Monitored Anesthesia Care
Robert R. Kirby
Emilio B. Lobato
CASE SUMMARY
A 67-year-old man with anemia, abdominal swelling, and constipation was scheduled for flexible colonoscopy with monitored anesthesia care (MAC). A prior scheduled colonoscopy was changed to a flexible sigmoidoscopy because of bradycardia as low as 46 beats per minute. During repeated clinic visits, he was frequently bradycardic.
An untimed preanesthetic assessment by a Certified Registered Nurse Anesthetist (CRNA) contained the statement, “Patient informed concerning slow heart rate—he needs to ask his physician to check further. Dr. informed of bradycardia … ASA 3.” No airway assessment was recorded, and no electrocardiogram was obtained.
Oxygen was administered at 1.5 to 2 L per minute through a nasal cannula. Initial heart rate was 45 beats per minute. Midazolam, 1 mg, and fentanyl 100 µg, were followed by propofol, 100 mg. Blood pressure (BP) of 150/80 mm Hg and pulse of 65 beats per minute progressively decreased over 25 minutes to 80/45 mm Hg and “unobtainable”, respectively. Three recordings of SpO2 (100%, 98%, 97%) were noted during this interval. A fourth value of 89% was crossed out.
Twenty-seven minutes into the procedure, a “code” was called for respiratory arrest and “pulseless brady.” Bag-mask ventilation was started, and ephedrine was administered 8 minutes into the resuscitation. The CRNA recorded, “not able to intubate for 8-9 min.” Epinephrine, 0.3 mg, was administered for the first time 12 minutes into the resuscitation, and the gastroenterologist simultaneously inserted a 7.5 mm endotracheal tube.
Afterward, a detailed analysis of the events revealed that the emergency airway cart did not contain a variety of laryngoscope blades or oral and nasopharyngeal airways. No laryngeal mask airway or an alternative device by which the CRNA could secure the airway or intubate the trachea was available. The cart had been set up by a nurse supervisor with no input from the anesthesia providers.
The patient remained in a vegetative state due to anoxic encephalopathy. Sick sinus syndrome with persistent bradycardia was diagnosed. He died 9 months later.
Is Monitored Anesthesia Care Safer than General or Regional Anesthesia?
The historic concept of MAC stems from the era in which anesthesiologists were requested to remain on “standby” while procedures were performed in patients considered to pose an unacceptable risk for general anesthesia. MAC was later extended to the administration of drugs to ease discomfort while minor procedures were performed under local anesthesia.
Although many practitioners still consider local anesthesia safer than general or regional anesthesia, published data demonstrates that this assumption is not always the case.1 Serious complications were almost as frequent following local or general anesthesia in young outpatients undergoing oral surgery.2 Similarly, in a British study, a significant proportion of deaths during dental surgery occurred as a result of excessive sedation whereby drugs were administered by the operators. The most common precipitating causes were respiratory obstruction, hypoxia, and malignant dysrhythmias,3 thereby emphasizing the necessity of adding qualified individuals whose only function was to monitor the patient and evaluate the effects of sedatives and analgesics.
Despite the presence of anesthesia care providers responsible for sedation/analgesia and monitoring, serious and life-threatening complications associated with MAC still occur. A recent update from the American Society of Anesthesiologists (ASA) closed claims project compared liability claims associated with MAC against general and regional anesthesia.4 Claims from injuries associated with MAC after 1990 increased by 40% compared with those in the prior decade (3% to 5%). Proportionally, deaths during MAC and general anesthesia were twice as common as those associated with regional anesthesia. Claims for brain damage were comparable in all three groups (approximately 10% to 13%). The primary damaging event was inadequate oxygenation/ventilation during MAC compared to general or regional anesthesia (15% vs.
7% for general anesthesia and 5% for regional anesthesia). Eye damage and thermal burns were also more common during MAC.
7% for general anesthesia and 5% for regional anesthesia). Eye damage and thermal burns were also more common during MAC.
