Etiology of polyuria in patients undergoing clipping of aneurysm for subarachnoid hemorrhage A correlation with BNP levels.

Abstract

Objective: Natriuresis with polyuria is common after subarachnoid hemorrhage (SAH). It may be multifactorial in origin. The use of drugs as mannitol and furosemide or the occurrence of diabetes insipidus and cerebral salt wasting syndrome (CSW) may be responsible for polyuria after SAH. We investigated the role of brain natriuretic factor (BNP) levels in patients with polyuria undergoing surgery for sub-arachnoid hemorrhage.

Our primary objective was to find the incidence and etiology of polyuria in patients undergoing surgery for SAH. Our secondary objective was to study the association of plasma BNP levels with polyuria in patients undergoing surgery for SAH.

Methods: This was a prospective study. All patients undergoing surgery for SAH were enrolled. All patients were evaluated before surgery. All patients underwent base line hemogram, kidney and liver function tests in the preoperative period. Blood samples for serum osmolality, urine osmolality and BNP level were collected after induction of anesthesia. Polyuria was defined as the urine output more than 6 litres in 24 hours in patients receiving mannitol. Serum osmolality, urine osmolality, serum sodium, urine sodium, urine specific gravity and serum BNP levels were done on days of polyuria till polyuria settled. Patients were followed till their discharge from the hospital.

Results: Out of 57 patients in the study population, 9 (15.8%) patients had polyuria. The mean  (SD) of patients with polyuria was 136.1 meq/l  4.31. The mean  (SD)  serum osmolality of patients with polyuria in the study population was 290.1  11.29 mOsm/kg.  The mean  (SD) urine specific gravity of patients with polyuria 1.013  0.005 mOsm/kg. The mean  (SD) base line BNP level of the nine patients with polyuria was 88.02 95.12 pg/ml. During the days of polyuria the mean  (SD) BNP was 141.03  134.69 pg/ml. Majority (77.8%) of patients in the study group had polyuria of indeterminate origin. There was no case of DI. Only two patients (22.2%) had a clear profile of CSW.

Conclusion: Polyuria is more common after SAH and its incidence was 15.8% in our study population. Moreover, etiology was found out to indeterminate in majority of the patients. Mean BNP levels were above the mean level in most of the polyuria patients, however BNP levels were not significantly higher of polyuria patients than the control groups.