New Data on Rates and Risk Factors of Patient Awareness during Anesthesia

Newswise — How many patients experience unwanted awareness during general anesthesia for surgery? The true rate is low but difficult to determine, while certain factors seem to increase the risk, according to a pair of studies in the February issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS). "It's hard to study something that's rare," comments Dr. Steven L. Shafer of Columbia University, Editor-in-Chief of Anesthesia & Analgesia. "Because intraoperative awareness is an important issue but a rare occurrence, anesthesiologists are using a variety of research methods to increase their understanding of the problem."

No Difference in Awareness with General vs Non-General AnesthesiaTo gain insight into the frequency of intraoperative awareness, Dr. George A. Mashour and colleagues of University of Michigan Medical School reviewed the records of more than 116,000 surgical patients (Mashour: A Retrospective Study of Intraoperative Awareness with Methodological Implications). The final analysis included complete information on approximately 44,000 patients undergoing surgery with general anesthesia and 23,000 patients receiving other types of anesthesia—mainly intravenous sedatives.

The records mentioned "undesired intraoperative awareness" in ten patients receiving general anesthesia, a rate of 0.023 percent (about two-hundredths of one percent). However, intraoperative awareness was also recorded for seven patients receiving other types of anesthesia, a rate of 0.03 percent. The difference between groups was not considered significant.

Even with such a large database, simply reviewing medical records is "probably inadequate" to study such an uncommon problem, Dr. Mashour and colleagues write. They also raise questions about the reports of "awareness" during non-general anesthesia. Since patients are often awake and even talking during procedures with sedation, the researchers believe these cases may be more related to patient expectations than to a problem with the anesthesia.

Some Factors Increase Risk of AwarenessIn the second study, Dr. Mohamed M. Ghoneim and colleagues of University of Iowa Hospitals and Clinics analyzed potential risk factors for intraoperative awareness, based on cases reported in the medical literature (Ghoneim: Awareness During Anesthesia: Risk Factors, Causes and Sequelae: A Review of Reported Cases in the Literature). They compared characteristics and potential causative factors in 271 patients with intraoperative awareness and 19,500 patients who did not have awareness.

There were several significant differences between groups. Patients with intraoperative awareness were younger, more likely to be women, and more likely to be undergoing cardiac and obstetric operations. Other characteristics previously suggested as risk factors—for example, obesity—were not significant in the new study.

About half of the patients with awareness reported lasting problems related to their experience, such as sleep problems or fears about undergoing anesthesia in the future. Twenty-two percent had continued psychological problems related to intraoperative awareness. The findings suggested two significant risk factors for intraoperative awareness: overly light anesthesia and a previous history of awareness during anesthesia. Of the two, light anesthesia seemed to be the most important. Based on these factors, Dr. Ghoneim and colleagues outline some potentially effective measures for reducing the risk of intraoperative awareness, focusing on equipment checks and patient monitoring to ensure an adequate level of anesthesia.

Many unanswered questions remain in studying the problem of intraoperative awareness, according to an accompanying editorial by Dr. Peter S. Sebel of Emory University School of Medicine. (Sebel: To Sleep, Perchance To Dream? NOT!) Key issues include the rate of lasting problems related to awareness and the risk of "unexpected" awareness—that is, patients who develop intraoperative awareness despite receiving apparently adequate levels of anesthesia.

Meanwhile, Dr. Shafer has advice for patients facing surgery who may be concerned about the risk of awareness during anesthesia. "If you have a concern about awareness, discuss it with your anesthesiologist before your procedure," he says. "If you experience awareness, it's important to tell your doctor about it. Anesthesiologists are aware of the problem and are being proactive in isolating the causes, but it's difficult because awareness is so rare." About the IARSThe International Anesthesia Research Society (www.iars.org) is a nonpolitical not-for-profit medical society founded in 1922 to encourage, stimulate, and fund ongoing anesthesia-related research and projects that will enhance and advance the anesthesiology specialty. The IARS has a worldwide membership of 15,000 physicians and others with doctoral degrees. The mission of the IARS includes publication of a monthly scientific journal, Anesthesia & Analgesia in print and online (www.anesthesia-analgesia.org), the oldest publication for the specialty of anesthesiology. The IARS is located in San Francisco, California.