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Overview of anesthesia

Overview of anesthesia
Literature review current through: Aug 2023.
This topic last updated: May 13, 2022.

INTRODUCTION — Anesthesia allows performance of surgical and other interventional procedures by rapidly and safely producing analgesia (pain control), absence of anxiety (or absence of awareness with general anesthesia [GA]), and adequate muscle relaxation. A critically important aspect of perioperative anesthetic care is maintenance of physiologic homeostasis (eg, hemodynamic stability, oxygenation, ventilation, temperature).

Anesthesia clinicians (anesthesiologists, Certified Registered Nurse Anesthetists [CRNAs], Anesthesia Assistants [AAs]), select and manage intraoperative general, neuraxial, or regional anesthesia (eg, peripheral nerve blocks), or sedation with monitored anesthesia care (MAC). Anesthesia teams provide care in operating room (OR) and non-OR locations such as endoscopy suites, interventional radiology suites, and interventional cardiology laboratories. Other anesthesia services include preoperative evaluation, postoperative management in the post-anesthesia care unit (PACU) or intensive care unit (ICU), and management of both acute and chronic perioperative pain.

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.

PREANESTHESIA EVALUATION

Focused evaluation and planning — Before elective anesthesia for noncardiac surgical or other interventions, all patients are evaluated by an anesthesia provider to assess medical status and readiness for the planned procedure, implement strategies to reduce risks, and create an anesthetic plan [1].

Preanesthesia fasting guidelines to prevent pulmonary aspiration of gastric contents are applied in all patients having elective surgery including procedures performed under general anesthesia (GA), regional anesthesia, and monitored anesthesia care (MAC). (See "Preoperative fasting in adults".)

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 1). 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. (See "Airway management for induction of general anesthesia", section on 'Airway assessment'.)

Details regarding preanesthetic evaluation and testing for noncardiac surgery, medication management, and planning for intraoperative anesthetic care and postoperative pain management are available (see "Preoperative evaluation for anesthesia for noncardiac surgery"). Preanesthetic evaluation of patients undergoing cardiac surgery is discussed separately. (See "Preoperative evaluation for anesthesia for cardiac surgery".)

Risk assessment

Morbidity and mortality — 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 2) [2]. 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 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). (See "Preoperative evaluation for anesthesia for noncardiac surgery", section on 'ASA physical status' and "Preoperative evaluation for anesthesia for noncardiac surgery", section on 'Risk assessment tools'.)

Risk assessment tools that combine patient and surgical risk factors have been developed (see "Preoperative evaluation for anesthesia for noncardiac surgery", section on 'Risk assessment tools'). Other topics address assessment and management of patients at risk for perioperative cardiovascular complications (table 3 and table 4 and algorithm 1) or pulmonary complications (algorithm 2):

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

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

(See "Evaluation of perioperative pulmonary risk".)

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

In older adults, frailty predicts postoperative mortality, morbidity, and discharge disposition, including longer hospital stay, discharge to a skilled nursing facility, and postoperative cognitive impairment and functional decline [3-8]. Thus, identification of preoperative frailty may inform patient and family discussions regarding surgical techniques, postoperative recovery strategies, and likely outcomes (table 5) [9]. (See "Frailty" and "Anesthesia for the older adult", section on 'Assessment for frailty'.)

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 [10,11]. This is primarily a result of improvements in anesthesia equipment and monitoring, anesthetic agents and techniques, and intense focus on an anesthesia safety culture.

Postoperative neurocognitive disorders — Alterations in behavior, affect, and cognition after surgery and anesthesia are symptoms of different forms of perioperative neurocognitive disorder (PND), including delirium in the immediate postoperative period or later cognitive concerns expressed by the individual, informant, or clinician. Evidence is insufficient to recommend specific anesthetic techniques to avoid PND, although some anesthetic or adjunct agents such as benzodiazepines, opioids, and gabapentinoids should be minimized. (See "Perioperative neurocognitive disorders in adults: Risk factors and mitigation strategies", section on 'Choice of anesthetic techniques and agents'.)

Preoperative communication and reassurance — Communication regarding the entire perioperative process while offering reassurance is important [12]. Many patients wish to be involved in shared decision-making, as discussed in a separate topic (table 6). (See "Preoperative evaluation for anesthesia for noncardiac surgery", section on 'Consent and decision making'.)

