Ultrasonographic measurement of optic nerve sheath diameter to detect raised intracranial pressure in adult head injury patients in the intensive care unit and its correlation with computed tomography scan findings

Background: Our objective was to evaluate if ultrasonographic measurement of optic nerve sheath diameter can be used for early and accurate diagnosis of raised intracranial pressure as seen in cranial CT scan in patients of traumatic brain injury. Methods: Prospective, observational study. 40 adult traumatic head injury patients with altered sensorium suspected to have elevated intracranial pressure admitted to the ICU. Single optic nerve sheath diameter was measured 3.0 mm behind the globe in each eye, and optic nerve sheath diameter from each eye were averaged to create a binocular optic nerve sheath diameter measurement. A binocular optic nerve sheath diameter or uni-ocular measurement in patients with single eye measurement greater than 5.00 mm was considered abnormal. A CT scan of the head was performed within 2 hrs of USG measurement. The radiologist was blinded to the USG measurement of optic nerve sheath diameter and patient's CT considered to be positive for raised ICP Results: Mean age of the patients was 41.15 years. Mean ONSD recorded was 5.613. Highest ONSD was 6.300 and the lowest was 4.750. CT scan findings of raised ICT were present in 36 patients and mean ONSD was >5.00 mm in all the patients. CT scan finding of raised ICT was not present in 4 patients out of which raised ONSD was present in 1 patient. Hence study showed that USG of ONSD has 100% sensitivity and 75% specificity with a positive predictive value of 97.3% and a negative predictive value of 100%. Conclusions: Bedside ultrasonographic measurement of optic nerve sheath diameter has the potential as a sensitive screening test for elevated intracranial pressure in adult head injury patients in ICU.