Choosing Anesthetic Agents. Which One?

Richard D. Urman

Fred E. Shapiro

A wide variety of anesthetic techniques and agents may be utilized for a given surgical procedure in the hospital-based operating room (OR) setting. However, the office-based OR is unique because of the types of procedures, patient population, anesthetic techniques, and resources employed. This chapter outlines information and practice guidelines that will allow office-based anesthesiology personnel to choose the anesthetic agents and techniques best suited for the procedure being performed. This is critical, in order to ensure that each patient has a safe, pleasant, and comfortable surgical experience.

THE BASICS OF CHOOSING ANESTHETIC AGENTS

The anesthesiologist must choose drugs that fulfill procedure and patient requirements, and facilitate safe and effective administration of anesthesia. This knowledge must be coordinated with the patient’s medical history, in order to formulate an optimal plan for the anesthesia care.

There are at least five basic aspects of anesthesia that should be considered for each patient undergoing surgery in the office (see Box 9.1).

To meet these requirements, drugs must be chosen that facilitate the administration of anesthesia (see Box 9.2). Because there is no single drug or agent that satisfies all of these requirements and characteristics, several different classes of drugs with different profiles must be utilized in combination to achieve these effects.

The next step is to assess each patient individually and review his or her medical history, in order to select appropriate drugs and minimize side effects and dangerous drug interactions (see Box 9.3).

If the patient has previously undergone surgery, it is prudent to look at the old records, noting both the positive and negative experiences, so that the most appropriate perioperative plan may be formulated.

ANESTHETIC TECHNIQUES

Once the anesthesiologist is familiar with the requirements of anesthesia, the characteristics of drugs that facilitate the administration of anesthesia, and the patient’s medical history, an anesthetic plan may be further tailored to each patient by choosing an anesthetic technique. Fast-track anesthesia and monitored anesthesia care (MAC) are the two techniques often employed in the office-based OR.

Fast-track anesthesia refers to the art and science of swiftly moving patients into the OR, out of the OR, through the postanesthesia care unit (PACU), and then discharging them home in a relatively short time. This is the true definition of “outpatient surgery.” It evolved out of the need for a cost-effective measure to accommodate an increasing number of patients undergoing minimally invasive surgical procedures. The development of short-acting anesthetics, improved methods of pain control, new anesthetic monitoring, more advanced technology devices, and new recovery protocols have facilitated this process. Because of their rapid onset, peak effect, and metabolism, ultra short-acting induction agents and narcotics allow patients to have their procedure with the requirements discussed in the preceding text, awaken in a clear-headed manner, recover quickly, and be discharged home in a relatively short time.

The use of MAC is rapidly gaining acceptance and popularity in plastic surgery. This is due to increasing experience and small modifications of surgical technique and local anesthesia. Currently, a variety of aesthetic procedures are being performed combining a local anesthetic with some form of intravenous sedation. These include breast augmentation and reduction, mastopexy, abdominoplasty, rhytidectomy, rhinoplasty, blepharoplasty, and liposuction.

Before any type of sedation is considered, the anesthesiologist must first evaluate the patient to determine whether the patient is a good candidate for this type of anesthesia. Second, the anesthesiologist must be familiar with the medications used for intravenous sedation and must realize that every patient acts differently with respect to drugs. For instance, “light” sedation for one person might be “deep” sedation for another. Patient safety is of primary concern to any person administering intravenous sedation. The essentials include proper patient selection, careful management of each case by skilled personnel, appropriate drug selection and administration, and adequate continuous monitoring during and after surgery.

The American Society of Anesthesiologists (ASA) has provided guidelines for the safe use of conscious sedation for anesthesiologists and
nonanesthesiologists, as outlined in Chapter 5. The obvious benefits of conscious sedation versus general anesthesia include avoidance of the cardiopulmonary effects of general anesthesia, airway injury, postoperative nausea and vomiting (PONV), and positional nerve injuries. The risk of developing deep vein thrombophlebitis as a result of blood pooling in the lower extremities during general anesthesia is also lessened. Refer to the ASA’s definition and discussion of MAC in Chapter 5.

ANESTHETIC AGENTS

The discussion in the subsequent text focuses on different classes of drugs currently used in anesthesia. The goal is to provide the office-based anesthesiology personnel with all the necessary information, in order to plan the correct “pharmacologic cocktail” that will guarantee the patient a safe, pleasant, and comfortable experience. Table 9.1 summarizes the most commonly used drug classes and their effects on sedation, anxiolysis, pain, and cardiovascular and respiratory systems. A more extensive discussion of each drug class, with specific emphasis on office-based anesthesia follows.

