Scientific Evidence
Study findings from published scientific literature were aggregated and are reported in summary form by evidence category.
Category A: Supportive: 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 for the purpose of this Advisory.
Level 3: The literature contains a single randomized controlled trial.
§ All meta-analyses are conducted by the ASA methodology group. Meta-analyses from other sources are reviewed but not included.
Category B: Suggestive: 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, case-control research designs) of two or more 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, correlation) or descriptive statistics.
Level 3: The literature contains case reports.
Category C: Equivocal: 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: There is an insufficient number of studies to conduct meta-analysis and (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: the lack of scientific evidence in the literature is described by the following terms.
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 it does not permit a clear interpretation of findings due to methodologic concerns (e.g., confounding in study design or implementation).
Opinion-based Evidence
Opinion surveys were developed by the Task Force to address each clinical intervention identified in the document. Identical surveys were distributed to two groups of respondents: expert consultants and American Society of Anesthesiologists (ASA) members.
Category A: Expert Opinion. Survey responses from Task Force-appointed expert consultants are reported in summary form in the text. A complete listing of consultant survey responses is reported in appendix 2 in the original guideline document.
Category B: Membership Opinion. Survey responses from a random sample of members of the ASA and, when appropriate, responses from members of other organizations with expertise in the selected topics of interest are reported in summary form in the text. A complete listing of ASA member survey responses is reported in appendix 2 in the original guideline document.
Survey responses are recorded using a five-point scale and summarized based on median values.
Strongly Agree: Median score of 5 (at least 50% of the responses are 5)
Agree: Median score of 4 (at least 50% of the responses are 4 or 4 and 5)
Equivocal: Median score of 3 (at least 50% of the responses are 3, or no other response category or combination of similar categories contains at least 50% of the responses)
Disagree: Median score of 2 (at least 50% of responses are 2 or 1 and 2)
Strongly Disagree: Median score of 1 (at least 50% of responses are 1)
Category C: Informal Opinion. Open-forum testimony, Web-based comments, letters, and editorials are all informally evaluated and discussed during the development of the Advisory. When warranted, the Task Force may add educational information or cautionary notes based on this information.