Altered CSF Ionic Homeostasis Predicts Persistent Hydrocephalus After Aneurysmal Subarachnoid Hemorrhage. (16th November 2020) - Sadegh, Cameron
Abstract: INTRODUCTION: The transition from acute to persistent hydrocephalus often occurs following aneurysmal subarachnoid hemorrhage (aSAH). Several anatomic, clinical, and radiographic factors can indirectly predict the need for permanent CSF diversion. However, few studies have directly explored local CSF ionic homeostasis in this setting. We hypothesize that CSF alterations are most pronounced nearest to the choroid plexus, the dominant regulator of net CSF production and ionic homeostasis, and that these changes provide prognostic value in the acute setting. METHODS: Samples from 20 adult patients with aSAH were acquired from a published prospective single-center cohort study (Stapleton, 2019). CSF was collected from external ventricular drains with 3 - 6 day intervals between serial samplings for up to 16 days, totaling 54 unique CSF samples. Measurements included osmolarity (vapor pressure osmometer, Wescor) and potassium concentration (inductively coupled plasma optical emission spectrometry, ICP-OES). RESULTS: We describe CSF composition in terms of 1) osmolarity (mEq/L) and 2) potassium concentration as a fraction of total mEq/L. The primary outcome was the need for shunt surgery. Despite normal serum osmolarity measurements, we identified CSF hypo-osmolarity in 60% of patients (mean +/− s.e.m.; 201 mEq/L +/− 16). CSF osmolarity alone was not associated with the need for shunting, but potassium as a fraction of osmolarity was significantly higher in patients requiring shunt surgery (1.20 vs 1.06%, P < .05). Logistic regression analysis using both parameters confirmed their high predictive value for shunt requirement. CONCLUSION: Following aSAH with acute hydrocephalus, a majority of patients develop persistently low CSF osmolarity lasting up to two weeks. A subset of these patients develops relatively high CSF potassium, here termed hyperkalirrhachia, which is predictive of a transition toward persistent hydrocephalus. We hypothesize that local CSF ionic disequilibrium represents superlative physiologic attempts to restore fluid balance within the lateral ventricles or a physiologic failure due to IVH. Further characterizations of the choroid plexus are needed to better understand CSF regulation in the acute setting and to identify therapeutic targets in these patients.