An additional 51,427 patients underwent procedures during the time period of study, but did not receive general anesthesia. Of the patients who received other anesthetic modalities, 22,885 had complete postoperative documentation for a compliance of 45%. Of this cohort, seven patients complained of being aware during the case, an incidence of 1/3269 or 0.03%. These patients had been managed with a variety of anesthetic modalities (Table 3). Of the seven patients complaining of awareness in this population, six were women. In the case of the one male patient, the report of awareness was given by his daughter. This was the only patient in the study who did not report intraoperative awareness independently.
There was no statistically significant difference between the incidence of awareness in the general anesthesia (0.023%) and nongeneral anesthesia (0.03%) populations at our institution (P = 0.54). Relative risk of undesired intraoperative awareness during a general anesthetic compared with a nongeneral anesthetic was 0.74, with 95% confidence interval [0.28, 2.0].
Awareness during general anesthesia is a problem that has captured the attention of clinicians, patients, and the general public. Although awareness is a significant source of fear for many patients undergoing surgery, the actual incidence and sequelae of awareness remain a matter of controversy. This is highlighted by recent studies reporting rates of awareness and subsequent PTSD that were lower than previously thought.2,6
In this retrospective study, we found the incidence of complaints of intraoperative awareness during general anesthesia to be 1/4401 or 0.023%. We acknowledge that these data likely represent an under-estimate of the actual incidence of awareness in the population studied. As Sebel et al.4 noted: “A single short postoperative visit by an anesthesiologist without use of a structured interview is unlikely to elicit many cases of awareness,” an effect also noted by Moerman et al.10 Sandin et al. and Sebel et al. found considerably increased reports of awareness during the second interview at 1 wk postoperatively.4,5 Indeed, our data were obtained retrospectively, our patients did not receive a Brice interview or other technique of specifically assessing awareness, and our patients were interviewed on postoperative day 1, all of which might result in an under-estimation of the true incidence.
Even with suboptimal conditions for detection of awareness, our rate of undesired awareness was still more than three times that of 0.0068% reported by Pollard et al.,6 in which a structured interview was used. It is important to note that the structured interview in the Pollard et al. study omitted a question specifically assessing recall that is present in the standard Brice interview. Our demographic data appeared comparable, with an average ASA classification of 2.27 (vs 2.37 in. Pollard et al.), an average age of 49 ± 18 years (vs 46 ± 16), and a male:female ratio of 1:1.1 (vs 1:1.3). Although data reported in the Pollard et al. study were gathered, in part, at an academic medical center, no resident or nurse trainees were identified as being involved in patient care. Since resident physicians are routinely involved in patient care at our institution, this may account for some disparity in outcome.
Another possible difference relates to the use of TIVA at our institution. The centers in the Pollard et al. study “rarely used” IV drugs as the sole anesthetic; in our study, 1 of the 10 patients who complained of awareness during general anesthesia experienced the event during a failed TIVA. Given the large number of cases analyzed, it is difficult to establish the precise number of anesthetics in which TIVA was used at some point. We have established, however, that approximately 9/10 cases used an inhaled anesthetic. Thus, the rate of awareness during known TIVA (1/10) is comparable to the overall use of TIVA in the study population (1/10).
Although our incidence of 0.023% was considerably less than that reported by Myles et al.11 and Sebel et al.4 (which ranged from approximately 0.10% to 0.20%), this disparity is likely mitigated by our lack of a structured interview and a 1 wk postoperative interview. Although not in perfect agreement with either study, it is easier to reconcile our data with that of Sebel et al.3 than Pollard et al.6
All patients who have postoperative complaints receive follow-up phone calls. Those reporting intraoperative awareness are offered psychiatric counseling. Of the 17 patients reporting undesired intraoperative awareness, only one requested psychiatric care (patient 10 receiving general anesthesia, described in Table 1). Although formal postawareness psychiatric evaluation was not systematically performed on all patients, it would appear that the occurrence of sustained psychiatric sequelae in our population was likely closer to that reported by Samuelsson et al.2 rather than Osterman et al.1 It must be noted, of course, that patients afflicted with PTSD often avoid health care professionals and clinical settings because they can serve as triggers that evoke traumatic memories.12
The most surprising finding of the present study is that the incidence of intraoperative awareness in patients who did not undergo general anesthesia (0.03%, n = 22,885) was not statistically different compared with those who did (0.023%, n = 44,006) (P = 0.54). There are several possible interpretations of this finding. We could postulate that, since sedation also suppresses consciousness and memory, perhaps the incidence was truly the same in anesthetized and sedated patients. This is, however, an absurd conclusion. Sedated patients are often very aware of their surroundings, as well as talking with the anesthesiologist and surgical team during the procedure. We therefore reject this interpretation. The more likely interpretation is that the resolution of this retrospective study of more than 100,000 anesthetics at a single institution was too low to capture the incidence with accuracy. Thus, the current study suggests critical methodological limitations to retrospective analyses, despite large sample sizes, and supports prospective approaches to assessing intraoperative awareness.
The finding of awareness complaints in patients not receiving general anesthesia is provocative. It is important to note that it was not simply awareness of pain, but awareness itself that was a source of distress. Several patients reported that they heard conversations during their procedure, indicating that this level of consciousness was inconsistent with their expectations. Furthermore, although 5/7 patients in this group reported pain, it was not the sole complaint. For example, patient 3 (Table 3) had a functioning spinal anesthetic but was distraught at hearing conversations, seeing bright lights, and feeling as if she had died. Although the significance is unclear, complaints of intraoperative awareness in patients receiving general anesthesia had a 1:1 male:female ratio, whereas this ratio was 1:6 in patients who did not have general anesthesia. Undesired intraoperative awareness in patients not receiving general anesthesia indicates the potential for disparity between the expectations of the patient and those of the anesthesiologist. We must also recognize that prior patient conversations with our surgical colleagues may establish expectations (e.g., complete unconsciousness) that are not met during the procedure itself. Unmet expectations, rather than events in themselves, may contribute to patient distress.
In conclusion, the incidence of undesired awareness during general anesthesia at our institution was more than three times as high as that recently reported by Pollard et al.,6 despite the fact that no formal awareness interview was used. The self-reported incidence of intraoperative awareness was not statistically different in patients receiving general anesthesia and those who did not. These results suggest that large retrospective analyses are probably inadequate to study intraoperative awareness. Furthermore, the dissatisfaction with awareness during nongeneral anesthetics suggests that prospective studies should evaluate the relationship between patient’s pre-procedure expectations and post-procedure perceptions of anesthetic adequacy.
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© 2009 International Anesthesia Research Society
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