Causes

Normovolaemic	Hypervolaemic	Hypovolaemic
SIADH	CCF	GI loss
Hypothyroidism	Liver cirrhosis	Addison's disease
Iatrogenic e.g. inappropriate IV fluids	Nephrotic syndrome	Renal loss
		Other causes of dehydration

Exclude drugs e.g. diuretics, psychiatric drugs Investigate and refer to Endocrine team if persistent hyponatraemia with no obvious cause

Investigation

• Early morning urine sample for osmolality and sodium
• Serum osmolality
• U&E, creatinine
• TFT
• LFT
• Serum lipids including triglycerides, glucose
• CXR
• Short Synacthen Test if there is a strong suspicion of Addison's disease

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SIADH

Diagnosis

Patient normovolaemic
Hyponatraemia and hypotonic plasma (osmolality <270mOsm/kg)
Inappropriately high urine sodium (>20mmol/l) and osmolality (>100mOsm/kg)
Normal renal, thyroid and adrenal function

Causes

Idiopathic

Respiratory disorders e.g. pneumonia, Asthma, PPV

Malignancy e.g. Lung, leukaemia, lymphoma

CNS disorders e.g. infection, CVA, SAH, psychiatric disorders

Drugs e.g. antipsychotics, antidepressants, antiepileptics, chemotherapy

Treatment

Of underlying cause

Restrict fluid intake to 500-1000ml/24 hrs