title: Prospective analysis of single operator sonographic optic nerve sheath diameter measurement for diagnosis of elevated intracranial pressure.
abstract: BACKGROUND
  The accurate diagnosis of elevated intracranial pressure (eICP) in the emergent setting is a critical determination that presents significant challenges. Several studies show correlation of sonographic optic nerve sheath diameter (ONSD) to eICP, while others show high inter-observer variability or marginal performance with less experienced sonographers. The objective of our study is to assess the ability of bedside ultrasound measurement of ONSD to identify the presence of eICP when performed by a single experienced sonographer. We hypothesize that ONSD measurement is sensitive and specific for detecting eICP and can be correlated with values obtained by external ventricular device (EVD).
  
  
  METHODS
  This was a prospective blinded observational study conducted in a neurocritical care unit of a level 1 trauma center. ONSD measurement was performed on a convenience sample of 27 adult patients who required placement of an invasive intracranial monitor as part of their clinical care. One certified sonographer/physician performed all ultrasounds within 24 hours of placement of EVD. The sonographer was blinded to the ICP recorded by invasive monitor at the time of the scan. A mean ONSD value of ≥5.2 mm was taken as positive.
  
  
  RESULTS
  The sonographer performed 27 ocular ultrasounds on individual patients. Six (22%) of these patients had eICP (EVD measurement of >20 mmHg). Spearman rank correlation coefficient of ONSD and ICP was 0.408 (p=0.03), demonstrating a moderate positive correlation. A ROC curve was created to determine the optimal cut off value to distinguish an eICP greater than 20 mmHg. The area under the receiver operator characteristic curve was 0.8712 (95% confidence interval [CI]=0.67 to 0.96). ONSD ≥5.2 mm was a good predictor of eICP (>20 mmHg) with a sensitivity of 83.3% (95% CI=35.9% to 99.6%) and specificity of 100% (95% CI=84.6% to 100%).
  
  
  CONCLUSIONS
  While the study suggests ONSD measurements performed by a single skilled operator may be both sensitive and specific for detecting eICP, confirmation in a much larger sample is needed. Ocular ultrasound may provide additional non-invasive means of assessing eICP.
authors.affiliation: University of California at Irvine School of Medicine, Irvine, California.
authors.forename: Erica
authors.initials: E
authors.lastname: Frumin
authors.affiliation: University of California at Irvine School of Medicine, Irvine, California.
authors.forename: Joelle
authors.initials: J
authors.lastname: Schlang
authors.affiliation: University of California at Irvine School of Medicine, Irvine, California.
authors.forename: Warren
authors.initials: W
authors.lastname: Wiechmann
authors.affiliation: University of California at Irvine School of Medicine, Irvine, California.
authors.forename: Stacy
authors.initials: S
authors.lastname: Hata
authors.affiliation: University of California at Irvine School of Medicine, Irvine, California.
authors.forename: Sasha
authors.initials: S
authors.lastname: Rosen
authors.affiliation: University of California at Irvine School of Medicine, Irvine, California.
authors.forename: Craig
authors.initials: C
authors.lastname: Anderson
authors.affiliation: University of California at Irvine School of Medicine, Irvine, California.
authors.forename: Laura
authors.initials: L
authors.lastname: Pare
authors.affiliation: University of California at Irvine School of Medicine, Irvine, California.
authors.forename: Mark
authors.initials: M
authors.lastname: Rosen
authors.affiliation: University of California at Irvine School of Medicine, Irvine, California.
authors.forename: John Christian
authors.initials: JC
authors.lastname: Fox
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D019586:Intracranial Hypertension / Q000175:diagnosis / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D009900:Optic Nerve / Q000000981:diagnostic imaging*; D019095:Point-of-Care Systems; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D016037:Single-Blind Method; D014463:Ultrasonography; D055815:Young Adult