INTRODUCTION

Ambulatory anesthesia is one of the more common adjunctive procedures performed by an oral maxillofacial surgeon (OMS) in private or academic practice. Anesthetic states ranging from mild sedation to general anesthesia are achieved, mainly through the use of intravenous agents but occasionally with inhalational agents as well. When indicated, the provision of anesthesia can greatly facilitate many dentoalveolar and other outpatient surgical procedures, and often enhances patient comfort and satisfaction as well as surgeon efficiency. Ambulatory anesthesia is frequently recommended to patients as an adjunct for particular procedures such as third molar removal, and many patients request anesthesia regardless of the planned surgical procedure. In the special case of pediatric patients, where patient cooperation can be unreliable and anxiety is frequently at a high level, the utility of ambulatory anesthesia can be even greater. In both children and adults, ambulatory anesthesia allows for more procedures to be performed in an outpatient setting that would otherwise require a trip to the operating room.

Given the many benefits of outpatient anesthesia, it is not surprising that a great number of anesthetics are performed each year by OMSs in outpatient settings. Adjunctive anesthesia is provided to thousands of patients per year, and the number of complications reported during the provision of ambulatory anesthesia remains quite low—less than 1% of anesthetic cases.¹ Of these reported complications, serious adverse events make up an even smaller number. Much conscientious effort has gone toward ensuring the safety of ambulatory anesthesia, particularly in the areas of surgeon training, prevention, patient monitoring, and emergency protocols. While OMSs can exhibit confidence in the use and safety of ambulatory anesthesia, we must also maintain a high level of vigilance in order to prevent anesthetic complications and appropriately manage them in the cases when they arise.

Many OMSs who provide anesthesia in an outpatient setting also perform surgery in a hospital operating room (OR), and there is frequently overlap in the types of surgical procedures that are performed in either setting. However, there are some notable differences in the anesthetic as it is conducted in the OR versus an outpatient facility. In the OR, the anesthesia is nearly always provided by someone other than the surgeon—an anesthesiologist or certified registered nurse anesthetist (CRNA). This allows the surgeon to focus single-mindedly on the surgery at hand. In contrast, in outpatient anesthesia, the OMS typically acts as surgeon-operator, or the “operator-anesthetist” model, providing both the anesthesia and performing the surgery simultaneously. Support for this dual role of the OMS can be gleaned from data demonstrating a very low incidence of anesthetic-related complications in outpatient settings where surgeon-operators administered the anesthesia.¹ The administration of outpatient anesthesia requires extra attention from the surgeon who must monitor both the anesthesia and the surgical procedure simultaneously. Maintaining this balance of attention can be challenging and may require a different set of skills than those utilized in the OR.

Other important differences between anesthesia administered in the OR and ambulatory anesthesia can contribute to the relative safety of outpatient anesthesia. Two important factors are the greater risk and complexity of surgical procedures performed in an OR setting, and the greater distribution of lower-risk patients (ASA I and II) in outpatient settings versus higher-risk patients (ASA III and above) who may be treated more frequently in the OR setting. These factors emphasize that careful patient and procedure selection contribute to the prevention of complications in outpatient anesthesia.

Lastly, emergency equipment and equipment available for patient monitoring is often more extensive in the OR than outpatient setting, though this difference is decreasing in large part due to the decreasing cost of equipment and technology. Certain invasive modes of patient monitoring, such as arterial or central venous lines, remain confined to the operating room; however, many of the same modalities of monitoring cardiac and respiratory function exist for both OR and outpatient use. In addition, the emergency equipment of the OR has been feasibly reproduced for efficient use in an outpatient setting. The OR, by virtue of being located within the hospital, will retain an advantage in terms of emergency preparedness, access to trained staff, blood and tissue products, and specialist consultation. However, anesthesia in the OR setting can have increased risk due to increased complexity of surgical procedures and/or higher-risk patient populations. These differences are important for the OMS who treats patients in both settings because they have important implications for the prevention and management of anesthetic complications.

