Anesthesia for Procedures outside the Operating Room

Anesthesiologists are being called on to provide anesthetic care for an increasing number of procedures in remote locations (see Chapter 69 ). The most common of these procedures are electroconvulsive therapy (ECT), ESWL, and neuroradiologic procedures, including magnetic resonance imaging (MRI) and computed tomography. The anesthetic machines and monitors used in these locations may be old or unfamiliar models, and the monitoring equipment and supplies are often limited in comparison to the operating room. Experienced assistants may be unavailable, and nursing staff members in these locations are frequently unaccustomed to the anesthetic drugs, equipment, and procedures used by anesthesiologists. Consequently, the anesthesiologist must be vigilant when checking the anesthetic machine and must know where to locate emergency resuscitation drugs and equipment.

As with any ambulatory or office-based surgical procedure, patients must be carefully selected and evaluated before the procedure. The anesthetic techniques used for these procedures should provide for prompt recovery with minimal side effects (e.g., MAC), and patients must fulfill the same discharge criteria as those undergoing procedures in an operating room facility. Many of these procedures have specific anesthetic considerations and potential complications. For example, the anesthetic techniques used for ESWL procedures have changed dramatically over the past several years. With the development of newer lithotriptors, the water bath is no longer required and targeting is more precise, so fewer shocks are required. These improvements have essentially eliminated the use of general or epidural regional anesthesia, and most of these procedures can be performed with intravenous sedation-analgesic techniques. ^{[534] [557] [558]} These MAC techniques reduce anesthesia and recovery times without compromising patient safety and satisfaction.^{[557] [558] [559]} Monk and colleagues^[558] compared alfentanil and ketamine infusions in combination with midazolam and described both techniques as effective, although patients receiving alfentanil had a better recovery profile and

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Magnetic Resonance Imaging

MRI has become an increasingly popular noninvasive radiologic diagnostic procedure because of the high-quality images provided. MRI requires that patients be confined for 30 to 60 minutes in a magnetic, closed noisy space. Therefore, because of age, altered mental state, or pain, some patients cannot fully cooperate for this length of time and require either general anesthesia or intravenous sedation-analgesia to obtain a high-quality image. Patient movement during any part of the examination can compromise the quality of the image. Therefore, anesthesiologists are increasingly being involved in patient care for MRI and spectroscopy. Special anesthetic considerations are necessary for MRI because of the high magnetic field and the specialized rooms and buildings for housing the MRI scanners.^{[565] [566] [567]} Problems in monitoring patients undergoing MRI include the following:

1. Ferromagnetic equipment must be removed from the magnetic field, including credit cards, key chains, paper clips, pins, and pens, as well as conventional monitoring devices.
2. While in the scanner, access to the patient and viewing of the patient are limited.
3. Malfunction of monitoring equipment or interference produced by the changing magnetic field (e.g., syringe infusion pumps) can occur.
4. Stray radiofrequency current produced by the monitoring equipment can degrade the quality of the images.

These issues make it difficult to achieve an adequate balance between meeting the ASA standards for monitoring during anesthesia and acquiring a high-quality image.^[565] Newer anesthesia machines and nonferrous monitoring equipment are available. Because the older monitors may have to be located far from the patient (e.g., outside the room), the chance of disconnection and kinks in the intravenous tubing, anesthesia circuit tubing, monitoring leads, and cables is increased. The ideal situation is to have two anesthesia personnel: one close to the patient and an assistant outside the room with the monitoring equipment. Unfortunately, the personnel costs of this type of care would be higher than most institutions are willing to accept.

Gastroenterology Suite

For many years, endoscopists have used conscious sedation techniques for gastroenterology patients. Sedation improves not only patient comfort during the examination but also patient acceptance of follow-up examinations. Specific monitoring guidelines and sedation techniques for assisting the endoscopist are available. ^{[568] [569] [570]} However, many situations arise that can benefit from the services of an anesthesiologist, such as endoscopic procedures performed on patients with complex coexisting medical conditions or in situations in which previous attempts at operator-administered sedation were unsuccessful.

An important consideration in the planning of an anesthetic technique is the position of the patient during the examination. Patients undergoing endoscopic procedures are often positioned lateral or prone to facilitate the examination, and these positions may pose difficulty should resuscitative efforts be required. During upper endoscopic procedures or endoscopic retrograde cholangiopancreatography, the endoscope is inserted orally, which necessitates sharing the patient's airway with the endoscopist. Cooperation and a team approach by the endoscopist, the radiology staff, and the anesthesiologist are essential to the expeditious performance of these procedures.

Electroconvulsive Therapy

The use of ECT to provoke a generalized epileptic seizure was first described in 1938 and was performed without anesthesia for almost 30 years. ^[571] At the present time, the number of ECT procedures performed each year under general anesthesia in the United States exceeds the number of coronary revascularization, appendectomy, and herniorrhaphy procedures.^[572] In recent years, ECT has assumed an increasingly important role in the treatment of acute and medication-resistant chronic depression and mania, as well as the management of schizophrenic patients with affective disorders, suicidal drive, delusional symptoms, vegetative dysregulation, inanition, and catatonic symptoms.^[573] ECT is both extremely safe and highly effective in a wide variety of high-risk patient populations. Typically, the acute phase of ECT is performed three times a week for 6 to 12 treatments. In successful cases, initial clinical improvement is usually evident after three to five treatments. Maintenance therapy can be performed at progressively increasing intervals from once a week to once per month to prevent relapses.

Anesthetic management for ECT has recently been reviewed^[574] and typically involves the use of an induction dose of an intravenous anesthetic (e.g., methohexital, thiopental, etomidate, or propofol), followed by a muscle relaxant (e.g., succinylcholine or mivacurium). Although the overall recovery profiles are similar with all the intravenous anesthetics, methohexital remains the drug of choice because of longer seizure times (versus propofol), shorter awakening times (versus thiopental), and fewer side effects (versus etomidate). In situations in which the intravenous anesthetic precludes an adequate seizure (>30 seconds), adjunctive use of remifentanil (50 to 100 µg IV) can produce an anesthetic-sparing effect. ^[575] Because remifentanil has no direct effect on the ECT-induced seizure duration,^[576] its use can lead to an improved response to the ECT stimulus. A wide variety of cardiovascular drugs (e.g., esmolol, labetalol, nicardipine) are used to minimize the acute hemodynamic changes produced by the electrical stimulus and the resultant

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The optimal dosage of anesthetic, muscle relaxant, and sympatholytic drugs requires careful titration to the needs of the individual patient, and further adjustments during the course of a series of ECT treatments should be based on the patient's earlier responses. Although a simple "modal" approach to anesthesia for ECT was advocated by Kellner,^[578] patients vary widely in their sensitivity to these drugs, depending on their age, body habitus, concurrent drug therapy, and underlying medical conditions. Given the large number of elderly patients with underlying cardiovascular disease (e.g., hypertension, coronary artery disease, peripheral vascular disease), careful titration of the commonly used sympatholytic drugs (e.g., labetalol, esmolol, nicardipine, clonidine) is also important to obtain the best possible outcome with ECT. Anesthesiologists should be aware of anesthetic factors that influence the duration of seizure activity because the clinical effectiveness of ECT is predicted on achieving an adequate seizure.