Monitored anesthesia care

Published on 07/02/2015 by admin

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Last modified 22/04/2025

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Monitored anesthesia care

Jeffrey W. Simmons, MD and Michael J. Murray, MD, PhD

Monitored anesthesia care (MAC) refers to a service in which an anesthesia provider monitors a patient’s vital signs during a diagnostic or therapeutic intervention while administering anxiolytic and analgesic drugs for patient comfort. Occasionally during MAC, no or minimal drugs are administered to the patient—the anesthesia provider is present to closely monitor a seriously ill patient and to intervene to maintain vital functions as necessary. In these patients, who may require only minimal sedation, even the smallest doses of sedative or analgesic agents, because of the patient’s comorbid conditions, could adversely affect hemodynamics or respiratory function such that immediate intervention and resuscitation are required.

At other times, the surgeon injects a local anesthetic agent or the anesthesia provider performs a peripheral nerve block for intraoperative and postoperative analgesia, and MAC is provided so that the patient has the highest level of monitoring possible and the anesthesia provider is available to intervene to maintain the patient’s vital functions, with the option to convert the MAC to a general anesthetic, if necessary. This is a critical difference between MAC and moderate (conscious) sedation; the latter refers to a situation in which a physician supervises another healthcare provider, who monitors the patient and administers sedative and analgesic drugs under the supervising physician’s direction while the supervising physician performs a procedure, or the physician may administer drugs himself or herself. The type and amount of medication administered to a patient are supposed to achieve a “moderate” level of sedation such that the patient’s vital signs and respiratory drive are not significantly altered. Accordingly, the healthcare provider who administers moderate sedation must know how to monitor a patient’s vital signs and be able to recognize the transition into deep sedation.* In this event, the provider must understand how to support the patient’s vital functions and to increase the level of consciousness so that the level of sedation is again “moderate.”

If a procedure being planned is likely to require a deep level of sedation or MAC, most hospitals have policies mandated by government agencies or third-party payers that specify that only a practitioner credentialed and privileged to deliver an anesthetic is permitted to perform the service. In such situations, there is a high probability that “deep” sedation will result in the patient’s loss of consciousness or transition into general anesthesia. An anesthesia provider is required to monitor and manage the patient and produce the level of sedation necessary to safely complete the procedure.

Unfortunately, some anesthesia providers consider that MAC is less complicated and requires less vigilance than a general anesthetic. A review of the American Society of Anesthesiologists’ closed-claims database has shown that claims for cases that occurred outside the operating room more often involved MAC than general anesthesia and were more likely to occur, percentage wise, than were claims that came from cases performed in operating rooms. The most common findings were insufficient oxygenation and ventilation due to inadequate monitoring, and cases with MAC outside the operating room more often resulted in death than did cases inside the operating room.

Specifics of monitored anesthesia care

In essence, no difference exists between a MAC and a general anesthetic in terms of the type or level of services that the anesthesia provider delivers. The anesthesia provider evaluates the patient prior to the procedure—including reviewing the patient’s history, discussing the procedure, and examining the patient (including documenting when the patient last took anything by mouth and assessing the patient’s airway)—and develops an anesthetic plan. The anesthesia provider should discuss the plan with the patient, explain the options and the risks and benefits of those options (allowing the patient time to ask questions), and once those questions have been answered, obtain the patient’s consent to proceed. Management of the patient in the procedure suite includes monitoring the patient’s vital signs using the American Society of Anesthesiologists, standard monitors, delivering supplemental O₂ (by either a nasal cannula or a facemask), and placing an intravenous catheter with infusion of crystalloid as a carrier for any medications that may be administered during the procedure. Equipment for managing an airway and for emergency resuscitation must be readily available, as should an anesthesia workstation if conversion to a general anesthetic becomes necessary. During MAC, it would not be uncommon for a patient to lose consciousness; in reality, MAC has become a general anesthetic whether or not any airway instrumentation occurs. The anesthesia provider must be able to diagnose and treat any problems that might occur during the procedure and to provide other medical services as necessary to ensure the patient’s safety during the procedure. Following the procedure, the anesthesia provider also manages the recovery of the patient, maintaining responsibility for the patient until the patient meets discharge criteria from the postanesthetic care unit or from the procedural suite in which the procedure was performed.

