Monitored anesthesia care in adults

INTRODUCTION — Monitored anesthesia care (MAC) is a type of anesthesia service in which an anesthesia clinician continually monitors and supports the patient's vital functions; diagnoses and treats clinical problems that occur; administers sedative, anxiolytic, or analgesic medications if needed; and converts to general anesthesia if required. Approximately one-third of ambulatory anesthesia services for diagnostic or therapeutic procedures in the United States are provided as MAC [1], often in out-of-operating-room locations.

This topic will discuss preoperative evaluation for patients who will receive MAC, monitoring during MAC, and the medications and sedation techniques commonly used during MAC. Procedural sedation by non-anesthesia clinicians and the drugs and techniques used for general anesthesia are discussed separately. (See "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications" and "Gastrointestinal endoscopy in adults: Procedural sedation administered by endoscopists" and "Induction of general anesthesia: Overview" and "Maintenance of general anesthesia: Overview".)

Sedation during procedures for which the primary anesthetic is a regional anesthesia technique, either neuraxial anesthesia or peripheral nerve block, is not considered MAC. However, the basic principles of sedation that are discussed here apply to those anesthetics as well.

PREPROCEDURE EVALUATION — A medical history and anesthesia-directed physical examination should be performed for all patients who undergo anesthesia, including those having MAC. Preoperative laboratory evaluation should be the same for MAC as it would be for general anesthesia (GA). (See "Preoperative medical evaluation of the healthy adult patient", section on 'Laboratory evaluation'.)

Patient medical status — The goals for preoperative evaluation are to identify underlying medical and physical conditions that may increase risk and to create an anesthetic plan that minimizes risk. In anticipation of MAC, the patient should be evaluated for conditions that increase sensitivity to sedative and analgesic medications (eg, older age; obstructive sleep apnea; advanced chronic lung disease; pulmonary hypertension; malnutrition [2]; coronary, liver, or renal disease; anxiety disorders; chronic pain; use of opioids, sedatives, or recreational drugs) to allow appropriate drug dosing and administration. According to the European Society of Anesthesiology guidelines for procedural sedation and analgesia, patients with the following comorbidities and conditions are at higher risk of complications: severe cardiovascular disease, documented or suspected risk of obstructive sleep apnea syndrome, morbid obesity, chronic renal failure, chronic hepatic disease (model for end-stage liver disease score >10), age >70 years, and American Society of Anesthesiologists' (ASA) physical status III to IV [3].

Airway evaluation — Airway management may be necessary if sedation becomes deeper than intended or if GA is required during a planned MAC anesthetic. Therefore, the preoperative consultation should include an assessment of the airway (table 1 and table 2) and risk factors for aspiration (table 3) and education about routine preoperative fasting guidelines as for GA (table 4). (See "Airway management for induction of general anesthesia", section on 'Airway assessment' and "Airway management for induction of general anesthesia", section on 'Prediction of the difficult airway' and "Preoperative fasting in adults", section on 'Fasting guidelines'.)

Appropriateness of monitored anesthesia care — The decision to use MAC must take into consideration the level of sedation required and whether the clinician will have easy access to the airway if immediate airway control is necessary. Procedures that limit access to the airway (eg, head and neck procedures, computed tomography [CT], or magnetic resonance imaging [MRI]) may be performed under light levels of sedation or under GA with airway control.

GA with endotracheal intubation may be a more appropriate choice than MAC for procedures that limit airway access and require deeper levels of sedation, especially in patients at high risk of aspiration if airway protective reflexes are diminished. Alternatively, for some procedures, regional anesthesia techniques (eg, peripheral nerve blocks, local anesthetic infiltration) or neuraxial anesthesia may be used to allow lighter levels of sedation that maintain airway reflexes.

When assessing the appropriateness of MAC, we also evaluate the following patient abilities:

●Lie motionless in the position required for the procedure – MAC may not be appropriate for procedures that require immobility in patients who may not be able to remain still in supine position without excessively deep sedation or general anesthesia (eg, essential tremor, persistent cough, orthopnea). Patients with arthritis or other joint problems may be unable to lie in the lateral position because of shoulder or hip pain, or prone because of neck pain, without excessively deep sedation.

●Cooperate, if necessary – Patients with cognitive dysfunction, dementia, extreme anxiety, and barriers to communication may be unable to cooperate when necessary (eg, during awake craniotomy or thyroplasty).

