Ultrasonographic assessment of optic nerve sheath diameter as a screening tool for intracranial hypertension in traumatic brain injury

Background: Severe traumatic brain injury (TBI) is a condition burdened by high morbidity and mortality. Prevention of secondary insults is one of the main goals of management and intracranial pressure monitoring is a cornerstone in management of TBI. The relationship between intracranial pressure and optic nerve sheath is known from the literature. Optic nerve sheath ultrasonography could represent a method added to our armamentarium for monitoring intracranial pressure. Methods: We investigated how ultrasound-measured optic nerve sheath diameter varies as a function of intracranial pressure in a cohort of patients with severe blunt head injury in whom an intraparenchymal sensor was placed. We evaluated the accuracy of optic nerve sheet diameter (ONSD) in distinguishing dichotomized ICP cut-offs and analyzed the learning curve and its potential as screening tool to select TBI patients most in need of invasive ICP monitoring in a setting with constraints on resources. Results: ONSD and ICP have a linear relationship. Nevertheless, there are limits of evaluating the one-to-one correspondence between those two variables. We selected a cut-off of sonographic ONSD above which there is a concernable elevation of intracranial pressure (ICP>15 mmHg) worthy of invasive second line invasive monitoring. Thus, it is possible to use ONSD as a first line non-invasive tool to intercept patients at risk of developing frank intracranial hypertension. Conclusions: We propose the use of ONSD ultrasound as a screening investigation for post-traumatic intracranial hypertension in the context of an emergency department, especially in contexts where there is limited availability of intracranial pressure monitors.