While the number of patients who report awareness during surgery general anesthesia is low, there are several factors that appear to increase the risk, according to findings published in the current issue of the journal Anesthesia & Analgesia. Two major risk factors are light anesthesia and a history of awareness.

The number of reported cases of awareness during anesthesia is insufficient to identify and estimate the risks and causes, note Dr. Mohamed M. Ghoneim and colleagues from the University of Iowa, Iowa City. To assemble more information, they reviewed cases reported in the medical literature.

The authors identified 271 subjects with anesthesia awareness and compared them with 19,504 subjects who did not experience awareness. Patients who experienced awareness were more likely to be female, younger and more likely to have cardiac and obstetric procedures.

Patients who experienced awareness received fewer anesthetic drugs, and had more episodes of rapid heart rate and high blood pressure during the operation.

Overall, 52 percent of patients who experienced awareness during surgery reported continuing problems related to their experience, such as sleep difficulties and fears about undergoing anesthesia in the future, and 22 percent of the patients had continued psychological symptoms related to their experience.

Ghoneim and colleagues report that 1.6 percent of patients who experienced awareness during their operation had a history of awareness and 4.5 percent had “difficult and prolonged” throat examinations and intubations.

“The most frequent cause of awareness was overly light anesthesia,” they note. Obesity and the use of nitrous oxide did not increase the risk.

The team suggests that the use of neuromuscular blockers should be avoided unless needed, arguing that a non-paralyzed patients is likely to move if inadequately anesthetized, “which alerts the anesthesia provider to deepen the anesthetic and this lessens the incidence of recall.”

SOURCE: Anesthesia & Analgesia, February 2009.