Options for local anesthesia for eye surgery include topical application of local anesthetic or placement of a retrobulbar, peribulbar, or sub-Tenon (episcleral) block. All of these techniques are commonly combined with intravenous sedation. Local anesthesia is preferred to general anesthesia for eye surgery because local anesthesia involves less physiological trespass and is less likely to be associated with postoperative nausea and vomiting. However, eye block procedures have potential complications and may not provide adequate ophthalmic akinesia or analgesia. Some patients may be unable to lie perfectly still for the duration of the surgery. For these reasons, appropriate equipment and qualified personnel required to treat the complications of local anesthesia and to induce general anesthesia must be readily available.
In this technique, local anesthetic is injected behind the eye into the cone formed by the extraocular muscles (Figure 36–2), and a facial nerve block is utilized to prevent blinking (Figure 36–3). A blunt-tipped 25-gauge needle penetrates the lower lid at the junction of the middle and lateral one-third of the orbit (usually 0.5 cm medial to the lateral canthus). Awake patients are instructed to stare supranasally as the needle is advanced toward the apex of the muscle cone. Commonly, patients undergoing such eye blocks will receive a brief period of deep sedation or general anesthesia during the block (using such agents as etomidate, propofol, or remifentanil). After aspiration to preclude intravascular injection, 2 to 5 mL of local anesthetic is injected, and the needle is removed. Choice of local anesthetic varies, but lidocaine 2% or bupivacaine (or ropivacaine) 0.75% are common. Addition of epinephrine may reduce bleeding and prolong the anesthesia. A successful retrobulbar block is accompanied by anesthesia, akinesia, and abolishment of the oculocephalic reflex (ie, a blocked eye does not move during head turning).
A: During administration of a retrobulbar block, the patient looks supranasally as a needle is advanced 1.5 cm along the inferotemporal wall of the orbit. B: The needle is then redirected upward and nasally toward the apex of the orbit and advanced until its tip penetrates the muscle cone.
Facial nerve block techniques: van Lint (1), Atkinson (2), and O’Brien (3).
Complications of retrobulbar injection of local anesthetics include retrobulbar hemorrhage, perforation of the globe, optic nerve injury, intravascular injection with resultant convulsions, oculocardiac reflex, trigeminal nerve block, respiratory arrest, and, rarely, acute neurogenic pulmonary edema. Forceful injection of local anesthetic into the ophthalmic artery causes retrograde flow toward the brain and may result in an instantaneous seizure. The postretrobulbar block apnea syndrome is probably due to injection of local anesthetic into the optic nerve sheath, with spread into the cerebrospinal fluid. The central nervous system is exposed to high concentrations of local anesthetic, leading to mental status changes that may include unconsciousness. Apnea occurs within 20 min and resolves within an hour. Treatment is supportive, with positive-pressure ventilation to prevent hypoxia, bradycardia, and cardiac arrest. Adequacy of ventilation must be constantly monitored in patients who have received retrobulbar anesthesia.
The adjuvant hyaluronidase is frequently added to local anesthetic solutions used in eye blocks to enhance the spread and density of the block. Patients may rarely experience an allergic reaction to hyaluronidase. Retrobulbar hemorrhage, cellulitis, occult injury, and contact allergy to topical eye drops must be ruled out in the differential diagnosis. Retrobulbar injection is usually not performed in patients with bleeding disorders or receiving anticoagulation therapy because of the risk of retrobulbar hemorrhage, extreme myopia because the elongated globe increases the risk of perforation, or an open eye injury because the pressure from injecting fluid behind the eye may cause extrusion of intraocular contents through the wound.
In contrast to retrobulbar blockade, in the peribulbar blockade technique, the needle does not penetrate the cone formed by the extraocular muscles. Advantages of the peribulbar technique include less risk of penetration of the globe, optic nerve, and artery, and less pain on injection. Disadvantages include a slower onset and an increased likelihood of ecchymosis. Both techniques will have equal success at producing akinesia of the eye.
The peribulbar block is performed with the patient supine and looking directly ahead (or possibly under a brief period of deep sedation). After topical anesthesia of the conjunctiva, one or two transconjunctival injections are administered (Figure 36–4). As the eyelid is retracted, an inferotemporal injection is given halfway between the lateral canthus and the lateral limbus. The needle is advanced under the globe, parallel to the orbital floor; when it passes the equator of the eye, it is directed slightly medial (20°) and cephalad (10°), and 5 mL of local anesthetic is injected. To ensure akinesia, a second 5-mL injection may be given through the conjunctiva on the nasal side, medial to the caruncle, and directed straight back parallel to the medial orbital wall, pointing slightly cephalad (20°).
Anatomic landmarks for the introduction of a needle or catheter in most frequently employed eye blocks: (1) medial canthus peribulbar anesthesia, (2) lacrimal caruncle, (3) semilunaris fold of the conjunctiva, (4) medial canthus episcleral anesthesia, and (5) inferior and temporal peribulbar anesthesia.
