Chapter 8 – Anesthesia Techniques: Mild, Moderate, and Deep Sedation in Clinical Practice

Summary

Selection of the anesthetic technique to be employed during a procedure begins during the preoperative evaluation with consideration of factors such as the patient’s comorbidities and preferences and the type of procedure to be performed. Oftentimes, general anesthesia is not necessary and the procedure can be performed under a lesser depth of sedation. Procedural sedation is a technique that allows the patient to tolerate the discomfort of a procedure while still maintaining cardiorespiratory function. In order to accomplish this, the anesthesia provider administers sedative, dissociative, and/or analgesic agents alone or in combination [1].

Background

Although commonly regarded as one entity, procedural sedation is a heterogeneous anesthetic technique that encompasses a variety of levels of consciousness. The various depths of sedation are differentiated by the physiologic changes induced by the agents used and the patient’s response to stimuli. The American Society of Anesthesiologists’s (ASA) continuum of sedation divides sedation into three categories: minimal, moderate, and deep. Table 8.1 describes these categories of anesthetic depth. Minimal sedation is a drug-induced state defined by preserved response to verbal stimulation. While cognitive function and/or physical coordination may be impaired, a patient under minimal sedation maintains the ability to protect their own airway and ventilate spontaneously. Furthermore, cardiovascular function is unaffected when under minimal sedation. Under moderate sedation, patients retain the ability to respond purposefully to verbal or tactile stimuli. Patients maintain the ability to protect their own airway and perform adequate spontaneous ventilation without intervention from the anesthesia provider. Cardiovascular function also is usually maintained. This level of sedation is sometimes referred to colloquially as “conscious sedation.” Deep sedation is the greatest depth of sedation before a patient is considered to be under general anesthesia. A patient under deep sedation is still able to respond purposefully to stimuli but only demonstrates this ability following repeated or painful stimulation. Importantly, reflex withdrawal from painful stimuli is not considered purposeful. Patients under deep sedation may exhibit impairment of spontaneous ventilation and may require intervention to aid in protecting their airways. Just as in the lesser depths of sedation, cardiovascular function is usually maintained in patients under deep sedation. Since sedation is a continuum, it is difficult, and sometimes impossible, to predict how a particular patient will respond to the administered medications. As such, providers should always be prepared to “rescue” a patient from a level of sedation that is deeper than anticipated. Of note, the term monitored anesthesia care (MAC) is often used to describe situations in which patients are under a depth of sedation that is less than general anesthesia. It is important to note that MAC is not a particular depth of sedation, but rather a billing designation that indicates the involvement of an anesthesiologist [2].

Table 8.1 Depth of anesthesia

	Minimal sedation	Moderate sedation	Deep sedation	General anesthesia
Responsiveness	Normal response to verbal stimulation	Purposeful response to verbal or tactile stimulation	Purposeful response to repeated or painful stimulation	No response, even to painful stimulation
Airway	Unaffected	No intervention required	Intervention could be required	Intervention typically required
Spontaneous ventilation	Unaffected	Adequate	May be inadequate	Frequently inadequate
Cardiovascular function	Unaffected	Usually maintained	Usually maintained	May be impaired

Procedural sedation is appropriate for a wide array of procedures and can be performed in a variety of locations. In the hospital, procedural sedation is often required in the emergency department to facilitate procedures such as laceration repair and fracture reduction. Similarly, endoscopic procedures, such as colonoscopy, esophagogastroduodenoscopy (EGD), and transesophageal echocardiography, are often performed under sedation. Sedation is also utilized in the operating room for patients undergoing surgery. In these instances, it is often combined with other techniques such as regional or local anesthesia. Lastly, sedation can be performed out of the hospital in office-based settings to aid in the performance of procedures such dental or dermatologic procedures. Regardless of location or procedure, it is important for the provider in charge of administering sedation to possess the appropriate skill set and monitoring and resuscitation equipment to do so safely.

Provider Roles

A board-certified anesthesiologist is a physician who has completed medical school, was enrolled in, and completed, a certified anesthesiology residency program, and has passed all accreditation and licensing examinations, whether written or oral. The ASA believes that at least one physician anesthesiologist should be involved in the care of each patient receiving anesthetics [3]. This physician anesthesiologist may be directly providing care for the patient or often supervising another practitioner [Reference Abenstein and Warner4–6]. These practitioners can include a physician currently enrolled in training, either residency or fellowship, or a nonphysician anesthesia care provider. A nonphysician anesthesia care provider can include a certified registered nurse anesthetist (CRNA), a registered nurse who has completed an accredited program for nursing, has completed a set amount of time working in an intensive care unit environment, and has completed training and the accompanying licensing examinations as part of the nurse anesthetist accreditation [3–Reference Jones and Fitzpatrick5]. Additionally, nursing providers in both the preoperative area and the postanesthesia care unit, as well as intraoperatively, are important in providing assistance to the anesthesia care team. They are often able to identify or anticipate issues that may arise, be an advocate for the patient, and provide additional assistance to the anesthesiologist if necessary [7]. Thus, there are a multitude of individuals in various healthcare professions and levels of training who make important contributions to the perioperative care team of the patient.

