Tidwell 1990.

Methods	Phase 2 of study: cross‐over trial (4‐treatment, 2‐sequence, 6‐period design) Method of analysis: repeated measure ANOVA between T0 and TI (T0 = immediately before turning to next position within the sequence, T1 = 1 minute after body position change)
Participants	34 mechanically ventilated postoperative CABG surgery adults with FiO2 ≤ 0.6 Sex (M/F) 30/6 (phase 1), mean age 64 years (range 49 to 77 years) Exclusion: concomitant cardiac valvular disease, PEEP required post surgery Setting: ICU, major Pacific Northwest medical centre, December 1988 to September 1989 (study authors from USA)
Interventions	Six body position changes: S (baseline) to 30° HOB, 30° HOB to S, S to L, S to R, L to S, R to S Each body position maintained for 30 minutes, except baseline (unknown duration) Sequences/groups  S(baseline),30° HOB, S, R, S, L, S S(baseline),30° HOB, S, L, S, R, S
Outcomes	SvO2, VO2 and SaO2 at 0 minutes (T0, recorded before body position of interest), then minutely from 1 to 5 minutes (T1‐5), at 15 minutes (T15) and at 25 minutes (T25) in each body position
Standard management	Ventilator settings not described. Unclear whether standard management (reported in phase 1 study) applied within phase 2. Phase 1 study standards included participants sedated with morphine and diazepam, rewarmed to 37 to 38°C within first 4 hours postop (phase 2 study conducted 4 to 8 hours after surgery)
Position description	45 degrees lateral rotation, commercial rigid foam wedge, passive position changes, HOB elevation: recumbent (flat) for lateral positions, HOB position set at 30 degrees elevation, angle verification methods not described for rotation or HOB elevation
Washout period	Not described
Notes	Phase 2 study method reported in Osguthorpe 1990 No sample size calculation described SvO2 via fibreoptic oximetry thermodilution catheter VO2 calculation: participants connected to an in‐line computerized metabolic cart and blender system with Boehringer 1‐way valve connected to T‐piece of the ETT to isolate inspired and expired gas Pre‐specified Pearson's correlation between dependent variables not relevant for the review Pre‐specified ANOVA analysis between 2 body positions (treatment effect), but non‐equivalent time points (T0 vs T1) Summary statistics (mean and SD) for each time point (i.e. 7 data points) for each body position, including time point for prior body position (i.e. T0) and other time points (T1 to T25) presented within results table Comments: no extractable lateral position data for meta‐analysis because of unit of analysis error. Paired comparisons involving supine or HOB positions were not valid for extraction, as position order was not randomized Contact established with primary investigator to request additional information regarding study design and clarification of results. However, no further correspondence received
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described Quotation: "The sequence of position changes was randomized to eliminate ordering effect as source of bias"
Allocation concealment (selection bias)	Unclear risk	Not described
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not described
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Not described Comment: objective outcome measures taken from real‐time physiological monitoring systems; therefore, lack of outcome assessor blinding unlikely to bias results
Incomplete outcome data (attrition bias) All outcomes	Low risk	Phase 1 study (n = 36), 1 withdrawal before data collection (due to inability to haemodynamically tolerate position change), minor discrepancy (n = 1) for phase 2 sample size (n = 34). No numerator stated for outcome reporting. Unclear completeness of outcome data Comment: missing data points, if present, unlikely to bias within‐subject differences for primary outcomes
Selective reporting (reporting bias)	Unclear risk	Pre‐specified paired data analysis between T0 and T1 reported. Mean scores for repeated measures tabulated for all body positions and mean scores presented within a line graph of each time point (T0 to T25), changing from supine to each lateral position. No statistical tests or analyses reported for time points other than T0 and T1 Comment: Discussion and conclusion sections reported other results (table and line graph) and a descriptive inference of a correlation between dependent variables based on 4 individuals with greatest variation in SvO2, when no statistically significant correlation was found within the sample. Insufficient information within the report to rule out selective reporting of outcomes and possible risk of interpretation bias
Other bias	Unclear risk	Non‐uniform unbalanced cross‐over design Quotation: "The sequence of position changes was randomized to eliminate ordering effect as source of bias." No testing of sequence or period effects reported. Unclear whether participants within each group were comparable on trial entry or had similar management and care (ventilation settings, fluid management, vasoactive medication administration and titration), as group differences were not examined and minimal sample demographics and participant characteristics were described Comment: Bias associated with selection and/or performance may confound sequencing effects within an unbalanced non‐uniform trial. Unclear whether sequence effects, period effects or treatment‐by‐period interactions may have been sources of bias. Carryover effects may be due to short active and possibly insufficient washout. Carryover, if present, was unlikely to be equally applied across all treatments because of lack of balance and uniformity. Overall, unclear risk of carryover bias