A novel classification instrument for intraoperative awareness events.

BACKGROUND: Intraoperative awareness with explicit recall occurs in approximately 1-2 cases per 1000. Given the rarity of the event, a better understanding of awareness and its sequelae will likely require the compilation of data from numerous studies. As such, a standard description and expression of awareness events would be of value. METHODS: We developed a novel classification instrument for intraoperative awareness events: Class 0: no awareness; Class 1: isolated auditory perceptions; Class 2: tactile perceptions (e.g., surgical manipulation or endotracheal tube); Class 3: pain; Class 4: paralysis (e.g., feeling one cannot move, speak, or breathe); and Class 5: paralysis and pain. An additional designation of "D" for distress was also included for patient reports of fear, anxiety, suffocation, sense of doom, sense of impending death, or other explicit descriptions. We reviewed 15 studies of the incidence of awareness that provided specific information about awareness reports. Five anesthesiologists at three institutions who developed the categories independently classified the events. An additional 20 individuals (attending anesthesiologists, anesthesiology residents, nurse anesthetists, medical students, and ancillary staff) not involved in the development of the categories also independently classified the events. Fleiss's kappa statistic was used to evaluate inter-observer agreement. RESULTS: One hundred fifty-one cases of intraoperative awareness in adults were identified as valid for analysis. The overall kappa value was 0.851 (0.847-0.856, 95% confidence interval) for the basic Classes 1-5. Including additional designations of emotional distress, the overall kappa value was 0.779 (0.776-0.783, 95% confidence interval). CONCLUSION: We report a novel classification instrument for intraoperative awareness events that has excellent inter-observer agreement and that may facilitate the study of intraoperative awareness.

A novel electronic algorithm for detecting potentially insufficient anesthesia: implications for the prevention of intraoperative awareness.

OBJECTIVE: A recent clinical trial compared a minimum alveolar concentration (MAC)-based protocol to an electroencephalography (EEG)-based protocol for the prevention of intraoperative awareness. One limitation of this study design is that MAC-based protocols are not sensitive to the use of intravenous agents, while EEG-based protocols are. Our objective was to develop a MAC alert that incorporates intravenous agents. METHODS: We developed an electronic algorithm and alerting system that calculates a total age-adjusted MAC value based on inhalational agents, but also incorporates intravenous agents. We retrospectively applied the algorithm to adult general anesthesia cases over a 1 year period to assess the frequency of alert triggers, using thresholds of <0.8, <0.7, <0.6, <0.5 and <0.4 age-adjusted MAC. We also electronically analyzed 12 cases of intraoperative awareness that occurred over a 4-year period for the frequency of alert triggers using the same thresholds. Finally, we calculated positive and negative likelihood ratios based on these analyses. RESULTS: Over a 1-year period we identified 15,091 cases without self-reported awareness that were valid for analysis. At all age-adjusted MAC thresholds, the incidence of triggered alerts was higher in the awareness cases. The threshold of<0.8 age-adjusted MAC was associated with the highest negative likelihood ratio; the<0.5 age-adjusted MAC was associated with the highest positive likelihood ratio. CONCLUSIONS: Our novel electronic alerting system incorporates both age-adjusted MAC and intravenous anesthesia, and triggers with a higher frequency in cases of awareness. These data suggest the potential for our system to alert clinicians to insufficient anesthesia.

Levels of consciousness during regional anesthesia and monitored anesthesia care: patient expectations and experiences.

Complaints of "intraoperative awareness" after regional anesthesia and monitored anesthesia care have been reported. We hypothesized that this may be due to either unmet expectations regarding levels of consciousness or states of consciousness resembling general anesthesia. A structured interview assessing expected and experienced levels of consciousness was given to 117 patients who underwent regional anesthesia or monitored anesthesia care. Complete unconsciousness was the state most often expected and subjectively experienced. Furthermore, only 58% of patients had expectations set by the anesthesia provider. These data indicate that, from the patient's perspective, the boundary between general and nongeneral anesthesia is obscured.