Medications for monitored anesthesia care

For cases requiring minimal sedation, such as cataract operations, 12.5 to 25 mg of diphenhydramine or 1 to 2 mg of midazolam can be given intravenously. Along with topical application of a local anesthetic agent to the eye, this combination provides adequate sedation and operating conditions. Many procedures, such as colonoscopy or esophagoscopy, can be safely performed with a small dose of a benzodiazepine (1-2 mg of midazolam) and an opioid (25-100 μg of fentanyl). For a transesophageal echocardiogram, 30 to 50 mg of propofol given as an intravenous bolus after a local anesthetic agent is applied to the tongue allows placement of the probe, with subsequent boluses of 10 to 20 mg of propofol infused to maintain patient comfort during the acquisition of images.

For longer-lasting procedures, many providers use a bolus of a benzodiazepine at the beginning of the procedure and then a bolus followed by a continuous infusion of a hypnotic agent or a hypnotic agent and an opioid for the duration of the procedure. Propofol infused at 25 to 100 μg·kg⁻¹·min⁻¹ works very well for many patients undergoing many different procedures and is preferred by many anesthesia providers. Others have equal success using a combination of propofol in a lower dose (25-75 μg·kg⁻¹·min⁻¹), along with alfentanil, (0.3-0.4 μg·kg⁻¹·min⁻¹). Remifentanil has also been used by some with success, but many anesthesia providers find that the opioid-induced side effects of remifentanil limit its usefulness. As an alternative to an opioid infusion, ketamine, because of its salutary effects on the respiratory system, can be used. An infusion of a solution of 40 mL of 1% propofol, 250 μg (5 mL) of fentanyl, and 250 mg (5 mL, 50 mg/mL) of ketamine in 50 mL of saline (final concentration: 4 mg of propofol, 2.5 mg of ketamine, and 2.5 μg of fentanyl per mL) may be used because, by increasing the rate of infusion, general anesthesia can be induced with adequate analgesia and maintenance of spontaneous respiration. Adjuvants to the drugs mentioned here, to provide a more balanced approach, include the preoperative use of a nonsteroidal anti inflammatory agent, pregabalin, gabapentin, or clonidine or a bolus of a benzodiazepine and opioid (midazolam and fentanyl) followed by an infusion of the α-adrenergic receptor agonist, dexmedetomidine.

Benefits of monitored anesthesia care

In patients for whom MAC is an option, studies have demonstrated that the use of MAC, as compared with general anesthesia, is associated with a shorter time to emergence and orientation, decreased time in the postanesthesia care unit, decreased time before the patient is able to leave the hospital (for those patients having an outpatient procedure), a decreased incidence of postoperative nausea and vomiting, and better patient satisfaction. Despite these benefits, it is naïve to assume that providing MAC to a patient is a straightforward easy process. For example, delivering MAC to an elderly patient in the cardiac catheterization laboratory who is undergoing an electrophysiologic procedure requires considerable skill (and patience), knowledge of pharmacology, and a very high level of vigilance. However, overall, the increase in patient satisfaction and the superior outcomes associated with MAC justify its continued use in appropriate patients.

^*A level of consciousness induced by hypnotic, sedative, and analgesic drugs from which patients cannot be readily aroused but do respond to painful stimuli. Respiratory function may be impaired, as manifested by an inability to protect the airway; decreased respiratory rate, decreased tidal volume, or both; and hypercapnia. Patients may require assistance in maintaining a patent airway and ventilation. Blood pressure and heart rate are usually normal or decreased unless hypoxia and hypercapnia become severe.

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