The editors and publisher would like to thank Dr. Ronald D. Miller for contributing to this chapter in the previous edition of this work. It has served as the foundation for the current chapter.
The decision-making process regarding anesthetic technique begins with the preoperative evaluation (see Chapter 13 ). The three most important factors include type of surgical procedure, the patient’s coexisting diseases, and patient preferences. The ultimate responsibility for anesthetic choice lies with the anesthesia provider. Often, there is no single best choice. 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).
Although there is some debate about the clinical definition of general anesthesia, the components include immobility, amnesia, analgesia, and lack of patient harm. The American Society of Anesthesiologists (ASA) defines general anesthesia as “a drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation.” Modern approaches to general anesthesia involve administration of a combination of medications, such as hypnotic drugs (see Chapter 7, Chapter 8 ), neuromuscular blocking drugs (see Chapter 11 ), and analgesic drugs (see Chapter 9 ).
Regional anesthesia includes neuraxial (spinal, epidural, caudal) anesthesia (see Chapter 17 ) as well as 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 phrase monitored anesthesia care was created by the 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 in which an anesthesiologist has been requested to participate in the care of a patient undergoing a diagnostic or therapeutic procedure.” The ASA has also described a continuum of depth of sedation that includes progressive levels of sedation ( Table 14.1 ). These definitions are used by regulatory bodies such as The Joint Commission to create standards for administration of sedation by nonanesthesiologist personnel. The term MAC is not part of the description of the sedation continuum, as the level of consciousness may change during a procedure and even progress to an “unplanned” general anesthetic. The preoperative evaluation, monitoring, and other anesthesia care standards apply equally to the patient receiving MAC.
| Function | Minimal Sedation (Anxiolysis) | Moderate Sedation (Conscious Sedation) | Deep Sedation | General Anesthesia |
|---|---|---|---|---|
| Response (stimulation type) | Normal (verbal stimulus) | Purposeful (verbal or tactile stimulus) | Purposeful (repeated or painful stimulus) | None (even with painful stimulus) |
| Ability to maintain airway and spontaneous ventilation | Not affected | Airway maintained without intervention; ventilation adequate | Airway intervention may be required; ventilation may be inadequate | Airway intervention often required; ventilation frequently inadequate |
| Cardiovascular function | Not affected | Usually maintained | Usually maintained | May be impaired |
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 chosen, the anesthesia provider must then determine a plan for airway management, induction of anesthesia, maintenance of anesthesia, and immediate postoperative care. If general anesthesia is not chosen, other anesthetic options include regional anesthesia or MAC.
A requirement for systemic neuromuscular blockade
A requirement for establishment of a secure airway
Due to surgical procedures that may compromise native airway integrity, oxygenation, or ventilation
Due to level of consciousness required to provide immobility, analgesia, or anxiolysis
Patient or procedural characteristics that are not appropriate for monitored anesthesia care
Uncooperative patient or patient refusal
Surgical pain not amenable to local or topical anesthesia
Patient or procedural characteristics that are not suitable for regional anesthetic
Preferences of the patient, anesthesia provider, and/or surgeon
Certain patient or procedure characteristics may preclude safe regional anesthesia ( Box 14.2 ). 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. Regional anesthesia cannot provide surgical analgesia for all procedures. The most important factor is the planned location of the surgical incision ( Fig. 14.1 ).
Preferences and experience of the patient, anesthesia provider, and surgeon
The need for an immediate postoperative neurologic examination in the anatomic area impacted by the regional anesthetic
Coagulopathy
Preexisting neurologic disease (e.g., multiple sclerosis, neurofibromatosis)
Infected or abnormal skin at the planned cutaneous puncture site
Specific Considerations for Neuraxial Anesthesia
Hypovolemia increases the risk for significant hypotension
Coagulopathy (including anticoagulant and antiplatelet medication therapy) increases risk of epidural hematoma
Increased intracranial pressure may result in cerebral herniation with intentional or inadvertent dural puncture
If the analgesic requirements for the planned procedure can be met with local or topical anesthesia, or if the planned procedure is not associated with pain (e.g., diagnostic radiology procedure such as magnetic resonance imaging), MAC may be the most appropriate choice. However, the anesthesia provider must be prepared to convert to general anesthesia if it becomes apparent that appropriate analgesia and immobility cannot be achieved by other means. The anesthetic risks associated with MAC are not necessarily different from general or regional anesthesia. An ASA Closed Claims study of patient injury documented a comparable incidence of injury severity with MAC compared to general anesthesia. In patients receiving MAC, respiratory depression from sedative drugs (e.g., propofol, benzodiazepines, opioids) is an important mechanism of injury.
Anesthetic techniques can be combined to meet patient or surgical goals. For example, a patient with subarachnoid hemorrhage who requires diagnostic cerebral angiography may initially receive MAC. If the imaging reveals a cerebral aneurysm requiring endovascular coiling, the anesthesia provider may be asked to convert to general anesthesia to provide patient immobility and control of ventilation during the procedure.
Neuraxial and peripheral nerve blockade may be combined with general anesthesia to provide long-lasting postoperative analgesia following a surgical procedure that may not be amenable to regional anesthesia alone (also see Chapter 40 ). A 2013 systematic review documented that, in a broad range of surgical procedures, use of local infiltration or peripheral nerve block in addition to general anesthesia improved postoperative pain scores and decreased opiate consumption. This result may be directly due to analgesia provided by the technique or by “preventive analgesia,” which is defined as analgesia lasting longer than 5.5 half-lives of an analgesic drug. Even use of a peripheral nerve block in addition to a single-shot spinal block improves postoperative analgesia for many surgeries of the lower extremity.
The addition of a regional technique to general anesthesia may reduce intraoperative blood loss and, in some situations, the rate of perioperative transfusion. Addition of neuraxial or peripheral nerve blockade to general anesthesia also reduces rates of postoperative chronic pain. A meta-analysis of systematic reviews did not find a mortality rate benefit for the addition of neuraxial anesthesia to general anesthesia. The same meta-analysis suggested that neuraxial anesthesia was associated with lower 30-day mortality rates compared to general anesthesia alone in patients with an intermediate risk of cardiac complications. However, most of the studies reviewed were performed in the 1970s to 1990s, and management of cardiovascular disease has evolved significantly in subsequent decades.
There is increasing emphasis on improving patient outcomes not just in the immediate term (e.g., intraoperatively) but facilitating in-hospital recovery, mitigating risks for development of postoperative chronic pain, and improving long-term survival.
Fig. 14.2 provides a summary of the decision-making process in choosing an appropriate anesthetic for an individual patient.
