The relationship between transorbital ultrasound measurement of the optic nerve sheath diameter (ONSD) and invasively measured ICP in children

Purpose: The aim of this study was to investigate the relationship between optic nerve sheath diameter (ONSD) measurement and invasively measured intracranial pressure (ICP) in children. Methods: ONSD measurement was performed prior to invasive measurement of ICP. The mean binocular ONSD measurement was compared to the ICP reading. Physiological variables including systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), pulse rate, temperature, respiratory rate and end tidal carbon dioxide (ETCO2) level were recorded at the time of ONSD measurement. Diagnostic accuracy analysis was performed at various ICP thresholds and repeatability, intra- and inter-observer variability, correlation between measurements in different imaging planes as well the relationship over the entire patient cohort were examined in part I of this study. Results: Data from 174 patients were analysed. Repeatability and intra-observer variability were excellent ( alpha = 0.97-0.99). Testing for inter-observer variability revealed good correlation (r = 0.89, p < 0.001). Imaging in the sagittal plane demonstrated a slightly better correlation with ICP (r = 0.66, p < 0.001). The ONSD measurement with the best diagnostic accuracy for detecting an ICP greater than or equal to 20 mmHg over the entire patient cohort was 5.5 mm, sensitivity 93.2 %, specificity 74 % and odds ratio (OR) of 39.3. Conclusion: Transorbital ultrasound measurement of the OSND is a reliable and reproducible technique, demonstrating a good relationship with ICP and high diagnostic accuracy for detecting raised ICP.