Evaluation of Optic Nerve Sheath Diameter and Transcranial Doppler As Noninvasive Tools to Detect Raised Intracranial Pressure in Children.

OBJECTIVES

To compare the diagnostic accuracy of the ultrasonography-guided optic nerve sheath diameter with transcranial Doppler-guided middle cerebral artery flow indices against the gold standard invasive intraparenchymal intracranial pressure values in children.

DESIGN

A single-center prospective cohort study.

SETTING

PICU of a tertiary care teaching hospital in North India.

PATIENTS

Eligible children (2-12 yr) are admitted to ICU and are undergoing intracranial pressure monitoring using an intraparenchymal catheter. Observations with a parallel measured intracranial pressure greater than or equal to 20 mm Hg were included as case-observations. Children with an invasive intracranial pressure of less than or equal to 15 mm Hg were taken as neurologic-control-observations and healthy children served as healthy-control-observations.

INTERVENTIONS

The horizontal and vertical diameters of the optic nerves were measured, and averages were calculated and compared. Middle cerebral artery flow indices (pulsatility index and resistive index) were measured bilaterally and averages were calculated and compared in the three groups. Twenty-two measurements of optic nerve sheath diameter were assessed by two different observers in quick succession for interrater reliability.

MEASUREMENTS AND MAIN RESULTS

A total of 148 observations were performed in 30 children. Four observations were excluded (intracranial pressure between 16 and 19 mm Hg). Of the 144 observations, 106 were case-observations and 38 were neurologic-control-observations. Additional 66 observations were healthy-control-observations. The mean optic nerve sheath diameter was 5.71 ± 0.57 mm in the case-observations group, 4.21 ± 0.66 mm in the neurologic-control-observations group, and 3.71 ± 0.27 mm in the healthy-control-observations group (p < 0.001 for case-observations vs neurologic-control-observations/healthy-control-observations). The mean pulsatility index in case-observations was 0.92 ± 0.41 compared with controls 0.79 ± 0.22 (p = 0.005) and the mean resistive index was 0.56 ± 0.13 in case-observations compared with 0.51 ± 0.09 (p = 0.007) in controls (neurologic-control-observations and healthy-control-observations). For the raised intracranial pressure defined by intracranial pressure greater than or equal to 20 mm Hg, the area under the curve for optic nerve sheath diameter was 0.976, while it was 0.571 for pulsatility index and 0.579 for resistive index. Furthermore, the optic nerve sheath diameter cutoff of 4.0 mm had 98% sensitivity and 75% specificity for raised intracranial pressure, while the pulsatility index value of 0.51 had 89% sensitivity and 10% specificity by middle cerebral artery flow studies. The sensitivity and specificity of 0.40 resistive index value in the raised intracranial pressure were 88% and 11%, respectively. Kendall correlation coefficient between intracranial pressure and optic nerve sheath diameter, pulsatility index, and resistive index was 0.461, 0.148, and 0.148, respectively. The Pearson correlation coefficient between two observers for optic nerve sheath diameter, pulsatility index, and resistive index was 0.98, 0.914, and 0.833, respectively.

CONCLUSIONS

Unlike transcranial Doppler-guided middle cerebral artery flow indices, ultrasonography-guided optic nerve sheath diameter was observed to have a good diagnostic accuracy in identifying children with an intracranial pressure of greater than or equal to 20 mm Hg.