The Interrater Reliability of Optic Nerve Sheath Diameter Measurements Performed by Non-Ultrasound Fellowship Trained Emergency Medicine Physicians and Emergency Medicine Residents Using Bedside Ultrasound

Background: Several studies have proposed using point-of-care ultrasound measurements of the optic nerve sheath diameter (ONSD) for evaluation of increased intracranial pressure (ICP). The optic nerve sheath is continuous... [ view full abstract ]

Background: Several studies have proposed using point-of-care ultrasound measurements of the optic nerve sheath diameter (ONSD) for evaluation of increased intracranial pressure (ICP). The optic nerve sheath is continuous with the dura allowing free communication of the cerebral spinal fluid (CSF). When ICP increases the pressure is transmitted into the optic nerve sheath and causes its diameter to increase. A measurement greater than 5mm has been reported in the literature to provide good sensitivity, but poor specificity, for increased intracranial pressure (>20cmH20).

Objectives: To determine the interrater reliability of ultrasound measurement of the ONSD when performed by non-ultrasound fellowship trained emergency medicine physicians and residents.

Methods: Five non-ultrasound fellowship trained emergency medicine physicians and five emergency medicine residents received one hour of instruction on ocular ultrasound and measurement of the ONSD using a 13-6 MHz high frequency linear ultrasound transducer (Sonosite, Bothell, WA). The ten physicians then performed 3 replicate measurements of the ONSD on the right eye and then left eye of five normal volunteer test subjects. Results were evaluated for the reliability of measurements between participating physicians. We assessed reliability with the intraclass correlation coefficient (ICC) and its 95% confidence interval. We then calculated a p-value for our data to determine if the ICC results were significantly greater than the lower cutoff for substantial reliability (ICC of 0.60).

Results: The calculated intraclass correlation coefficient (ICC) was 0.735 (95% CI 0.353-0.924) for the left eye, 0.708 (95% CI 0.307-0.914) for the right eye, 0.789 (95% CI 0.493-0.939) for both eyes. While the mean ICC values were >0.6, none of the values reached statistical significance (p>0.05).

Conclusion: The ICC values calculated in this study did not reach significance for the lower cutoff for substantial reliability (0.60), indicating a wide variance and poor interrater reliability. Future studies are needed to further determine both the accuracy and reliability of ultrasound measurements of the ONSD when performed by non-ultrasound fellowship trained practitioners.