General Anesthesia for Ophthalmic Surgery

General Anesthesia for Ophthalmic Surgery

The choice between general and local anesthesia should be made jointly by the patient, anesthesiolo-gist, and surgeon. Patients may refuse to considerlocal anesthesia due to fear of being awake during the operation, fear of the eye block procedure, or unpleas-ant recall of a previous eye block or local eye proce-dure. General anesthesia is indicated in children and uncooperative patients, as even small head move-ments can prove disastrous during microsurgery.

PREMEDICATION

Patients undergoing eye surgery may be apprehen-sive, particularly if they have undergone multiple procedures or there is a possibility of permanent blindness. However, premedication must be admin-istered with caution and only after careful consider-ation of the patient’s medical status. Adult patients are often elderly, with myriad systemic illnesses, such as hypertension, diabetes mellitus, and coro-nary artery disease. Pediatric patients may have associated congenital disorders.

INDUCTION

The choice of induction technique for eye surgery usually depends more on the patient’s other medical problems than on the patient’s eye disease or the specific operation contemplated. One exception isthe patient with a ruptured globe. The key to inducing anesthesia in a patient with an openeye injury is controlling intraocular pressure with a smooth induction. Specifically, coughing during intubation must be avoided by achieving a deep level of anesthesia and profound paralysis. The intraocu-lar pressure response to laryngoscopy and endotra-cheal intubation can be moderated by prior administration of intravenous lidocaine (1.5 mg/kg) or an opioid (eg, remifentanil 0.5–1 mcg/kg or alfen-tanil 20 mcg/kg). A nondepolarizing muscle relax-ant or succinylcholine may be used. Despite theoretical concerns, succinylcholine has not been shown to increase the likelihood of vitreous loss with open eye injuries. Many patients with open globe injuries have full stomachs and require a rapid-sequence induction technique because of the risk of aspiration (see Case Discussion below).

MONITORING & MAINTENANCE

Eye surgery necessitates positioning the anesthesia provider away from the patient’s airway, making close monitoring of pulse oximetry and the cap-nograph particularly important. Endotracheal tube kinking, breathing circuit disconnection, and unin-tentional extubation may be more likely because of the surgeon working near the airway. Kinking and obstruction can be minimized by using a wire-rein-forced or preformed oral RAE^® (Ring-Adair-Elwyn) endotracheal tube (see Figure 36–1). The possibil-ity of arrhythmias caused by the oculocardiac reflex increases the importance of constantly scrutinizing the electrocardiogram (ECG) and making sure that

the pulse tone is audible. In contrast to most other types of pediatric surgery, infant body temperature may rise during ophthalmic surgery because of head-to-toe draping and insignificant body surface exposure. End-tidal CO ₂ analysis helps to differenti-ate this phenomenon from malignant hyperthermia.

The pain and stress evoked by eye surgery are considerably less than during a major intraabdominal or intrathoracic procedure. A lighter level of anesthe-sia would be satisfactory if the consequences of patient movement were not so potentially catastrophic. The lack of cardiovascular stimulation inherent in most eye procedures combined with the need for adequate anesthetic depth can result in hypotension in elderly individuals. This problem is usually avoided by ensur-ing adequate intravenous hydration and administer-ing small doses of ephedrine or phenylephrine. The practice of substituting muscle relaxation with non-depolarizing muscle relaxants for sufficient depth of anesthesia requires constant attention to the level of neuromuscular blockade to avoid patient movement, injury to the eye, and a malpractice claim.

Emesis caused by vagal stimulation is a common postoperative problem following eye surgery, partic-ularly with strabismus repair. The Valsalva effect and the increase in central venous pressure that accom-pany vomiting can be detrimental to the surgical result and will increase the risk of aspiration. Intraoperative intravenous administration of a 5-HT₃ antagonist (eg, ondansetron) decreases the incidence of postopera-tive nausea and vomiting (PONV). Dexamethasone (8–10 mg in adults) should also be considered for patients with a strong history of PONV.

EXTUBATION & EMERGENCE

A smooth emergence from general anesthesia is very important in order to minimize the risk of postop-erative wound dehiscence. Coughing or gagging due to stimulus from the endotracheal tube can be minimized by extubating the patient at a moderately deep level of anesthesia. As the end of the surgical procedure approaches, muscle relaxation is reversed, and spontaneous respiration is allowed to return. Anesthetic agents may be continued during gentle suction of the airway. Nitrous oxide, if used, is then discontinued, and intravenous lidocaine (1.5 mg/ kg) can be given to blunt cough reflexes temporar-ily. Extubation proceeds 1–2 min after the lidocaineadministration and during spontaneous respira-tion with 100% oxygen. Proper airway maintenance is crucial until the patient’s cough and swallowing reflexes return. Obviously, this technique is not appropriate in patients at increased risk of aspiration.

Severe discomfort is unusual following eye sur-gery. Scleral buckling procedures, enucleation, and ruptured globe repair are the most painful opera-tions. Modest incremental doses of intravenous opi-oid (eg, fentanyl 25 mcg or hydromorphone 0.25 mg for an adult) usually provide sufficient analgesia. The surgeon should be alerted if severe pain is noted fol-lowing emergence from general anesthesia, as it may signal intraocular hypertension, corneal abrasion, or other surgical complications.