Overview of anesthesia

INTRODUCTION — 

Anesthesia allows surgical and other interventional procedures to be performed without pain by rapidly and safely producing analgesia, absence of anxiety (or absence of awareness with general anesthesia), and adequate muscle relaxation. A critically important aspect of perioperative anesthetic care is maintenance of physiologic homeostasis (eg, hemodynamic stability, oxygenation, ventilation, normothermia).

This topic presents an overview of anesthetic choices and services. Detailed discussions of each type of anesthetic care are found in separate UpToDate topics, as noted in each section below.

SCOPE OF ANESTHETIC CARE — 

Anesthesia clinicians (anesthesiologists, Certified Registered Nurse Anesthetists [CRNAs], Anesthesia Assistants [AAs]) manage patients having surgical or other interventional procedures using various techniques that include general anesthesia, neuraxial anesthesia (eg, spinal, epidural), regional anesthesia (eg, peripheral nerve blocks), or sedation with monitored anesthesia care (MAC).

Settings for anesthetic care — Anesthesia teams provide in-hospital care in:

●Operating rooms

●Labor and delivery suites – (See "Neuraxial analgesia for labor and delivery (including instrumental delivery)" and "Anesthesia for cesarean delivery".)

●Magnetic resonance imaging or computed tomography suites – (See "Anesthesia for magnetic resonance imaging and computed tomography procedures".)

●Interventional radiology and cardiology suites – (See "Considerations for non-operating room anesthesia (NORA)".)

●Electrophysiology suites – (See "Anesthetic considerations for electrophysiology procedures".)

●Gastrointestinal endoscopy suites – (See "Anesthesia for gastrointestinal endoscopy in adults".)

Over 60 percent of surgical and other interventional procedures in the United States are outpatient procedures, either performed in a hospital setting or in a freestanding surgery center or surgical specialty office that may be distant from a hospital [1]. Guidelines for the decision to proceed with outpatient surgery have been published for these settings, with consideration for both patient comorbidities and surgical risks [2]. The key questions are whether surgical risk factors increase the probability of overnight hospital admission or emergency treatment, and whether exacerbation of an underlying patient disease could be managed without admission to a hospital. Similar guidelines are applicable for anesthetic care performed in surgical subspecialty office-based settings (Guidelines for Office-Based Anesthesia).

Other anesthesia services include preoperative evaluation, immediate postoperative care in the post-anesthesia care unit (PACU) or intensive care unit (ICU), and management of both acute and chronic perioperative pain.

Safety of anesthetic care — The specialty of anesthesiology has been at the forefront of international efforts to improve patient safety with continuing improvements in anesthetic equipment, monitoring technology, and anesthetic agents and techniques, as well as efforts to implement standards that reduce medication errors and ensure excellent communication (eg, “handoffs” between caregivers during perioperative care, use of cognitive aids in emergencies) [3]. Details are discussed in separate topics:

●(See "Patient safety in the operating room".)

●(See "Cognitive aids for perioperative emergencies".)

●(See "Handoffs of surgical patients".)

●(See "Prevention of perioperative medication errors".)

Overall anesthesia-related mortality rates have decreased from two deaths per 10,000 anesthetics to one death per 200,000 to 300,000 anesthetics in the last several decades [4-6].

PREANESTHETIC EVALUATION — 

Before elective anesthesia for surgical procedures or other interventions, all patients are evaluated by an anesthesia provider to assess medical status, risk, and readiness for the planned procedure, implement strategies to reduce risks, and create an anesthetic plan [7]. General considerations for preanesthetic evaluation for noncardiac or cardiac surgery are discussed in separate topics:

●Noncardiac surgery – (See "Preoperative evaluation for noncardiac surgery in adults".)

●Cardiac surgery – (See "Overview of preoperative evaluation and management for cardiac surgery in adults".)

Additional considerations for specific types of surgery are found in individual UpToDate topics.

Risk assessment — The American Society of Anesthesiologists (ASA) physical status classification system is a relatively simple system that has proven effective in stratifying overall perioperative risk of morbidity and mortality for patient-specific risk factors (table 1) [8] (see "Preoperative evaluation for noncardiac surgery in adults", section on 'ASA physical status'). Patients are classified according to the degree to which underlying medical problems produce functional limitations. A higher ASA physical status is associated with increased risk of medical complications, unexpected hospital admission after ambulatory surgery, postoperative admission to the intensive care unit (ICU), longer hospital length of stay, higher costs, and mortality due to patient-specific and surgery-specific factors (figure 1). The ASA system and other risk assessment tools are discussed in detail in a separate topic. (See "Preoperative evaluation for noncardiac surgery in adults", section on 'Risk assessment tools'.)