PREVENTION OF COMPLICATIONS IN AMBULATORY ANESTHESIA

Patient Characteristics/Selection

The best and most effective management of anesthetic complications is to prevent their occurrence. There is well-documented evidence that certain perioperative patient characteristics contribute significantly to anesthetic and surgical risk. Some of these characteristics, such as patient age, are easy to quantify and have fairly predictable patterns of anesthetic risk. Other patient characteristics such as underlying medical conditions, medications, previous surgical history, allergies, cardiac and respiratory reserve, and body mass index can be more difficult to assign risk. A detailed history and physical examination with appropriate preoperative laboratory workup and communication with the primary care physician are paramount in identification of those patients who may safely undergo anesthesia in an outpatient setting.

Several algorithms and systems of classifying anesthetic risk based on patient characteristics are in common use, with the ASA (American Society of Anesthesiology) criteria being among the most widespread (see Table 1.1). The utility of the ASA classification has been shown in scientific literature that demonstrates a clear association between ASA status (I–V) and the risk of anesthetic complications.² The ASA classification is widely recognized and simple to use, and it is a valid starting point into which other patient risk determinants can be incorporated. The Duke Activity Index is another useful measure of a patient’s physical status. It presents a functional assessment of physical capacity based on an individual’s exercise tolerance and ability to perform various activities of daily living (see Table 1.2). The ability to engage in exercise or everyday physical activities is inversely correlated with risk of anesthetic complications and provides an additional parameter for patient screening.

Table 1.1. ASA Physical Status Classification

NIDDM: non-insulin-dependent diabetes mellitus; IDDM: insulin-dependent diabetes mellitus; CVA: cerebrovascular accident; MI: myocardial infarction; CHF: congestive heart failure; COPD: chronic obstructive pulmonary disease; DM: diabetes mellitus; HTN: hypertension

Table 1.2. Duke Activity Scale Index

An adjunctive measure of patient risk for ambulatory anesthesia includes specific classification of the airway. Mallampati’s classification is a simple visual classification system, divided into four categories, which attempts to assess the posterior oropharyngeal airway patency based on the visibility of structures of the posterior oropharynx (uvula, fauces, soft and hard palates). The distance between the hyoid bone and the chin can be estimated as an additional, albeit crude, indicator of airway patency and ease of intubation with shorter mental-hyoid distances indicating greater airway risk. In addition, specific characteristics of patient body habitus such as obesity or the presence of a short, thick neck can be general predictors of risk of airway collapse during anesthesia.

Obesity, defined as a body mass index greater than 30, is a recognized risk factor for complications related to anesthesia. Obesity is associated with a decreased respiratory functional residual capacity (FRC) and can lead to an increased incidence of respiratory complications, particularly airway collapse and desaturation. Obese patients have a fourfold increased risk of respiratory complications during ambulatory anesthesia procedures.³ In the pediatric population as well, obesity has been recognized as a growing problem. A study by Setzer et al. found an increased incidence of respiratory complications and unexpected overnight hospital admission in a group of obese pediatric patients undergoing ambulatory anesthesia for dental surgery procedures (compared to their nonobese counterparts).⁴ Patient positioning during surgery may play a role in preventing adverse respiratory complications in obese patients, as a recent study demonstrates an increase in time to desaturation in obese patients who were preoxygenated in an upright (90-degree sitting) position prior to induction of general anesthesia.⁵ Maintaining obese OMS patients in an upright position during anesthesia may help to prevent respiratory complications by maximizing FRC and minimizing the effects of gravity on posterior oropharyngeal airway collapse.

