Regardless of the type of anesthesia contemplated for vitreoretinal (VR) surgery, the patient should undergo a thorough preoperative evaluation prior to the procedure. Under most circumstances, this evaluation should occur well before the day of surgery so that required treatment can be performed in advance to help ensure that the patient is in optimal condition prior to surgery. Specific investigations, such as chest X-ray, ECG, and blood chemistries, should be performed only when dictated by the findings of thorough history and physical examinations. So-called “screening labs” are not indicated when the appropriate history and physical examinations are negative.

GENERAL VERSUS LOCAL ANESTHESIA

Both general and local anesthetic techniques are acceptable for VR surgery; however, the authors prefer to do the vast majority of their cases using monitored local anesthesia for a variety of reasons: (a) local anesthesia offers increased safety for patients, especially those in high-risk categories, (b) local anesthesia saves time and reduces cost, and (c) local anesthesia provides rapid recovery and prolonged analgesia, both of which are especially important in the outpatient population.

Not all patients are appropriate candidates for VR surgery under local anesthesia. Immature, mentally deficient, claustrophobic, and uncooperative patients are best managed with general anesthesia. Patients with language barriers, however, can frequently be managed extremely well with local anesthesia if a competent translator can be found. Estimated surgical time is an additional consideration when choosing general versus local anesthesia. Surgeons requiring more than 90 minutes for a given VR procedure should consider general anesthesia over local anesthesia, as patients may become restless and uncomfortable when asked to lie completely still for such long periods. An additional indication for general anesthesia is the patient who insists upon it, although these patients will be rare if properly informed and reassured by a sympathetic surgical team. Nitrous oxide should be avoided not only because of the potential interaction with intraocular gas bubbles but also because it has been shown in large, randomized multicenter trials to result in a 30% higher incidence of nausea and vomiting.

MONITORING DURING SURGERY

Regardless of the type of anesthesia used, the patient must be carefully monitored during surgery. Appropriate monitoring begins with the continuous presence of an anesthesiologist or certified registered nurse anesthetist during the entire procedure. If sedation is being given, it is not in the patient’s best interest to have the surgeon or circulating nurse monitoring the patient, as may be the case in a brief procedure performed under strictly local anesthesia without sedation. Basic monitoring includes continuous ECG, noninvasive blood pressure, and pulse oximetry. End-tidal CO₂ monitoring is additionally essential during general anesthesia and can also be helpful during local anesthesia. Core temperature monitoring is indicated during longer procedures under general anesthesia to help ensure that thermal preservation procedures are successful and to help in monitoring for the rare occurrence of malignant hyperthermia. In diabetic patients, the ability to monitor blood glucose in the intraoperative and perioperative periods is also important in order to recognize and treat extremes of both hyperglycemia and hypoglycemia.

BLOOD PRESSURE CONSIDERATIONS DURING GENERAL ANESTHESIA

It is common for VR surgeons to become angry if the patient moves at all during surgery. An unintended consequence of this tendency is for the anesthesia provider to maintain deeper levels of anesthesia to prevent movements, which may result in low enough systemic blood pressures to compromise cerebral, myocardial, and retinal perfusions. During VR surgery, intraocular pressure (IOP) should be controlled in the 35 to 45 mm Hg range. Ocular ischemia and central retinal artery occlusion can occur if low systemic blood pressures are allowed to persist during the procedure. To ensure adequate levels of general anesthesia and immobility of the patient, adequate, monitored muscular relaxation combined with processed EEG (i.e., bispectral analysis) monitoring should be considered so that excessively deep levels of general anesthesia can be avoided.

SEDATION DURING LOCAL ANESTHESIA

In general, patients having VR surgery under local anesthesia should have minimal sedation, most of which should be given at the time of the block. Patients should not be sedated too deeply during VR surgery for a number of reasons. In the first place, airway obstruction may occur, requiring manual support and interruption of the procedure. This has been described as AWAC (anesthesia without airway control). Secondly, respiratory movements during sleep or near sleep often result in magnified movements of the head, which greatly hinder the progress of the surgeon who is seeing these movements magnified 20 to 40 times through the operating microscope. Thirdly, some patients become quite talkative and social when overly sedated. It may be impossible for them to quit talking and moving despite the most vigorous admonitions to do so. The only way to manage these patients is to stop all sedation completely or to convert to general anesthesia. Finally, patients who are asleep or nearly asleep are prone to awakening suddenly and being totally disoriented, resulting in movements, which can be devastating, even in the hands of the finest surgeon. The goal of sedation should be control of anxiety, rather than true sedation with decreased awareness of surroundings.

Judicious amounts of sedatives and/or opioid agents can be helpful during local anesthesia for VR surgery, especially in the patient who is very apprehensive or slightly claustrophobic. Brevital, thiopental, midazolam, propofol, alfentanil, remifentanil, ketamine, and others have been promoted to provide good operating conditions and acceptable patient sedation for a variety of procedures performed under local anesthesia. Brevital, thiopental, and alfentanil have been largely supplanted by propofol. Remifentanil has a higher profile of nausea and vomiting than the other narcotics. Ketamine will cause nystagmus and probably increases IOP. Although the regional block should prevent ocular movements, ketamine is a questionable choice unless a mentally challenged or combative patient had to be done under regional anesthesia. The cost of propofol has significantly decreased since the drug became generic, but this drug only remains sterile in a syringe for a maximum of 12 hours, which may be a consideration in developing countries. For VR surgery, the emphasis must be placed on balancing patient comfort and satisfaction while providing the most stable conditions for surgery. In general, this means using small doses of rapid-onset, short-acting drugs given continuously with very careful monitoring of effect. The goals are to assist the patient in lying perfectly still for 60 to 90 minutes without falling asleep, to enhance analgesia, and to provide a measure of amnesia. These are not easily achieved, but they can be accomplished in most patients by an experienced and knowledgeable anesthesia team.

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