LOCATION OF CARE — Surgery may be performed on either an inpatient or outpatient basis. Over 60 percent of cases in the United States are outpatient procedures, performed in a hospital setting or in a freestanding surgery center that may be distant from a hospital. Guidelines for the decision to proceed with outpatient surgery have been published with consideration for both patient comorbidities and surgical risks [13]. The key questions are whether exacerbation of underlying patient disease can be managed in a setting that may be distant from a hospital (eg, treatment of worsening pulmonary hypertension), and whether surgical risk factors increase probability of overnight hospital admission or emergency treatment.

SELECTION OF ANESTHETIC TECHNIQUE — Factors affecting selection of appropriate anesthetic techniques for an individual patient include surgical requirements for performance of the procedure, anticipated duration of surgery, patient comorbidities and preferences, plans for providing postoperative analgesia, and experience and preferences of the anesthesia care provider.

As a general rule, there are no clear-cut indications for one type of anesthesia over another when either would be appropriate [14]. The lack of superiority of any specific technique was demonstrated in a large-scale randomized trial in older adults with hip fracture in which spinal anesthesia was not superior to general anesthesia with respect to survival, recovery of ambulation at 60 days with a similar incidence of postoperative delirium [15].

However, there is emerging evidence for use of certain anesthetic techniques for specific procedures based on outcome studies. As an example, neuraxial anesthesia may be associated with some outcome benefits for hip and knee arthroplasty [16] (see "Anesthesia for total knee arthroplasty", section on 'Neuraxial analgesic techniques'). For major or prolonged procedures, general anesthesia (GA) with airway management using an endotracheal tube (ETT) or supraglottic airway (SGA) device is usually the most appropriate primary technique, particularly if a deep level of sedation is required and/or if airway access is limited (table 7). GA may be selected for minor procedures as well, particularly if this is the patient's preference. Depending on the location of the procedure, neuraxial anesthesia, a regional anesthetic technique (eg, peripheral nerve block, intravenous regional anesthesia), or local anesthetic infiltration by the surgeon may be selected. These techniques are often supplemented with lighter levels of sedation so that airway reflexes are maintained (ie, sedation with monitored anesthesia care [MAC]).

There are benefits and risks to any type of anesthetic (table 7) (see 'Types of anesthesia' below). When assessing whether avoidance of GA is appropriate, considerations include the patient's ability to lie motionless in the position required for the procedure, cooperate, and communicate, as well as willingness to undergo the procedure given the possibility of awareness with recall. In many cases, a combined technique (ie, GA plus epidural or peripheral nerve block for supplemental analgesia) will provide both optimal intraoperative conditions and excellent multimodal management of postoperative pain.

TYPES OF ANESTHESIA

General anesthesia — General anesthesia (GA) is appropriate for most major surgical procedures. A reversible state of Stage III surgical anesthesia is established, including the following goals (table 8):

Hypnosis/unconsciousness

Amnesia

Analgesia

Muscle relaxation or immobility as appropriate for the procedure

Autonomic and sensory blockade of responses to noxious surgical stimulation

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

Induction and airway management

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 9)) and one or more adjuvant IV agents (eg, an opioid, lidocaine, and/or a benzodiazepine [usually midazolam] (table 10)) is typical, as well as a neuromuscular blocking agent (NMBA) if endotracheal intubation is planned (table 11). An inhalation agent is usually added as a component of anesthetic induction once initial loss of consciousness has been achieved with IV agents, although inhalation induction of anesthesia may be selected for certain patients (table 12). (See "Induction of general anesthesia: Overview".)

Anesthetic agents demonstrate a dose-response effect, with progressively higher doses providing progressively deeper levels of sedation and anesthesia. Notably, sedation progresses to GA as a continuum of effect during induction, rather than as a consecutive series of distinct states with clear transitions (table 8 and table 13). 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 (figure 2). (See "Induction of general anesthesia: Overview", section on 'Continuum of sedation during anesthetic induction'.)

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 induction of general anesthesia"):

Facemask – Facemask ventilation is the most basic of airway management techniques. Ventilation by facemask 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 facemask alone may be used when the anesthesia clinician will have full access to the patient's airway. (See "Basic airway management in adults", section on 'Bag-mask ventilation'.)

