title: Relationship between intracranial pressure as measured by an epidural intracranial pressure monitoring system and optic nerve sheath diameter in healthy dogs.
abstract: OBJECTIVE
  To evaluate the association between ultrasonographically measured optic nerve sheath diameter (ONSD) and acute increases in intracranial pressure (ICP) as measured by an epidural intracranial pressure monitoring system (EICPMS) in healthy dogs.
  
  
  METHODS
  6 young healthy dogs.
  
  
  METHODS
  An EICPMS connected to a pressure monitor was used to generate a continuous pressure waveform in each anesthetized dog. A 22-gauge IV catheter was inserted into the brain parenchyma through the contralateral parietal bone, and 0.5 to 2.0 mL of anticoagulated autologous blood was injected at predetermined intervals. At baseline (immediately after EICPMS placement) and following each injection, the ICP as indicated by EICPMS was recorded, and 3 ultrasonographic images of the optic nerve sheath of each eye were obtained. The ONSD was measured at maximum diameter and at 5 mm caudal to the optic disk.
  
  
  RESULTS
  In linear models, the maximum ONSD was positively associated with increasing ICP. Specifically, the rate of maximum ONSD increase was greater for pressures ≤ 20 mm Hg above baseline (0.0534 mm/1 mm Hg ICP increase) than for pressures > 40 mm Hg above baseline (0.0087 mm/1 mm Hg ICP increase). The relationship of ICP to maximum ONSD was slightly nonlinear and best explained by comparison of fractional polynomial regression models.
  
  
  CONCLUSIONS
  ICP was positively and nonlinearly associated with increasing maximum ONSD, especially when ICP was ≤ 20 mm Hg above baseline, supporting the conclusion that ultrasonographic measurement of maximum ONSD may provide a noninvasive monitoring tool for evaluation of ICP in dogs. Further research is needed to assess the utility of these measurements in clinical patients.
authors.forename: Laura A
authors.initials: LA
authors.lastname: Ilie
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Thomovsky
authors.forename: Paula A
authors.initials: PA
authors.lastname: Johnson
authors.forename: R Timothy
authors.initials: RT
authors.lastname: Bentley
authors.forename: Hock Gan
authors.initials: HG
authors.lastname: Heng
authors.forename: Hee C
authors.initials: HC
authors.lastname: Lee
authors.forename: George E
authors.initials: GE
authors.lastname: Moore
mesh_terms: D000818:Animals; D002404:Catheterization / Q000662:veterinary; D004285:Dogs / Q000502:physiology*; D005260:Female; D019586:Intracranial Hypertension; D007427:Intracranial Pressure / Q000502:physiology*; D009186:Myelin Sheath / Q000000981:diagnostic imaging*; D009900:Optic Nerve / Q000000981:diagnostic imaging*; D014463:Ultrasonography