Appendix 1. MEDLINE (via Ovid)

1 Pain, Postoperative/ (27231)

2 ((postoperative adj4 pain*) or (post‐operative adj4 pain*) or post‐operative‐pain* or (post* adj4 pain*) or (postoperative adj4 analgesi*) or (post‐operative adj4 analgesi*) or "post‐operative analgesi*").mp. (47695)

3 ((post‐surgical adj4 pain*) or ("post surgical" adj4 pain*) or (post‐surgery adj4 pain*)).mp. (338)

4 ("pain‐relief after surg*" or "pain following surg*" or "pain control after").mp. (605)

5 (("post surg*" or post‐surg*) and (pain* or discomfort)).mp. (1302)

6 ((pain* adj4 "after surg*") or (pain* adj4 "after operat*") or (pain* adj4 "follow* operat*") or (pain* adj4 "follow* surg*")).mp. (2803)

7 ((analgesi* adj4 "after surg*") or (analgesi* adj4 "after operat*") or (analgesi* adj4 "follow* operat*") or (analgesi* adj4 "follow* surg*")).mp. (586)

8 exp Surgical Procedures, Operative/ (2400632)

9 or/1‐8 (2420214)

10 analgesia/ or analgesia, patient‐controlled/ (16633)

11 PRN.tw. (1208)

12 "pro re nata".tw. (194)

13 required analg*.tw. (227)

14 10 or 11 or 12 or 13 (18100)

15 9 and 14 (7354)

16 child/ or child, preschool/ (1551429)

17 child*.tw. (1004275)

18 16 or 17 (1870247)

19 15 and 18 (795)

20 randomized controlled trial.pt. (379463)

21 controlled clinical trial.pt. (88883)

22 randomized.ab. (300411)

23 placebo.ab. (156435)

24 drug therapy.fs. (1718784)

25 randomly.ab. (217206)

26 trial.ab. (312139)

27 or/20‐26 (2352062)

28 exp animals/ not humans.sh. (3970931)

29 27 not 28 (2106550)

30 19 and 29 (391)