A Prospective Observational Study on Evaluating the Efficacy of Bedside Optic Nerve Sheath Diameter in Assessing Clinical Progression of Patients Admitted in Neurosurgical ICU with Comparisons to CT Scans and GCS Score

Abstract

Background: Ultrasound Optic nerve sheath diameter ultrasound (ONSD) assessment is a non-invasive, bedside, and easily repeatable tool for dynamic measurement of intracranial pressure with high diagnostic accuracy. The goal of this study was to find out if an ONSD can accurately predict the findings of the progression of intracranial lesions in computed tomography (CT) scans and associated deterioration in Glasgow Coma Scale (GCS) among neurosurgical patients.  Methods: We conducted a prospective analysis of ONSD assessment among 54 patients admitted to neurosurgical intensive care unit for clinical and radiological evaluation of raised intracranial pressure. Both horizontal and vertical optic nerve sheath diameters were measured 3 mm beneath the globe in each eye using a 7.5-10MHz ultrasonography probe. A binocular change in optic nerve sheath diameter of more than 2.00 mm in two consecutive readings in the same patient was deemed abnormal. The accuracy of ONSD was correlated with the concurrent neurological deterioration in the GCS and the progression of lesions in the CT images. Results: When compared to CT scan progression, ONSD assessment had 86.7% sensitivity and 89.7% specificity for detecting elevated ICP. The Receiver operating curve (ROC) for the change in ONSD had a high ability to predict progression in ICP with the area under curve (AUC) value of 0.882. The drop in GCS with respect to CT progression of lesions has an AUC value of 0.849. The drop in GCS while compared to progressive lesions in CT images had a positive predictive value of 80% and the negative predictive value of 89.7% respectively. Conclusions: The sensitivity, specificity, and positive predictive value of bedside ONSD ultrasonography in predicting raised intracranial pressure are significant when compared to the progression of lesions in CT images and concurrent drop in GCS. A bedside ONSD measurement is therefore a reliable armamentarium to predict elevated ICP since it is cheap, non-invasive, and repeatable.