title: A retrospective study of intraoperative awareness with methodological implications.
abstract: BACKGROUND
  Awareness during general anesthesia is a problem receiving increased attention from physicians and patients. Large multicentered studies have established an accepted incidence of awareness during general anesthesia as approximately 1-2 per 1000 cases or 0.15%. More recent retrospective data, however, suggest that the actual incidence may be as low as 0.0068%.
  
  
  METHODS
  To assess the incidence of awareness at our institution, we conducted a review of adult patients undergoing surgical procedures over a 3-year period. Information on awareness came from entries of "Intraoperative Awareness" captured during our standard evaluations on postoperative day one in our perioperative information system. Patients were not questioned specifically about awareness.
  
  
  RESULTS
  We reviewed 116,478 charts; 65,061 patients received general anesthesia and 51,417 received other types of anesthesia. Of the patients receiving general anesthesia, 44,006 had complete postoperative documentation. The reported incidence of undesired intraoperative awareness in this population was 10/44,006 (1/4401 or 0.023%). Of the patients who received other anesthetic modalities, 22,885 had complete postoperative documentation. Undesired intraoperative awareness was reported in 7/22,885 patients who did not receive general anesthesia (1/3269 or 0.03%). The reported incidence of intraoperative awareness was not statistically different between the two groups (P = 0.54). Relative risk of intraoperative awareness during a general anesthetic compared with a nongeneral anesthetic was 0.74, with 95% confidence interval [0.28, 2.0].
  
  
  CONCLUSIONS
  Using a retrospective methodology, reports of intraoperative awareness are not statistically different in patients who received general anesthesia compared with those who did not. These results suggest that, despite success with other rare perioperative events, the resolution of retrospective database analyses may be too low to study intraoperative awareness.
authors.affiliation: Department of Anesthesiology, University of Michigan Medical School, Michigan, USA. gmashour@umich.edu
authors.forename: George A
authors.initials: GA
authors.lastname: Mashour
authors.forename: Luke Y-J
authors.initials: LY
authors.lastname: Wang
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Turner
authors.forename: John C
authors.initials: JC
authors.lastname: Vandervest
authors.forename: Amy
authors.initials: A
authors.lastname: Shanks
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Tremper
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000758:Anesthesia / Q000009:adverse effects*; D000777:Anesthetics / Q000009:adverse effects; D001364:Awareness; D003627:Data Interpretation, Statistical; D016208:Databases, Factual; D005260:Female; D006801:Humans; D007431:Intraoperative Complications / Q000453:epidemiology* / Q000523:psychology*; D008297:Male; D016347:Medical Records Systems, Computerized; D008875:Middle Aged; D016017:Odds Ratio; D011247:Pregnancy; D011786:Quality Control; D012189:Retrospective Studies
chemical_list: D000777:Anesthetics