Utility of Optic Nerve Sheath Diameter Measurement by Point of Care Ultrasound to Detect Raised Intracranial Pressure: A Prospective Observational Study
Author(s): Hemanth VS, Sethu Babu* and Mithun Murali
Introduction: The main objective of the study was to evaluate the diagnostic utility of Optic Nerve Sheath Diameter (ONSD) measured by Point of Care Ultrasound (POCUS) to detect raised Intracranial Pressure (ICP) among high risk patients in the Emergency Department (ED).
Materials and Methods: Patients above the age of 18 years who presented to the Emergency department with signs and symptoms of raised ICP were included in the study. Patients with cataracts, severe maxillofacial injury, previous history of traumatic brain injury, or ocular surgery were excluded from the study. As per the institutional protocol, the patient was taken for CT head after initial stabilisation. Once the patient had returned back to the ED, investigator performed POCUS to measure ONSD. ONSD value equal to or greater than 5 mm (whether on right eye or left eye) was taken as abnormal. Raised ICP was diagnosed based on the findings of CT brain. Receiver Operating Characteristic curve (ROC) was drawn with ONSD to predict raised ICP and to determine the standard diagnostic test characteristics like Sensitivity, Specificity, Positive Predictive Value (PPV), Negative Predictive Value (NPV) and Accuracy.
Results: A total of 69 subjects with high clinical suspicion of raised ICP were included in the study. Of this, 50 subjects (72.5%) had CT findings consistent with raised ICP. 44 (63.8%) patients had the ONSD value of a single eye more than 5 mm. The average ONSD in patients with features of raised ICP in CT brain was 5.4 mm while that in those patients without features of raised ICP on CT brain was 4.4 mm. At the cut-off of 5 mm, ONSD measured by POCUS had a sensitivity of 88%, Specificity of 100%, Positive Predictive Value of 100% and Accuracy of 91.3% to diagnose raised ICP. ROC analysis revealed that the Area under curve (AUC) was 0.983 suggesting excellent discriminative capacity for ONSD to detect patients with raised ICP.
Conclusion: ONSD measurement by POCUS carries excellent accuracy to diagnose raised ICP among high risk patients in acute care settings.
Keywords: Optic nerve sheath diameter, Raised intracranial pressure, Point of care ultrasound