• M J Hannon, L A Behan, M M C O'Brien, W Tormey, S G Ball, M Javadpour, M Javadpur, M Sherlock, and C J Thompson.
• Departments of Endocrinology (M.J.H., L.A.B., M.M.C.O'B., M.S., C.J.T.), Chemical Pathology (W.T.), Neurosurgery (M.J.), Beaumont Hospital/Royal College of Surgeons in Ireland Medical School, Dublin 9, Ireland; and Department of Endocrinology (S.G.B.), Newcastle University, Newcastle-Upon-Tyne, Tyne and Wear, NE1 7RU, United Kingdom.
• J. Clin. Endocrinol. Metab. 2014 Jan 1; 99 (1): 291-8.

ContextHyponatremia is common after acute subarachnoid hemorrhage (SAH) but the etiology is unclear and there is a paucity of prospective data in the field. The cause of hyponatremia is variously attributed to the syndrome of inappropriate antidiuresis (SIAD), acute glucocorticoid insufficiency, and the cerebral salt wasting syndrome (CSWS).ObjectiveThe objective was to prospectively determine the etiology of hyponatremia after SAH using sequential clinical examination and biochemical measurement of plasma cortisol, arginine vasopressin (AVP), and brain natriuretic peptide (BNP).DesignThis was a prospective cohort study.SettingThe setting was the National Neurosurgery Centre in a tertiary referral centre in Dublin, Ireland.PatientsOne hundred patients with acute nontraumatic aneurysmal SAH were recruited on presentation.InterventionsClinical examination and basic biochemical evaluation were performed daily. Plasma cortisol at 0900 hours, AVP, and BNP concentrations were measured on days 1, 2, 3, 4, 6, 8, 10, and 12 following SAH. Those with 0900 hours plasma cortisol<300 nmol/L were empirically treated with iv hydrocortisone.Main Outcome MeasuresPlasma sodium concentration was recorded daily along with a variety of clinical and biochemical criteria. The cause of hyponatremia was determined clinically. Later measurement of plasma AVP and BNP concentrations enabled a firm biochemical diagnosis of the cause of hyponatremia to be made.ResultsForty-nine of 100 developed hyponatremia<135 mmol/L, including 14/100<130 mmol/L. The cause of hyponatremia, and determined by both clinical examination and biochemical hormone measurement, was SIAD in 36/49 (71.4%), acute glucocorticoid insufficiency in 4/49 (8.2%), incorrect iv fluids in 5/49 (10.2%), and hypovolemia in 5/49 (10.2%). There were no cases of CSWS.ConclusionsThe most common cause of hyponatremia after acute nontraumatic aneurysmal SAH is SIAD. Acute glucocorticoid insufficiency accounts for a small but significant number of cases. We found no cases of CSWS.

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