●Communicate with care providers – Verbal communication is required during MAC for assessment of the depth of sedation, explanation, and reassurance. Language barriers and hearing deficits may require a plan for communication aids during the procedure or may make general anesthesia a better choice than MAC.

Conversion from MAC to GA — During the preoperative evaluation, the possibility of needing to convert to GA must always be considered. In a single institution retrospective study of over 200,000 MAC cases in adults, conversion to GA occurred in 0.5 percent of cases [4]. Frequent reasons for conversion included patient's inability to tolerate MAC, hypoxia or airway obstruction, failure of local/regional technique, aspiration, and unplanned extension of surgical area. Risk factors associated with conversion to GA included body mass index >35 kg/m²; male sex; ASA physical status IV; anesthesia provider being a resident or nurse anesthetist rather than a solo attending; and procedures for oral and maxillofacial surgery, otorhinolaryngology, or orthopedic surgery [4].

Patient expectations — Patients should realize that they may be aware and remember some or all of the procedure performed under sedation during MAC. Studies of patients who have reported awareness with recall have found that many patients expected to be unconscious during sedation or regional anesthesia [5,6]. Total lack of awareness and amnesia cannot be expected without general anesthesia. (See "Accidental awareness during general anesthesia", section on 'Management of patient expectations'.)

MONITORING DURING MONITORED ANESTHESIA CARE

Standard physiologic monitors — In addition to clinical observation, standard American Society of Anesthesiologists (ASA) monitors should be employed during MAC (ie, electrocardiogram [ECG], noninvasive blood pressure [BP], oxygenation via pulse oximeter, temperature) [7,8] as they would be for general anesthesia. In addition, exhaled carbon dioxide (CO₂) monitoring (capnography) is a standard monitor for patients who receive moderate or deep sedation or general anesthesia [8,9]. During sedation, capnography facilitates early detection of apnea and airway obstruction [10], predicts the development of hypoxemia [11], and may reduce patient injury related to respiratory depression [12]. (See "Carbon dioxide monitoring (capnography)", section on 'Procedural sedation' and "Basic patient monitoring during anesthesia", section on 'Capnography'.)

More advanced cardiovascular monitoring (eg, intraarterial BP monitor) may be indicated based on patient factors and the planned procedure.

Monitoring depth of sedation and analgesia — Sedation is a continuum of drug-induced depression of consciousness that can range from wakefulness to general anesthesia [13]. If sedatives and/or analgesic medications are administered during MAC, the depth of sedation must be continually assessed to avoid oversedation or general anesthesia.

Clinical assessment of sedation — The ASA has created widely accepted definitions for minimal, moderate, and deep sedation based on responsiveness to verbal, tactile, and painful stimulation (table 5). According to these definitions, patients who have received deep sedation respond only to either repeated or painful stimulation, may require airway intervention, and may have inadequate spontaneous ventilation. Importantly, any patient who is unarousable with a painful stimulus is, by definition, under general anesthesia.

In addition to the ASA definitions, other validated instruments for assessment of level of sedation that can be used during MAC include the Ramsay Sedation Scale (table 6) [14] and the Modified Observer's Assessment of Alertness/Sedation Scale (MOASS) (table 7) [15]. However, these scales are most commonly used in intensive care settings or for research purposes. In clinical practice, in the author's experience, depth of sedation is usually assessed by repeated evaluations of the patient's arousability.

Processed electroencephalography — Processed electroencephalography (EEG) monitors are often used during general anesthesia to provide information about the depth of anesthesia. The most commonly used device is the bispectral index (BIS) monitor, which provides a score from 0 to 100, with 100 representing the awake state; a score <60 corresponds to general anesthesia [16]. (See "Accidental awareness during general anesthesia", section on 'Brain monitoring'.)

The utility of processed EEG monitors for assessing the depth of sedation for MAC is unclear, and we do not routinely use BIS for these cases. The relationship between BIS values and the level of sedation varies among patients [17], and the literature on this correlation is conflicting. Several observational studies have reported good correlation between the BIS value and sedation scale scores [18-22], while others have reported poor correlation, especially during light to moderate sedation [23-25]. There is weak evidence to support the use of other processed EEG monitoring systems for MAC (eg, spectral entropy, Narcotrend, and SedLine) [3].

