Epidemiology of Anesthesia-related Mortality in the United States, 1999–2005

Abstract

MORTALITY risk associated with anesthesia has been the subject of extensive research for many decades.1–5In a landmark study involving 10 academic medical centers and 599,500 surgical patients in the United States during 1948–1952, Beecher and Todd6found that the anesthesia-related death rate was 64 deaths per 100,000 procedures, varying markedly by anesthetic agents, types of providers, and patient characteristics. Based on their study results, Beecher and Todd estimated that the annual number of anesthesia-related deaths in the United States was more than 5,100, or 3.3 deaths per 100,000 population, which was more than twice the mortality attributable to poliomyelitis at that time. The report by Beecher and Todd helped to identify anesthesia safety as a public health problem and spawned many follow-up studies in the United States7–10and other countries.11–14This intense research effort has played an important role in the continuing improvement of anesthesia safety. In the advent of new anesthesia techniques, drugs, and enhanced training, anesthesia mortality risk has declined from approximately 1 death in 1000 anesthesia procedures in the 1940s to 1 in 10,000 in the 1970s and to 1 in 100,000 in the 1990s and early 2000s.15–18It is noteworthy that contemporary estimates of anesthesia mortality risk are based on studies conducted in Europe, Japan, and Australia.17–20The paucity of anesthesia mortality studies in the United States in recent years is compounded by several factors. First, improvement in anesthesia safety has made anesthesia-related deaths rare events, and studying rare events usually requires large sample sizes and considerable resources. Second, there is not an established national surveillance data system for monitoring anesthesia mortality. Last, clinical practice of anesthesia has expanded so much that it is extremely difficult to gather exposure data. It is estimated that most surgical anesthesia procedures are now performed in ambulatory care settings.21,22The use of anesthesia for therapeutic and diagnostic purposes is also on the rise.23After the 1999 publication of the Institute of Medicine’s report on medical error,24patient safety has become a priority area of health services research. To facilitate the measurement of patient safety and the evaluation of intervention programs, the Agency for Healthcare Research and Quality developed more than 20 patient safety indicators for use with routinely collected hospital inpatient discharge data. Each indicator refers to a group of complications or adverse events identified through specific International Classification of Diseases , 9th Revision, Clinical Modification codes.25The first indicator, purportedly measuring the safety of anesthesia, is limited to adverse effects of anesthetics in therapeutic use and overdose of anesthetics. Complications of anesthesia during labor and delivery and systemic complications, such as malignant hyperthermia due to anesthesia, are not included. The objectives of this study are to develop a comprehensive set of anesthesia safety indicators based on the latest version of the International Classification of Diseases and to apply these indicators to a national data system for understanding the epidemiology of anesthesia-related mortality.The study protocol was reviewed and approved for exemption of informed consent by the Columbia University Institutional Review Board, New York, New York.The International Statistical Classification of Diseases and Related Health Problems (ICD) is the standard classification system for recording and reporting diseases, injuries, and other health conditions.26Sponsored by the World Health Organization, this disease classification system is revised periodically and used by many countries for the compilation of mortality and morbidity data. It also serves as the basis for international comparison of health statistics. The 10th revision (ICD-10) was implemented for coding and classifying mortality data from death certificates in the United States as of January 1, 1999. For the purpose of the current study, we developed a list of ICD-10 codes for medical conditions related to anesthesia or anesthetics (table 1). These codes were identified by screening all the chapters of ICD-10 and informed by a thorough review of the research literature pertaining to anesthesia mortality and ICD.In previous studies,6,18anesthesia-related deaths were usually divided into two groups based on clinical judgment: deaths caused primarily by anesthesia and deaths in which anesthesia played a partial role. In this study, the role anesthesia played in the death was based on the causal chain of events leading to death as identified by the order on the death certificate and ICD coding guidelines. Anesthesia-related deaths were operationally defined as deaths that included one of the anesthesia-related codes (table 1) as the underlying cause of death or included at least one anesthesia-related code as a lis