While ophthalmologic procedures are not particularly dangerous in and of themselves, many patients are elderly and have multiple comorbid conditions. (1)
Normally 10-22 mm Hg, varying 1-2 mm Hg per beat (HR) and 2-5 mm Hg over the course of the day (highest in the AM). IOP is generated by ocular muscle contractions and is partially-dependent on scleral rigidity (which increases with aging), intraocular content (lens, vitreous) rigidity (also increases with age), and venous congestion.
When the globe is open (either during surgical procedures or secondary to trauma), the globe is highly sensitive to forces which would normally raise IOP – in the open globe, IOP cannot be raised, and the eye responds by draining aqueous fluid or extruding vitreous through the wound, the latter of which can permanently worsen vision.
IOP can be lowered with hyperventilation, lowered arterial or central venous pressure, or hypothermia. IOP can be increased with hypoventilation, hypoxemia, or increased central venous or arterial pressure.
Succinylcholine and IOP
By an unknown mechanism (initially thought to be due to extraocular muscle contraction, however now there is evidence to the contrary (2), SCh increases IOP by 5-10 mm Hg for 5-10 minutes, with onset 2-4 minutes after administration. Classically there has concern that this increase in IOP could lead to extrusion in open eye injuries, however this has never been substantiated – there is now at least one report IV SCh administration which did not lead to extrusion. (3)
Anesthetic Agents and IOP
Inhalational anesthetics decrease intraocular pressure due to decreased blood pressure (reduces choroidal volume), relaxation of the extraocular muscles, and pupillary constriction (facilitates aqueous outflow).
Intravenous anesthetics, with the possible exception of ketamine, also decrease intraocular pressure.
Oculocardiac Reflex (trigeminal afferent [V1], vagal efferent)
Stimulation of the eye leading to cardiac dysrhythmias, most commonly bradycardia but almost any rhythm, including AV block, bigeminy, PVCs, V-tach, or aystole can occur. The OCR is not suppressed by general anesthesia, and occurs secondary to globe pressure, traction on the extraocular muscles or conjunctiva, and sometimes retrobulbar blocks.
The OCR most commonly occurs in children undergoing strabismus surgery but can occur in adults as well. Prophylaxis with medications (atropine, glycopyrrolate) or retrobulbar block (4) may be effective in children but has not been effective in adults. Considering that many elderly ophthalmologic surgery patients have significant comorbidities associated with aging (ex. CAD), prophylaxis is absolutely contraindicated in adults.
Interestingly, remifentanyl may potentiate the OCR. (5)
Treatment is removal of stimulus and atropine (10 ucg/kg) or glycopyrrolate if needed. Some authors advocate ensuring adequate anesthesia however this may not be justified, and could be a waste of time, as anesthetic depth has not been shown to correlate with the OCR. If all else fails, consider injecting the rectus muscles with local anesthetic agents.
While ophthalmologic medications are administered topically, significant absorption is common, and can lead to untoward side effects. (6) Topically applied ophthalmologic drugs are absorbed by vessels in the conjunctival sac and the nasolacrimal duct mucosa at a rate intermediate between intravenous and SQ injection.
As a point of reference, the toxic subcutaneous dose of phenylephrine is 10 mg, thus the toxic dose of topic PHE should be < 10 mg, or less than two drops. Children and the elderly are at particular risk and should receive no more than a 2.5% phenylephrine solution.
Commonly used medications and side effects include the following:
Acetazolamide (carbonic anhydrase inhibition): diuresis, metabolic acidosis
Timolol (beta blocker): bradycardia (atropine-resistant), bronchospasm, CHF exacerbation
Echothiophate (irreversible cholinesterase inhibitor): SCh and mivacurium prolongation (lasts for up to 7 weeks), bradycardia, bronchospasm
Mydriasis (capillary decongestion)
Epinephrine: HTN, tachycardia, dysrhythmias
Phenylephrine: HTN (one drop contains 5 mg phenylephrine)
Atropine (anticholinergic): delirium, agitation, fever, flushing, xerostomia, anhidrosis, cycloplegia, photophobia
Scopolamine (anticholinergic): same as atropine
Cyclopentolate (anticholinergic): disorientation, psychosis, convulsions, dysarthria
Acetylcholine (cholinergic agonist): bronchospasm, bradycardia, hypotension
Anesthesia for Ophthalmology
Choice of Anesthetic Technique
Children usually require GA, but adults can often be anesthetized with retrobulbar or peribulbar blocks and MAC.
Special precautions should be taken to avoid coughing, bucking, and/or PONV, i.e. deep anesthesia, complete paralysis, IV lidocaine (1.5 mg/kg).
Consider using an oral RAE tube as the endotracheal tube may otherwise become dislodged by the ophthalmologist.
These patients tend to become hypotensive because, if under GA they NEED deep anesthesia to prevent catastrophic movements, however the operation itself is not very stimulating – volume resuscitation + ephedrine should be anticipated
Nitrous oxide must be avoided, as some ophthalmologists will inject air or sulfur hexafluoride (SF6, an inert gas) into the globe in order to flatten the retina – N2O, which is 35 times more soluble than nitrogen in blood, can lead to devastating increases in intraocular pressure.
