R-3 LECTURE SERIES 05-17-00
JOHN BRAMHALL PhD MD

ANESTHESIA AND THE EYE
One might think that one could pretty much ignore the eye as a source of peri-anesthetic problems - people with "bad eyes" don’t present the same challenge as people with "bad hearts"; however, eye surgery is very common and, even though a lot of procedures are performed in free-standing offices and procedure rooms with analgesia provided by the ophthalmic surgeon, there is a significant proportion of cases requiring the attention of anesthesiologists and the facilities of a major OR suite; in addition, eye injuries continue to represent a significant proportion of all anesthetic-related injuries:

CORNEAL ABRASIONS
Quite common, quite painful, quite preventable. Can be caused by trailing stethoscopes or name tags over patient’s face during intubation, or by faulty positioning of face mask. Tape the eyes closed early in the procedure and avoid the habit of attaching the 10cc syringe to the ETT cuff prior to intubation - you are looking at the tracheal opening so you can’t have your eye on the syringe while the syringe is in their eye!

MISPLACED GLASSES
Can lead to dysphoria in the PACU and an irritated patient. Label them and keep them safe.

CONJUNCTIVAL EDEMA
Decreased visual acuity temporarily, can lead to sloughing of the conjunctiva which can contribute to pain and increased risk of infection.

RETINAL BLINDNESS
Some surgical procedures are more frequently associated with damage to the eye structures leading to blindness. Although visual complications of this severity are far from frequent they are devastating. A distinction is made between anterior and posterior ischemic retinopathy, but the root causes of both are still poorly understood.

PRONE POSITION
Decreased venous return from the face, head and neck leading to venous congestion and decreased perfusion. Even in the absence of facial compression the generalized edema that accumulates around the face can lead to significant problems in early assessment of eye damage.

SPINAL SURGERY
All of the above, plus major blood loss leading to anemia (decreased oxygen transport) and hypotension (decreased perfusion). Unexplained visual loss as a complication of spine surgery has been recognized since the 1950s, has always been considered to be a rare event, and has received comparatively little attention in the literature of anesthesia. Case reports and reviews in the spine surgery literature have
suggested possible causes including patient positioning, blood loss and intraoperative hypotension but direct causal relationships have rarely been demonstrated and the precise causal mechanism of this unusual but devastating complication remains unclear.

Postoperative Ischemic Optic Neuropathy
Williams, Hart & Tempelhoff
Anesth Analg 1995;80:1018-29

Ophthalmic Complications after Spinal Surgery
Stevens, Glazer, Kelley, Lietman & Bradford
Spine 1997;22:1319-24

Ischemic Optic Neuropathy after Spinal Fusion
Dilger, Tetzlaff, Bell, Kosmorsky, Agnor & O'Hara
Can J Anaesth 1998;45:63-66

Note that the general assumption when retinal ischemia occurs during prone cases is that the eyes were not protected correctly; however, there are several case reports of retinal blindness following prone cases incorporating Mayfield tong support of the head - with no contact between bed and face.

OPHTHALMIC MEDICATIONS
Many patients take medications for ophthalmic disorders that can impact upon anesthetic management; most are highly concentrated topical solutions:

MYDRIATICS
Phenylephrine: hypertension (one drop of 10% contains 5 mg!)
Cyclopentolate: CNS symptoms (confusion, seizures)

MIOTICS
Acetylcholine: bradycardia, salivation, sweating

I.O.P. REDUCERS
Beta-blockers: bradycardia, hypotension, bronchospasm
Cholinesterase inhibitors: echothiophate can last 2-4 weeks
Carbonic anhydrase inhibitors: systemic acetazolamide can &hibar;K+

EYE DISORDERS
Glaucoma is the principal problem requiring medication. The problem with glaucoma is the elevation of IOP, leading to retinal ischemia and blindness. The eye is a fluid-filled sphere; IOP is determined largely by the ratio of aqueous humor production and drainage; if drainage is limited then medications can be taken to reduce production. More acutely, IOP can be elevated by increased CVP, increased PaCO2, increased MAP and decreased PaCO2; so intubation, airway obstruction, coughing etc. can all cause problems. Succinyl choline increases IOP, principally through prolonged contracture of the extraocular muscles (non-depolarizing muscle relaxants do not increase IOP). There are two types of glaucoma:

OPEN-ANGLE GLAUCOMA
chronic obstruction of aqueous humor drainage.

