Bedside ultrasonography of optic nerve sheath diameter for detection of raised intracranial pressure in nontraumatic neuro-critically ill patients

BACKGROUND: Delay in treatment of raised intracranial pressure (ICP) leads to poor clinical outcomes. Optic nerve sheath diameter (ONSD) by ultrasonography (US-ONSD) has shown good accuracy in traumatic brain injury and neurosurgical patients to diagnose raised ICP. However, there is a dearth of data in neuro-medical intensive care unit (ICU) where the spectrum of disease is different. AIM: To validate the diagnostic accuracy of ONSD in non-traumatic neuro-critically ill patients. METHODS: We prospectively enrolled 114 patients who had clinically suspected raised ICP due to non-traumatic causes admitted in neuro-medical ICU. US-ONSD was performed according to ALARA principles. A cut-off more than 5.7 mm was taken as significantly raised. Raised ONSD was corelated with raised ICP on radiological imaging. Clinical history, general and systemic examination findings, SOFA and APACHE 2 score and patient outcomes were recorded. RESULTS: There was significant association between raised ONSD and raised ICP on imaging (P < 0.001). The sensitivity, specificity, positive and negative predictive value at this cut-off was 77.55%, 89.06%, 84.44% and 83.82% respectively. The positive and negative likelihood ratio was 7.09 and 0.25. The area under the receiver operating characteristic curves was 0.844. Using Youden’s index the best cut off value for ONSD was 5.75 mm. Raised ONSD was associated with lower age (P = 0.007), poorer Glasgow Coma Scale (P = 0.009) and greater need for surgical intervention (P = 0.006) whereas no statistically significant association was found between raised ONSD and SOFA score, APACHE II score or ICU mortality. Our limitations were that it was a single centre study and we did not perform serial measurements or ONSD pre- and post-treatment or procedures for raised ICP. CONCLUSION: ONSD can be used as a screening a test to detect raised ICP in a medical ICU and as a trigger to initiate further management of raised ICP. ONSD can be beneficial in ruling out a diagnosis in a low-prevalence population and rule in a diagnosis in a high-prevalence population.