Effects of Crystalloid versus Colloid and the α-2 Agonist Brimonidine versus Placebo on Intraocular Pressure during Prone Spine Surgery A Factorial Randomized Trial

Background: Volume replacement with colloid solution and topical alpha-2 agonists may each moderate the progressive increase in intraocular pressure (TOP) during prone surgery. The authors tested the hypotheses that during prolonged prone surgery, IOP increases less with goal-directed intravenous administration of 5% albumin than with goal-directed administration of lactated Ringer's solution, and with topical alpha-2 agonist brimonidine than with placebo eye drops. Methods: Patients having complex prone spine surgery were factorially randomized to albumin and topical placebo (n = 15); albumin and topical brimonidine (n = 16); lactated Ringer's solution and topical placebo (n = 13); and lactated Ringer's solution and topical brimonidine (n = 16). IOP was measured with a pneumotonometer. The primary outcome was time-weighted average intraoperative IOP. Results: Prone positioning increased IOP a mean +/- SD of 12 +/- 6 mmHg. TOP increased to 38 +/- 10 mmHg at the end of anesthesia (approximately 5.5 h). Time- weighted average intraoperative TOP in the brimonidine group was 4 (95% CI: 1, 8) mmHg lower than in the placebo group (P = 0.023), but no different in the crystalloid and albumin groups (mean difference (95% CI) of -2 (-5, 2) mmHg (P = 0.34). There was no interaction between the two randomized factors. Conclusions: Brimonidine slightly reduced the primary outcome of intraoperative time-weighted average IOP, whereas there was no significant difference between goal-directed albumin or crystalloid administration. Brimonidine thus helps reduce IOP during spine surgery, but maintaining adequate blood pressure might play a more important role.