CLOSED-ANGLE GLAUCOMA
acute obstruction caused by narrowing of the anterior chamber as a result of pupilary dilation or lens edema.

OCULOCARDIAC REFLEX
Traction on extraocular muscles or pressure on the eyeball can elicit bradycardia, PVCs, sinus arrest and V-fib arrest. Treat by stopping the stimulus, also may give atropine. Commonly seen in pediatric strabismus surgery, usually self-extinguishes.

AFFERENT: Trigeminal
EFFERENT: Vagal

OPHTHALMIC SURGERY
Delicate work, usually with loupes or microscope; seldom major blood loss or other fluid shifts; intermittent and variable stimulation which can be intense at times. Often associated with postoperative nausea

OPEN-EYE PROCEDURES
cataract extraction
globe laceration/rupture repairs
corneal transplant
foreign body excision
trabeculectomy
vitrectomy
retinal repair

CLOSED-EYE PROCEDURES
laser keratotomy
making a wish

GENERAL ANESTHESIA FOR OPHTHALMIC SURGERY
Technique of choice for all longer cases (retinal repair, globe repair etc.) and also for patients likely to be "difficult" when awake (demented, anxious, pediatric, feeble-minded, belligerent etc. etc.) and for patients who have difficulty lying flat (CHF, COPD, GER, arthritis).

INDUCTION
Generally determined by patients overall medical condition, but with an open globe the induction must be smoooth - no coughing, gagging, bucking; probably need to use rapid sequence also; sufentanil can be a useful adjunct for smooth induction (0.5-1 mg/kg). Ketamine is relatively contraindicated (nystagmus), succinyl choline is also not a good choice with open globes - it raises IOP and increases the risk of extrusion of globe contents during induction (mechanism: not entirely clear, thought to be fasciculation of ocular muscles, but animal experiments in which muscles have been detached still reveal >IOP when sux is administered). Consider one of the newer NDMRs such as rocuronium, cis-atracurium or rapacuronium.

MONITORS
You may be away from the head, so use appropriate circuit monitors, watch for dysrhythmias, monitor muscle paralysis carefully. Trans-esophageal pacing can treat reflex bradycardia without resort to atropine.

MAINTENANCE
You may need light analgesia, but also want to prevent movement, consider the value of NDMRs; it’s a very good idea to have the patient relaxed during open globe procedures, unexpected movement could be catastrophic. PONV prophylaxis is worthwhile; be sparing with long-acting opioids - severe pain post-op is unusual (and may herald complications).

EMERGENCE
Consider deep extubation if appropriate; alternatively consider the benefits of iv lidocaine.

REGIONAL ANESTHESIA FOR OPHTHALMIC SURGERY
Very useful for procedures such as cataract excision (and IOL placement) where the patient profile is often that of an elderly, fragile person; retrobulbar blocks are usually placed under propofol anesthesia (50-100 mg iv bolus) with oxygen supplementation. Do not attempt regional techniques in patients likely to be fidgety or anxious or delirious during surgery, they have to be able to lie quietly without moving for up to 1 hour ("DON’T MOVE, I HAVE A KNIFE IN YOUR EYE!"). Be alive to the possibility of oxygen-fueled fires if you insuflate oxygen under the clear plastic drapes during surgery.

TOPICAL ANESTHESIA
Usually consists either of topical tetracaine or cocaine; complications of topical analgesia are corneal scratches and abrasions (because the eye is not guarded well).

RETROBULBAR BLOCK
Local anesthetic is injected into the cone formed by the extraocular muscles behind the eye. Complications of retrobulbar block include hemorrhage, globe perforation, CNS toxicity and apnea.

FACIAL NERVE BLOCK
Some surgeons consider this necessary to prevent squinting of the eyelids during surgery, others use retractors. Several variants with eponyms (van Lint, Atkinson, O’Brien).

THE EYE Transverse section through globe.