Local Anesthetics

Local anesthetics can be administered by local infiltration within the area of the wound, through topical administration, or through a peripheral nerve block. The instillation of local anesthetic may reduce the amount of perioperative opioid use, thereby reducing unfavorable side effects. There are obvious advantages of minimizing opioid use, so that patients are able to remain alert, maintain gastrointestinal (GI) function, and improve their ability to ambulate. Dosing is specific to each type of local anesthetic and is based on the patient’s weight. Dosages beyond the specified amount for each drug may result in toxicity, leading to mental status changes, seizures, cardiac arrhythmias, and death. Table 9.2 lists the most commonly used local anesthetics, their onset, duration of action, and maximum doses.

Local anesthetics of choice in ambulatory anesthesia include lidocaine, bupivacaine, ropivacaine, and levobupivacaine. Lidocaine has a relatively short duration of action. Bupivacaine has a longer duration of action and a very small therapeutic window. It is associated with profound cardiovascular (arrhythmias, cardiac arrest) and central nervous system (CNS) effects (seizures, CNS depression) in cases of unintentional intravascular injection or overdose. Two new local anesthetic agents, ropivacaine and levobupivacaine, have a greater safety profile with respect to cardiovascular and CNS toxicity. Therefore, these drugs may be safer alternatives to bupivacaine
for extending the duration of local anesthetic into the postoperative period. In addition, ropivacaine may be a good alternative with a shorter and less intense motor block than bupivacaine (1).

Table 9.1. Commonly used drug classes and their effects

Drug Class	Effects
	Sedation	Anxiolysis	Pain	Cardiovascular	Respiratory
Local anesthetics	0	0	+	++	+
Barbiturates	++	+	0	+	++
Benzodiazepines	++	++	0	+	++
Ketamine	++	+	++	+	0
Propofol	++	+	0	++	++
Inhalational agents	++	+	++	++	+
α₂ Agonists	++	+	++	+	0
Opioids	++	+	0	+	++

Table 9.2. Commonly used local anesthetics with dosage, onset, and duration of action

Local Anesthetic	Onset	Duration (min)	Maximum Single Dose (mg)
Lidocaine	Rapid	60-120	300
Mepivacaine	Slow	90-180	300
Prilocaine	Slow	60-120	400
Bupivacaine	Slow	240-480	175
Ropivacaine	Slow	240-480	200
Levobupivacaine	Slow	240-480	175
Procaine	Rapid	45-60	500
Chloroprocaine	Rapid	30-45	600
Tetracaine	Slow	60-180	100
From: Stoelting R, Miller R. Basics of Anesthesia, 4th ed. Churchill Livingstone, 2000.

Infiltration of local anesthetic may be performed for small- to moderatesized and relatively superficial procedures. Lidocaine 0.5% to 1.0% or bupivacaine 0.25% are most commonly used. The addition of epinephrine, a vasoconstrictor that delays absorption of the local anesthetic, in a 1:200,000 dilution (epi = 5 μg/mL) will prolong the duration of action. Bupivacaine 0.25%, ropivacaine 0.25% to 0.5%, or levobupivacaine 0.25% will produce up to 4 hours of pain relief. Surgical site infiltration, in combination with nonopioid analgesics such as acetaminophen or celecoxib may be adequate analgesia for minor surgical procedures and can be used as the basal analgesic technique for all surgical procedures (1).

Midazolam

Midazolam is a rapid, short-acting benzodiazepine that causes profound anxiolysis, amnesia, and sedation. Benzodiazepines act within the CNS to enhance the inhibitory tone of γ-aminobutyric acid (GABA) receptors. Because binding is specific, benzodiazepines have minimal cardiovascular depressant effects in doses used for sedation. Benzodiazepines cause a depression in the ventilatory response curve to CO₂ (a decrease in the slope of the curve). This can become significant when combined with other respiratory depressants.

If midazolam is to be used alone for MAC, the intravenous dose can generally range from 2.5 to 7.5 mg. If used for anxiolysis before induction of general anesthesia, a propofol infusion, or a remifentanil infusion, the typical intravenous dose of midazolam is 1 to 2 mg (2). The infusion rate of midazolam for MAC anesthesia is 1 to 2 μg/kg/min. Midazolam’s elimination half-life is approximately 2 hours (3). It is also important to note that there is a marked decrease in midazolam requirements as patients age. Complete recovery after a single dose of 0.1 μg/kg requires approximately 90 minutes. This is the main reason why midazolam is generally not used to induce or maintain loss of consciousness. It is most commonly used as a premedication or for conscious sedation.

