᭜ EDITORIAL VIEWS Anesthesiology 2002; 96:1039–41 © 2002 American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins, Inc. Perioperative Risk How Can We Study the Influence of Provider Characteristics? IN the 20th century, the medical community was in- prove outcome.7–10 The relatively high probability of tensely interested in understanding the factors associ- death associated with patient disease has allowed the ated with perioperative risk. In the current issue of majority of these studies to be performed in a single 1 ANESTHESIOLOGY, Silber et al. have added to this literature center or a small group of centers. and studied the influence of anesthesia provider charac- Although most of the research has focused on identi- teristics on outcome. fying and minimizing the impact of patient disease, in- One of the earliest systematic analyses of the factors creasing attention has been given to the two other com- Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/96/5/1039/404427/7i0502001039.pdf by guest on 27 September 2021 associated with perioperative risk occurred in 1935 ponents of perioperative risk: surgery and anesthesia. when Ruth helped to establish a commission to analyze Because of the lower probability of death associated perioperative deaths.2 The commission relied on volun- with these two factors, a different methodologic ap- tary submission of cases and determined the cause of proach is often needed. Single-site studies are frequently death by majority vote. This methodology was deemed not feasible, and assessments of cause of death by indi- inadequate in subsequent studies. vidual clinicians may not be appropriate. Because death A major advance in the analysis of perioperative risk is less common, outcomes other than death may be was the report by Beecher and Todd3 of the factors studied to obtain a statistically reliable number of adverse associated with anesthetic death in 10 institutions, pub- events. This approach has particularly been used with re- lished in 1954. Their study reviewed the administration spect to the development of clinical predictors of cardiac of 599,548 anesthetics to patients with a wide range of events, including nonfatal myocardial infarction.7,11 diseases. The cause of mortality was determined at the Although investigators have continued to rely on mul- local institution by consensus of a surgeon and the chief ticenter studies, the problem has increasingly been stud- anesthetist of the institution. Although the methodology ied through the use of administrative data sets.12 Exam- for assigning the cause of death was criticized as being ples of administrative databases include Medicare claims arbitrary, the major contributions were the recognition files, private insurance company claims, and hospital that there are three major causes of death in the periop- electronic records. These databases have a limited erative period and the quantification of these risks. They amount of data for an extremely large number of sub- found that a patient had an overall chance of mortality of jects. For example, the Medicare database includes both 1 in 75 cases in the perioperative period. Anesthesia was financial data and ICD-9 (disease) and CPT (procedure) reported as the primary cause of mortality in 1 in 2,680 codes for each patient. They also include information cases, and was either the primary or contributory cause regarding location of care and provider. of mortality in 1 in 1,560 cases. Surgical error in diagno- Administrative data sets have been used to derive risk- sis, judgment, or technique was the primary cause of adjusted provider specific mortality. For example, New death in 1 in 420 cases, and patient disease was the York and Pennsylvania have used this type of data to primary cause in 1 in 95 cases. develop a system of individual physician report cards for Subsequent researchers have adopted this framework cardiac surgery, which allow consumers to determine of the tripartite components of perioperative risk (sur- their surgeon’s risk-adjusted mortality rate.13,14 4–6 gery, anesthesia, patient disease). Because it is the In studying the influence of anesthesia-related factors, major cause of mortality, most of the subsequent analy- previous studies have suggested that its contribution is ses have focused appropriately on patient disease. Spe- several orders of magnitude lower than the influence of cifically, investigators have focused on identifying med- patient disease or surgical error. During the previous ical conditions associated with poor outcomes and have two decades, there have been attempts to quantify the attempted to identify specific interventions that will im- risk associated with anesthesia using a variety of sources. Slogoff and Keats15 reported on rates of perioperative This Editorial View accompanies the following article: Silber JH, myocardial ischemia and infarction after cardiac surgery ᭜ Kennedy SK, Even-Shoshan O, Chen W, Mosher RE, Showan AM, and found that one anesthesia provider (Anesthesiologist Longnecker DE: Anesthesiologist board certification and patient 7) had a significantly higher rate than the others. The outcomes. ANESTHESIOLOGY 2002; 96:1044–52. Confidential Enquiry into Perioperative Deaths assessed nearly 1 million cases of anesthesia during a 1-yr period in 1987 in three large regions of the United Kingdom.5 Accepted for publication January 29, 2002. The authors are not supported by, nor maintain any financial interest in, any commercial activity that may be There were 4,034 deaths within 30 days in an estimated associated with the topic of this article. 485,850 operations, resulting in a crude mortality rate of Anesthesiology, V 96, No 5, May 2002 1039 1040 EDITORIAL VIEWS 0.7–0.8%. Surgery had contributed totally or partially in First, it is not clear from the data whether the actions 30% of all patients. Progression of the presenting disease of the anesthesiologist contributed to the patient’s had contributed to death in 67.5% of all patients, with death. As noted in the article, the estimated number of progress of an intercurrent disease being relevant in excess deaths derived in this article—3.8 excess deaths 44.3% of patients. Anesthesia was considered to be the per 1,000 cases—is several magnitudes greater than the sole cause of death in only 3 individuals, for a rate of 1 in often-quoted risk of death from anesthesia of 0.005 185,000 cases, and anesthesia was contributory in 410 deaths per 1,000 cases. This is in the range of mortality deaths, for a rate of 7 in 10,000. Therefore, the ability to associated with the other components of perioperative determine the influence of the anesthesia provider on risk: surgery and patient disease. The data do not permit perioperative mortality would require either an ex- the authors to link specific actions of the anesthesiolo- tremely large sample size or alternative outcome mea- gist to the death rate, and therefore, there is no direct sures. Silber et al. have used large data sets and have evidence that all of the excess deaths can be attributed developed additive outcome measures in the study of to whether the anesthesiologist had a board certification. Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/96/5/1039/404427/7i0502001039.pdf by guest on 27 September 2021 the factors associated with anesthesia.12,16 However, extrapolating from the foundations of the fail- 1 In this issue of ANESTHESIOLOGY, Silber et al. have contin- ure-to-rescue concept, more skilled providers of care ued their inquiries into hospital and provider characteris- (e.g., board certification as a surrogate for “skill”) may tics for perioperative mortality by evaluating death and reduce the severity and fatality of a complication, which failure to risk in a large cohort of Medicare patients. Silber may not be directly related to anesthesia care. This may et al. developed the concept of failure to rescue as a means be related to such interventions as more skilled resusci- of studying quality of care for the manner in which hospi- tation or better pharmacologic management of coexist- tals handle 41 known “emergencies” or complications that ing disease. Information not available in the claims data are coded in the Medicare files.17,18 In brief, they evaluated would be required to demonstrate this link. the 30-day death rate in patients who died without a re- Second, the article attributes the difference in death corded complication or in whom a complication devel- rates to board certification based on a set of odds ratios. oped. The theoretical foundation for such an approach is In statistics, omitted variable bias occurs when variables that the presence of more “skilled” care would prevent not in the equation are correlated with a variable that is complications from becoming deaths. By evaluating both already in the equation. Board certification is included in mortality and failure to rescue, the number of relevant the equation; however, many variables that are probably outcomes dramatically increases, allowing investigators to correlated with board certification are not included in study the influence of care providers on outcome on a the equation. These include training at better medical smaller number of cases. schools and residency programs, being educated at US 16 In a previous issue of ANESTHESIOLOGY, Silber et al. medical schools, and other factors. These variables, not compared anesthesia care personally performed or med- board certification, could be responsible for the higher ically directed by an anesthesiologist with the outcomes death rate. Statistically, the greater the correlation be- of patients whose anesthesia was not personally per- tween the omitted variables and the variable included in formed or medically directed by an anesthesiologist and the equation (board certification), the greater the omit- reported that both 30-day mortality rate and failure to ted variable bias. That is, it is possible that some other rescue were lower when anesthesiologists directed an- factor highly correlated with board certification (i.e.,an esthesia care.