Age is also an important determinant of anesthetic and surgical risk. Age is easily quantified and there is evidence that increased risk of complications occur at the extremes of very young and very old age. There is greatly increased risk associated with anesthesia and surgery in the first one month and one year of life.⁶ In terms of increasing age and risk of complications, there remains a strong positive correlation though the association is more gradual and progressive. In the very young, much of the increased anesthetic risk can be attributed to the relative anatomical and physiological immaturity of infants and very young children. This makes the mechanics of anesthesia more difficult (airway management, fluid replacement, patient monitoring) while the decreased therapeutic index of anesthetic drugs in small children greatly increases their toxic potential. At the other end of the spectrum, advanced age leads to an increase in medical com­orbidities and decreased physiological reserve from the normal aging process. This likewise decreases tolerance for physiologic insults and lowers the therapeutic index of many drugs and interventions.

Aside from patient characteristics, another factor that can help prevent complications in the postoperative period is to ensure that patients will have a responsible adult who can accompany them home and care for them after the anesthesia and surgical procedure.⁷

Procedure Characteristics/Selection

In addition to appropriately screening patients for in-office procedures, it is also important to bear in mind the surgical complexity and length of time needed for the planned procedure. Certain procedures, such as third molar removal, are nearly always performed in an outpatient setting. Other surgical procedures, such as minimally invasive temporomandibular joint procedures (TMJ arthroscopy) and extensive bone grafting or implant procedures, can be performed either in the OR or in an outpatient setting. This is largely dependent upon the preference of the surgeon and patient, the availability of appropriate instruments and equipment, as well as financial issues. The most important consideration in preventing complications is to ensure that the surgical procedure planned is not more complex or lengthy than can be accommodated in a particular outpatient setting. Patient risk factors and procedure risk factors should be balanced such that longer and more complex procedures are avoided in patients who already represent increased surgical risk. Complex or lengthy procedures may benefit from having an additional practitioner or trained person to assist with the anesthetic management of the patient. This will help to offset some of the increased attention required for the surgery itself. With proper planning, a majority of routine OMS surgical procedures can potentially be accomplished in an outpatient setting.

Patient Screening

The goal of patient selection for ambulatory anesthesia procedures is to determine a particular patient’s risk factors for anesthesia and to identify those patients who may safely undergo the procedure in an outpatient setting. The first step is to perform a comprehensive history and targeted physical exam. Information to be elicited includes prior anesthetic experiences, prior hospitalizations, emergency room visits, prior surgeries, allergies or adverse reactions to any medications, and any and all medications taken (including over-the-counter medications and vitamins or herbal supplements). Herbal medications are surprisingly common (taken by almost 25% of patients) and garlic, ginkgo biloba, and ginseng (the “three Gs”) may be particularly risky when taken perioperatively as they affect platelet function and may increase bleeding risk.⁸

A review of systems can ascertain whether a patient has any undiagnosed medical conditions that could impact the planned anesthetic procedure. In particular, questions designed to elicit underlying respiratory, neurologic, or cardiac disease are especially important. A history of snoring, allergic rhinitis, wheezing, shortness of breath (exertional or spontaneous), and recent upper or lower respiratory infections can provide important information about the possible risk of respiratory complications. Certain medical conditions and risk factors to look for include history of asthma, chronic obstructive pulmonary disease (COPD), and tobacco use. Chung et al. identified asthma with a fivefold increase in respiratory complications during ambulatory anesthesia, and smoking carries an increased fourfold risk.³ Patients with COPD have twice the risk of respiratory complications during ambulatory anesthesia.⁹ Ascertaining a patient’s exercise tolerance can provide a great deal of information as well, including signs and symptoms of respiratory or cardiac disease, as well as musculoskeletal complaints or any limitations in range of motion. In patients who do not engage in regular exercise, one can substitute questions about activities of daily living such as walking several blocks, climbing more than one flight of stairs, grocery shopping, doing several loads of laundry, or performing vigorous housework.

