Abstract
BackgroundUltrasound measurement of optic nerve sheath diameter (ONSD) appears to be a promising, rapid, non-invasive bedside tool for identification of elevated intra-cranial pressure. With improvements in ultrasound technology, machines are becoming smaller; however, it is unclear if these ultra-portable handheld units have the resolution to make these measurements precisely. In this study, we estimate the accuracy of ONSD measurement in a pocket-sized ultrasound unit.MethodsUtilizing a locally developed, previously validated model of the eye, ONSD was measured by two expert observers, three times with two machines and on five models with different optic nerve sheath sizes. A pocket ultrasound (Vscan, GE Healthcare) and a standard portable ultrasound (M-Turbo, SonoSite) were used to measure the models. Data was analyzed by Bland–Altman plot and intra-class correlation coefficient (ICC).ResultsThe ICC between raters for the SonoSite was 0.878, and for the Vscan was 0.826. The between-machine agreement ICC was 0.752. Bland–Altman agreement analysis between the two ultrasound methods showed an even spread across the range of sheath sizes, and that the Vscan tended to read on average 0.33 mm higher than the SonoSite for each measurement, with a standard deviation of 0.65 mm.ConclusionsAccurate ONSD measurement may be possible utilizing pocket-sized, handheld ultrasound devices despite their small screen size, lower resolution, and lower probe frequencies. Further study in human subjects is warranted for all newer handheld ultrasound models as they become available on the market.
Highlights
Ultrasound measurement of optic nerve sheath diameter (ONSD) appears to be a promising, rapid, non-invasive bedside tool for identification of elevated intra-cranial pressure
Johnson et al Crit Ultrasound J (2016) 8:18 investigated including transcranial Doppler (TCD) ultrasonography and the pulsatility index calculated from its flow velocity waveform, and transorbital ultrasound measurement of optic nerve sheath diameter (ONSD)
We estimate the accuracy of ONSD measurement in a pocket-sized ultrasound unit (Vscan, GE Healthcare) utilizing a locally developed model of the eye and optic nerve sheath, and compare it to previously validated portable unit (M-Turbo, SonoSite) as a reference standard
Summary
Ultrasound measurement of optic nerve sheath diameter (ONSD) appears to be a promising, rapid, non-invasive bedside tool for identification of elevated intra-cranial pressure. Close ICP monitoring is fundamental to the Johnson et al Crit Ultrasound J (2016) 8:18 investigated including transcranial Doppler (TCD) ultrasonography and the pulsatility index calculated from its flow velocity waveform, and transorbital ultrasound measurement of optic nerve sheath diameter (ONSD). Both show promise in the emergency medicine and critical care literature for a variety of adult and pediatric patient populations [5,6,7,8,9,10,11,12,13,14]. To diagnose increased ICP, ONSD measurements require precise measurement of a 3–6 mm structure to the nearest 0.1 mm accuracy [8, 17] and it is unclear if these ultra-portable handheld units have the resolution to make these precise measurements
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