Learning and reproducibility of ultrasonographic assessment of the optic nerve sheath diameter: A cohort study.

Background: Ultrasound-guided measurement of the optic nerve sheath diameter (ONSD) is correlated with increased intracranial pressure (ICP). It has also been recognised as being useful in predicting intracranial hypertension, monitoring ICP and predicting outcome after resuscitation. The method has been described as easy to learn and with good inter-examiner reliability. But most studies were performed with only a few experienced examiners.

Objectives: This study aimed to evaluate the learning progression and inter-examiner variability in point-of-care ultrasonographic assessment of the ONSD.

Design: An observational cohort study.

Setting: Single tertiary centre in north-western Germany.

Patients and participants: For the first part, we recruited a total of nine individuals naive to the ONSD measurement method. These were divided into two groups, one with and one without previous ultrasound experience. These individuals served as both examiners and 'volunteers' for each other during the learning phase of ONSD measurements. For the second part, two intubated and sedated intensive care patients had their ONSD measured by some of these newly trained examiners plus other more experienced examiners.

Intervention: The examination was introduced following the Cognitive Apprenticeship method.

Main outcome measure: Learning progress was evaluated by time needed to perform the examination and by the decrease in the difference of the examination results to the mean ONSD of each individual. For the second part, examination results of the intensive care patients were used to calculate an interclass correlation coefficient.

Results: The mean examination time decreased from 79 ± 48 to 48 ± 14 s from the first to the eight measurement, nearly following an exponential manner (P = 0.054). The deviation of the ONSD compared to the reference ONSD of each proband did not decrease exponentially over time in general. Examiners with ultrasound experience had a significantly lower variation (0.50 ± 0.17 vs. 0.74 ± 0.29 mm; P = 0.012) regarding this particular point. The ICC calculated from results of measurement on the two patients was 0.832 (95% CI, 0.428 to 0.988).

Conclusion: According to our findings, the ultrasonographic assessment of the ONSD is easy to learn and expertise is gained quickly, especially for individuals with previous ultrasound experience. The data show good inter-examiner reliability on everyday patients.

Trial registration: Ethics Committee of the Medical Board of the State Bremen (No. 809/4).