SUPPLEMENTAL OXYGEN — Supplemental oxygen (O₂) may not be necessary in patients with normal cardiopulmonary function having MAC with minimal sedation. In contrast, supplemental O₂ is usually required when MAC involves moderate or deep sedation/analgesia, as higher doses of intravenous (IV) analgesic and sedative medications can cause respiratory depression.

Open delivery of O₂ (eg, via nasal cannulae or a face mask) is a significant risk factor for operating room fire during procedures around the head and neck that require electrocautery. For such procedures, supplemental O₂ should be avoided, or limited to a concentration of <30 percent. Risk of operating room fire and preventive strategies are discussed separately. (See "Fire safety in the operating room", section on 'Management of open oxygen delivery systems' and "Fire safety in the operating room", section on 'Risk-based approach to fire prevention'.)

DRUGS USED FOR SEDATION AND ANALGESIA FOR MONITORED ANESTHESIA CARE — In general, medications with rapid onset and short duration of action are preferred for sedation/analgesia during MAC to allow rapid titration of effects and quick recovery. Most of these medications have the potential to cause respiratory depression and hypotension (table 8).

Doses should be modified based on patient factors (eg, doses reduced for older adults) and when combinations of drugs are administered.

We often use a balanced approach to the choice of sedative/analgesics, with a combination of sedatives and opioids or local anesthesia, to allow reduced doses of each class of drugs. Medications are often chosen based on clinician preference and familiarity, formulary issues, and cost.

Benzodiazepines

Midazolam — Midazolam is a short-acting benzodiazepine with anxiolytic, amnesic, and sedative effects, without analgesic effects. Of the medications used for MAC, midazolam most reliably provides amnesia. Midazolam potentiates the effects of other sedatives and opioids, and can cause respiratory depression when given in high doses or with other sedatives or opioids.

The onset of action of an IV bolus of midazolam occurs in approximately one to three minutes, with peak effect at approximately five minutes. The elimination half-life of midazolam is one to four hours [26].

A small dose of midazolam (eg, 0.5 to 2 mg IV, doses adjusted in older adult patients) is commonly administered as premedication before entering the procedure room and is often administered before starting a propofol infusion. Midazolam premedication should be used cautiously in older adult patients, and is often avoided as part of enhanced recovery protocols. When used in small doses for premedication in low-risk patients, midazolam may have little effect on recovery. In a randomized trial of approximately 400 patients who underwent elective colonoscopy with propofol/opioid sedation with or without midazolam (0.04 mg/kg, maximum 5 mg) premedication, Postoperative Quality of Recovery Scores, including the cognitive domain scores, were similar at all time points in patients who received midazolam and those who did not [27]. Emergence and hospital discharge times were similar as well.

However, midazolam is rarely used as the primary sedative for longer cases under MAC because repeated doses or infusions can result in sedation, confusion, and amnesia that lasts into the postoperative period. A number of studies comparing recovery after sedation during MAC have reported more rapid psychomotor recovery with propofol than with midazolam [28-30].

The benzodiazepine antagonist flumazenil may be used to reverse the sedation induced by midazolam, but it has limited efficacy for reversal of respiratory depression caused by other types of drugs. Thus, patients with respiratory depression who have also received opioids should be treated with naloxone, an opioid antagonist, before or rather than flumazenil. The dose of flumazenil in adults is 0.2 mg IV given over 15 seconds, which may be repeated every minute to a maximum of 1 mg. The duration of action of flumazenil is approximately 20 to 40 minutes, which may be shorter than the residual effects of midazolam. Therefore, patients who have received flumazenil should be monitored for signs of resedation. In the event of resedation, flumazenil can be repeated at 20-minute intervals as needed, at 0.2 mg IV per minute, to a maximum dose of 1 mg, or 3 mg in an hour. When flumazenil is not available, some reports indicate that aminophylline (1 to 2 mg/kg IV over 5 minutes) can be at least partially effective in reversing sedation and respiratory depression caused by midazolam [31-34]. However, aminophylline should be used with caution in patients with seizures, cardiac or hepatic disease, and older adults.

