Retinal Surgery

Retinal detachments present sporadically but are not usually so urgent that they have to be done immediately on presentation. The patients are often hypertensive, though whether this is cause or effect is debatable. The surgery may be prolonged and is often carried out in semi-darkness. In this situation too soft an eye may be a disadvantage in that the low intra-ocular pressure may cause further tearing of the retina. Controlled ventilation is advantageous due to the duration of the surgery. A vagolytic agent should be given to prevent the oculo-cardiac reflex during surgical manipulation of the globe. The oculo-cardiac reflex also occurs during exenteration or enucleation. Occasionally the surgeon may wish to introduce a gas bubble between the vitreous and retina to tamponade the retina. If this is planned then nitrous oxide should be avoided or turned off as soon as the decision is made. Nitrous oxide diffuses into closed gas filled spaces and increases the volume of the bubble or, if the area has low compliance, the pressure will rise. While this may be acceptable during the procedure, it will diffuse out in the post operative period and the pressure or volume will reduce, reducing the tamponade effect.

Penetrating Eye Injury

Penetrating eye injuries may require induction of anaesthesia in the presence of a potentially full stomach. Unfortunately, suxamethonium causes a significant rise in intra-ocular pressure, which may cause further damage, especially if there is already vitreous loss or the lens is disrupted. An alternative is a rapid sequence induction using a generous dose of a rapid onset non depolarizing relaxant instead of suxamethonium. Vecuronium or rocuronium are suitable choices. Rocuronium at 1.5 mg/kg gives equivalent intubating conditions to suxamethonium. It should be noted, however, that this dose (3 x ED95) may last up to 1 H. If the penetration of the globe has been with metallic fragments then the search for these may involve magnets or repeated X-rays which can require multiple changes of position or prolonged surgery.

Dacrocystorhinostomy (DCR)

Dacrocystorhinostomy is a potentially bloody procedure usually requiring an anaesthetic technique designed to reduce blood loss. The patient is usually placed with the table head up to improve venous drainage. A vasoconstrictor is introduced inside the nose to reduce mucosal bleeding. The blood pressure is often lowered to further reduce bleeding. Hypotension may be achieved by increasing the inspired concentration of anaesthetic vapour, particularly halothane (which depresses the myocardium) or isoflurane (which causes peripheral vasodilatation) or by introducing agents which cause peripheral vasodilatation such as trimetaphan or sodium nitroprusside. These agents must be used with extreme caution. Mild hyperventilation will also help to reduce the blood pressure. The airway is usually maintained with a tracheal tube, though the laryngeal mask will avoid the pressor response to the presence of the tube and so may avoid the need for active reduction of blood pressure. A pharyngeal pack is essential to absorb blood that trickles down from the nasopharynx.

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