Study findings from published scientific literature were aggregated and are reported in summary form by evidence category, as described below. All literature (e.g., randomized controlled trials [RCTs], observational studies, 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, as identified below) 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 RCTs, and aggregated findings are supported by meta-analysis.‡
Level 2: The literature contains multiple RCTs, but the number of studies is insufficient to conduct a viable meta-analysis for the purpose of these Guidelines.
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, 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, 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 (P>0.01) among groups or conditions.
Level 2: The number of studies is insufficient to conduct meta-analysis, and (1) RCTs have not found significant differences among groups or conditions or (2) RCTs 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 the following terms.
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 Guidelines or does not permit a clear interpretation of findings due to methodological concerns (e.g., confounding in study design or implementation).
Silent: No identified studies address the specified relationships among interventions and outcomes.
All opinion-based evidence (e.g., survey data, open-forum testimony, Internet-based comments, letters, editorials) relevant to each topic was considered in the development of these updated Guidelines. However, only the findings obtained from formal surveys are reported.
Opinion surveys were developed for this update by the Task Force to address each clinical intervention identified in the document. Identical surveys were distributed to expert consultants and American Society of Anesthesiology (ASA) members.
Category A: Expert Opinion
Survey responses from Task Force-appointed expert consultants are reported in summary form in the text of the original guideline document, with a complete listing of consultant survey responses reported in Appendix 2 of the original guideline document.
Category B: Membership Opinion
Survey responses from active ASA members are reported in summary form in the text of the original guideline document, with a complete listing of ASA member survey responses reported in Appendix 2 of the original guideline document.
Opinion survey responses are recorded using a 5-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 contain 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 from the previous update, Internet-based comments, letters, and editorials are all informally evaluated and discussed during the development of Guideline recommendations. When warranted, the Task Force may add educational information or cautionary notes based on this information.
‡All meta-analyses are conducted by the American Society of Anesthesiologists methodology group. Meta-analyses from other sources are reviewed but not included as evidence in this document.
§When an equal number of categorically distinct responses are obtained, the median value is determined by calculating the arithmetic mean of the two middle values. Ties are calculated by a predetermined formula.