- Any factor that increases intraocular pressure in the setting of an open globe may cause 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. However, in studies of hundreds of patients with open eye injuries, no patient experienced extrusion of ocular contents after administration of succinylcholine.
- Traction on extraocular muscles, pressure on the eyeball, administration of a retrobulbar block, and trauma to the eye 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 injected by the ophthalmologist can be avoided by discontinuing nitrous oxide at least 15 min prior to the injection of air or sulfur hexafluoride, or by avoiding the use of nitrous oxide entirely.
- Medications applied topically to the mucosa are absorbed systemically at a rate intermediate between absorption following intravenous and subcutaneous injection (the toxic subcutaneous dose of phenylephrine is 10 mg).
- 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 is metabolized by this enzyme, echothiophate will prolong its duration of action.
- The key to inducing anesthesia in a patient with an open eye injury is controlling intraocular pressure with a smooth induction. Coughing and gagging during intubation is avoided by first achieving a deep level of anesthesia and profound paralysis.
- The postretrobulbar block 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 monitored, and equipment to provide positive-pressure ventilation must be immediately available.
Ophthalmic surgery poses unique problems, including regulation of intraocular pressure, control of intraocular gas expansion, prevention of the oculocardiac reflex and management of its consequences, management of systemic effects of ophthalmic drugs, and frequent utilization of only mild to moderate sedation. A thorough understanding of potentially complicating issues, in addition to the mastery of general, regional, local, and sedation anesthesia techniques for ophthalmic surgery, will favorably influence perioperative outcome in these cases.
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 36-1). Any event that ...