Optic nerve sheath diameter does not change with patient position

Objectives Optic nerve sheath diameter (ONSD) has been proposed as a marker for increased intracranial pressure. Trendelenburgʹs position is often used in hypotensive patients and reverse Trendelenburgʹs position (30° head up) is often used in head injury patients. We asked if there would be any change in OSND in healthy human adults between the supine, Trendelenburgʹs, and reverse Trendelenburgʹs positions. Methods Prospective case-control blinded study using consenting healthy adults. Three separate investigators measured the ONSD in each eye of 10 separate volunteers in the supine, Trendelenburgʹs, and reverse Trendelenburgʹs positions with 30° angulation from the horizontal. Data were analyzed using the paired t test. Results In the supine position, the mean ONSD was 4.6 ± 0.71 (SD) mm in the right eye and 4.5 ± 0.56 (SD) mm in the left eye. In Trendelenburgʹs position, the mean ONSD was 4.4 ± 0.72 (SD) mm in the right eye and 4.7 ± 0.53 (SD) mm in the left eye. In reverse Trendelenburgʹs position, the mean ONSD was 4.4 ± 0.49 (SD) mm in the right eye and 4.8 ± 0.76 (SD) mm in the left eye. There was no significant difference in OSND between positions for either eye by analysis of variance. Interobserver agreement was ±1 mm in at least 90% of the subjects regardless of position. Conclusion Optic nerve sheath diameter measurement by ultrasound does not significantly change with Trendelenburgʹs or reverse Trendelenburgʹs position in comparison with the supine position in healthy individuals.