Further analysis revealed that a significant proportion of patients suffering from complications associated with MAC were older and had an ASA physical status classification III (ASA III) or higher. This represents a growing trend of increased number of surgical procedures performed in elderly and sicker patients with this technique. Therefore, clinicians must be aware that in many patients, procedures performed under MAC should be considered challenging, with an increased risk of major complications.
What Are the Requirements for Monitored Anesthesia Care?
The ASA position on MAC states, in part:5
“Monitored anesthesia care is a specific anesthesia service for a diagnostic or therapeutic procedure. Indications for monitored anesthesia care include the nature of the procedure, the patient’s clinical condition and/or the potential need to convert to a general or regional anesthetic.
Monitored anesthesia care includes all aspects of anesthesia care—a preprocedure visit, intraprocedure care and postprocedure anesthesia management. During monitored anesthesia care, the anesthesiologist provides or medically directs a number of specific services, including but not limited to:
Diagnosis and treatment of clinical problems that occur during the procedure
Support of vital functions
Administration of sedatives, analgesics, hypnotics, anesthetic agents or other medications as necessary for patient safety
Psychological support and physical comfort
Provision of other medical services as needed to complete the procedure safely
Monitored anesthesia care may include varying levels of sedation, analgesia and anxiolysis as necessary. The provider of monitored anesthesia care must be prepared and qualified to convert to general anesthesia when necessary. If the patient loses consciousness and the ability to respond purposefully, the anesthesia care is a general anesthetic, irrespective of whether airway instrumentation is required.”
What Are the Levels of Sedation/Analgesia?
With reference to the varying levels of sedation, analgesia, and general anesthesia achieved by the chosen drugs, the ASA definitions6 (see Table 63.1) include:
MINIMAL SEDATION (ANXIOLYSIS): A drug-induced state during which patients respond normally to verbal commands. Although cognitive function and coordination may be impaired, ventilatory and cardiovascular functions are unaffected.
MODERATE SEDATION/ANALGESIA (“CONSCIOUS SEDATION”): A drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation. No interventions are required to maintain a patent airway, and spontaneous ventilation is adequate. Cardiovascular function is usually maintained.
DEEP SEDATION/ANALGESIA: A drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully following repeated or painful stimulation. The ability to independently maintain ventilatory function may be impaired. Patients may require assistance in maintaining a patent airway, and spontaneous ventilation may be inadequate. Cardiovascular function is usually maintained.
GENERAL ANESTHESIA: A drug-induced loss of consciousness during which patients are unarousable even with painful stimulus. Airway intervention often is required, and spontaneous ventilation may be inadequate. Cardiovascular function may be impaired.
TABLE 63.1 Characteristics of Minimal, Moderate, and Deep Sedation, and General Anesthesia | |||||||||||||||||||||||||
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How Do Monitored Anesthesia Care and Sedation/Analgesia Differ?
Although elements of sedation and analgesia are included in MAC, the two are not the same.7 MAC allows a maximal depth of sedation in excess of that provided during moderate sedation. The spectrum from full consciousness to general anesthesia provides maximal flexibility to match the level of sedation to the patient’s and the procedural requirements. In situations where the procedure is more invasive or when the patient is especially fragile, optimizing sedation level is necessary to achieve ideal procedural conditions.
Drugs used for general anesthesia can be a part of MAC. Because many of these drugs are anesthetics at a lower dose, the transition from a sedated, conscious patient to one who is unresponsive and anesthetized may occur subtly and go unrecognized. Patients may require minimal sedation, yet MAC might be indicated because even small drug doses can precipitate adverse effects that necessitate acute clinical interventions and resuscitation, particularly in patients with significant comorbid disease states.8 Indeed, this chain of events was well delineated in the case summary that opened this chapter.
The corollary to this relation is that MAC necessitates the same level of care as general anesthesia. Clinicians may be lulled into a rather lackadaisical approach to MAC, precisely because the patient is supposed to be awake, or at least easily arousable. Drugs are continually administered, “the sedated patient lies quietly, and the shallow, paradoxical movements escape critical notice, but death steps in suddenly, peacefully, naturally, and unnecessarily.”9 Such unanticipated general anesthesia should be avoided at all costs.
