Point-Of-Care Ultrasound in the Assessment of Optic Nerve Sheath Diameter After Out-Of-Hospital Cardiac Arrest

Introduction: Hypoxic-ischemic injury from cardiac arrest may cause cerebral edema, leading to increased intracranial pressure (ICP) and brain tissue damage. Optic nerve sheath diameter (ONSD) is associated with elevated ICP. Limited clinical studies have reported ONSD changes in the early post-resuscitation time frame. We sought to evaluate the utility of bedside ocular ultrasound measurements in the assessment of post-cardiac arrest brain injury. Methods: We studied adult out-of-hospital cardiac arrests treated at an urban academic ED and achieving return of spontaneous circulation (ROSC) between May 2018 to May 2019. We included witnessed and unwitnessed arrest as well as shockable and non-shockable rhythms. After ROSC, trained emergency physicians performed bedside ultrasonographic assessment of bilateral ONSD at 1, 6, 24, 48, and 72 hours using an ocular preset on a 15MHz linear probe. ONSD measurements at these time frames were compared between groups stratified by rhythm type and neurological outcome. Cerebral performance category (CPC) was measured at 72 hours and at discharge. Results: Out of 48 eligible patients, 15 were excluded from the study due to lack of consent or available ultrasound images. We included 33 patients, of which 11 were female and 22 were male, with a median age of 57 (IQR 20). There were 19 with an initial rhythm of asystole or pulseless electrical activity (PEA), 9 with ventricular fibrillation arrests, and 5 with an unclear rhythm. At 1 hour, patients with CPC 1-2 had smaller ONSD compared to patients with CPC 3-5 (5.5mm vs 6.1mm, p=0.03). At 72 hour, patients with CPC score of 1-2 had an average reduction in ONSD of 1.6mm verses 0.29mm increase in patients with CPC 3-5. Despite small sample size, a trend towards higher ONSD were seen in patients with non-shockable vs shockable rhythm. Females were also consistently found to have smaller ONSD measurements in all time periods compared to males. Conclusions: This is the first study in the USA to perform analysis using ONSD measurements in cardiac arrest patients. Preliminary analysis of this on-going pilot revealed a greater improvement in ONSD diameters in patients with a favorable neurological outcome. OSND may have utility in prognostication of the post-arrest state.