Remimazolam — In 2020 the US Food and Drug Administration (FDA) approved remimazolam, a new short-acting benzodiazepine, for intravenous administration as a slow bolus. The drug uniquely exhibits the organ independent ester hydrolysis of remifentanil, while retaining the gamma aminobutyric acid (GABA) agonist activities of midazolam. It can be safely used in patients with hepatic or renal impairment, without fear of prolonged duration of action, and can be reversed with flumazenil.

Because of its unique metabolism, remimazolam was expected to facilitate a faster recovery and earlier discharge from the postprocedure unit. Onset of clinical effect is similar to midazolam, whereas recovery is shorter [35]. However, the literature comparing remimazolam with other available agents is limited, and further study is required to determine its role in clinical care.

In our opinion, remimazolam does not provide significant advantages over midazolam for most uses. The FDA labeling recommends 5 mg push injection over a one-minute time period followed by supplemental doses of 2.5 mg intravenously over a 15 second time period after at least two minutes. This regimen is impractical for very brief procedures (eg, upper GI endoscopy), and for longer procedures that would require repeated administration. Use of remimazolam for GI endoscopy is discussed separately. (See "Anesthesia for gastrointestinal endoscopy in adults", section on 'Remimazolam'.)

Propofol — Propofol is a rapidly acting, short-acting sedative/hypnotic with modest amnestic and antiemetic properties at subhypnotic doses [36,37] without analgesic effects. Propofol is widely used for MAC because of its pharmacokinetic profile, including rapid effect site equilibration and short elimination half-time even after prolonged infusion. Thus, the depth of sedation can be adjusted rapidly, and patients recover quickly without residual psychomotor effects [28-30]. (See "Procedural sedation in adults in the emergency department: Medication selection, dosing, and discharge criteria", section on 'Propofol'.)

Propofol may be administered by intermittent boluses (eg, propofol ~20 mg IV). It is more commonly administered by titrated infusion (25 to 75 mcg/kg/minute), with or without an initial bolus.

Patients receiving propofol must be closely monitored for depth of sedation. Propofol has a narrow therapeutic index, meaning that patients may rapidly transition to deeper levels of sedation, including general anesthesia. There is no reversal agent for propofol, so oversedated patients must be managed with supportive measures, including proper airway management, until the drug wears off.

Propofol causes pain on injection in as many as 70 percent of patients [38]. A variety of methods for prevention and treatment of propofol pain have been used, including placement of intravenous (IV) catheters in antecubital veins rather than smaller veins, pretreatment with opioids, and injection of IV lidocaine, with or without proximal vein occlusion [39]. In the author's experience, the most effective way to prevent pain due to propofol injection is to apply a tourniquet proximal to the IV site, inject 1% lidocaine 0.5 to 1 mg/kg IV, and wait 45 to 60 seconds before releasing the tourniquet and injecting propofol. Administration of lidocaine 20 to 30 mg IV just prior to a bolus of propofol may also be effective to minimize pain on injection. (See "Procedural sedation in adults in the emergency department: Medication selection, dosing, and discharge criteria", section on 'Propofol'.)

Opioids — Opioids are administered during MAC to provide analgesia for procedures in which local anesthesia may be ineffective or inappropriate, for local anesthetic infiltration or block placement, for uncomfortable positioning, or for propofol injection pain. Opioids with rapid onset and short duration of action are generally preferred. The most commonly used opioids for MAC are fentanyl and remifentanil; the choice is often based on clinician preference, cost, duration of the procedure, and convenience. Remifentanil is more expensive than fentanyl and is only available as a powder that must be diluted for use.

Doses of opioids should be titrated to effect with both bolus and infusion techniques to minimize the risk of respiratory depression.

All opioids can cause intraoperative or postoperative nausea and vomiting (PONV), and prophylaxis for PONV during MAC should be considered as it would be for general anesthesia. We do not usually administer additional antiemetic medication during MAC that includes propofol, and we administer prophylaxis for other cases based on risk factors. (See "Postoperative nausea and vomiting", section on 'Risk factors'.)

●Fentanyl – Fentanyl is typically used in small, intermittent IV boluses of 25 to 50 mcg IV, with reduced doses in older adults or when administered in combination with other sedatives/hypnotics. The onset of action is approximately one to three minutes, with peak effect in approximately six minutes. The duration of action of fentanyl is approximately 30 to 60 minutes.

