Estimation of Intracranial Pressure by Ultrasound of the Optic Nerve Sheath in an Animal Model of Intracranial Hypertension

Background: Invasive monitoring of intracranial pressure (ICP) is currently the gold standard method for the safe diagnosis and treatment of intracranial hypertension (ICHy), but it is subject to hemorrhage, infection and malfunction. Ultrasound of the optic nerve sheath diameter (ONSD) has been applied as a non-invasive alternative that is cost effective and available at the bedside. However, ONSD time-lapse behavior in a set of ICHy and its relief by means of whether saline infusion or surgery is still unknown. The objective of this study was to correlate intracranial pressure and ultrasonography of the optic nerve sheath in an experimental animal model of ICHy, and the interval needed to ONSD to return to its baseline levels.Methods: An experimental study was conducted on 30 male and female pigs weighing about 20 kg. The diameter of the optic nerve sheath was evaluated by ultrasound at different measures of ICP given by intraventricular catheter and intracranial balloon inflation, saline infusion and balloon deflation. Laboratory and hemodynamic data were collected from the animals. ICP and ONSD values were correlated at each time point of the study.Results: All the variables obtained by ONSD ultrasonography as left optic nerve, right optic nerve and average of optic nerve sheath (AON) diameter were statistically significant to estimate ICP value. ONSD values changed immediately at balloon inflation, with a delay of 30 minutes average to return to baseline levels after balloon deflation (p = 0.016). No statistical significance was observed in ICP and ONSD values with hypertonic saline infusion. Correlation between ICP and ONSD was linear and can be estimated using the formula: -80.5 + 238.2 x AON, in this swine model. Conclusion: In the present study, ultrasound of optic nerve sheath diameter disclosed linear correlation with ICP, although a short delay in returning to its baseline levels may be observed in the case of sudden intracranial hypertension relief.