Monitored Anesthesia Care (MAC)

MAC is de ned as a speci c anesthesia service in which an anesthesiologist has been requested to participate in the care of a patient undergoing a diagnostic or therapeutic procedure. However, MAC does not describe the depth of sedation. Under MAC, the anesthesiologist can either provide sedation or general anesthesia and the post procedure recovery care. Situations where MAC is valuable are:

\1.\ When variable levels of sedation are needed to meet changes in the patient’s and the bronchoscopist’s needs during a procedure.

\2.\ Patients sensitive to small doses of sedatives where respiratory or hemodynamic complications can occur and resuscitation will be required.

\3.\ Patients who need a transient period of general anesthesia.

Therefore, the drugs of choice for MAC should be ultra-short-acting anesthetics that are easily titrated to match the patient tolerance to the procedure with rapid return to baseline status at the end of the procedure, e.g., remifentanil, alfentanil, propofol, dexmedetomidine, and fospropofol. In addition, midazolam, fentanyl, and morphine can also be an acceptable choice [18].

General Anesthesia

If general anesthesia is the chosen anesthesia technique for an interventional bronchoscopic procedure, an open discussion between the anesthesiologist and the bronchoscopist should take place before and throughout the procedure. The discussion should include procedure location (e.g., trachea vs. bronchi), degree of airway obstruction (e.g., complete vs. partial obstruction), depth of anesthesia needed (e.g., general

vs. sedation), airway device options (e.g., none, endotracheal tube, laryngeal mask airway, or rigid bronchoscope), and the most suitable mode of ventilation (e.g., spontaneous ventilation, noninvasive positive pressure, assisted ventilation, mechanical ventilation, or jet ventilation). In addition, the anesthesiologist should be familiar with the step-by-step plan the bronchoscopist has to manage the airway pathology and possible complications.

Total intravenous anesthesia (TIVA) is the anesthetic technique of choice for interventional bronchoscopic procedures when compared to inhalation anesthesia [12]. Inhalational anesthetics have multiple disadvantages, including the variable levels of anesthetic gas delivered because of frequent suctioning during the procedure and the contamination of the operating room air by inhalation agents. However, it is important to emphasize that inhalation agents can be a better choice in cases of bronchospasm or in patients with an anterior mediastinal mass, where maintenance of spontaneous ventilation is essential. The following medications are commonly used for TIVA.

Propofol, similar to benzodiazepines, acts to facilitate the inhibitory effect of GABA. When used for sedation for airway procedures, propofol has been shown to be superior to midazolam due to its short onset time of 30 s, metabolism independent of organ function, and rapid recovery time of 15 min after a 2 h infusion. In addition, propofol has been shown to result in signi - cantly better neuropsychometric recovery than midazolam [19]. When compared to inhalation anesthetics, propofol has been shown to reduce coughing and the depression in ciliary function as well as the release of cytokines and the stress hormone response [20–22].

Propofol infusion rates of 100–150 μg/kg/ min can be used for anesthesia induction while maintaining spontaneous ventilation. The bispectral index monitor (BIS) can be used to titrate the

propofol infusion rates to achieve and sustain an appropriate depth of anesthesia.

Remifentanil is the shortest acting narcotic available, with duration of action of 3–10 min and a rapid onset of action at 1 min. After interventional bronchoscopic procedures, patients do not suffer from postprocedure pain thus eliminating the need for the use of long-acting narcotics. Remifentanil is ideal for blunting airway refexes during the procedure with no residual effect in the recovery room [23].

Ketamine is a general anesthetic that induces a dissociative state in which sensory stimuli are blocked from reaching the cerebral cortex, causing amnesia and analgesia. Although ketamine is an old drug, its use has been revived because it has profound analgesic property. Ketamine-­ induced analgesia makes it a good adjunct to propofol that lacks any analgesic properties [24]. Ketamine is particularly valuable for bronchoscopic procedures because of its bronchodilator properties and absence of respiratory depressant effect.

Dexmedetomidine is an α-2 agonist that inhibits norepinephrine release causing its unique ability to provide sedation and analgesia without respiratory depression [25]. Dexmedetomidine has also been found to offer cardio protective bene ts during surgery by lowering perioperative oxygen consumption and the stress response [26].

Muscle relaxants, such as succinylcholine, rocuronium, or cisatracurium, can be used safely during general anesthesia to prevent laryngospasm and coughing associated with the insertion of the bronchoscope in the airway. The use of muscle relaxation for therapeutic bronchoscopic procedures has many advantages. These include facilitating the insertion of airway devices (e.g., LMA, endotracheal tube, and the rigid bronchoscope); better lung compliance during positive pressure ventilation or jet ventilation; providing the bronchoscopist with a stilleld when precise targeting of lesions adjacent to major vessels and the heart is needed; and maintaining the glottis aperture open during multiple insertion and removal of the bronchoscope and other instruments thus minimizing trauma to the vocal cord.

On the other hand, indiscriminate use of muscle relaxant in interventional bronchoscopy can be associated with severe complications. For example, there are several reports of loss of the airway patency after muscle relaxant was given in patients with large anterior mediastinal mass. Pneumothorax and/or pneumomediastinum can develop in patients with tracheoesophageal stulas, bronchoesophageal stulas, or airway tears when muscle relaxant is given, and positive pressure ventilation is used. In addition, prolonged unwanted muscle relaxation has been reported in patients with lung cancer and paraneoplastic Lambert–Eaton myasthenia syndrome.

In the event that muscle relaxation is deemed unsuitable, instillation of lidocaine on the vocal cords and the proximal airway is a better alternative to the use of muscle relaxation prior to insertion of the rigid bronchoscope or other airway devices.

Fraction-inspired oxygen (FiO2) should be continuously adjusted to maintain patient oxygen saturation >90% during interventional bronchoscopic procedure. FiO2 of 100% is commonly needed during an advanced bronchoscopic procedure especially in patients with advanced lung pathology, poor baseline oxygen saturation, and / or the use of supplemental oxygen. In addition, FiO2 of 100% is valuable when periods of complete airway occlusion and/or inability to provide mechanical ventilation is anticipated, e.g., during deployment or extraction of stents, balloon dilation of the airway, removal of a tumor mass where positive pressure ventilation can force the excised tumor down the airway causing acute obstruction, or during exchange of one rigid bronchoscope to a different type or size rigid bronchoscope.

It is important to note that low FiO2 of less than 40% is required during electrocautery, laser, and argon plasma coagulation (APC) in order to avoid airway re.

Monitoring the Depth of Anesthesia

Processed electroencephalograms can be used to monitor the depth of anesthesia and in combina-