It can be helpful to obtain a family history, particularly from patients who are young or present with few medical history findings, especially to ascertain whether anyone in the patient’s immediate family has ever had an adverse event related to anesthesia, an unusual genetic illness, congenital heart defect, or premature or sudden unexpected death. Asking about a history of tobacco, alcohol, and illicit drug use is important. In a patient who drinks alcohol regularly, asking about usual intake and effects (e.g., drowsiness, tipsiness) can sometimes provide a crude indication of response to anesthesia. Vital signs should be recorded for every patient prior to the day of the planned procedure as they are helpful for establishing a particular patient’s baseline. For example, this may help to differentiate a patient who, on the day of surgery, develops hypertension as a result of anxiety from a patient whose baseline blood pressure is usually elevated.

The history and physical exam forms the basis for deciding whether a patient will need further testing or evaluation prior to the anticipated anesthetic. Further evaluation can take many forms, including laboratory testing, ECG/chest radiography, or consultation with the patient’s physician including referral to specialists as needed. Patients who give a complex medical history with multiple chronic conditions, recent surgeries or hospitalizations, multiple hospitalizations in the past year, clearly warrant further testing and consultation with the patient’s physician. These types of patients are obviously at higher risk and may or may not represent suitable candidates for outpatient anesthetic procedures. Of more concern, however, may be those patients whose risk for outpatient anesthesia is unclear or unknown. In this case, the role of laboratory testing and other investigations is to clarify whether the patient may be safely sedated in an outpatient setting. Patients who give an unclear or ambiguous medical history obviously fall into this category, as do patients with several positive findings in the review of systems or patients with chronic medical conditions that appear to be poorly controlled. In addition, one should approach cautiously patients who report no medical problems and who have not had a routine medical exam within the past three years or longer, particularly if they are middle-aged or older, or have other obvious medical risk factors. Patients such as these may have undiagnosed medical conditions that could greatly impact the safety of the planned outpatient procedure.

A diversity of laboratory tests may be ordered for a patient, but for routine use, relatively few are necessary. A complete blood count (CBC) and basic metabolic panel represent two of the most common basic laboratory tests. The CBC can give information about the presence of infection or inflammation (elevated white blood cell count), the relative proportions of blood cells, the presence of anemia (hemoglobin and hematocrit) and type (red blood cell size and morphology), and verify an adequate number of platelets for hemostasis. The CBC does not provide information about platelet function or the clotting ability of blood for which a partial thromboplastin time (PTT) and prothrombin time (PT, commonly reported as an international normalized ratio, or INR) are needed. A bleeding time test will give information about platelet function, but it is infrequently used. The basic metabolic panel will provide information about electrolyte and acid/base balance as well as renal function [blood urea nitrogen (BUN) and creatinine levels], and may be substituted by a complete metabolic panel that also includes markers of liver function (typically, aspartate and alanine transaminase liver enzyme levels). Markers of renal and liver function should be considered for patients with diabetes, liver, or kidney disease as they can indicate the progression of disease as well as the potential need for modification of anesthetic drug dosages. In women of reproductive age, some practitioners will also order a beta-human chorionic gonadotropin test (B-HcG) to verify a patient’s pregnancy status. A serum B-HcG is more sensitive, but urine B-HcG tests are less expensive and easy to administer. If a B-HcG will not be performed for a patient, it is important to ask about the possibility of pregnancy and document the conversation in the patient record. Laboratory tests performed within the preceding 30 days are generally considered recent enough and do not necessarily need to be repeated. Patients with more rapidly changing conditions, such as patients taking warfarin, will need more recent laboratory tests. B-HcG tests, if indicated, are ideally performed within 1 week of the scheduled anesthetic.