Supraglottic airway – Supraglottic airway (SGA) devices are inserted into the oropharynx and have a ventilation orifice above the glottis (figure 3). An SGA, typically a laryngeal mask airway (LMA), 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 used with an SGA in place, rather than volume-control ventilation. An 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 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) [17,18]. (See "Supraglottic devices (including laryngeal mask airways) for airway management for anesthesia in adults".)

Endotracheal tube – Laryngoscopy and placement of an endotracheal tube (ETT) with the distal end in the mid-trachea is employed for most patients undergoing GA for procedures that are longer (>3 hours) or that require use of a NMBA, or for patients with risk factors for aspiration (figure 4). 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 greater likelihood if larger endotracheal tubes are used (eg ≥7.0 mm internal diameter) [19-21]). More serious respiratory complications may occur after extubation of the trachea, as discussed separately. (See "Respiratory problems in the post-anesthesia care unit (PACU)".)

Special situations – Rapid sequence induction and intubation (RSII) for anesthesia is a technique designed to minimize the chance of pulmonary aspiration in patients who are at higher than normal risk (table 14). Techniques for management of RSII are discussed separately. (See "Rapid sequence induction and intubation (RSII) for anesthesia".)

Anesthetic techniques and devices for management of the difficult airway, including difficult mask ventilation (table 15), difficult SGA ventilation (table 16), and difficult endotracheal intubation (table 17) are discussed separately. In some cases, endotracheal intubation is performed in an awake patient before anesthetic induction (algorithm 3 and algorithm 4). (See "Management of the 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. Anesthesia is often maintained by employing a primary inhalation technique (table 12) (see "Maintenance of general anesthesia: Overview", 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) (see "Maintenance of general anesthesia: Overview", section on 'Total intravenous anesthesia'). 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.

If muscle relaxation or complete paralysis is necessary to facilitate surgery, a NMBA is employed. Details regarding selection, dosing, monitoring, and reversal of the effects of NMBAs are available in separate topics:

(See "Maintenance of general anesthesia: Overview", 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. This is more likely to occur with a TIVA maintenance technique, particularly if a NMBA is administered. Patients with a history of possible resistance or 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'.)

Emergence — Emergence from GA is the return of consciousness and movement at the end of the surgical procedure, after discontinuing 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 follow simple commands such as eye opening, and can protect his own airway. (See "Maintenance of general anesthesia: Overview", section on 'Transition to the emergence phase'.)

Transport from the operating room to the post-anesthesia care unit (PACU) is safely accomplished when the extubated patient continues to maintain adequate oxygenation and ventilation during spontaneous ventilation, can be aroused to follow verbal commands, and is hemodynamically stable. (See "Handoffs of surgical patients".)

Neuraxial (spinal or epidural) anesthesia — Techniques to provide neuraxial analgesia and/or anesthesia include spinal, epidural, and combined spinal-epidural (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)). 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".)

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. 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 a nerve stimulator 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. General considerations for selection and placement of peripheral nerve blocks are discussed elsewhere. (See "Overview of peripheral nerve blocks".)

Techniques and issues specific to particular blocks are discussed in individual topics:

Upper extremity blocks (see "Upper extremity nerve blocks: Techniques")

Lower extremity blocks (see "Lower extremity nerve blocks: Techniques")

Digital nerve blocks (see "Digital nerve block")

Nerve blocks of the trunk, neck, and scalp (see "Thoracic nerve block techniques")

Intravenous regional anesthesia — 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 such as carpal tunnel release, Dupuytren's contracture release, or reduction of wrist fracture. Less commonly, IVRA is used for surgery on the foot or ankle. The technique involves placement of an IV catheter in the hand, exsanguination of the arm using an Esmarch bandage, inflation of a tourniquet, and then injection of a short-acting local anesthetic through the IV catheter (typically lidocaine). Duration of anesthesia is limited by development of tourniquet pain and by duration of the local anesthetic. Details regarding the technique and potential complications are available in a separate topic. (See "Upper extremity nerve blocks: Techniques", section on 'Intravenous regional anesthesia (Bier block)'.)

Monitored anesthesia care (MAC) — Monitored anesthesia care (MAC) involves continuous monitoring of the patient's vital functions by an anesthesia provider; diagnosis and treatment of clinical problems; administration of sedative, anxiolytic, and/or analgesic medications if appropriate; or conversion to GA if necessary. Approximately one-third of ambulatory anesthesia services for diagnostic or therapeutic procedures in the United States are performed with MAC [22].

