Preparation of this update used the same methodological process as was used in the original Advisory to obtain new scientific evidence. Opinion-based evidence obtained from the original Advisory is reported in this update. The protocol for reporting each source of evidence is further described.
Study findings from published scientific literature were aggregated and are reported in summary form by evidence category, as described later. All literature (e.g., randomized controlled trials, observational studies, and case reports) relevant to each topic was considered when evaluating the findings. However, for reporting purposes in this document, only the highest level of evidence (i.e., level 1, 2, or 3 within category A, B, or C) is included in the summary.
Category A: Supportive Literature
Randomized controlled trials report statistically significant (P < 0.01) differences between clinical interventions for a specified clinical outcome.
Level 1. The literature contains multiple randomized controlled trials, and the aggregated findings are supported by meta-analysis.*
Level 2. The literature contains multiple randomized controlled trials, but there is an insufficient number of studies to conduct a viable meta-analysis.
Level 3. The literature contains a single randomized controlled trial.
Category B: Suggestive Literature
Information from observational studies permits inference of beneficial or harmful relationships among clinical interventions and clinical outcomes.
Level 1. The literature contains observational comparisons (e.g., cohort and case-control research designs) of clinical interventions or conditions and indicates statistically significant differences between clinical interventions for a specified clinical outcome.
Level 2. The literature contains noncomparative observational studies with associative (e.g., relative risk or correlation) or descriptive statistics.
Level 3. The literature contains case reports.
Category C: Equivocal Literature
The literature cannot determine whether there are beneficial or harmful relationships among clinical interventions and clinical outcomes.
Level 1. Meta-analysis did not find significant differences among groups or conditions.
Level 2. The number of studies is insufficient to conduct meta-analysis. In addition, (1) randomized controlled trials have not found significant differences among groups or conditions, or (2) randomized controlled trials report inconsistent findings.
Level 3. Observational studies report inconsistent findings or do not permit inference of beneficial or harmful relationships.
Category D: Insufficient Evidence from Literature
The lack of scientific evidence in the literature is described by using the terms described below.
Silent. No identified studies address the specified relationships among interventions and outcomes.
Inadequate. The available literature cannot be used to assess relationships among clinical interventions and clinical outcomes. The literature either does not meet the criteria for content, as defined in the "Focus" of the Advisory, or does not permit a clear interpretation of findings because of methodological concerns (e.g., confounding in study design or implementation).
The original Advisory contained formal survey information collected from expert consultants and a random sample of members of the American Society of Anesthesiologists (ASA). Additional information was obtained from open-forum presentations and other invited and public sources. All opinion-based evidence relevant to each topic (e.g., survey data, open-forum testimony, Internet-based comments, letters, and editorials) was considered in the development of the original Advisory. Survey responses from task force–appointed expert consultants are reported in summary form in the text, with a listing of consultant survey responses reported in appendix 2. In addition, survey responses from active ASA members are reported in summary form in the text, with a listing of survey responses reported in appendix 2 of the original guideline document.
*Practice Advisories lack the support of a sufficient number of adequately controlled studies required to conduct an appropriate meta-analysis. Therefore, category A1 evidence is not reported in this document.