Sub-Tenon (Episcleral) Block
Tenon’s fascia surrounds the globe and extraocular muscles. Local anesthetic injected beneath it into the episcleral space spreads circularly around the sclera and to the extraocular muscle sheaths (Figure 36–4). A special blunt curved cannula is used for a sub-Tenon block. After topical anesthesia, the conjunctiva is lifted along with Tenon’s fascia in the inferonasal quadrant with forceps. A small nick is then made with blunt-tipped scissors, which are then slid underneath to create a path in Tenon’s fascia that follows the contour of the globe and extends past the equator. While the eye is still fixed with forceps, the cannula is inserted, and 3 to 4 mL of local anesthetic is injected. Complications with sub-Tenon blocks are significantly less than with retrobulbar and peribulbar techniques. Globe perforation, hemorrhage, cellulitis, permanent visual loss, and local anesthetic spread into cerebrospinal fluid have been reported.
A facial nerve block prevents squinting of the eyelids during surgery and allows placement of a lid speculum. There are several techniques of facial nerve block: van Lint, Atkinson, and O’Brien (Figure 36–3). The major complication of these blocks is subcutaneous hemorrhage. The Nadbath technique blocks the facial nerve as it exits the stylomastoid foramen under the external auditory canal, in close proximity to the vagus and glossopharyngeal nerves. This block is not recommended because it has been associated with vocal cord paralysis, laryngospasm, dysphagia, and respiratory distress.
TOPICAL ANESTHESIA OF THE EYE
Simple topical local anesthetic techniques have been used for anterior chamber (eg, cataract) and glaucoma operations, and, increasingly, the trend has been to eliminate local anesthetic injections entirely. A typical regimen for topical local anesthesia consists of application of 0.5% proparacaine (also known as proxymetacaine) local anesthetic drops, repeated at 5-min intervals for five applications, followed by topical application of a local anesthetic gel (lidocaine plus 2% methyl-cellulose) with a cotton swab to the inferior and superior conjunctival sacs. Ophthalmic 0.5% tetracaine may also be utilized. Topical anesthesia is not appropriate for posterior chamber surgery (eg, retinal detachment repair with a buckle), and it works best for faster surgeons with a gentle surgical technique that does not require akinesia of the eye.
Many techniques of intravenous sedation are available for eye surgery, and the particular drug used is less important than the dose. Deep sedation, although sometimes used during placement of ophthalmic nerve blocks, is almost never used intraoperatively because of the risks of apnea, aspiration, and unintentional patient movement during surgery. An intraoperative light sedation regimen that includes small doses of midazolam, with or without fentanyl or sufentanil, is recommended. Doses vary considerably among patients but should be administered in small increments.
Patients may find administration of eye blocks uncomfortable, and many anesthesia providers will administer small incremental doses of propofol to produce a brief state of unconsciousness during the regional block. Some will substitute a bolus of opioid (remifentanil 0.1–0.5 mcg/kg or alfentanil 375–500 mcg) to produce a brief period of intense analgesia during the eye block procedure.
Administration of an antiemetic should be considered if an opioid is used. Regardless of the anesthetic technique, American Society of Anesthesiologists standards for basic monitoring must be employed, and equipment and drugs necessary for airway management and resuscitation must be immediately available.
CASE DISCUSSION An Approach to a Patient with an Open Eye & a Full Stomach
A 12-year-old boy is brought to the emergency department after being shot in the eye with a pellet gun. A brief examination by the ophthalmologist reveals intraocular contents presenting at the wound. The boy is scheduled for emergency repair of the ruptured globe. What should be emphasized in the preoperative evaluation of this patient?
Aside from taking a medical history and performing a physical examination, the time of last oral intake before or after the injury should be established. The patient must be considered to have a full stomach if the injury occurred within 8 h after the last meal, even if the patient did not eat for several hours after the injury: Gastric emptying is delayed by the pain and anxiety that follow trauma. What is the significance of a full stomach in a patient with an open globe injury?
Managing patients who have sustained penetrating eye injuries provides a challenge because of the need to deal with at least two conflicting objectives: (1) preventing further damage to the eye by avoiding increases in intraocular pressure, and (2) preventing pulmonary aspiration in a patient with a full stomach. However, many of the common strategies used to achieve these objectives are in conflict with one another (Tables 36–5 and 36–6). For example, although regional anesthesia (eg, retrobulbar block) minimizes the risk of aspiration pneumonia, it is relatively contraindicated in patients with penetrating eye injuries because injecting local anesthetic behind the globe increases intraocular pressure and may lead to expulsion of intraocular contents. Therefore, these patients require general anesthesia—despite the increased risk of aspiration pneumonia. What preoperative preparation should be considered in this patient?
One clearly will want to minimize the risk of aspiration pneumonia by decreasing gastric volume and acidity (see Case Discussion, Chapter 17). The risk of aspiration in patients with eye injuries is reduced by proper selection of drugs and anesthetic techniques. Evacuation of gastric contents with a nasogastric tube may lead to coughing, retching, and other responses that can dramatically increase intraocular pressure.