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 throughout the procedure. Classically, MAC anesthesia does not involve complete loss of consciousness. Often, the surgeon or interventionalist provides local anesthesia since sedation does not ensure pain control. Similar techniques and agents are used to provide sedation during procedures performed with neuraxial anesthesia or a peripheral nerve block. In all such cases, patients should understand that they will probably have recall of intraoperative events, and that they will likely feel pushing and pulling, but should not experience sharp pain. Further details are available in separate topics. (See "Monitored anesthesia care in adults" and "Spinal anesthesia: Technique", section on 'Sedation during spinal anesthesia'.)

Supplemental oxygen is typically administered via nasal cannulae or a face mask during spontaneous ventilation in a 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. (See "Monitored anesthesia care in adults", section on 'Supplemental oxygen'.)

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 [23] (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. By contrast, during MAC, an anesthesia provider must be prepared and qualified to immediately convert to GA with management of the patient's airway if necessary, particularly if deep sedation is required. (See 'Induction and airway management' above.)

MONITORING DURING ANESTHESIA — Standard American Society of Anesthesiologists (ASA) monitors are basic physiologic monitors including pulse oximetry, electrocardiography (ECG), and a noninvasive blood pressure device, as well as a temperature monitor when clinically significant changes in body temperature are likely (table 21 and table 22) [24]. These standard monitors are discussed in detail separately. (See "Basic patient monitoring during anesthesia".)

ASA monitoring standards also include measurement of end tidal carbon dioxide and inspired oxygen concentration, as well as use of low oxygen concentration and ventilator disconnect alarms. Quantitative monitoring of the volume of expired gas is strongly encouraged. Other integrated monitors on all anesthesia machines generate alarms for common and/or serious potential problems due to misuse by the operator or machine malfunction. (See "Anesthesia machines: Prevention, diagnosis, and management of malfunctions", section on 'Anesthesia workstation alarms'.)

In many patients undergoing general anesthesia (GA), end-tidal inhalation anesthetic concentrations are measured to aid in monitoring anesthetic depth and preventing awareness. Neuromonitoring such as processed electroencephalography (EEG; eg, the bispectral index [BIS]) or raw unprocessed EEG provides supplemental information and is used in selected cases. (See "Accidental awareness during general anesthesia", section on 'Monitoring'.)

In selected cases, invasive hemodynamic monitoring requires insertion of an intra-arterial, central venous, or pulmonary artery catheter (PAC), 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 "Intraoperative fluid management", section on 'Monitoring intravascular volume status'.)

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

Maintenance of perioperative hemodynamic stability, including fluid administration to maintain optimal intravascular volume status and use of vasoactive drugs when necessary, is based on assessment of standard and/or invasive hemodynamic monitoring parameters. (See "Intraoperative fluid management" and "Hemodynamic management during anesthesia in adults".)

POSTOPERATIVE ANESTHETIC CARE — Most patients who received general or regional anesthesia are monitored in a post-anesthesia care unit (PACU), which provides standardized assessment of recovery with reduced postoperative adverse events and streamlined postoperative care and discharge criteria [25]. Medical oversight of the PACU is typically the responsibility of the anesthesiology service.

After monitored anesthesia care (MAC) with minimal sedation, 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) may go directly to the predischarge unit for more rapid discharge. Critically ill patients and those who are intubated are admitted directly to an intensive care unit (ICU).

General care — An overview for post-anesthetic care is available in a separate topic (see "Overview of post-anesthetic care for adult patients"). Specific problems commonly encountered in this setting are discussed in individual topics:

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

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

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

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

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

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')

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

Management of acute and chronic pain — Control of acute postoperative pain in the PACU setting is discussed in detail separately (see "Use of opioids for postoperative pain control", section on 'Treating pain in the postanesthesia care unit (PACU)'). Postoperative pain control in the critical care setting is reviewed in a different topic. (See "Pain control in the critically ill adult patient".)

Occasionally, patients experience persistent or chronic pain in the postoperative period, as discussed in other topics. (See "Approach to the management of chronic non-cancer pain in adults".)