Other topics address the assessment and management of risk factors for specific perioperative complications including:

●Airway complications – Prediction of the degree of difficulty with mask ventilation and/or endotracheal intubation using standard devices is an important part of the preanesthetic evaluation (table 2 and table 3 and table 4 and table 5). The plan for anesthetic and airway management follows from this prediction since sedation or induction of anesthesia may result in airway obstruction and at least temporarily render the patient apneic. Details are discussed in a separate topic. (See "Airway management for general anesthesia in adults", section on 'Airway assessment'.)

●Pulmonary complications (algorithm 1):

•(See "Evaluation of perioperative pulmonary risk".)

•(See "Strategies to reduce postoperative pulmonary complications in adults".)

●Cardiovascular complications (table 6 and table 7) [9]:

•(See "Evaluation of cardiac risk prior to noncardiac surgery".)

•(See "Management of cardiac risk for noncardiac surgery".)

•(See "Overview of preoperative evaluation and management for cardiac surgery in adults", section on 'Cardiovascular conditions'.)

●Adverse outcomes associated with anemia (algorithm 2) [10] – (See "Perioperative blood management: Strategies to minimize transfusions", section on 'Treatment of anemia and iron deficiency'.)

●Neurocognitive impairment (table 8) – (See "Perioperative neurocognitive disorders in adults: Risk factors and mitigation strategies".)

●Postoperative functional decline:

•(See "Anesthesia for the older adult", section on 'Assessment for frailty'.)

•(See "Overview of prehabilitation for surgical patients".)

Communication, reassurance, and informed consent — Communication regarding the entire perioperative process while offering reassurance is important [11]. Many patients wish to be involved in shared decision-making as part of the informed consent process for anesthetic care (table 9). Details are discussed separately. (See "Preoperative evaluation for noncardiac surgery in adults", section on 'Informed consent and decision making'.)

Fasting guidelines — Preanesthesia fasting guidelines to prevent pulmonary aspiration of gastric contents are relevant for all patients having elective surgery, including procedures performed under general anesthesia (GA), regional or neuraxial anesthesia, or sedation with monitored anesthesia care (MAC). Details are included in the table and discussed in a separate topic (table 10). (See "Preoperative fasting in adults".)

TYPES OF ANESTHESIA

Selection of anesthetic technique — There are benefits and risks to any type of anesthetic (table 11). Risks and benefits for anesthetic techniques for specific surgical or other interventional procedures are discussed in various individual UpToDate topics.

Factors affecting the selection of appropriate anesthetic techniques for an individual patient include surgical requirements for the performance of the procedure, anticipated duration of surgery, patient comorbidities, plans for providing postoperative analgesia, and patient preferences. As a general rule, there are no clear-cut indications for one type of anesthesia over another when either would be appropriate. However, GA is appropriate for most major surgical procedures, and is typically selected for procedures that require airway control, neuromuscular blockade, or will be prolonged, as well as for patients who are unable to lie motionless in the position required for the procedure, unable to communicate or cooperate, or are unwilling to undergo the procedure if awareness is possible.

When neuraxial anesthesia (eg, spinal, epidural, and combined spinal-epidural [CSE]), regional anesthetic techniques (eg, peripheral nerve block), or local anesthetic techniques (eg, infiltration by the surgeon) are selected, sedatives or analgesics may be employed to supplement the anesthetic technique. In some cases, a combined technique (ie, general anesthesia [GA] plus an epidural or peripheral nerve block) may be selected to provide both favorable intraoperative conditions and optimize multimodal management of postoperative pain.

Mild, moderate, or deep sedation with monitored anesthesia care (MAC) is adequate for some procedures, although conversion to GA may become necessary and should be discussed in advance with the patient.

General anesthesia — A reversible state of Stage III surgical anesthesia is established, including the following goals:

●Hypnosis/unconsciousness

●Amnesia

●Analgesia

●Muscle relaxation or immobility as appropriate for the procedure

●Blockade of adverse autonomic responses to painful surgical stimulation

GA has three distinct phases: induction, maintenance, and emergence, as described below.

