Abstract:
BACKGROUND : Today, invasive intracranial pressure (ICP) measurement remains the standard, but its invasiveness limits
availability. Here, we evaluate a novel ultrasound-based optic nerve sheath parameter called the deformability index
(DI) and its ability to assess ICP noninvasively. Furthermore, we ask whether combining DI with optic nerve sheath
diameter (ONSD), a more established parameter, results in increased diagnostic ability, as compared to using ONSD
alone.
METHODS : We prospectively included adult patients with traumatic brain injury with invasive ICP monitoring, which
served as the reference measurement. Ultrasound images and videos of the optic nerve sheath were acquired. ONSD
was measured at the bedside, whereas DI was calculated by semiautomated postprocessing of ultrasound videos.
Correlations of ONSD and DI to ICP were explored, and a linear regression model combining ONSD and DI was compared
to a linear regression model using ONSD alone. Ability of the noninvasive parameters to distinguish dichotomized
ICP was evaluated using receiver operating characteristic curves, and a logistic regression model combining
ONSD and DI was compared to a logistic regression model using ONSD alone.
RESULTS : Forty-four ultrasound examinations were performed in 26 patients. Both DI (R = − 0.28; 95% confidence
interval [CI] R < − 0.03; p = 0.03) and ONSD (R = 0.45; 95% CI R > 0.23; p < 0.01) correlated with ICP. When including
both parameters in a combined model, the estimated correlation coefficient increased (R = 0.51; 95% CI R > 0.30;
p < 0.01), compared to using ONSD alone, but the model improvement did not reach statistical significance (p = 0.09).
Both DI (area under the curve [AUC] 0.69, 95% CI 0.53–0.83) and ONSD (AUC 0.72, 95% CI 0.56–0.86) displayed ability
to distinguish ICP dichotomized at ICP ≥ 15 mm Hg. When using both parameters in a combined model, AUC
increased (0.80, 95% CI 0.63–0.90), and the model improvement was statistically significant (p = 0.02).
CONCLUSIONS : Combining ONSD with DI holds the potential of increasing the ability of optic nerve sheath parameters
in the noninvasive assessment of ICP, compared to using ONSD alone, and further study of DI is warranted.