Although a fundamental principle of MAC is that the patient generally should remain conscious, if deep sedation or a transient period of general anesthesia is deemed necessary, only practitioners who are credentialed or privileged to provide anesthesia services should manage the case. Deep sedation, intentionally or not, can transit to general anesthesia, necessitating an anesthesia provider who is capable of managing the anesthetic state and converting it back again to the level of sedation. However, to reiterate the same point made earlier, the mere presence of such an individual does not guarantee this outcome. Constant vigilance is essential, as is emphasized by the ASA Seal in which it is described thusly:
“The patient is represented as … sailing in the troubled sea with the clouds of doubt and waves of terror being guided by the skillful … anesthesiologist with constant and eternal … vigilance … by the dependable… knowledge of the art and science of sleep… a safe … and happy outcome of his voyage through the realms of the unknown. The perfect circle denotes the unity of a closed group (the Society).10”
Monitored anesthesia care necessitates postprocedure responsibilities beyond those of moderate sedation, insuring a return to full consciousness, relief of pain, management of the side effects from medications administered during the procedure, and the management of coexisting medical problems.”
What Problems May Be Anticipated Preoperatively?
▪ GENERAL CONSIDERATIONS
The initial step is to determine if MAC is appropriate for the patient and the surgeon. The preanesthetic (pre-MAC) assessment should be no less comprehensive than that for a patient undergoing general or regional anesthesia. In some respects, one can argue, it should be more extensive. MAC often is chosen for patients with significant health problems, perhaps because the practitioner believes the technique poses less of a risk than a more complex anesthetic and, therefore, has the greatest margin of safety. However, in a large-scale study, MAC was associated with the highest incidence of 30-day mortality.11 Indeed, this finding may have reflected a bias in which patients with significant coexisting disease were selected preferentially for surgery with MAC.
In a previous analysis of MAC malpractice cases in the ASA Closed Claims Project, the proportion of claims for death in MAC cases was similar to general anesthesia claims, but twice as high as in regional anesthesia claims.4 Complications that occurred during MAC are shown in Table 63.2. Brain damage had a higher frequency in MAC than in general or regional anesthesia. Inadequate oxygenation and ventilation were the most common damaging events. MAC patients were generally older and sicker than patients in the other categories. Patients were undergoing ophthalmologic and plastic surgery procedures more often with MAC than with general anesthesia or regional block. This observation perhaps reflected the feeling that MAC patients were older and sicker than other
patients and therefore were assigned to MAC rather than to the perceived more complex anesthetic procedures. Oversedation leading to respiratory depression was an important mechanism of patient injuries during MAC. Appropriate use of monitoring, vigilance, and early resuscitation could have prevented many of these injuries.4
patients and therefore were assigned to MAC rather than to the perceived more complex anesthetic procedures. Oversedation leading to respiratory depression was an important mechanism of patient injuries during MAC. Appropriate use of monitoring, vigilance, and early resuscitation could have prevented many of these injuries.4
TABLE 63.2 American Society of Anesthesiologists (ASA) Closed Claims Project Analysis of Injury from Monitored Anesthesia Care (MAC) (n = 83 Claims) | ||||||||||||||||||||||||||||||||||||
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Although MAC can eliminate some undesirable effects of general or neuraxial anesthesia, it may not suppress the stress response. If the local anesthetic block is less than satisfactory or fails, MAC can result in an increased incidence of myocardial ischemia and cardiac dysfunction. To achieve the desired effect, the anesthesiologist may administer an excess of sedative and analgesic drugs, leading to the possibility of depressed oxygenation and ventilation. These potential risks should be considered during the pre-MAC assessment. In such cases, selection of general or regional anesthesia may be preferable.