Avoid deep sedation because it increases the risk of apnea and unintentional patient. Some authors recommend moderately deep sedation for placement of the regional block, followed by lower doses during the actual surgical procedure. Remifentanil (0.1–0.5 g/kg) may be a reasonable alternative, although it may increase the risk of OCR. (7)
Placed by the ophthalmologist in corneal, anterior chamber, and lens operations lasting less than two hours. Should be used with caution/consideration as the block may not provide adequate akinesia or analgesia, and some patients cannot lie perfectly still. Preparations for induction of general anesthesia must be made in advance. Between the two, peribulbar blocks are easier and have fewer side effects.
The major advantage of the peribulbar block is that the needle does not penetrate the extraocular muscle cone, thus lowering the overall risks. Downsides include slower onset and an increased risk of ecchymosis.
Classic Peribulbar Block
There are two methods to achieve peribulbar block. In the first, the patient is placed supine and the conjunctiva is topicallized, as well as injected. The eyelid is retracted, and an inferotemporal a needle is placed 1.5 cm medial to the lateral canthus and advanced parallel to the orbital floor (slowly injecting 2% lidocaine), until at passes through the lower orbital septum, at which point the needle is aimed 20° medially and 10° cephalad and 5 cc of 2% lidocaine is deposited. After the first injection, a second 5cc injection can be attempted, either into the upper lid (1-2 mm inferomedial to the supraorbital notch) or through the conjunctiva on the nasal side, medial to the caruncle and directed straight back parallel to the medial orbital wall pointing 20° cephalad.
The other peribulbar technique is the sub-tenon Block. Tenon’s fascia surrounds the globe and extraocular muscles, and any injectate will diffuse into the retrobulbar space. The ophthalmologist can use a blunt 25-mm or 19-gauge curved cannula to inject after a small nick is made and a plane dissected in the inferonasal quadrant (gives access to Tenon’s fascia) with Westcott scissors – with the eye is fixed with forceps the needle/cannula is inserted and 3–4 mL injected. Complications with the sub-Tenon blocks are significantly less than with retrobulbar and classic peribulbar techniques.
The retrobulbar block involves placement of a 25 ga. needle in the inferior orbital margin (0.5 cm medial to the lateral canthus) and directing towards the tip of the orbital pyramid – once the needle tip is past the inferior apex of the globe, the needle can be angled up (towards the orbital pyramid) and advanced to 35 mm, where 2-5 cc of local anesthetic is deposited, followed by massage. Sometimes a facial nerve block (LA at the outer canthus) is combined with the retrobulbar block in order to prevent squinting
Retrobulbar blocks can lead to retrobulbar hemorrhage, CRAO, optic nerve injury, perforated globe (esp. if longer than 26 mm), intradural injection,
frank convulsions, oculocardiac reflex, acute neurogenic pulmonary edema. Post-retrobulbar apnea syndrome is due to injection of local anesthetic into the optic nerve sheath, with subsequent spread into the CSF – apnea begins within 20 minutes and resolves within an hour, necessitating positive pressure ventilation.
Retrobulbar injections are contraindicated in patients with bleeding disorders (retrobulbar hemorrhage), with open eye injuries (extrusion), or in those with extreme myopia (globe > 26 mm increases the risk of perforation).
Recently, advances in ophthalmology have led to less-traumatic procedures for anterior chamber (e.g., cataract) and glaucoma operations, in some cases allowing the surgeon and anesthesiologist to avoid injections altogether. Topical anesthesia is not appropriate for posterior chamber surgery, in lengthy procedures, or in those which require akinesia.
After topicalization, 0.5% proparacaine (lidocaine chlorhydrate plus 2% methylcellulose) q5m x 5 doses can be applied with a cotton swab to the inferior and superior conjunctival sacs. Ophthalmic 0.5% tetracaine may be used instead.
Specific Ophthalmologic Cases
Almost always an emergency, thus in these instances regional/MAC combination is not indicated and a RSI followed by GA is best.
In the case of an open eye injury, the key to induction is controlling intraocular pressure by achieving a deep level of anesthesia and profound paralysis prior to intubation.
Three major risks to consider – high incidence of OCR, high incidence of PONV, and relatively high risk of malignant hyperthermia (two reasons – incidence of masseter rigidity is 4-fold higher in these patients, and underlying pathology is thought to be a myopathy). Avoid SCh in these patients, limit the use of opiates, and adequately prophylax for PONV.
Open-angle glaucoma (trabecular tissue sclerosis) is treated medically, but close-angle glaucoma can sometimes require operative intervention. The most common procedure is a trabeculectomy (often can be done under MAC), and if this fails, a seton is placed under general anesthesia. Miosis drugs should be continued during these procedures.
Usually done with a combined retrobulbar block / MAC.
Regional and general anesthesia are acceptable.
Anesthesia Related Eye Injuries
Excruciatingly painful, can be confirmed with flourescin-staining. Treat with antibiotic ointment and a patch for 48 hours.
Treat with mannitol and acetazolamide.
Ischemic Eye Injuries
Often caused by unrecognized globe pressure during prone positioning.