title: The relationship between transorbital ultrasound measurement of the optic nerve sheath diameter (ONSD) and invasively measured ICP in children : Part I: repeatability, observer variability and general analysis.
abstract: OBJECTIVE
  The aim of this study was to investigate the relationship between optic nerve sheath diameter (ONSD) measurement and invasively measured intracranial pressure (ICP) in children.
  
  
  METHODS
  ONSD measurement was performed prior to invasive measurement of ICP. The mean binocular ONSD measurement was compared to the ICP reading. Physiological variables including systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), pulse rate, temperature, respiratory rate and end tidal carbon dioxide (ETCO2) level were recorded at the time of ONSD measurement. Diagnostic accuracy analysis was performed at various ICP thresholds and  repeatability, intra- and inter-observer variability, correlation between measurements in different imaging planes as well the relationship over the entire patient cohort were examined in part I of this study.
  
  
  RESULTS
  Data from 174 patients were analysed. Repeatability and intra-observer variability were excellent (α = 0.97-0.99). Testing for inter-observer variability revealed good correlation (r = 0.89, p < 0.001). Imaging in the sagittal plane demonstrated a slightly better correlation with ICP (r = 0.66, p < 0.001). The ONSD measurement with the best diagnostic accuracy for detecting an ICP ≥ 20 mmHg over the entire patient cohort was 5.5 mm, sensitivity 93.2 %, specificity 74 % and odds ratio (OR) of 39.3.
  
  
  CONCLUSIONS
  Transorbital ultrasound measurement of the OSND is a reliable and reproducible technique, demonstrating a good relationship with ICP and high diagnostic accuracy for detecting raised ICP.
authors.affiliation: Paediatric Neurosurgery Unit, Division of Neurosurgery, Faculty of Health Sciences, University of Cape Town, Red Cross War Memorial Children's Hospital, Cape Town, South Africa. llewesp@yahoo.com.
authors.forename: Llewellyn C
authors.initials: LC
authors.lastname: Padayachy
authors.affiliation: Trauma Unit, Red Cross War Memorial Children's Hospital, University of Cape Town, Cape Town, South Africa.
authors.forename: Vaishali
authors.initials: V
authors.lastname: Padayachy
authors.affiliation: Department of Statistical Sciences, University of Cape Town, Cape Town, South Africa.
authors.forename: Ushma
authors.initials: U
authors.lastname: Galal
authors.affiliation: Department of Paediatric Aneasthesia, Red Cross War Memorial Children's Hospital, University of Cape Town, Cape Town, South Africa.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Gray
authors.affiliation: Paediatric Neurosurgery Unit, Division of Neurosurgery, Faculty of Health Sciences, University of Cape Town, Red Cross War Memorial Children's Hospital, Cape Town, South Africa.
authors.forename: A Graham
authors.initials: AG
authors.lastname: Fieggen
mesh_terms: D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007223:Infant; D019586:Intracranial Hypertension / Q000473:pathology* / Q000503:physiopathology*; D007427:Intracranial Pressure / Q000502:physiology*; D008297:Male; D009186:Myelin Sheath / Q000473:pathology*; D009900:Optic Nerve / Q000000981:diagnostic imaging*; D009915:Orbit / Q000000981:diagnostic imaging*; D012372:ROC Curve; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D014463:Ultrasonography
keywords: ICP monitoring; Non-invasive; Optic nerve sheath diameter; Ultrasound