Induction

●Induction agents – Induction of GA may be accomplished with intravenous (IV) and/or inhalation agents. Adult patients usually prefer IV induction. Administration of a sedative-hypnotic (eg, propofol, etomidate, ketamine (table 12)) and one or more adjuvant IV agents (eg, an opioid, lidocaine, and/or a benzodiazepine [usually midazolam] (table 13)) is typical, as well as a neuromuscular blocking agent (NMBA) if endotracheal intubation is planned (table 14). (See "General anesthesia: Intravenous induction agents".)

An inhalation agent is often added as a component of anesthetic induction once initial loss of consciousness has been achieved with IV agents (table 15). In some cases, induction is accomplished with inhalation anesthetic agents alone. (See "Inhalation anesthetic agents: Clinical effects and uses", section on 'Clinical uses'.)

Anesthetic agents demonstrate a dose-response effect, with progressively higher doses providing progressively deeper levels of sedation and anesthesia. Notably, sedation transitions to GA as a continuum of effect during induction, rather than as a consecutive series of distinct states (table 16). As the patient progresses from Stage I to Stage III surgical anesthesia, airway reflexes and patency, spontaneous ventilation, cardiovascular function, and muscle tone become increasingly depressed.

●Airway management – Airway management is an integral part of GA, allowing ventilation and oxygenation, as well as a mode for anesthetic gas delivery. Devices for airway management include (see "Airway management for general anesthesia in adults"):

•Facemask – Facemask ventilation is the most basic of airway management techniques, and is typically used during induction of anesthesia before placement of an airway device. For short cases that do not require muscle relaxation, airway management with a facemask alone may be used when the anesthesia clinician will have full access to the patient's airway. (See "Airway management for general anesthesia in adults", section on 'Mask ventilation'.)

•Supraglottic airway – Supraglottic airway (SGA) devices are inserted into the oropharynx and have a ventilation orifice above the glottis (figure 2). An SGA may be used as the primary airway device with either spontaneous or controlled ventilation, but does not provide complete protection against aspiration. Since the SGA does not seal the pharynx, the pressure that can be safely used to ventilate is limited by leak around the device, with resultant gastric insufflation and/or hypoventilation. Therefore, pressure-limited ventilation (ie, pressure support or pressure control) is usually selected with an SGA in place, rather than volume-control ventilation. A laryngeal mask airway (LMA) may also be used as a conduit for intubation or as a rescue device in a patient with a difficult airway. Sore throat, dysphonia, and/or dysphagia are the most common adverse events associated with the use of an SGA, with an incidence ranging from 13 to 49 percent, and greater likelihood if higher SGA cuff pressures are used (eg, ≥44 mmHg) [12,13]. (See "Supraglottic airways (SGAs) for airway management for anesthesia in adults".)

•Endotracheal tube – Laryngoscopy and placement of an endotracheal tube (ETT) (figure 3), with the distal end in the mid-trachea, is employed for most patients with risk factors for aspiration and for those undergoing GA for longer procedures (>3 hours) or those that require use of a NMBA. Typically, an ETT with an inflatable cuff is used to create a seal for positive pressure ventilation and to protect the airway from secretions. (See "Direct laryngoscopy and endotracheal intubation in adults".)

Postoperative sore throat is the most common adverse event related to endotracheal intubation, with an incidence ranging from 21 to 72 percent and a greater likelihood if larger endotracheal tubes are used (eg, ≥7.0 mm internal diameter) [14-16]). More serious respiratory complications may occur after extubation, as discussed separately. (See "Postoperative airway and pulmonary complications in adults: Etiologies and initial assessment and stabilization".)

●Special situations

•High risk for aspiration – Rapid sequence induction and intubation (RSII) for anesthesia is a technique designed to minimize the chance of pulmonary aspiration in patients at higher than normal risk (table 17). Techniques for management of RSII are discussed separately. (See "Rapid sequence induction and intubation (RSII) for anesthesia".)

•Potentially difficult airway – Anesthetic techniques and devices for management of the difficult airway, including difficult mask ventilation (table 3), difficult SGA ventilation (table 4), and difficult endotracheal intubation (table 5) are discussed separately. In some cases, endotracheal intubation is performed in an awake patient before anesthetic induction (algorithm 3 and figure 4). (See "Management of the anatomically difficult airway for general anesthesia in adults" and "Flexible scope intubation for anesthesia".)

Maintenance — Additional agents are necessary to maintain the anesthetic state immediately after induction of GA. Most commonly, combinations of inhalation and/or IV anesthetics are administered to maintain GA, with the goal of reducing the total dose of any one agent.

