Abstract
Cataract surgery is probably the most frequently performed surgical procedure in industrialized nations. Patients’ multiple medical comorbidities and advanced age make ocular regional anesthesia a safe modality. The anesthesiologist needs to understand the advantages and drawbacks of the different types of eye anesthesia, ranging from invasive but effective retrobulbar blocks to less invasive peribulbar blocks to infiltration of the sub-Tenon’s space or topicalizing of the corneal surface. Knowledge of eye anatomy improves technical performance of anesthesia for the eye and heightens patient-protective vigilance against potential complications such as brainstem anesthesia.
Keywords
anatomy of the eye, brainstem anesthesia, cataract surgery, occular or ophthalmic anesthesia, peribulbar blocks, retrobulbar blocks, sub-Tenon capsular infiltration
Case Synopsis
Monitored anesthesia care is provided for an active 70-year-old patient undergoing phacoemulsion of a cataract with intraocular lens implantation. The patient has stable hypertension, coronary artery disease, mild emphysema, and renal insufficiency. Sedation with 1 mg midazolam is administered along with verbal reassurance while the anesthesiologist performs a retrobulbar block. Five minutes later the patient becomes unresponsive, is hypotensive with a heart rate of 35 beats per minute, and is breathing irregularly with oxygenation saturation of 83%.
Problem Analysis
Definition
Cataract surgery is likely to remain the most frequently performed surgical procedure in industrialized nations with their burgeoning Baby Boomer populations. Yet many anesthesiologists are unaware of the potential sight- and life-threatening complications associated with ophthalmic regional anesthesia, either from a lack of technical familiarity or from a lack of follow-up in predominantly same-day surgical patients. Anesthesiologists must be aware of these rare but possibly fatal consequences of local anesthesia injected into a patient’s eye to anticipate complications and treat them appropriately.
A review of the literature reveals an evolving practice to less invasive ocular anesthesia. From Knapp’s use of 4% retrobulbar cocaine in 1884, Atkinson advocated the “modern” approach in 1936 of a blind insertion of a needle into the intraconal space. In 1986 Davis and Mandel described the posterior peribulbar technique as an alternative. In 1992 Stevens published an article about cataract extraction by a medial quadrant sub-Tenon capsular infiltration. Subconjunctival and topical anesthesia are useful in modern ophthalmic surgical techniques that do not mandate total ocular akinesia and analgesia.
Retrobulbar block combined with facial nerve block provides superior akinesia, anesthesia, and analgesia compared with other regional techniques. Indications include the following:
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Avoidance of general anesthesia in elderly patients who have multiple medical comorbidities
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Achievement of optimal surgical conditions for extracapsular cataract extraction, phacoemulsification, intraocular lens implantation, and open globe surgery (e.g., vitrectomy, glaucoma treatment, repair of retinal detachment)
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Prolonged, difficult surgeries (e.g., previous eye surgeries) or in patients with hard cataracts or nystagmus
Contraindications to retrobulbar block include the following:
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True allergy to local anesthetic drugs
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Patient refusal, despite explanations regarding the use of intravenous sedation to minimize pain and lack of perioperative awareness
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Patient inability to cooperate
The operating room team must determine its own level of comfort concerning contraindications to local anesthetic blocks. The spectrum of “uncooperative” patients includes impaired mental status, youth, dementia, deafness, severe emphysema or congestive heart failure, excessive anxiety, inability to keep still from Parkinson tremor or restless legs syndrome, or inability to lie flat. Which of these patients may be managed safely with regional anesthesia, minimal intravenous sedation, or verbal reassurance and which patients will require general anesthesia care should be answered by discussion among the ophthalmologist, anesthesiologist, and patient.
Coagulation abnormalities must also be considered. Evidence suggests that patients who take nonsteroidal antiinflammatory drugs, aspirin, or warfarin can undergo eye surgery safely.
Recognition
Complications
Sight-threatening injuries include predominantly needle-related penetration into the globe, the optic nerve, central retinal vein and artery, and muscles surrounding these structures. Wrong (nonsurgical) eye injection has occurred. Injection of anesthetic into the surgical globe has resulted in scleral perforation, vitreous hemorrhage, loss of vitreous fluid and hypotony, diminished red reflex, and retinal detachment. Local anesthetic into the optic nerve sheath has been postulated to cause transient vision loss of the nonsurgical eye due to spread of the anesthetic agent through the subarachnoid space to the optic chiasm to the contralateral optic nerve. Hemorrhage from the central vein and artery cause occlusion of the blood vessels, as well as compression and ischemia of the optic nerve. Immediate, delayed, and partial-to-total visual losses have been reported. Injections into the inferior rectus and superior rectus muscles have resulted in diplopia, vertical tropia, and permanent myopathies leading to persistent strabismus because of unopposed antagonist muscle contractures. Subconjunctival hematomas or hyphemas in the anterior chamber of the eye are visually striking but of a lesser danger to patients.
Life-threatening injuries have been reported with retrobulbar, peribulbar, and even the less invasive ophthalmic anesthetic techniques. Brainstem anesthesia from direct subarachnoid injection of local anesthetic can be immediate, the ultimate high spinal anesthetic, requiring cardiopulmonary resuscitation for bradycardia or asystole, apnea, and hypotension. More difficult to diagnose is a slow onset of brainstem anesthesia (described earlier) when the patient demonstrates mild confusion, gradual unresponsiveness to verbal or painful stimuli, shivering or convulsive fit, bilateral ocular nerve palsy and amaurosis, hemiplegia to quadriplegia, respiratory depression, and hemodynamic instability. Acute pulmonary edema and trigeminal nerve blockade and “coma,” severe orbital cellulitis in immunocompromised patients, myopic staphylomas, and chemosis after retrobulbar block have been reported anecdotally. Should the patient already be under surgical drapes, diagnosis and treatment may be delayed unless a vigilant anesthesia provider is focused to detect these possibilities. Adequate resuscitative capabilities should always be within reach to prevent death.
During a retrobulbar or peribulbar block, activation of the oculocardiac reflex–related bradycardia, asystole, or other arrhythmias may be confused with brainstem anesthesia. Ocular injection, pressure on the globe, or traction on the extraocular muscles, conjunctiva, or globe transmits signals through the ophthalmic branch of the trigeminal nerve to the vagus nerve. Young children who have not received atropine pretreatment are especially prone to the oculocardiac reflex.
Other medical causes such as angina, poorly controlled hypertension, insidious onset of myocardial infarction, or stroke must be recognized as strong differential diagnoses in the predominantly geriatric population. In the absence of eye injection or ocular pressure a vasovagal episode from starting intravenous access can occur. Diabetic patients with retinopathies may be symptomatic from hypoglycemia or slipping into diabetic ketoacidosis. Appropriate preanesthetic assessments and optimization of patient health may reduce some of the confounding perioperative factors.
Complication rates with regional anesthesia are very low. They range from 1 in 1300 to 1 in 16,000 for globe perforation and 1 in 300 to 1 in 500 for brainstem anesthesia ( Box 75.1 ). More recent observational studies in the United Kingdom suggest an incidence for ocular perforation between 0.009% and 0.13%, and between 0.09% and 0.79% for brainstem depression. There was a 0.25% incidence of anesthesia-related diplopia in one retrospective review, with retrobulbar block accounting for 0.39% of cases.