Metoclopramide increases lower esophageal sphincter tone, speeds gastric emptying, lowers gastric fluid volume, and exerts an antiemetic effect. It should be given intravenously (10 mg) as soon as possible and repeated every 2 to 4 h until surgery.
Ranitidine (50 mg intravenously), cimetidine (300 mg intravenously), and famotidine (20 mg intravenously) are H2-receptor antagonists that inhibit gastric acid secretion. Because they have no effect on the pH of gastric secretions present in the stomach prior to their administration, they have limited value in patients presenting for emergency surgery.
Unlike H2-receptor antagonists, antacids have an immediate effect. Unfortunately, they increase intragastric volume. Nonparticulate antacids (preparations of sodium citrate, potassium citrate, and citric acid) lose effectiveness within 30 to 60 min and should be given immediately prior to induction (15–30 mL orally). Which induction agents are recommended in patients with penetrating eye injuries?
The ideal induction agent for patients with full stomachs would provide a rapid onset of action in order to minimize the risk of regurgitation. Propofol and etomidate have essentially equally rapid onsets of action and lower intraocular pressure. Although investigations of the effects of ketamine on intraocular pressure have provided conflicting results, ketamine is not recommended in penetrating eye injuries, owing to the increased risk of blepharospasm and nystagmus.
Although etomidate may prove valuable in some patients with cardiac disease, it is associated with an incidence of myoclonus ranging from 10% to 60%. An episode of severe myoclonus may have contributed to complete retinal detachment and vitreous prolapse in one patient with an open globe injury and limited cardiovascular reserve.
Propofol has a rapid onset of action and decreases intraocular pressure; however, it does not entirely prevent the hypertensive response to laryngoscopy and intubation or entirely prevent the increase in intraocular pressure that accompanies laryngoscopy and intubation. Prior administration of fentanyl (1–3 mcg/kg), remifentanil (0.5–1 mcg/kg), alfentanil (20 mcg/kg), esmolol (0.5–1.5 mg/kg), or lidocaine (1.5 mg/kg) attenuates this response with varying degrees of success. How does the choice of muscle relaxant differ between these patients and other patients at risk of aspiration?
Succinylcholine moderately increases intraocular pressure, but that is a small price to pay for a rapid onset of action that decreases the risk of aspiration and profound muscle relaxation that decreases the chance of a Valsalva response during intubation. Advocates of succinylcholine point to the lack of evidence documenting further eye injury when succinylcholine has been used with open eye injuries.
Nondepolarizing muscle relaxants do not increase intraocular pressure, but the onset of deep muscle relaxation is much slower than with succinylcholine. Regardless of the muscle relaxant chosen, intubation should not be attempted until a level of paralysis is achieved that will reliably prevent coughing on the endotracheal tube. How do induction strategies vary in pediatric patients without an intravenous line?
A hysterical child with a penetrating eye injury and a full stomach provides an anesthetic challenge for which there is no perfect solution. Once again, the dilemma is due to the need to avoid increases in intraocular pressure yet minimize the risk of aspiration. Screaming and crying can lead to tremendous increases in intraocular pressure. Attempting to sedate children with rectal suppositories or intramuscular injections often heightens their state of agitation and may worsen the eye injury. Similarly, although preoperative sedation may increase the risk of aspiration by obtunding airway reflexes, it is often necessary for establishing an intravenous line for a rapid-sequence induction. Although difficult to achieve, an ideal strategy would be to administer enough sedation painlessly to allow the placement of an intravenous line, yet maintain a level of consciousness adequate to protect airway reflexes. However, the most prudent strategy is to do everything reasonable to avoid aspiration—even at the cost of further eye damage. Are there special considerations during extubation and emergence?
Patients at risk of aspiration during induction are also at risk during extubation and emergence. Therefore, extubation must be delayed until the patient is awake and has intact airway reflexes (eg, spontaneous swallowing and coughing on the endotracheal tube). Deep extubation increases the risk of vomiting and aspiration. Intraoperative administration of antiemetic medication and nasogastric or orogastric tube suctioning may decrease the incidence of emesis during emergence, but they do not guarantee an empty stomach.
TABLE 36–5Strategies to prevent increases in intraocular pressure (IOP). ||Download (.pdf) TABLE 36–5 Strategies to prevent increases in intraocular pressure (IOP).
Avoid direct pressure on the globe
Patch eye with Fox shield
No retrobulbar or peribulbar injections
Careful face mask technique
Avoid increases in central venous pressure
Prevent coughing during induction and intubation
Ensure a deep level of anesthesia and relaxation prior to laryngoscopy1
Avoid head-down positions
Extubate under deep anesthesia1
|Avoid pharmacological agents that increase IOP |
TABLE 36–6Strategies to prevent aspiration pneumonia. ||Download (.pdf) TABLE 36–6 Strategies to prevent aspiration pneumonia.
|Regional anesthesia with minimal sedation1 |
Evacuation of gastric contents
Rapid induction with rapid onset of paralysis
Avoidance of positive-pressure ventilation via mask
Intubation as soon as possible
|Extubation awake |