●Remifentanil – Remifentanil is an ultrashort-acting opioid with a very rapid onset of effect (60 to 90 seconds) and a context-sensitive half-time of elimination of approximately three minutes independent of the duration of infusion [40]. Remifentanil can be used to provide intense, titratable analgesia during stimulating portions of a procedure of any duration, without residual respiratory depression when stimulation is over.

Remifentanil is usually administered as an infusion, with or without an initial or intermittent boluses. Commonly used doses, which should be adjusted for patient factors, are as follows. All doses should be reduced to half with concomitant midazolam administration.

•Single dose 90 seconds prior to local anesthetic (LA) infiltration – Remifentanil 0.5 to 1 mcg/kg over 30 to 90 seconds.

•Infusion – Beginning five minutes prior to LA infiltration, remifentanil 0.1 mcg/kg/minute, wean to 0.05 mcg/kg/minute as tolerated (range 0.025 to 0.2 mcg/kg/minute) or target-controlled infusion at 1 to 3 ng/mL [41]. (See 'Target-controlled infusion' below.)

•Intermittent boluses – Remifentanil 25 mcg IV over 15 to 30 seconds, or remifentanil 12.5 mcg IV over 15 to 30 seconds with background infusion [42].

Dexmedetomidine — Dexmedetomidine is a selective alpha₂-adrenergic agonist with sedative, anxiolytic, and modest analgesic effects. In doses used for sedation, dexmedetomidine has been thought to have less respiratory depressant effects than other sedatives [43,44]. Clinical studies have reported a lower incidence of airway obstruction during sedation with dexmedetomidine compared with propofol [45]. However, some studies have reported upper respiratory obstruction and apneic episodes during sedation with dexmedetomidine, particularly during bolus administration [46,47]. In a small non-blinded randomized crossover volunteer study that compared the respiratory effects of dexmedetomidine or propofol at comparable degrees of sedation, the ventilatory response to hypoxia and hypercarbia were reduced to a similar degree with each drug [48]. In other randomized crossover volunteer studies, sedation with dexmedetomidine and propofol produced similar levels of upper airway collapse and reduced ventilatory drive [49,50]. Thus, dexmedetomidine should not be viewed as protective against respiratory depression or airway obstruction, particularly in high-risk patients.

The onset of action of dexmedetomidine is relatively slow compared with other sedatives used for MAC. Clinical effects are often not seen until approximately 15 minutes after the start of a loading dose. In one study of sedation during regional anesthesia, targeted sedation was achieved within 10 minutes with a propofol infusion and took 25 minutes with dexmedetomidine [51]. Recovery from dexmedetomidine infusion is variable, with a context-sensitive half-time of elimination ranging from four minutes after a 10-minute infusion to 250 minutes after an eight-hour infusion [52].

Dexmedetomidine is usually administered with a loading dose of 0.5 to 1 mcg/kg IV over 10 minutes, followed by infusion at 0.2 to 1 mcg/kg/hour. Rapid administration and high doses may cause bradycardia and hypotension, or hypertension.

Dexmedetomidine has been used for sedation during MAC for a variety of procedures. The slow onset of action, hemodynamic effects, and prolonged sedation may make dexmedetomidine less suitable for some procedures (eg, cataract surgery [53], intra-arterial acute stroke therapy [54]) [55,56].

Ketamine — Ketamine produces a dissociative state accompanied by amnesia and intense analgesia with minimal respiratory depression at sedative doses (ketamine 0.25 to 0.5 mg/kg IV). We often administer small doses of ketamine during MAC to enhance analgesia and decrease the need for opioids.

Ketamine has a rapid onset of action (one minute) and a relatively short duration of action (10 to 20 minutes, with an elimination half-life of two to three hours) [57,58].

During ketamine sedation, the patient's eyes may remain open, and purposeful skeletal muscle movements are possible. Hemodynamic effects of ketamine include increases in heart rate (HR) and blood pressure (BP). However, ketamine can be cardio-depressant in patients with catecholamine depletion [59]. Adverse effects of ketamine include increased oral secretions that may lead to laryngospasm, and emergence reactions including vivid dreams and hallucinations. Concomitant use of benzodiazepines and other hypnotics and restriction of the dose to 0.25- to 0.5-mg/kg boluses with a maximum of 2 mg/kg over a 30-minute period may reduce the risk of such adverse effects [60].

