Preoperative Brimonidine on IOP of Patients Undergoing RALP

Overview

Patients with prostate cancer undergoing robot assisted radical laparoscopic prostatectomy (RALP) in steep Trendelenburg position (sTBURG) are noted to have elevated intraocular pressures (IOP) intraoperatively. One study showed an increase in IOP of 13 millimeters of mercury (mmHg) from baseline IOP levels intraoperatively. Other studies have shown the IOP to more than double intraoperatively during RALP in sTBURG. IOP is found to be directly related to angle of inclination and increases time dependently with sTBURG. The IOP may remain significantly elevated until the first postoperative day after RALP. There are no previously published data concerning the safe threshold for IOP elevation and the effects of this increased IOP on vision and on generalized eye health are still not entirely known. One study showed postoperative visual field defects in 28% (7/25) of patients who underwent RALP in sTBURG. It has been theorized that sTBURG and subsequent increased IOP are risk factors for postoperative vision loss (PVL). It is believed that the increased IOP decreases optic nerve perfusion pressure causing ischemic optic neuropathy. Some previously recommended ways to reduce the intraoperative IOP spike during RALP include shorter operating times, decreased angle of inclination, modified Trendelenburg position, use of Propofol for maintenance anaesthesia and intraoperative topical hypotensive agents to reduce IOP. Given the challenges with some of the above options, this study aims to evaluate the effect of pre-operative treatment with topical Brimonidine Tartrate 0.2% on the IOP of patients undergoing RALP with sTBURG. The goal is to prevent the anticipated IOP spike thereby reducing risk of postoperative vision loss.

With completed informed consent, study participants will undergo a pre-operative comprehensive ophthalmic evaluation to document best corrected visual acuity (VA), IOP measurements, visual field assessments (VF), optical coherence tomography measurements (OCT) of the retinal nerve fiber layer, optic disc photography and screening for other ophthalmologic abnormalities. Height and weight measurements will also be recorded. Using opaque envelopes with the aid of Sequentially Numbered Opaque Sealed Envelopes (SNOSE) schemes, each patient will be randomized to either right eye or left eye. Thereafter patients will be randomized to placebo (carboxymethylcellulose) or drop (Brimonidine tartrate 0.2%) which will be given 30 minutes before the start of surgery with the patient in horizontal supine position. Eyes randomized to receive a drop will be treated with one drop of Brimonidine tartrate 0.2% while eyes randomized to receive placebo will receive one drop of Carboxymethylcellulose eye drops (Control group). IOP measurements will be recorded for both eyes pre-operatively in the upright seated position (baseline), pre-anaesthetized in supine horizontal position, intra-operatively in anaesthetized supine horizontal position, hourly intra-operatively in anaesthetized sTBURG, awake post-operatively in supine horizontal position and at 1 month postoperatively in the upright seated position. Three IOP measurements will be recorded, each with 5% confidence interval (CI). Blood pressure and end tidal carbon dioxide will be recorded hourly intra-operatively. The following surgical data will also be recorded: procedure duration, angle of inclination of surgical bed, anesthetic agents used, fluid volume given, transfusions given, blood loss volume and complications. Best corrected VA, IOP, VF, OCT and optic disc photography will also be recorded for each patient at the 1-month post-operative visit.