New Studies Show Rates, Risk Factors of Patient Awareness during Anesthesia

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," said 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."

To 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. 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, 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.

In 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. 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, 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.

For more information, go to www.iars.org.

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