Chapter 38

• Any factor that normally increases intraocular pressure will tend to decrease intraocular volume by causing drainage of aqueous or extrusion of vitreous through the wound. The latter is a serious complication that can permanently worsen vision.
• Succinylcholine increases intraocular pressure by 5–10 mm Hg for 5–10 min after administration, principally through prolonged contracture of the extraocular muscles.
• Traction on extraocular muscles or pressure on the eyeball can elicit a wide variety of cardiac dysrhythmias ranging from bradycardia and ventricular ectopy to sinus arrest or ventricular fibrillation.
• Complications involving the intraocular expansion of gas bubbles can be avoided by discontinuing nitrous oxide at least 15 min prior to the injection of air or sulfur hexafluoride.
• Topically applied drugs are absorbed at a rate intermediate between absorption following intravenous and subcutaneous injection.
• Echothiophate is an irreversible cholinesterase inhibitor used in the treatment of glaucoma. Topical application leads to systemic absorption and a reduction in plasma cholinesterase activity. Because succinylcholine and mivacurium are metabolized by this enzyme, echothiophate will prolong their duration of action.
• The key to inducing anesthesia in a patient with an open eye injury is controlling intraocular pressure with a smooth induction. Specifically, coughing during intubation must be avoided by achieving a deep level of anesthesia and profound paralysis.
• The postretrobulbar apnea syndrome is probably due to injection of local anesthetic into the optic nerve sheath, with spread into the cerebrospinal fluid.
• Regardless of the technique employed for intravenous sedation, ventilation and oxygenation must be carefully monitored, and equipment to provide positive-pressure ventilation must be immediately available.

Eye surgery provides several unique challenges for the anesthesiologist, including regulation of intraocular pressure, prevention of the oculocardiac reflex, management of its consequences, control of intraocular gas expansion, and the need to deal with the possible systemic effects of ophthalmic drugs. An understanding of the mechanisms and management of these potential problems can favorably influence surgical outcome. This chapter also considers specific techniques of general and regional anesthesia in ophthalmic surgery.

### Intraocular Pressure Dynamics

#### Physiology of Intraocular Pressure

The eye can be considered a hollow sphere with a rigid wall. If the contents of the sphere increase, the intraocular pressure (normal: 12–20 mm Hg) must rise. For example, glaucoma is caused by an obstruction to aqueous humor outflow. Similarly, intraocular pressure will rise if the volume of blood within the globe is increased. A rise in venous pressure will increase intraocular pressure by decreasing aqueous drainage and increasing choroidal blood volume. Extreme changes in arterial blood pressure and ventilation can also affect intraocular pressure (Table 38–1). Any anesthetic event that alters these parameters can affect intraocular pressure (eg, laryngoscopy, intubation, airway obstruction, coughing, Trendelenburg position).

Table 38–1. the Effect of Cardiac and Respiratory Variables on Intraocular Pressure (IOP).1

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