title: Optic nerve sheath diameter on computed tomography is correlated with simultaneously measured intracranial pressure in patients with severe traumatic brain injury.
abstract: OBJECTIVE
  Assess the relationship between optic nerve sheath diameter (ONSD) measured on bedside portable computed tomography (CT) scans and simultaneously measured intracranial pressure (ICP) in patients with severe traumatic brain injury.
  
  
  METHODS
  Retrospective cohort study of 57 patients admitted between 2009 and 2013. Linear and logistic regression were used to model the correlation and discrimination between ONSD and ICP or intracranial hypertension, respectively.
  
  
  RESULTS
  The cohort had a mean age of 40 years (SD 16) and a median admission Glasgow coma score of 7 (IQR 4-10). The between-rater agreement by intraclass coefficient was 0.89 (95 % CI 0.83-0.93, P < 0.001). The mean ONSD was 6.7 mm (SD 0.75) and the mean ICP during CT was 21.3 mmHg (SD 8.4). Using linear regression, there was a strong correlation between ICP and ONSD (r = 0.74, P < 0.001). ONSD had an area under the curve to discriminate elevated ICP (≥20 mmHg vs. <20 mmHg) of 0.83 (95 % CI 0.73-0.94). Using a cutoff of 6.0 mm, ONSD had a sensitivity of 97 %, specificity of 42 %, positive predictive value of 67 %, and a negative predictive value of 92 %. Comparing linear regression models, ONSD was a much stronger predictor of ICP (R(2) of 0.56) compared to other CT features (R(2) of 0.21).
  
  
  CONCLUSIONS
  Simultaneous measurement of ONSD on CT and ICP were strongly correlated and ONSD was discriminative for intracranial hypertension. ONSD was much more predictive of ICP than other CT features. There was excellent agreement between raters in measuring ONSD.
authors.affiliation: Division of Critical Care Medicine, Department of Medicine, Vancouver General Hospital, University of British Columbia, Room 2438, Jim Pattison Pavilion, 2nd Floor, 855 West 12th Avenue, Vancouver, BC, V5Z 1M9, Canada, mypindersekhon@gmail.com.
authors.forename: Mypinder S
authors.initials: MS
authors.lastname: Sekhon
authors.forename: Donald E
authors.initials: DE
authors.lastname: Griesdale
authors.forename: Chiara
authors.initials: C
authors.lastname: Robba
authors.forename: Nick
authors.initials: N
authors.lastname: McGlashan
authors.forename: Edward
authors.initials: E
authors.lastname: Needham
authors.forename: Katherine
authors.initials: K
authors.lastname: Walland
authors.forename: Alyssa C
authors.initials: AC
authors.lastname: Shook
authors.forename: Peter
authors.initials: P
authors.lastname: Smielewski
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
authors.forename: Arun K
authors.initials: AK
authors.lastname: Gupta
authors.forename: David K
authors.initials: DK
authors.lastname: Menon
mesh_terms: D000328:Adult; D001930:Brain Injuries / Q000150:complications / Q000503:physiopathology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015601:Injury Severity Score; D019586:Intracranial Hypertension / Q000175:diagnosis* / Q000209:etiology; D007427:Intracranial Pressure; D008297:Male; D009900:Optic Nerve / Q000000981:diagnostic imaging*; D019095:Point-of-Care Systems; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed