History of ambulatory anesthesia

The origins of anesthesia began with a series of events in the mid 1800s. While training in New York City, Crawford Long experienced the recreational use of ether and nitrous oxide during student parties: the so-called “ether frolics”. After starting his practice, he applied the use of diethyl ether to anesthetize a patient during removal of two small tumors from a man’s neck in 1842. He did not publish his methods until 1849, several years after the use of nitrous oxide was reported by Horace Wells and the first successful public demonstration of nitrous oxide by William T.G. Morton in 1846. These pioneers set the stage for the rapid integration of anesthesia into surgical practice, which proceeded over the latter half of that century.

Shortly after World War I, with increasing popularity of office-based surgery, the utilization of a dedicated anesthesiologist in the office setting was first described by Ralph Waters in 1919. He described his experiences administering anesthesia in the surgeon’s office, where his responsibilities included supplying the operating room, recovery room, and his private doctor’s “loafing and smoking room”. He recognized the financial potential of his situation, and noted that success was intimately tied to the satisfaction of the surgeon.¹

Later in the mid-20th century, with rising costs and inefficiency of inpatient care and increasing shortage of hospital beds, there was significant transition to outpatient surgery. In an effort to maximize patient throughput, cut costs, and maximize reimbursement, John Ford and Wallace Reed designed the first freestanding ambulatory surgicenter in Phoenix, Arizona in 1969. Most cases in this facility were performed under general anesthesia. Based on their drive for efficiency, this stimulated the development of anesthetic regimens and postoperative medications that would allow patients to return home sooner. These techniques continue to evolve today.

Over 60% of all surgical procedures performed in the US are in an ambulatory setting. In aesthetic surgery, the vast majority of procedures are performed in the outpatient or office setting. Functional knowledge about of the practice of anesthesia and how it can be applied to the aesthetic surgeon’s practice is vital to success.

Preoperative evaluation – patient safety

Ambulatory anesthesia has evolved as a means of convenience, efficiency, and cost cutting to surgical practice. However, a critical determinant in these benefits is patient selection and safety. The objective of preoperative evaluation is to manage risk – to identify patients who are at low risk, and to reduce these risks at the time of surgery. In some cases the risk of anesthesia is equal to or greater than the surgical procedure at hand. There is no consistent classification of preoperative risk, but particular attention to details of the patient’s history, physical exam, and other diagnostic screening tools can determine whether surgery should be deferred while pre-existing medical conditions are addressed.

The objective of anesthesia is to maintain a state of physiologic homeostasis during the stress of surgery. The physiologic response to surgery is similar to the “fight or flight” response, altering blood flow from non-vital organs to the brain and heart. In order to maintain homeostasis, preoperative determination of cardiac reserve, ability to exchange oxygen, and patient factors which may negatively impact these processes must be known. To this end, the Rule of Threes can simplify the approach to preoperative screening and focus practitioners on the aspects of the history and physical exam which influence patient outcomes in the perioperative period (Table 3.1).² Exercise tolerance approximates cardiac reserve, and can be approximated using metabolic equivalents (METs). Several studies have demonstrated that the ability to do four or more METs correlates to improved perioperative outcomes. Walking five city blocks, climbing two flights of stairs, running over short distances, and participating in moderate recreational activity (i.e. dancing or golf) without the need to stop for rest is the equivalent of four METs.

Table 3.1 The Rule of Threes

From Miller RD. Miller’s anesthesia, 6th edn. New York: Elsevier/Churchill Livingstone, 2005.

As there is no reliable classification system of preoperative risk, a standardized approach to data collection in the preoperative period can facilitate decision making throughout the patient’s course. The initial collection should happen shortly after the decision to proceed with surgery in the surgeon’s office. In addition to medical history pertinent to the specific surgical procedure, a standard set of questions designed to identify risk factors should be answered, such as those found in the Preoperative and Preprocedure Assessment Clinic (PPAC) Form.² The physical exam should be similarly structured and standardized with some notable additions. Airway assessment is performed according to the Mallampati airway classification based on observations of oral structures visible with tongue maximally protruded, which correlates to ease of intubation (Table 3.2). Additional factors to consider which may limit airway visualization are a short neck, limited cervical spine mobility, poorly mobile or retruded mandible.

Table 3.2 Mallampati airway classification system

Based on the history and physical, patients are broadly classified according to their medical fitness. The current classification system endorsed by the American Society of Anesthesiology (ASA) is a modification of the Saklad classification developed in the 1940s. Useful more as a global assessment of preop status rather than a measure of risk, the ASA system classifies patients based on the presence of medical illness (Table 3.3).

Table 3.3 ASA classification system

Following a focused history and physical intake, surgeons must then determine the need for additional preoperative screening tests. The tendency of surgeons is to order a large range of ancillary tests, some of which are not necessarily indicated, in an effort to have any conceivable test result available to the anesthesiologist on the morning of surgery. This poses several potential problems. Testing not indicated by medical history may lead to treatment of borderline abnormalities, which may result in patient harm and distress. In addition, since most preoperative abnormalities are not documented in the chart, the failure to investigate abnormal tests is a greater risk of medico-legal liability than the failure to detect it in the first place. Therefore, the guidelines published by the American Society of Anesthesiologists (ASA) summarized in Table 3.4 should be utilized to determine the need for additional preoperative screening tests. In addition, preoperative evaluation should include tests relevant to the type of surgery being performed. For instance, if intraoperative and postoperative bleeding is a significant risk, then a baseline hematocrit should be included in the preoperative work-up.

Table 3.4 Guidelines for preoperative screening tests (based on ASA standards)

Adapted from American Society of Anesthesiologists. Practice advisory for preanesthesia evaluation: a report by the American Society of Anesthesiologists Task Force on Preanesthesia Evaluation. Anesthesiology 2002;96:485–496.

Based on current practice, patient assessment by the anesthesiologist frequently occurs on the morning of surgery. While adequate for the majority of patients without significant medical co-morbidity or risk factors, there is a select group of patients with significant medical problems or preoperative risk that would benefit from an evaluation well before surgery. It is the role of the surgeon to identify these patients and ensure they receive a focused assessment by an anesthesiologist to minimize their operative risk prior to the morning of surgery (Table 3.5). Failure to do so may result in case cancellation which is frustrating for all parties involved.

Table 3.5 Indications for preoperative anesthesia evaluation prior to day of surgery (based on ASA standards)