The incidence and pathophysiology of hyponatraemia after subarachnoid haemorrhage

Abstract

Background Hyponatraemia is common following subarachnoid haemorrhage (SAH) but the pathogenesis is unclear. Objective To establish the incidence, pathophysiology and consequences of hyponatraemia following SAH. Methods A retrospective case‐note analysis of all patients with SAH admitted to Beaumont Hospital between January 2002 and September 2003. Three hundred and sixteen cases of SAH were substantiated by computed tomography (CT) scan and angiogram findings. Hyponatraemia was defined as plasma sodium < 135 mmol/l. Results One hundred and seventy‐nine patients (56·6%) developed hyponatraemia and 62 (19·6%) developed significant hyponatraemia (plasma sodium < 130 mmol/l). The incidence of severe hyponatraemia following hypophysectomy was lower in the period of analysis (5/81, 6·2%, P < 0·01). Hyponatraemia was more common in patients with identified aneurysms (anterior circulation 102/168, 60·7%, posterior circulation 56/95, 60·8%) than in those with no radiological aneurysm (21/54, 38·8%, P < 0·001). Hyponatraemia was more common after aneurysmal clipping (68/103, 66%) or coiling (82/132, 62%) than after conservative treatment (29/81, 36%, P < 0·001). The aetiology of significant hyponatraemia was the syndrome of inappropriate antidiuretic hormone secretion (SIADH) 39/62 (69·2%), cerebral salt‐wasting syndrome (CSWS) 4/62 (6·5%), hypovolaemic hyponatraemia 13/62 (21%), hypervolaemic hyponatraemia 3/62 (4·8%) and mixed CSW/SIADH 3/62 (4·8%). Hyponatraemia was associated with longer hospital stay (24·0 ± 2·6 vs. 11·8 ± 0·8 days, P < 0·001) but did not affect mortality (P = 0·07). Hyponatraemia developed more than 7 days following SAH in 21·4% and more then 7 days following intervention in 31·8%. Conclusions Hyponatraemia is common following SAH and is associated with longer hospital stay. Clipping and coiling of aneurysms are associated with higher rates of hyponatraemia. SIADH is the commonest cause of hyponatraemia after SAH. Delayed hyponatraemia is common, and has implications for early discharge strategies.