Ultrasonographic Measurement of Optic Nerve Sheath Diameter in Patients Undergoing Open Heart Surgery: A Prospective Cross-sectional Study

Abstract

Introduction: Adverse neurologic outcomes following cardiac surgery can be catastrophic to the patient, next of kin, healthcare facility and community at large. Ultrasonographic measurement of Optic Nerve Sheath Diameter (ONSD) has emerged as a promising modality to reflect Intracranial Pressure (ICP) and neurological status in various neurological settings. Aim: To explore ONSD as a tool to reflect ICP changes and predict neurologic outcomes in a cardiac surgical perioperative setting during Cardiopulmonary Bypass (CPB). Materials and Methods: This was an open-label, prospective and observational study conducted in Department of Anaesthesia, Command Hospital, Karnataka, India, from June 2016 to July 2018. All patients aged between 15 and 80 years who underwent open heart surgeries irrespective of gender, primary diagnosis and preoperative American society of Anaesthesiologist’s Physical Status (ASA PS) grade were enrolled in the study. Serial ultasonographic ONSD of both eyes in two planes (viz. sagittal and transverse) were acquired by a single observer at the following time intervals: baseline (prior to general anaesthesia induction, immediately postintubation, and every 15 minutes interval during CPB (until 150 minutes or end of the CPB whichever was earlier). Postoperative neurologic reassessment was done at 6 hours/postextubation (whichever earlier), at 24 hours and after 7 days, postoperatively. Continuous variables were compared using the student t-tests, while Chi-square or Fisher’sexact test was used to compare categorical variables. To assess inter-rater reliability for categorical variables, the Cohen’s Kappa statistic was used. Results: The mean age of the study cohort was 56.30±11.42 years. A slight male preponderance (56%) was observed. With regards to mean of total CPB time, it was insignificantly higher in patients with adverse neurologic outcomes as compared to those without adverse neurological outcomes (165.83±53.61 minutes vs. 121.36±21.41 minutes; p-value=0.098). Patients with adverse neurologic outcomes had significantly higher ONSD (average of both planes) on CPB from 60 minutes through 150 minutes/end of CPB timeline for right eye (p-value < 0.001), left eye (p-value <0.001), and both eyes (p-value <0.001). For patients with ONSD value (average of both eyes in both planes of each eye) ≥5.5 mm had more likelihood to develop adverse neurologic outcomes, postoperatively. With respect to maximum ONSD anytime during CPB (average of both eyes in both planes of each eye), an arbitrary cut-off of ≥5.5 mm showed a sensitivity of 100%, specificity of 95%, diagnostic accuracy of 100%, and predictive value of 100% with significant p-value of <0.001. Conclusion: Serial ultrasonographic ONSD measurement is assuredly a promising tool to monitor elevated level of ICP as well as a good predictor for the assessment of major adverse neurologic outcomes secondary to open heart cardiac surgeries.