What is the likely cause of this patient's confusion?

A 46 year old woman presents sudden onset of severe occipital headache associated nausea vomiting. Cerebrospinal fluid examination a subsequent cerebral angiography confirms diagnosis of an intracranial haemorrhage secondary a bleed from a posterior communicating artery aneurysm. After consultation neurosurgeons, patient sent surgical clipping of her aneurysm. She seems be doing well until third day post operatively when she begins get drowsy confused. Urea electrolytes on her day of admission her third post operative day are reviewed a 1 litre a day fluid restriction instituted. However, her clinical condition fails improve further tests are carried out. The summary of results as follows: Day 1 Day 3 Day 4 Plasma sodium 136 113 114 mmol/l Plasma potassium 4.9 3.5 3.3 mmol/l Plasma urea 6.5 2.8 2.8 mmol/l 24 hour urinary sodium 70 mmol Urine osmolality 710 mmol/kg H2O What is the likely cause of this patient’s confusion?

1 ) Addison’s disease

2 ) Cranial diabetes 

3 ) Fluid overload

4 ) Sick cell syndrome 

5 ) Syndrome of inappropriate ADH secretion

Comments: The low serum sodium level associated high urine osmolality suggestive of syndrome of inappropriate antidiuretic hormone (SIADH) secretion. SIADH essentially occurs when water retention accompanies water intake, leading plasma hyponatraemia hypo osmolality. Urine more concentrated than plasma. In Addison’s disease, plasma sodium will be low plasma potassium level will be high. In cranial diabetes insipidus, urine osmolality low plasma osmolality high. In fluid overload, urine osmolality low. Sick cell syndrome occurs when hyponatraemia due a subnormal setting of hypothalamic osmoreceptors, associated usually a chronic debilitating disease