Non-invasive assessment of intracranial pressure using ocular sonography in neurocritical care patients

Objective: To assess the relationship between optic nerve sheath diameter (ONSD) and intracranial pressure (ICP) in neurocritical care patients. Design: Prospective, observational study. Setting: Surgical critical care unit, level 1 trauma center. Patients: A total number of 37 adult patients requiring sedation and ICP monitoring after severe traumatic brain injury, subarachnoid hemorrhage, intracranial hematoma, or stroke. Measurements and main results: Optic nerve sheath diameter was measured with a 7.5 MHz linear ultrasound probe. ICP was measured invasively via a parenchymal device. Simultaneous measurements were performed atleast once a day during the first 2 days after ICP insertion and in cases of acute changes. There was a significant relationship between ONSD and ICP (78 simultaneous measures, r = 0.71, P < 0.0001). Changes in ICP were strongly correlated with changes in ONSD (39 measures, r = 0.73, P < 0.0001). Enlarged ONSD was a suitable predictor of elevated ICP (> 20 mmHg) (area under ROC curve = 0.91). When ONSD was less than 5.86 mm, the negative likehood ratio for raised ICP was 0.06. Conclusion: In sedated neurocritical care patients, non-invasive sonographic measurements of ONSD are correlated with invasive ICP, and the probability to have raised ICP if ONSD is less than 5.86 mm is very low. This method could be used as a screening test when raised ICP is suspected.