Ketamine

Ketamine is a phencyclidine (PCP) derivative that produces a dissociative state, which is accompanied by amnesia and profound analgesia. The patient
appears conscious but is unable to process or respond to sensory input. Its mode of action is not well defined, but the mechanism of action is thought to be through N-methyl-D-aspartate (NMDA) receptor antagonism. In contrast to other anesthetic agents, ketamine stimulates the sympathetic nervous system to increase heart rate (HR), systemic blood pressure (BP), and pulmonary artery BP. Ketamine can therefore be used to balance the negative cardiovascular effects of propofol. Owing to its effects on the sympathetic nervous system, ketamine should be avoided in patients with the following:

Coronary artery disease
Uncontrolled hypertension
Congestive heart failure
Arterial aneurysms

Respiratory depressant effects of ketamine are minimal, upper airway reflexes remain largely intact, and the sympathomimetic effect may alleviate bronchospasm. Ketamine does increase salivation, which can be attenuated by premedication with an anticholinergic agent. Ketamine also increases cerebral oxygen consumption, cerebral blood flow, and intracranial pressure. It should therefore be avoided in patients with space occupying intracranial lesions, head trauma, or intracranial hypertension. The induction dose of ketamine is 1 to 2 mg per kg IV and 3 to 4 mg IM. The intravenous sedative dose is in the range of 5 to 15 μg/kg/min and must be titrated to effect (2). The elimination half-life is 2 to 4 hours. Ketamine is associated with a high incidence of psychomimetic effects. Restlessness and agitation may occur on emergence, and hallucinations and unpleasant dreams may occur postoperatively. Patients at higher risk for psychomimetic effects include females, older age, and patients receiving doses >2 mg per kg. These effects can be greatly reduced by the concurrent use of propofol and midazolam (4,5) (see Tables 9.3 and 9.4).

Table 9.3. Examples of dosing regimens for various anesthetic intravenous agents during general anesthesia in the ambulatory setting

Drug	Induction Bolus Dose	Maintenance Infusion Rate	Maintenance Intermittent Boluses
Thiopental	5-7 mg/kg	—	—
Midazolam	Not recommended as hypnotic agent in ambulatory general anesthesia
Etomidate	0.3 mg/kg	—	—
Propofol	2-3 mg/kg	6-10 mg/kg/h	—
Fentanyl	50-100 μg	—	25-50 μg
Alfentanil	0.5-1.5 mg	1-3 mg/h	0.2-0.5 mg
Remifentanil	1 μg/kg	0.1-0.25 μg/kg/min	—
Ketamine	0.1-0.2 mg/kg	5-10 μg/kg/min	—
From: Tesniere A, Servin F. Intravenous techniques in ambulatory anesthesia. Anesthesiol Clin North America. 2003; 21:273-288.

Table 9.4. Examples of dosing regimens for the various anesthetic intravenous agents during conscious sedation in the ambulatory setting

Drug	Induction Bolus Dose	Maintenance infusion Rate	Maintenance intermittent Boluses
Midazolam	1-5 mg	—	1-2 mg
Propofol	0.5-1 mg/kg	2-4 mg/kg/h	0.3-0.5 mg/kg
Fentanyl	25-50 μg	—	25-50 μg
Alfentanil	0.2-0.5 mg	0.5-2 mg/h	0.2-0.5 mg
Remifentanil	—	0.025-0.1 μg/kg/min	25 μg
Ketamine	0.1 mg/kg	2-4 μg/kg/min	—
From: Tesniere A, Servin F. Intravenous techniques in ambulatory anesthesia. Anesthesiol Clin North America. 2003; 21:273-288.

Inhalational agents

Inhalational anesthesia remains the most common anesthetic technique used in the ambulatory setting (see Box 9.4).

The correct choice of an inhalational agent can help facilitate the “fast track” philosophy, enable the transfer of patients directly from the OR to the phase II recovery area, bypassing the PACU. Each of the newer short-acting inhaled anesthetics (e.g., desflurane and sevoflurane) is tolerated well by patients, achieves a rapid depth of anesthesia, has minimal side effects and metabolism, and permits rapid patient awakening. Studies have shown that propofol, sevoflurane, and desflurane facilitate rapid emergence from anesthesia, and there was no difference in recovery endpoints such as home readiness and actual time for discharge. In a study comparing the recovery profile of propofol versus desflurane and sevoflurane, it was observed in a 10-year review of the literature that PONV was significantly more common with the inhaled agents compared with propofol (6,7).

A meta-analysis of randomized controlled studies published before 1994 examined the differences in recovery time (e.g., emergence and home readiness) with desflurane and isoflurane (eight studies) and with desflurane and propofol (six studies) (8

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