Efficacy of Intravenous Mannitol in the Management of Orbital Compartment Syndrome: A Nonhuman Primate Model

Purpose: To report the efficacy of intravenous mannitol in the treatment of orbital compartment syndrome. Methods: An experimental study was conducted on 4 nonhuman primates (8 orbits). Orbital compartment syndrome was simulated by injecting autologous blood into both orbits of each nonhuman primate until a pressure of 80 mm Hg was reached (time 0). After 10 minutes, nonhuman primates were randomized to receive an infusion of either mannitol or saline, given over 15 minutes. Five minutes after the infusion was complete, lateral canthotomy and cantholysis was performed on both orbits in isolated steps every 5 minutes. During the study protocol, orbital and intraocular pressures were recorded every 5 minutes, with a final set of measurements at 60 minutes. The primary outcome measures were the mean change in pressure from time 0 to 60 minutes, as well as the mean change in pressure during the infusion period. Results: There was no statistically significant difference in the mean changes in orbital or intraocular pressure from time 0 to 60 minutes of the protocol. However, during the infusion period there was significantly greater decrease in both orbital and intraocular pressure in the mannitol compared with saline group (-34.0 vs. -9.3 mm Hg for orbital pressure [p = 0.03]; -34.8 vs. -9.7 mm Hg for intraocular pressure [p = 0.04]). Conclusions: While the definitive treatment of orbital compartment syndrome is lateral canthotomy and cantholysis, mannitol results in a rapid and clinically meaningful drop in orbital and intraocular pressure. The authors believe that their data support the routine use of mannitol in orbital compartment syndrome, especially when there is a delay in timely surgical management.