Special considerations exist for preoperative screening of patients with known or suspected cardiovascular disease. Cardiovascular disease is increasingly common and cardiovascular complications of anesthesia are among the most serious. Basic methods of screening for cardiovascular disease include the standard 12-lead ECG and chest radiography. More advanced diagnostic methods include echocardiography and cardiac stress testing. Depending on the institution and surgeon preference, some oral maxillofacial surgery practices routinely order ECGs and chest radiography for patients over a certain age. Sometimes this practice is restricted to patients who are scheduled for OR procedures and sometimes it extends to outpatient anesthetic procedures as well. For low-risk procedures in ASA I (and most ASA II) patients for whom a detailed history and physical exam have been performed, an ECG and chest radiograph are largely unnecessary. Cardiac testing may be considered for patients with clinical risk factors for cardiac complications, as assessed by the American College of Cardiology and American Heart Association in the 2007 Revised Cardiac Risk Index. These factors include a history of ischemic heart disease, compensated heart failure or prior heart failure, cerebrovascular disease, diabetes mellitus, or renal insufficiency.¹⁰ Minor predictors of cardiac risk include being over 70 years of age, uncontrolled hypertension, abnormal ECG, and nonsinus rhythm, but these have not demonstrated utility as independent markers of cardiac risk during noncardiac surgery.¹⁰ A patient’s functional capacity as measured by “metabolic equivalents” is an important parameter assessed in the 2007 ACC/AHA guidelines on perioperative cardiovascular evaluation. Patients who have poor functional capacity represent a greater risk of cardiac complications than those with good functional reserve. The 2007 ACC/AHA guidelines recommend 12-lead ECG testing and noninvasive stress testing for asymptomatic patients with cardiac risk factors who will undergo intermediate-risk surgical procedures or vascular surgery, but are typically not recommended for low-risk surgeries such as ambulatory surgery. The guidelines were developed based on level of evidence from the professional literature indicating a clinical advantage to preoperative intervention in various patient groups prior to noncardiac surgery.

If additional testing is indicated, the patient’s physician should be contacted prior to the planned anesthetic, as patients may have had an ECG or other cardiac test performed recently. Chest radiographs or ECGs that are abnormal are always an indication for further investigation, though further testing may not be needed. If previous ECGs or chest radiographs show an abnormality that has remained stable with time and if the patient’s physician has indicated this, further testing is unlikely to change the clinical assessment. However, any abnormal finding that is new or has progressed from previous test results should result in follow-up with the patient’s treating physician and additional testing as indicated.

Preoperative testing can help to identify abnormalities and quantify the level and type of disease a patient may have, but the clinician must ultimately gather this data and interpret it in a clinically useful manner. Several algorithms and classification schemes have been developed to aid in converting clinical data into a measure of anesthetic risk that can aid the surgeon in determining the relative risk of a particular patient for undergoing an outpatient anesthetic procedure. One of the most popular, the ASA classification, has already been mentioned. Several risk stratification schemes exist for cardiovascular risk factors in particular, including the most recent guidelines from the American College of Cardiology and the American Heart Association (described above).

Preoperative patient screening not only helps to identify those patients who represent a poor risk for outpatient anesthesia, but for low- and moderate-risk patients it can help to identify any patient-specific risks and aid in planning ahead.

Intraoperative Patient Monitoring

Technological advances have produced an increasing number of new and improved devices for the intraoperative monitoring of patient vital signs and sedation level. Patient monitors not only provide peace of mind that the patient is stable, but they can also provide an early warning when complications begin to occur. Ideally, effective intraoperative monitoring can allow for potentially serious situations to be recognized early and effectively managed. Basic measurements during outpatient anesthesia include pulse oximetry, a heart rate monitor, and intermittent blood pressure monitoring. Additional monitors can include capnography, BIS (bispectral monitoring), and a precordial (esophageal) stethoscope.

Pulse Oximetry

Pulse oximeters are designed to estimate blood oxygen saturation and work via measurements of infrared energy transmission. In smokers, pulse oximetry readings may be artificially increased due to the level of carboxyhemoglobin present in the circulation. This is especially true for those who have smoked tobacco within a few hours of the anesthetic procedure. The pulse oximeter cannot distinguish between carboxyhemoglobin and oxygen-carrying hemoglobin in the blood of smokers and thus provides an overestimate of the true blood oxygen saturation.