Often, anesthesia is primarily maintained with inhalation agents, as discussed in other topics (table 15). (See "Maintenance of general anesthesia", section on 'Inhalation anesthetic agents and techniques' and "Inhalation anesthetic agents: Clinical effects and uses", section on 'Maintenance of general anesthesia (all inhalation agents)'.)

An alternative technique is total intravenous anesthesia (TIVA), as discussed separately. (See "Maintenance of general anesthesia", section on 'Total intravenous anesthesia technique'.).

If muscle relaxation or complete paralysis is necessary to facilitate surgery, a NMBA is also administered (table 14). Selection, dosing, monitoring, and reversal of the effects of NMBAs are discussed in separate topics:

●(See "Maintenance of general anesthesia", section on 'Neuromuscular blocking agents'.)

●(See "Clinical use of neuromuscular blocking agents in anesthesia".)

●(See "Monitoring neuromuscular blockade".)

Anesthetic underdosing is a risk factor for awareness during anesthesia. Although rare, awareness is more likely to occur with a TIVA maintenance technique, particularly if an NMBA is administered. Patients with a history of tolerance to anesthetic agents are at higher risk, as are those undergoing certain types of surgery (eg, emergency procedures and cardiac surgery requiring cardiopulmonary bypass) (see "Accidental awareness during general anesthesia", section on 'Risk factors'). Strategies to prevent awareness are discussed separately. (See "Accidental awareness during general anesthesia", section on 'Prevention'.)

Emergence — Emergence from GA is the return of consciousness and movement at the end of the surgical procedure, after discontinuing the administration of anesthetic and adjuvant agents, and reversing residual NMBA effects. The trachea may be extubated (or SGA removed) when the patient has adequate spontaneous ventilation without assistance, can protect their own airway, and can be aroused to follow simple commands such as eye opening. (See "Emergence from general anesthesia".)

Transport from the operating room to the post-anesthesia care unit (PACU) or intensive care unit (ICU) is safely accomplished when the extubated patient continues to remain hemodynamically stable and maintain airway integrity, with adequate oxygenation and ventilation during spontaneous ventilation. (See "Transport of surgical patients".)

Neuraxial (spinal or epidural) anesthesia — Techniques to provide neuraxial anesthesia include spinal, epidural, and CSE. These techniques are performed by placing a needle and/or a catheter between vertebrae for injection of medication into the subarachnoid space (for spinal anesthesia (figure 5)) or the epidural space (for epidural anesthesia (figure 6)). Spinal anesthesia is usually administered as a single injection, whereas epidural anesthesia is usually administered via a catheter for continuous infusion. A CSE technique combines the two. The advantages and disadvantages of each neuraxial anesthetic technique are shown in a table (table 18). The most common uses of neuraxial anesthesia are for lower abdominal and lower extremity surgery (table 19 and table 20). (See "Overview of neuraxial anesthesia".)

Supplemental sedative, analgesic, and/or anxiolytic medications can be administered as needed. In some cases, these techniques are planned to be combined with GA. More rarely, unanticipated conversion to GA becomes necessary.

Details regarding technical aspects, anesthetic agents used, and patient management after placement of a spinal, epidural, or CSE are available in separate topics:

●Spinal anesthesia (see "Spinal anesthesia: Technique")

●Epidural analgesia and anesthesia (see "Epidural and combined spinal-epidural anesthesia: Techniques")

●Combined spinal-epidural anesthesia (see "Epidural and combined spinal-epidural anesthesia: Techniques", section on 'Combined spinal-epidural anesthesia')

Peripheral nerve blocks — Peripheral nerve blocks are widely used for surgical anesthesia, particularly for procedures in an upper or lower extremity. Ultrasound guidance with or without nerve stimulation is typically used for placement of a needle or catheter. Use of long-acting local anesthetics via continuous peripheral nerve blocks often provides superior postoperative analgesia. Similar to neuraxial anesthesia, these techniques may be combined with GA. Occasionally, unanticipated conversion to GA becomes necessary. Techniques and issues specific to particular blocks are described in individual topics describing those blocks.

General considerations for selection and placement of peripheral nerve blocks are discussed in a separate topic. (See "Overview of peripheral nerve blocks".)

