title: Optic nerve sheath diameter does not change with patient position.
abstract: OBJECTIVE
  Optic nerve sheath diameter (ONSD) has been proposed as a marker for increased intracranial pressure. Trendelenburg's position is often used in hypotensive patients and reverse Trendelenburg's position (30 degrees 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, Trendelenburg's, and reverse Trendelenburg's 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, Trendelenburg's, and reverse Trendelenburg's positions with 30 degrees 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 Trendelenburg's 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 Trendelenburg's 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.
  
  
  CONCLUSIONS
  Optic nerve sheath diameter measurement by ultrasound does not significantly change with Trendelenburg's or reverse Trendelenburg's position in comparison with the supine position in healthy individuals.
authors.affiliation: Department of Emergency Medicine, Carolinas Medical Center, Box 32861, Charlotte, NC 28232, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Romagnuolo
authors.forename: Vivek
authors.initials: V
authors.lastname: Tayal
authors.forename: Christian
authors.initials: C
authors.lastname: Tomaszewski
authors.forename: Timothy
authors.initials: T
authors.lastname: Saunders
authors.forename: H James
authors.initials: HJ
authors.lastname: Norton
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009186:Myelin Sheath / Q000502:physiology*; D009900:Optic Nerve / Q000033:anatomy & histology*; D011187:Posture / Q000502:physiology*; D011446:Prospective Studies; D016683:Supine Position / Q000502:physiology