The reading provided by pulse oximetry is a good approximation of blood oxygen partial pressure, and 90% oxygen saturation is the standard cut-off value below which desaturation begins to have noticeable clinical effects. There is a time delay between a patient’s true oxygen saturation and the pulse oximeter reading, and many oximetry machines will sound an alarm when a patient’s oxygen saturation reading drops below 93% or 94% to allow for this. Most healthy adults will have an O₂ saturation of between 98% and 100% on room air, but occasionally patients with underlying respiratory compromise will have a baseline O₂ saturation of 94–95%. It can be important to know this prior to beginning a procedure to avoid the erroneous assumption that a patient with a low baseline O₂ saturation is experiencing respiratory depression as a result of anesthesia.

Heart Rate and Rhythm Monitoring

A simple heart rate monitor will be sufficient in many circumstances; however, a 3-lead or 5-lead ECG monitor will provide a tracing of the cardiac rhythm, which can be indispensible if a complication arises that involves a cardiac arrhythmia, cardiac depression, or ischemia/infarction.

Blood Pressure

Blood pressure readings should be taken, at a minimum, both before and after an anesthetic procedure as well as prior to discharge. An automatic blood pressure cuff that can be set to take readings at different time intervals [noninvasive blood pressure (NIBP)] is an efficient choice. Routine interval blood pressure measurements are useful in all patients because even low-risk patients may experience anesthetic complications involving blood pressure changes. In higher-risk patients, blood pressure monitoring is especially important, particularly when there is concern about hypertension, hypotension, or changes in cardiac output.

Capnography

Capnography devices utilize a chemical probe that measures the level of expired carbon dioxide and can be used to monitor respirations. Capnography has been extensively utilized in the OR but much less frequently in outpatient settings. It can be extremely useful, however, as it provides a measure of tidal volume, respiratory rate, and respiratory depth. While it does not provide an estimate of blood oxygen saturation, it is more sensitive than pulse oximetry for detecting respiratory depression and apnea.

Precordial (Esophageal) Stethoscope

The precordial or esophageal stethoscope is a bell-type stethoscope that is placed on the pretracheal region of the patient’s chest. By listening through one or two earpieces, or using a speaker system, a practitioner can auscultate a patient’s respirations and will be immediately alerted to any change in respiratory rate, depth, or quality. While this method of intraoperative monitoring is sensitive, it does not appear to be particularly popular among OMSs. The study by D’Eramo reported only 36% of practitioners used a precordial stethoscope, compared to a 93% utilization rate for blood pressure and pulse oximetry monitoring.¹ The stethoscopes become less reliable in situations of increased ambient noise or excessive patient movement that can displace the bell of the stethoscope. Nevertheless, the esophageal stethoscope can provide additional clinical information regarding a patient’s respiratory status. It may be most useful when treating small children (or others at increased risk of rapid respiratory compromise) and obese patients, in whom it can sometimes be difficult to observe chest rise and other signs of ventilatory effort.

Bispectral (BIS) Monitor

Of the available patient monitors, the BIS monitor is unique because it quantifies the level of anesthetic sedation at the level of central nervous system (CNS) activity. Consisting of an adhesive strip that is positioned on the forehead and a monitor that reads EEG activity, the BIS monitor is typically used in an OR setting. It can help to determine a patient’s level of sedation and is useful for maintaining a desired level of anesthesia. It is also useful for accelerating emergence from anesthesia. There is some suggestion that the BIS monitor may increase patient safety by decreasing the amount of anesthesia given while also minimizing complications of anesthesia that is too light. However, most of the benefit of the BIS monitor may be outweighed by the cost of the system.

Personnel Preparedness

Specific guidelines, in addition to individual state law specifications, regarding the appropriate number of personnel and specifics of their training requirements when administering outpatient anesthesia exist and should be adhered to strictly. Familiarity with the equipment used for monitoring, as well as emergency equipment and setup, medications, and dosages, are crucial for administrat/>