Intravenous regional anesthesia (IVRA), also called Bier block, is an alternative to a peripheral nerve block for short (ie, 30 to 45 minutes) procedures on the hand and forearm. The technique involves placement of an IV catheter in the distal extremity, exsanguination of the extremity using an Esmarch bandage, inflation of a tourniquet above the IV site, and then injection of a short-acting local anesthetic (typically lidocaine) through the IV catheter. Duration of anesthesia is limited by duration of the local anesthetic and by eventual development of tourniquet pain. Details regarding the technique are available in a separate topic. (See "Upper extremity nerve blocks: Techniques", section on 'Intravenous regional anesthesia (Bier block)'.)

Monitored anesthesia care (MAC) — MAC involves continuous monitoring of the patient's vital functions by an anesthesia provider, with the administration of sedative, anxiolytic, and/or analgesic medications as needed, and with the ability to convert to GA if necessary. Classically, MAC anesthesia does not involve complete loss of consciousness. Often, the surgeon or interventionalist provides local anesthesia since sedation does not ensure adequate analgesia. For all cases, patients should understand that they will likely have some recall of intraoperative events and feel some pushing and pulling (but not sharp pain). Supplemental oxygen is typically administered via nasal cannulae or a face mask in a spontaneously ventilating sedated patient. Supplemental oxygen delivery is more likely to be necessary during moderate or deep sedation since higher doses of IV sedative and/or analgesic medications can cause respiratory depression. Details regarding techniques and anesthetic agents are described in a separate topic. (See "Monitored anesthesia care in adults".)

Approximately one-third of ambulatory anesthesia services for diagnostic or therapeutic procedures in the United States are performed with MAC [17]. Considerations in the decision to select a MAC technique include the level of sedation required for the surgical procedure, whether the anesthesia provider will have easy access to the airway if immediate airway control is necessary, and whether the patient is willing and able to lie motionless, cooperate, and communicate for the duration of the procedure.

Conscious sedation without anesthesia personnel — The American Society of Anesthesiologists (ASA) makes a clear distinction between light or moderate conscious sedation (often administered by personnel who are not anesthesia clinicians) versus MAC with an anesthesia provider [18]. (See 'Monitored anesthesia care (MAC)' above.)

During light or moderate conscious sedation without anesthesia personnel, the depth of sedation should not render the patient unable to independently maintain airway integrity. Details are discussed in a separate topic. (See "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications".)

By contrast, during MAC, an anesthesia provider must be present, prepared, and qualified to immediately convert to GA with management of the patient’s airway if necessary (see 'Induction' above). This is more likely to occur when deep sedation is used.

MONITORING DURING ANESTHESIA

●Standard monitors for all cases – For all patients receiving anesthetic care under general anesthesia (GA), neuraxial or regional anesthesia, or monitored anesthesia care (MAC), standard American Society of Anesthesiologists (ASA) monitors include pulse oximetry, capnography, electrocardiography (ECG), a noninvasive blood pressure device, and a temperature monitor if clinically significant changes in body temperature are likely. These standard monitors are discussed in detail separately (table 21 and table 22). (See "Basic patient monitoring during anesthesia".)

●Additional monitors for general anesthesia – During GA, ASA monitoring standards also include measurement of end tidal carbon dioxide (ETCO₂) and inspired oxygen concentration (FiO₂), as well as alarm systems for low oxygen concentration, ventilator disconnect, and quantitative monitoring of the volume of expired gas. Additional integrated monitors on all anesthesia machines generate alarms for other serious potential problems due to operator misuse or machine malfunction. These monitors are discussed in detail in a separate topic. (See "Anesthesia machines: Prevention, diagnosis, and management of malfunctions", section on 'Anesthesia workstation alarms'.)

For patients undergoing GA with inhalation anesthetics, end-tidal anesthetic concentration (ETAC) is measured to aid in monitoring anesthetic depth and preventing awareness. In many institutions, neuromonitoring with processed electroencephalography (EEG) monitors such as the bispectral index (BIS) or a raw unprocessed EEG is used to provide supplemental information regarding anesthetic depth. (See "Accidental awareness during general anesthesia", section on 'Monitoring'.)

●Additional invasive cardiovascular monitors – In selected cases, invasive hemodynamic monitoring is used. Examples include insertion of an intra-arterial catheter, central venous catheter (CVC), pulmonary artery catheter (PAC), and/or a transesophageal echocardiography (TEE) probe. Indications and techniques for such advanced monitoring are discussed in separate topics:

•(See "Basic patient monitoring during anesthesia", section on 'Other monitors of circulation'.)