The combination of ketamine with propofol ("ketofol") has been administered for sedation, most commonly in the emergency department (ED) setting [61]. The benefits of this combination are unclear; the use of ketofol is discussed separately. (See "Procedural sedation in adults in the emergency department: Medication selection, dosing, and discharge criteria", section on 'Premixed with propofol (ketofol)'.)

STRATEGY FOR MONITORED ANESTHESIA CARE — Selection of medications and administration technique for MAC should be individualized to fit the needs of each particular patient (including medical issues that increase sensitivity to sedatives and opioids), the desired degree of sedation/analgesia, and the procedure to be performed. (See 'Patient medical status' above.)

There are many ways to provide safe and effective sedation/analgesia for MAC. Our usual approach to the choice of medications based on the degree and duration of expected painful stimulation is as follows.

Procedures with minimal or no pain — For short, painless diagnostic procedures (eg, magnetic resonance imaging [MRI], computed tomography [CT] scans), we often administer a bolus of midazolam (1 to 2 mg IV) followed by small supplemental doses (eg, 0.5 to 1 mg IV) titrated to effect. Alternatively, for patients with morbid obesity, obstructive sleep apnea, acute or chronic pain, or severe anxiety, we administer dexmedetomidine (0.1 to 0.7 mcg/kg/hour IV infusion) and may supplement with ketamine (0.5 to 1 mg/kg IV).

Procedures with brief, initial pain — Procedures that involve only an initial, brief painful stimulus (eg, local anesthetic infiltration, peripheral nerve blocks, eye block, diagnostic puncture) usually require administration of larger doses of hypnotics or analgesics. A variety of drugs, alone or in combination, can be used. We usually administer midazolam 1 to 2 mg IV with fentanyl 50 to 100 mcg IV, or propofol 0.5 to 1 mg/kg IV, or remifentanil 0.5 to 1 mcg/kg IV over 60 to 90 seconds. For eye blocks for ophthalmologic surgery, we administer a bolus of propofol or remifentanil as described, and for local anesthesia or peripheral nerve blocks, we administer midazolam and fentanyl.

Procedures with variable pain throughout — Infusions or repeated boluses of hypnotics and analgesics are usually used for procedures that cause variable degrees of pain throughout. Examples of such clinical scenarios are as follows:

●For gastrointestinal endoscopy, we commonly administer propofol (initial bolus of 0.5 to 1 mg/kg followed by 25 to 75 mcg/kg/minute), supplemented as necessary with fentanyl 25 to 50 mcg or ketamine 0.5 to 1 mg/kg IV.

●For laryngeal framework procedures (eg, thyroplasty, arytenoid adduction), we usually administer dexmedetomidine (0.3 to 0.7 mcg/kg/hour IV) with remifentanil (0.03 to 0.04 mcg/kg/minute IV) [62]. This combination of medications has been described for MAC for electrophysiology procedures as well [63]. Alternatively, for patients who are at increased risk of airway obstruction or respiratory depression (eg, patients with obstructive sleep apnea or morbid obesity), we often administer dexmedetomidine (0.1 to 0.7 mcg/kg/hour IV infusion) and may supplement with ketamine (0.5 to 1 mg/kg IV).

DRUG ADMINISTRATION TECHNIQUES — Anesthesia clinicians can administer sedative and analgesic medications for MAC by bolus administration, continuous infusion, or a combination of the two. Computer-controlled methods of administration (used primarily outside the United States) and patient-controlled methods of administration have also been used.

Bolus versus infusion — The optimal method for drug delivery may depend on the duration and stimulation of the procedure and the drugs administered. In general, continuous infusion is often used for drugs with very short duration of action (eg, propofol, remifentanil) in an attempt to maintain stable blood levels of the drug. However, the benefits of continuous infusion versus intermittent bolus are not clear and may depend on the procedure and patients. Studies on the use of propofol for short gynecologic procedures, flexible bronchoscopy, and colonoscopy have reported that bolus techniques result in less total propofol administered, though with similar recovery times, compared with continuous infusion techniques [64-66].