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 5th to 6th 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 10th to 12th 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 (The Basics)")

SUMMARY AND RECOMMENDATIONS

Preanesthesia evaluation – Before elective anesthesia for noncardiac surgical or other interventions, all patients are evaluated by an anesthesia provider to assess medical status and readiness for the planned procedure , assess potential difficulty with airway management, implement strategies to reduce risks, create an anesthetic plan, and communicate with the patient (table 2 and figure 1 and table 5 and table 1 and table 15 and table 16 and table 17 and algorithm 4 and algorithm 3 and table 3 and table 4 and algorithm 1 and algorithm 2). (See 'Preanesthesia evaluation' above.)

Selection of anesthetic technique – Anesthetic care may include provision of general anesthesia (GA), neuraxial anesthesia via spinal or epidural techniques, peripheral nerve blocks, intravenous regional anesthesia, or monitored anesthesia care (MAC) with conversion to GA if necessary. Factors affecting selection of appropriate anesthetic techniques for an individual patient include surgical requirements for performance of the procedure, anticipated duration of surgery, patient comorbidities and preferences, plans for providing postoperative analgesia, and experience and preferences of the anesthesia care provider (table 7). (See 'Selection of anesthetic technique' above and 'Types of anesthesia' above.)

General anesthesia

Goals – GA provides hypnosis/unconsciousness, amnesia, analgesia, and immobility or muscle relaxation as appropriate for the procedure, as well as autonomic and sensory blockade of responses to noxious surgical stimuli (table 8 and table 13). (See 'General anesthesia' above.)

Phases – The three phases of GA are:

-Induction (see 'Induction and airway management' above)

-Maintenance (see 'Maintenance' above)

-Emergence (see 'Emergence' above)

Neuraxial anesthesia – Neuraxial anesthesia and analgesia techniques (eg, spinal, epidural, or combined spinal-epidural [CSE]) involve placement of a needle and/or a catheter between vertebrae for injection of medication into the subarachnoid space (for spinal anesthesia) or the epidural space (for epidural anesthesia). Spinal anesthesia is usually administered as a single injection, whereas epidural anesthesia is usually administered via a catheter for continuous infusion, and a CSE technique combines the two (table 18). The most common uses of neuraxial anesthesia are for lower abdominal and lower extremity surgery (table 19 and table 20). (See 'Neuraxial (spinal or epidural) anesthesia' above.)

Peripheral nerve blocks – Peripheral nerve blocks include upper extremity blocks, lower extremity blocks, digital nerve blocks, and nerve blocks of the trunk, neck, and scalp. These are widely-used for surgical anesthesia as well as for postoperative analgesia. (See 'Peripheral nerve blocks' above.)

Intravenous regional anesthesia (IVRA) – IVRA, also called Bier block, is an alternative to peripheral nerve blocks for short (ie, 30 to 45 minutes) procedures, usually on the hand and forearm (eg, carpal tunnel release, Dupuytren's contracture release, reduction of wrist fracture). (See 'Intravenous regional anesthesia' above.)

Monitored anesthesia care – MAC involves continuous monitoring and support of the patient's vital functions by an anesthesia provider, including diagnosis and treatment of clinical problems, administration of sedative, anxiolytic, and/or analgesic medications as needed, or conversion to GA if necessary (table 13). (See 'Monitored anesthesia care (MAC)' above.)

Monitoring – Standard American Society of Anesthesiologists (ASA) monitors include pulse oximetry, electrocardiography (ECG), a noninvasive blood pressure device, and temperature, as well as integrated monitors on all anesthesia machines that generate alarms for common and/or serious potential problems (table 21 and table 22). End-tidal inhalation anesthetic concentrations is often used to aid in prevention of awareness during GA, and processed electroencephalography (EEG) is employed in selected cases. Invasive hemodynamic monitoring is selectively employed (eg, intra-arterial, central venous, or pulmonary artery catheter [PAC], or transesophageal echocardiography [TEE]). (See 'Monitoring during anesthesia' above.)

Postoperative care – Most patients who received general or regional anesthesia are monitored in a post-anesthesia care unit (PACU) with standardized assessment of recovery and timely management of postoperative adverse events (eg, pain, respiratory, cardiovascular, or neurologic complications, delayed emergence or delirium, temperature derangements, inability to void). (See 'Postoperative anesthetic care' above.)

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Topic 399 Version 47.0

References

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