Elements to be considered are identical to those for other anesthetics, such as the patient’s general medical history and prior anesthetics, in particular whether the patient has undergone MAC on other occasions. In addition, medications and any known allergies to medications should be documented, as should the use of tobacco, alcohol, illicit drugs, and over-the-counter herbal preparations. Physical examination should include a comprehensive airway assessment. The tendency in MAC cases may be to perform a perfunctory airway examination, or none at all, because the practitioner does not intend to intubate the trachea or use a face mask. However, as seen in the case at the beginning of this chapter, failure to assess the airway can represent a dangerous omission. The 8- to 9-minute delay in establishing an airway (it actually was 12 minutes from the time of respiratory arrest) might have been anticipated had the airway examination been properly conducted.
Ophthalmologic procedures, such as cataract phacoemulsification and intraocular lens placement, make up a large percentage of MAC cases in many hospitals and clinics. The patients tend to be older, often in their eighth decade, with diseases attendant to increasing age. We have cared for two noteworthy examples in the last 5 years. Both patients experienced postassessment, preprocedure, myocardial ischemia that led to cardiac arrest in one patient and profound hypotension in the other. Neither patient had a prior documented history of coronary artery disease. Both were rushed to the cardiac catheterization laboratory after resuscitation and were found to have significant four- and five-vessel coronary artery disease. Emergency coronary artery bypass surgery was performed, and the patients survived.
Certainly a vast majority of such patients undergo the same ophthalmologic procedures without these complications. But how many of them are prone to these complications? And would more comprehensive pre-MAC assessment reduce the morbidity or even mortality? Returning again to the patient described in this chapter, the telltale signs of potential difficulty, including recurrent episodes of significant and documented bradycardia, were present on numerous occasions before his colonoscopy. However, neither the endoscopist nor the CRNA paid more than lip service to them. This procedure was completely elective, and assessment by a cardiologist ahead of time would, more probably than not, have led to interventions that should have prevented the devastating outcome.
▪ SPECIFIC CONCERNS
During assessment, the anesthesia provider should determine several things. First, can the patient lie still while undergoing surgery with MAC? Slight movement generally is not a major problem for removal of skin lesions, but it may be critical during ophthalmologic surgery with an open globe. Second, can the patient assume whatever position is necessary to accomplish the surgery? Degenerative joint disease may prevent assumption of the required position because of lack of mobility or pain. A morbidly obese patient likely will have difficulty lying prone for a protracted period of time. Third, does the patient have problems with coughing and expectoration of oral and bronchial secretions? The same problems involving an open globe surgical procedure apply in this situation. Fourth, can the procedure reasonably be performed under MAC? More extensive surgical procedures are being performed with MAC nowadays than were common in the past.12,13,14 (In some cases, the procedures did not exist in the past). However, the fact that a procedure can be performed with MAC does not necessarily mean that it should. The anesthesia provider should be reasonably sure that his or her skills are up to the task of supporting the patient for a complex procedure lasting a significant time. A yes answer to any of these questions may indicate the need to reassess the proposed MAC and to consider the relative merits of conversion to a general anesthetic.
Oxygen Administration and the Risk of Operating Room Fires
Oxygen is administered to many, if not most, patients undergoing MAC. Normally, such therapy causes no problems. However, if the surgery is conducted on the head, neck, and upper chest (plastic surgery and ENT are two prime examples), oxygen can be problematic because of the risk of fire in and around the operative site.15,16 The anesthesia provider should ascertain preoperatively whether the patient requires oxygen because of the associated disease and, if so, how much? Low oxygen flows can be concentrated because of surgical draping that prevents free egress of oxygen from the operative field to the ambient environment.
In this setting, the essential elements to produce a fire are present: An ignition source, such as an electrocautery unit (responsible for 68% of operating room fires) or laser (responsible for 13% of operating room fires); a source of fuel, including surgical drapes, skin, hair, flammable preparatory agents17,18; and an oxidizer (oxygen, nitrous oxide, medical air). Substances such as polyvinylchloride that will not burn in ambient air will burn in a 26% oxygenenriched environment, whereas others, such as red rubber medical products, will burn in <21% oxygen.19
TABLE 63.3 Ignition Sources, Oxidizers, and Fuels in the Operating Room | |||||||||
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