Intracranial Pressure and Optic Nerve Sheath Diameter as Cephalic Venous Pressure Increases in Swine

Background: Nontraumatic, nonhydrocephalic increases in intracranial pressure (ICP) are often difficult to diagnose and may underlie space-flight-related visual changes. This study looked at the utility of a porcine animal model of increasing cephalic venous pressure to mimic acute changes in ICP and optic nerve sheath diameter (ONSD) from cephalic venous fluid shifts observed during spaceflight. Methods: Anesthetized juvenile piglets were assigned to groups of either naive (N = 10) or elevated superior vena cava pressure (SVCP; N = 20). To elevate SVCP, a 6F custom latex balloon catheter was inserted and inflated to achieve SVCP of 20 and 40 mmHg for 1 h at each pressure. In both groups, serial measurements of ICP, internal jugular pressure (EJP), and external jugular pressure (EJP) were made hourly for 3 h, and ONSD of the right eye was measured hourly by ultrasound (US). Results: There was a significant linear correlation between IJP and ICP (slope: 0.9614 +/- 0.0038, r = 0.9683). With increasing SVCP, resulting ONSD was also well correlated with the ICP (slope: 0.0958 +/- 0.0061, r = 0.7841). The receiver operating characteristic curve for ONSD in diagnosing elevated ICP had an area under the curve of 0.9632 with a sensitivity and specificity of 92% and 91%, respectively, for a cutoff of 5.45 mm. Conclusions: Increases in SVCP result in ICP changes that are well correlated with alteration in ONSD. These changes are consistent with observed ONSD changes monitored during spaceflight.