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CHOICE OF ANESTHETIC TECHNIQUE
The decision-making process regarding anesthetic technique begins with the proposed surgical procedure and incorporates the patient's coexisting diseases and preferences for care. The ultimate responsibility for anesthetic choice lies with the anesthesia provider. Once the anesthesia type is selected, additional management details such as choice and sequence of medications must be planned. The anesthesia provider must have the ability to implement a range of anesthetic plans and be prepared to address unexpected events that may necessitate a sudden change in plan.
TYPES OF ANESTHESIA
Choices for anesthesia include (1) general anesthesia, (2) regional anesthesia, and (3) monitored anesthesia care (MAC).
General anesthesia is a drug-induced, reversible state characterized by unconsciousness, amnesia, immobility, and control of the autonomic nervous system (ANS) responses to noxious stimulation. Control of the ANS responses can be construed as “analgesia,” but pain requires conscious perception. The term nociception refers to the propagation of impulses through the sensory system with noxious or harmful stimuli; antinociception can be considered another goal of general anesthesia. Modern approaches to general anesthesia involve administration of a combination of medications, such as hypnotic drugs (see Chapters 7 and 8 ), neuromuscular blocking drugs (see Chapter 11 ), and analgesic drugs (see Chapter 9 ).
Regional anesthesia includes neuraxial (spinal, epidural, caudal) anesthesia (see Chapter 17 ) and peripheral nerve blocks (see Chapter 18 ). With a cooperative patient, regional anesthesia may ensure the appropriate immobility and analgesia required for surgery, without exposing the patient to the risks of general anesthesia.
The term monitored anesthesia care was created by the American Society of Anesthesiologists (ASA) in the 1980s to replace the term standby anesthesia and to facilitate professional fee billing. The original description of MAC referred to the anesthesiologist providing anesthesia services to a patient receiving local anesthesia or no anesthesia at all. The ASA currently defines MAC as “a specific anesthesia service performed by a qualified anesthesia provider, for a diagnostic or therapeutic procedure.” MAC may include varying levels of sedation, analgesia, and anxiolysis. The anesthesia provider of MAC must be prepared to convert to general anesthesia if necessary. The ASA has described a continuum of depth of sedation that includes progressive levels of sedation and a definition of general anesthesia ( Table 14.1 ). The preoperative evaluation, monitoring, and other anesthesia care standards apply equally to the patient receiving MAC.
Table 14.1
Continuum of Depth of Sedation: Definition of General Anesthesia and Levels of Sedation/Analgesia
| Minimal Sedation (Anxiolysis) | Moderate Sedation/Analgesia (“Conscious Sedation”) | Deep Sedation/Analgesia | General Anesthesia | |
|---|---|---|---|---|
| Responsiveness | Normal response to verbal stimulation | Purposeful a response to verbal or tactile stimulation | Purposeful a response after repeated or painful stimulation | Unarousable even with painful stimulus |
| Airway | Unaffected | No intervention required | Intervention may be required | Intervention often required |
| Spontaneous ventilation | Unaffected | Adequate | May be inadequate | Frequently inadequate |
| Cardiovascular function | Unaffected | Usually maintained | Usually maintained | May be impaired |
a Reflex withdrawal from a painful stimulus is NOT considered a purposeful response. Minimal Sedation (Anxiolysis) is a drug-induced state during which patients respond normally to verbal commands. Moderate Sedation/Analgesia (“Conscious Sedation”) is a drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation. Deep Sedation/Analgesia is a drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully after repeated or painful stimulation. General Anesthesia is a drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation. From American Society of Anesthesiologists. Continuum of Depth of Sedation: Definition of General Anesthesia and Levels of Sedation/Analgesia. Last amended October 23, 2019. ( https://www.asahq.org/standards-and-guidelines/continuum-of-depth-of-sedation-definition-of-general-anesthesia-and-levels-of-sedationanalgesia . Accessed February 27, 2022.)
CHOOSING AN APPROPRIATE ANESTHETIC TECHNIQUE
Factors identified in the preoperative evaluation can indicate that general anesthesia may be the most appropriate anesthetic choice ( Box 14.1 ). If general anesthesia is not chosen, other anesthetic options include regional anesthesia or MAC.
Box 14.1
Clinical Settings Appropriate for General Anesthesia
Pain (nociception) of surgical procedure cannot be addressed with local, topical, or regional anesthesia
Surgical procedure requires secure airway (e.g., procedure compromises airway integrity, oxygenation, or ventilation)
Patient or procedure characteristics that are not suitable for regional anesthetic (see Box 14.2 )
Patient or procedure characteristics that are not suitable for monitored anesthesia care (e.g., risk of airway, respiratory, or cardiovascular compromise)
Certain patient or procedure characteristics may preclude safe regional anesthesia ( Box 14.2 ). The planned location of the surgical incision and operative field is a major factor in determining whether regional anesthesia can provide surgical analgesia ( Fig. 14.1 ). Depending on the level of sedation required, a regional technique may allow surgical anesthesia with complete preservation of upper airway reflexes, even in the patient at risk for aspiration of gastric contents.
Box 14.2
Situations in Which Regional Anesthesia May Not Be Appropriate
Preferences and experience of the patient, anesthesia provider, and surgeon
Need for an immediate postoperative neurologic examination in the anatomic area affected by the regional anesthetic
Coagulopathy
Preexisting neurologic disease (e.g., multiple sclerosis, neurofibromatosis)
Infected or abnormal skin at the planned cutaneous puncture site
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