Anaesthetic management in vitreo-retinal surgery

Abstract

EDITOR: We read about the analgesic effects of sub-Tenon's block in vitreo-retinal surgery under general anaesthesia by Farmery and colleagues with great interest [1]. Their study reported that all the patients scheduled for vitreo-retinal surgery under general anaesthesia received a standardized general anaesthetic technique consisting of propofol infusion and 50% oxygen in nitrous oxide. The duration of administration of nitrous oxide was not mentioned. Among the 43 patients, 16 had already been treated by injection of gas/oil. The movement of nitrous oxide into gascontaining spaces in the body has been known for a long time. The use of nitrous oxide during vitreous surgical procedures in which gas bubble injection is used will lead the bubble to increase in size and elevate the intraocular pressure. Stinson and Donlon, in 1982, conducted a study to predict the effect of 70% nitrous oxide anaesthesia on the volume of the intravitreal bubble by using a mathematical method. They suggested that nitrous oxide, independent of the duration it is used, causes an increase in volume of the injected gas bubbles in varying sizes, with the risk of occlusion of the central retinal artery [2]. In addition, after vitreous surgery in which a gas bubble was used for retinal re-attachment, subsequent administration of nitrous oxide should be avoided until the bubble is absorbed. Re-administration of nitrous oxide may cause occlusion of the central retinal artery by moving into the pre-existing intravitreal bubbles, leading to blindness [3,4]. To avoid these complications, we have been using remifentanil infusion (0.05 μg kg−1 min−1) for its analgesic effect instead of nitrous oxide due to the fact that nitrous oxide is 35 times more soluble in blood than nitrogen (the major component of air). We use 50% oxygen in air with volatile anaesthetics [5]. We have administered a remifentanil infusion to 50 patients undergoing vitreous surgery. At the end of surgery, 15 min before anaesthesia was stopped, a single dose of metoclopramide and metamizol were administered intravenously. During surgery, we did not observe any large swings in arterial pressure or increase in postoperative opioid requirement leading to nausea and vomiting, as reported by Farmery and colleagues. We have been able to provide smooth intraoperative haemodynamic conditions by using a remifentanil infusion with volatile anaesthetic agents. We recommend our technique of anaesthesia including remifentanil infusion instead of nitrous oxide in vitreo-retinal surgery in order to avoid the undesirable effects of nitrous oxide on intraocular pressure. It is important to know of the existence of a residual intravitreal gas bubble injected in recent vitreal surgery, so that nitrous oxide can be avoided. D. Dal T. Aykut F. Demirtaş Department of Anesthesiology and Reanimation; Hacettepe University; Ankara, Turkey