•(See "Intra-arterial catheterization for invasive monitoring: Indications, insertion techniques, and interpretation".)

•(See "Central venous access in adults: General principles of placement".)

•(See "Pulmonary artery catheterization: Interpretation of hemodynamic values and waveforms in adults".)

•(See "Intraoperative transesophageal echocardiography for noncardiac surgery".)

POSTOPERATIVE ANESTHETIC CARE

Disposition — Most patients are transported to a post-anesthesia care unit (PACU) after procedures performed under general anesthesia (GA), or with neuraxial or regional anesthesia or monitored anesthesia care (MAC). (See "Transport of surgical patients", section on 'Operating room to post-anesthesia care unit' and "Handoffs of surgical patients", section on 'Operating room to post-anesthesia care unit'.)

Medical oversight of the PACU is typically the responsibility of the anesthesiology service. An overview of care in the PACU is available in a separate topic [19]. (See "Overview of post-anesthetic care for adult patients".)

Critically ill patients and those who remain intubated are transported directly to an intensive care unit (ICU). (See "Transport of surgical patients", section on 'Transport of critically ill patients' and "Handoffs of surgical patients", section on 'Operating room to intensive care unit'.)

In some cases, patients who had MAC with minimal sedation, patients who have completely recovered (ie, breathing spontaneously without the need for any form of airway support, alert, speaking, responding appropriately to commands, and hemodynamically stable) may go directly to a predischarge unit for more rapid discharge.

Management of problems in the PACU — Specific problems commonly encountered in the immediate postoperative period are discussed in individual topics:

●Control of acute postoperative pain (see "Approach to the management of acute pain in adults", section on 'Options for managing postoperative analgesia')

●Postoperative nausea and/or vomiting (see "Postoperative nausea and vomiting")

●Respiratory complications (see "Postoperative airway and pulmonary complications in adults: Etiologies and initial assessment and stabilization")

●Cardiovascular complications (see "Cardiovascular problems in the post-anesthesia care unit (PACU)")

●Hypothermia or hyperthermia (see "Perioperative temperature management", section on 'Postoperative temperature derangements')

●Inability to void (see "Overview of post-anesthetic care for adult patients", section on 'Inability to void')

●Delayed emergence or delirium (see "Delayed emergence and emergence delirium in adults")

●Rare neurologic complications (visual disturbance, spinal epidural hematoma) (see "Overview of post-anesthetic care for adult patients", section on 'Neuropsychiatric complications')

●Distress due to awareness during anesthesia (see "Accidental awareness during general anesthesia", section on 'Postoperative recognition and management')

INFORMATION FOR PATIENTS — 

UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Anesthesia in adults (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Scope of anesthetic care – Anesthesia clinicians (anesthesiologists, Certified Registered Nurse Anesthetists [CRNAs], Anesthesia Assistants [AAs]) manage patients having surgical or other interventional procedures using various techniques that include general anesthesia (GA), neuraxial (eg, spinal, epidural) anesthesia, regional anesthesia (eg, peripheral nerve blocks), or sedation with monitored anesthesia care (MAC).

•Settings – Settings for anesthetic care include operating rooms, labor and delivery suites, magnetic resonance imaging or computed tomography suites, interventional radiology and cardiology suites, electrophysiology suites, and gastrointestinal endoscopy suites. Over 60 percent of surgical and other interventional procedures in the United States are outpatient procedures. Other anesthesia services include preoperative evaluation, postoperative care, and managing acute and chronic perioperative pain. (See 'Settings for anesthetic care' above.)

•Safety – Continuing improvements in anesthetic equipment, monitoring technology, and anesthetic agents and techniques, as well as efforts to implement standards that reduce medication errors and ensure excellent communication, have greatly improved the safety of anesthesia. Details are discussed in separate topics:

-(See "Patient safety in the operating room".)

-(See "Cognitive aids for perioperative emergencies".)

-(See "Handoffs of surgical patients".)

-(See "Prevention of perioperative medication errors".)

●Preanesthetic evaluation – The anesthesia provider assesses and manages risks for airway, pulmonary, and cardiovascular complications, as well as anemia-associated adverse outcomes, neurocognitive impairment, or functional decline (table 1 and table 3 and table 4 and table 5 and algorithm 1 and table 7 and table 6 and algorithm 2 and table 8 and table 23). The anesthesia provider also communicates regarding the entire perioperative process, provides reassurance, provides fasting guidelines (table 10), and obtains informed consent for anesthetic care (table 9). (See 'Preanesthetic evaluation' above.)

