Appendix 1. GRADE Assessment

The GRADE system uses the following criteria for assigning grade of evidence:

High = further research is very unlikely to change confidence in the estimate of effect
Moderate = further research is likely to have an important impact on confidence in the estimate of effect and may change the estimate
Low = further research is very likely to have an important impact on confidence in the estimate of effect and is likely to change the estimate
Very low = any estimate of effect is very uncertain

Grade of evidence is decreased further if the following are present:

• Serious (‐1) or very serious (‐2) limitation to study quality

• Important inconsistency (‐1)

• Some (‐1) or major (‐2) uncertainty about directness

• Imprecise or sparse data (‐1)

• High probability of reporting bias (‐1)

Grade of evidence may be increased if:

• Strong evidence of association ‐ significant relative risk of > 2 (< 0.5) based on consistent evidence from two or more observational studies, with no plausible confounders (+1)

• Very strong evidence of association ‐ significant relative risk of > 5 (< 0.2) based on direct evidence with no major threats to validity (+2)

• Evidence of a dose response gradient (+1)

• All plausible confounders would have reduced the effect (+1)

(GRADEpro 2015)

Appendix 2. MEDLINE search strategy

1. "water soluble contrast".tw.

2. Contrast Media/

3. Diatrizoate Meglumine/

4. "water‐soluble contrast".tw.

5. (gastrografin or urografin or amidotrizoato).tw.

6. (sodium diatrizoate or meglumine diatrizoate).tw.

7. or/1‐6

8. exp Intestinal Obstruction/

9. ((bowel* or intestin*) adj3 (obstruct* or block*)).tw.

10. ((bowel* or intestin*) adj3 adhes*).tw.

11. or/8‐10

12. 7 and 11

13. randomized controlled trial.pt.

14. controlled clinical trial.pt.

15. randomized.ab.

16. placebo.ab.

17. drug therapy.fs.

18. randomly.ab.

19. trial.ab.

20. groups.ab.

21. 13 or 14 or 15 or 16 or 17 or 18 or 19 or 20

22. exp animals/ not humans.sh.

23. 21 not 22

24. 12 and 23