Drug Selection

This section will discuss the most commonly utilized pharmacologic agents in sedation anesthesia practice. Table 8.2 provides a summation of the below medications.

Table 8.2 Commonly used anesthetic agents in sedation practice and their pharmacologic properties

Drug	Administration	Initial intravenous dosage	Infusion rate	Sedative effect
Benzodiazepine (midazolam)	Intravenous, oral, intramuscular	0.02–0.04 mg kg⁻¹	0.25–1.0 g/(kg min)	+++
Propofol	Intravenous	20–30 mg bolus	25–75 μg/(kg min)	+++
Opioids (fentanyl, remifentanil, alfentanil)	Intravenous, oral, intramuscular	Fentanyl: 2–50 μg kg⁻¹ Remifentanil: 1 μg kg⁻¹ Alfentanil: 8–100 μg kg⁻¹	Bolus in 5-min intervals to obtain titrated effect 0.1 μg/(kg min) 0.5–3 μg/(kg min)	Intensifies effects of other sedative anesthetics
Dexmedetomidine	Intravenous, oral	1 g kg⁻¹ over 10 minutes	0.3–0.7 g/(kg hr)	++
Ketamine	Intravenous, oral, intramuscular	0.25–0.5 mg kg⁻¹	2.5–15 μg/(kg min)Footnote ^a	+++
Nitrous oxide	Inhaled	n/a	n/a	+/− Intensifies effects of other sedative anesthetics

^a Usually administered with propofol.

+, weak effect; ++, moderate effect; +++, strong effect; −, no effect.

Benzodiazepines

Benzodiazepines act on type A gamma-aminobutyric acid (GABA) receptors in the brainstem, causing anxiolytic, amnesic, and sedative effects, without an analgesic effect [Reference Whitlock and Pardo1]. Lorazepam, diazepam, and midazolam are commonly used benzodiazepines in anesthesia. These drugs have various ways of administration for sedation (e.g., intravenously, intramuscular, oral). Lorazepam and diazepam are insoluble (formulated with propylene glycol) and well absorbed in the gastrointestinal tract, making oral administration favorable [2]. Midazolam is water-soluble at low pH and commonly used as an anesthesia premedication in adults intravenously or intramuscularly (0.02–0.04 mg kg⁻¹) and orally in children (0.4–0.8 mg kg⁻¹) [Reference Whitlock and Pardo1]. Minimal risk of cardiopulmonary depression exists when using midazolam in small dosages for procedural sedations. Midazolam is also preferred to maintain hypnosis and amnesia, with continuous infusion rates of 0.25–1.0 g/(kg min), while given with an inhalational agent or opioids. In addition, midazolam can enhance the effects of other opioids and sedatives when administered concomitantly [3]. Due to a prolonged emergence, administration of midazolam as an infusion for sedation should be reserved for short cases or patients who are expected to remain intubated [Reference Whitlock and Pardo1]. Benzodiazepines can be pharmacologically reversed with flumazenil (0.5–1 mg intravenously), a competitive antagonist, making them favorable for sedation in the setting of a threatened airway [Reference Whitlock and Pardo1]. Benzodiazepines are usually avoided during pregnancy because newborns can exhibit withdrawal symptoms from benzodiazepine administration to the mothers.

Propofol

Propofol is a rapid- and short-acting drug that acts on the type A GABA channel to provide sedative, amnesia, and antiemetic properties [2, Reference Abenstein and Warner4]. Similar to benzodiazepines, propofol does not cause analgesia. Propofol is commonly used for moderate procedural sedation by intermittent boluses (20–30 mg) or titrated infusion (25–75 μg/(kg min)) intravenously [Reference Whitlock and Pardo1]. Children will need a higher dose to overcome the accelerated clearance and larger volume of distribution to achieve an ideal sedative effect. Propofol has a narrow therapeutic index and can deepen the levels of sedation quickly. Consequently, close monitoring for adverse effects (e.g., myocardial depression) in patients receiving propofol is imperative. Because there is no reversal agent for propofol, oversedated patients should be managed with supportive therapy (e.g., airway support) until the agent is metabolized [Reference Whitlock and Pardo1, 2]. Prolonged use of a high-dose propofol infusion in a critically ill population may cause propofol infusion syndrome (PRIS), which is characterized by rhabdomyolysis, cardiac failure, renal failure, metabolic acidosis, hepatomegaly, hyperkalemia, and hypertriglyceridemia [Reference Whitlock and Pardo1]. If PRIS is suspected, propofol must be discontinued immediately and an alternative sedative should be used.