal insufficiency

Dry: Vomiting; 1o adrenal insufficiency; Salt-wasting

> 100 mOsm/kg

Urine Na+ < 30 Urine Na+ >30

• CT Chest: normal

• CT Brain: Three locules of intracranial gas of unknown cause.

• MRI Brain: intermediate density material layering in the occipital horns which may represent infected material/ pus ? ventriculitis

• Treated with antibiotics. Na+ 132mmol/L

Case 2

• Admitted with confusion and hyponatraemia

• Treated as SIADH

– Fluid restriction

– Improvement in symptoms

• Readmission with the same

Rule out other causes – check glucose (cortisol, thyroid, lipids)

Hypotonic hyponatraemia – Osm <275

Check urinary Osmolality and sodium

Oedematous: Heart failure; cirrhosis; nephrotic synd

Dry: D&V; Third spacing; burns

Euvolaemic: SIADH; 2o adrenal insufficiency

Dry: Vomiting; 1o adrenal insufficiency; Salt-wasting

> 100 mOsm/kg

Urine Na+ < 30 Urine Na+ >30

Case 2 - hyponatraemiaand confusion

• Sodium dropping to 127mmol/L

• Associated with progressive weakness and some weight loss

• Biochemistry fits with SIAD.

• Worry about malignancy – CXR and CT head normal (empty sella)

• Secondary adrenal insufficiency– SST – 0’ 76nmol/L 30’ 292 nmol/L

Case 3 – hyponatraemia and shortness of breath

• Short of breath and confusion

• Type 2 diabetes –glucose = 20.4mmol/L

• Na+ - 128mmol/L

• Corrected Na+ = Na+ + 2.4 x (glucose-5.5)/5.5

• Corrected Na+ = 134.5

• ? SIAD too?

Rule out other causes – check glucose (cortisol, thyroid, lipids)

Hyponatraemia: in summary

• Most often is mild, self-limiting and responds to simple measures

– Stopping offending drugs

– Treating underlying infection

• When more resistant an investigatory framework is useful

• SIAD is a diagnosis of exclusion

Spasovski G et al. Eur J Endocrinol; Nephrol Dial Transplant;Intensive Care Med 2014Verbalis JG et al. Am J Med 2013