Sodium disorders

Objectives

Manage low sodium levels on operations

Scope

Initial management of symptomatic low sodium in the deployed environment

Audience

Clinical decision makers in R1-R3

Initial Assessment & Management

Clinical features:

Worsening symptoms suggest cerebral oedema, which is a medical emergency

Classification:

Na <130 mmol/l

• Mild: Na 125-129 mmol/l
• Moderate: Na 115 – 125 mmol/l
• Severe: Na <115 mmol/l or mild symptoms

ACUTE = onset <48 hours/ Na fallen >10mmol/l in 48 hours

CHRONIC = onset >48 hours or not known

Na <120

ANY acute or severe symptoms (vomiting, seizure, cardiorespiratory arrest, deep/ abnormal somnolence); AND no other cause for symptoms identified:

• Administer hypertonic saline* IV over 20 mins
• Indication is to improve symptoms NOT correct Na back to normal
• If no clinical improvement after 20 mins and Na remains the same, a repeat dose may be given
• Extreme caution about over-correcting which may induce central demyelination. Target sodium improvement of 5-8 mmol/L; max 10mmol/L OVER 24 hours – no faster. If over-corrected start 5% dextrose 10 ml/kg/h while seeking specialist advice ASAP

Refer to next role*Hypertonic saline. Where 3% saline unavailable, dilute 50ml of 5% saline in 50ml 0.9% saline (remove 50ml from 100ml 0.9% saline bag); give 100ml over 20 mins through a large bore cannula.

Advanced Assessment & Management

Na >120. Proceed to investigate non-urgently as follows:

Clinical assessment. The treatment of hyponatraemia depends on the volume status (however clinicians are poor at assessing this. Where possible request urine sodium).

• Assess fluid status
• Measure glucose, blood osmolality, urine osmolality, lipids if available
• If possible, ask BMS to give an indicative urine sodium (run using Benchtop biochem analyser). If undetected on serum analyser, assume cause is dehydration
• Urinalysis – check for renal disease
• Refer to next role for full workup

Hypovolaemic (Low BP, dehydrated)

• Dehydration (GI losses commonest cause; low urine sodium on serum analyser)
• Diarrhoea and vomiting (low urine sodium on serum analyser)
• Diuretics or kidney disease (detectable urine sodium on serum analyser)
• Primary adrenal insufficiency (detectable urine sodium on serum analyser)

Treatment with IV 0.9% saline, 125-250 ml/h (send urine sodium before initiating)

Euvolaemic (warm, well perfused)

• Primary polydipsia or low salt intake (urine osmolality <100)
• Diuretics or kidney disease (detectable urine sodium)
• SIADH (no other cause found; urine sodium >30mmol/L)
• Hypothyroid, secondary adrenal insufficiency*
• Chronic alcoholism

Consider admission to monitor fluid balance and sodium; fluid restrict 1.5L. Seek specialist advice via reachback.

Hypervolaemic (volume expanded, i.e. elevated jugular venous pressure/ oedematous/ other evidence of congestive cardiac failure)

• Fluid overload (low urine sodium)
• Heart failure
• Chronic kidney disease
• Liver failure/ ascites
• Low albumin

Treat underlying cause.