●Selection of anesthetic technique – There are benefits and risks to any type of anesthetic (table 11). Factors affecting the selection of appropriate anesthetic techniques for an individual patient include surgical requirements for the performance of the procedure, anticipated duration of surgery, patient comorbidities, plans for providing postoperative analgesia, and patient preferences. GA is typically selected for procedures requiring airway control, neuromuscular blockade, or prolonged duration, as well as for patients who are unable to lie motionless in the position required for the procedure, communicate and cooperate, or are unwilling to undergo the procedure if awareness is possible. (See 'Selection of anesthetic technique' above.)

●General anesthesia – GA provides hypnosis/unconsciousness, amnesia, analgesia, and muscle relaxation with muscle relaxation or immobility if necessary for the procedure, as well as blockade of responses to painful surgical stimuli (table 16). (See 'General anesthesia' above.)

GA has three distinct phases:

•(See 'Induction' above.)

•(See 'Maintenance' above.)

•(See 'Emergence' above.)

●Neuraxial anesthesia – Neuraxial anesthesia involves the placement of a needle and/or a catheter between vertebrae for injection of medication into the subarachnoid space (spinal anesthesia) or epidural space (epidural anesthesia) (table 18), most commonly used for lower abdominal and lower extremity surgery (table 19 and table 20). Spinal anesthesia is usually administered as a single injection, whereas epidural anesthesia is usually administered via a catheter for continuous infusion, while a combined spinal-epidural (CSE) technique combines both. Supplemental sedative, analgesic, and/or anxiolytic medications can be administered as needed. Neuraxial anesthesia or peripheral nerve blocks can be combined with GA. (See 'Neuraxial (spinal or epidural) anesthesia' above.)

●Peripheral nerve blocks – Peripheral nerve blocks are often used for procedures in an upper or lower extremity. Ultrasound guidance with or without a nerve stimulator is typically used for placement of a needle or catheter. Administration of long-acting local anesthetics via continuous peripheral nerve blocks can provide superior postoperative analgesia. Selection techniques for placement of peripheral nerve blocks are discussed in a separate overview topic, and in various individual UpToDate topics. (See "Overview of peripheral nerve blocks".)

●Intravenous regional anesthesia (IVRA) – IVRA (ie, Bier block) is an alternative to peripheral nerve blocks for short (ie, 30 to 45 minutes) procedures on the hand and forearm. The technique is described separately. (See "Upper extremity nerve blocks: Techniques", section on 'Intravenous regional anesthesia (Bier block)'.)

●Monitored anesthesia care (MAC) – MAC involves continuous monitoring of vital functions by an anesthesia provider who can convert to GA if necessary, with or without administration of sedative, anxiolytic, and/or analgesic medications (table 16). Anesthetic agents and techniques are described separately. (See 'Monitored anesthesia care (MAC)' above.)

●Monitoring – Standard American Society of Anesthesiologists (ASA) monitors include pulse oximetry, capnography, electrocardiography (ECG), noninvasive blood pressure device, and temperature (table 21). Invasive hemodynamic monitors are selectively employed (eg, intra-arterial, central venous catheter [CVC], pulmonary artery catheter [PAC], transesophageal echocardiography [TEE]). (See "Basic patient monitoring during anesthesia".)

During GA, end tidal carbon dioxide (ETCO₂), inspired oxygen concentration (FiO₂), volume of expired gas, and end-tidal anesthetic concentration (ETAC) are monitored. Additional alarm systems and other serious potential problems that can occur due to operator misuse or machine malfunction. These monitors are discussed in detail in a separate topic (table 22). (See "Anesthesia machines: Prevention, diagnosis, and management of malfunctions", section on 'Anesthesia workstation alarms'.)

●Postoperative care – Most patients are transported to a post-anesthesia care unit (PACU) after any type of anesthesia to assure timely management of postoperative adverse events (eg, pain, respiratory, cardiovascular, or neurologic complications, delayed emergence or delirium, temperature derangements, inability to void). Critically ill or intubated patients are transported directly to an intensive care unit. (See 'Postoperative anesthetic care' above.)

ACKNOWLEDGMENT — 

The UpToDate editorial staff acknowledges Lee Fleisher, MD, who contributed to earlier versions of this topic review.