Target-controlled infusion — Target-controlled infusion (TCI) is a mode of drug administration with an infusion pump that uses pharmacokinetic models to calculate infusion rates necessary to achieve desired plasma or effect-site concentrations. The anesthesia clinician sets a desired effect-site target concentration (ie, mcg/mL or ng/mL) rather than the infusion rate that would be selected for a standard infusion pump (eg, mcg/kg/minute). The primary difference between TCI and manually adjusted infusion and/bolus administration is that the TCI system reduces infusion rates to account for drug distribution and elimination. Examples of plasma concentrations of propofol that correlate with different levels of sedation using TCI are shown in a table (table 9).

The literature comparing the use of TCI systems with manual administration of sedatives is inconclusive. Some studies have reported faster recovery and a reduced incidence of respiratory depression with TCI for deep sedation [67,68]. However, there is no definitive evidence that, overall, TCI is clinically superior to manual methods of delivery of sedation.

TCI systems are not available in the United States.

COMPLICATIONS DURING MONITORED ANESTHESIA CARE — In contrast with popular belief, the overall rate of complications during and after MAC appears to be similar to that for general anesthesia [69-73]. The true incidence of anesthetic complications is notoriously difficult to ascertain, as many nonfatal complications are not reported. Nonetheless, data from the American Society of Anesthesiologists (ASA) Closed Claims Database suggest that, at least among cases that result in malpractice claims, the severity of injury for MAC cases is similar to claims after general anesthesia, with 40 percent of claims made for death or permanent brain damage [12]. The most common mechanism of injury in closed claims was respiratory depression resulting from oversedation, and nearly half of these were thought to have been preventable with better monitoring.

Patients who have MAC tend to be older and sicker and more commonly have anesthesia in offsite or out-of-operating-room locations, all of which increase the risk of complications [74-76]. (See "Office-based anesthesia" and "Anesthesia for magnetic resonance imaging and computed tomography procedures".)

Potential complications include:

●Respiratory complications, including airway obstruction, respiratory depression with hypoxemia and hypercarbia, and aspiration due to depression of airway reflexes.

●Cardiovascular compromise, including hypotension, cardiac ischemia, cardiac arrest, and arrhythmias. (See "Arrhythmias during anesthesia".)

●Complications related to patient movement (eg, protrusion of eye contents or eye injury during eye surgery).

●Burn injuries, particularly involving the head and neck. (See "Fire safety in the operating room".)

●Local anesthetic systemic toxicity (LAST). (See "Overview of peripheral nerve blocks", section on 'Local anesthetic systemic toxicity'.)

POST-ANESTHESIA CARE — The pharmacologic effects of drugs used for sedation/analgesia usually extend beyond the duration of the therapeutic or diagnostic procedure. Monitoring and supplemental oxygen (O₂) should be maintained while the patient recovers from the effects of the sedative medications. Patient care should be transferred to personnel in the phase I recovery area (post-anesthesia care unit [PACU]) capable of prompt detection of respiratory or cardiovascular compromise.

Patients who have completely recovered (ie, breathing spontaneously without need for any form of airway support, alert, speaking, responding appropriately to commands, and hemodynamically stable [8]) can be fast-tracked to the phase II recovery area (predischarge unit) for rapid discharge.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Procedural sedation in adults".)

SUMMARY AND RECOMMENDATIONS

●Definition of monitored anesthesia care (MAC) – During monitored anesthesia care (MAC), an anesthesia clinician continually monitors and supports the patient's vital functions; diagnoses and treats clinical problems that occur; administers sedative, anxiolytic, or analgesic medications if needed; and converts to general anesthesia if required.

●Preanesthesia evaluation – Preanesthesia evaluation and preparation for MAC should be the same as for those who will undergo general anesthesia (GA). The patient's ability to lie still, cooperate, and communicate, if necessary, should also be assessed. (See 'Preprocedure evaluation' above.)

●Monitoring – Standard physiologic monitors should be employed during MAC, as they would be during general anesthesia. Capnography should be used for patients who receive moderate or deep sedation. (See 'Standard physiologic monitors' above.)

In addition, the level of sedation should be assessed continually during MAC to avoid oversedation or general anesthesia. Any patient who is unarousable with a painful stimulus is, by definition, under general anesthesia. (See 'Monitoring depth of sedation and analgesia' above.)

●Choice of medications – In general, we prefer medications with rapid onset and short duration of action to allow rapid titration of effects and quick recovery. (See 'Drugs used for sedation and analgesia for monitored anesthesia care' above.)

Drugs commonly administered for MAC include the following:

•Midazolam – Midazolam is a short-acting benzodiazepine with anxiolytic, amnesic, and sedative effects, without analgesic effects. Midazolam potentiates the effects of other sedatives and opioids and can cause respiratory depression when given in high doses or with other sedatives or opioids. (See 'Midazolam' above.)

•Propofol – Propofol is a rapidly acting, short-acting sedative/hypnotic with modest amnestic and antiemetic properties at subhypnotic doses, without analgesic effects. Propofol is commonly administered as an infusion. Patients may rapidly transition to deeper levels of sedation, including general anesthesia. (See 'Propofol' above.)

•Opioids – Fentanyl and remifentanil are the most commonly administered opioids during MAC. Fentanyl is a short-acting opioid that is usually administered by intermittent bolus. Remifentanil is an ultrashort-acting opioid that is often administered by infusion, with or without initial or supplemental bolus. Clinical recovery is very rapid after remifentanil, with an elimination half-life of approximately three minutes regardless of the duration of infusion. (See 'Opioids' above.)

•Dexmedetomidine – Dexmedetomidine is a selective alpha₂-adrenergic agonist with sedative, anxiolytic, and modest analgesic effects. In doses used for sedation, dexmedetomidine does not produce respiratory depression and maintains the normal ventilatory response to hypercarbia. With its slow onset of action, this drug is most useful for longer procedures and for patients who are at higher risk of respiratory depression or airway obstruction. (See 'Dexmedetomidine' above.)

•Ketamine – Ketamine produces a dissociative state accompanied by amnesia and intense analgesia with minimal respiratory depression at sedative doses. Ketamine can be administered as a supplement to other sedatives and analgesics to reduce the need for opioids. (See 'Ketamine' above.)

●Medication administration – Sedatives and analgesics may be administered by intravenous (IV) bolus, continuous infusion, or by a computer-assisted administration system. (See 'Drug administration techniques' above.)

●Our approach – Our usual strategy for MAC, which is modified for patient factors that increase sensitivity to sedatives and opioids, is as follows:

•Procedures with minimal or no pain – For short, painless diagnostic procedures (eg, magnetic resonance imaging [MRI], computed tomography [CT] scans), we often administer a bolus of midazolam (1 to 2 mg IV) followed by small, titrated supplemental doses (eg, 0.5 to 1 mg IV). For patients with morbid obesity, obstructive sleep apnea, acute or chronic pain, or severe anxiety, we administer dexmedetomidine (0.1 to 0.7 mcg/kg/hour IV infusion) and may supplement with ketamine (0.5 to 1 mg/kg IV).

•Procedures with brief, initial pain – For procedures that involve only an initial, brief painful stimulus (eg, local anesthetic infiltration, peripheral nerve blocks, eye block, diagnostic puncture) we administer:

-Midazolam 1 to 2 mg IV with fentanyl 50 to 100 mcg IV,

or

-Propofol 0.5 to 1 mg/kg IV,

or

-Remifentanil 0.5 to 1 mcg/kg IV

•Procedures with variable pain throughout – We use infusions or repeated boluses of hypnotics and analgesics for procedures that cause variable degrees of pain throughout. As examples:

-For gastrointestinal endoscopy, we administer propofol (initial bolus of 0.5 to 1 mg/kg followed by 25 to 75 mcg/kg/minute), supplemented as necessary with fentanyl 25 to 50 mcg or ketamine 0.5 to 1 mg/kg IV.

-For laryngeal framework procedures (eg, thyroplasty, arytenoid adduction), we usually administer dexmedetomidine (0.3 to 0.7 mcg/kg/hour IV) with remifentanil (0.03 to 0.04 mcg/kg/minute IV). Alternatively, for patients who are at increased risk of airway obstruction or respiratory depression (eg, patients with obstructive sleep apnea or morbid obesity), we often administer dexmedetomidine (0.1 to 0.7 mcg/kg/hour IV infusion) and may supplement with ketamine 0.5 to 1 mg/kg IV).

●Complications – The rate of serious complications during and after MAC appears to be similar to that seen with general anesthesia. The most frequent mechanism for injury is respiratory depression due to oversedation, and in many cases, the injury may be preventable with appropriate monitoring. (See 'Complications during monitored anesthesia care' above.)