Table 1.

Characteristics of the studies included in the meta-analysis

Study	Country	Study type	Opioid	Opioid injection dose and time	Group	Weight (kg)	Age (years)	Gender M: F	ASA I/II	Intervention	Time 1	Time 2
Li et al., 2017 [10]	China	RCT	sufentanil	0.3 μg /kg, 5 s	Dezocine	62.2 ± 11.9	42.8 ± 11.5	80 (47/33)	55 /25	0.1 mg/kg, intravenous	10 min	2 min
					Placebo	64.1 ± 13.8	43.5 ± 10.4	80 (45/35)	56 /24	equal volume of 0.9% saline	10 min	2 min
Sun et al., 2015 [11]	China	RCT	sufentanil	0.5 μg/kg, 3 ~ 5 s	Dezocine	58 ± 9	51 ± 10	80 (36/44)	50 /30	0.1 mg/kg, 3 ~ 5 s, intravenous	3 min	2 min
					Placebo	59 ± 9	50 ± 9	80 (41/39)	55 /25	equal volume of 0.9% saline	3 min	2 min
Wang et al., 2015 [17]	China	RCT	sufentanil	0.3 μg /kg, 5 s	Dezocine	NP	NP	NP	NP	0.1 mg/kg, intravenous	10 min	2 min
					Placebo	NP	NP	NP	NP	equal volume of 0.9% saline	10 min	2 min
Liu et al., 2015 [6]	China	RCT	sufentanil	0.5 μg/kg, 3 s	Dezocine	62 ± 9	52 ± 13	185 (91/94)	125/60	0.1 mg/kg, 3 ~ 5 s, intravenous	2 min	2 min
					Placebo	60 ± 8	53 ± 11	185 (99/86)	117/68	equal volume of 0.9% saline	2 min	2 min
Xu et al., 2014 [18]	China	RCT	sufentanil	0.5 μg/kg, 3 s	Dezocine	61.2 ± 10.9	41.2 ± 14.3	50 (26/24)	NP	0.1 mg/kg, intravenous	5 min	2 min
					Placebo	62.1 ± 9.7	39.7 ± 16.1	50 (23/27)	NP	equal volume of 0.9% saline	5 min	2 min

RCT randomised controlled trial, M male, F female, ASA American Society of Anesthesiologists, NP not provided, Time 1 record the time of intervention earlier than anesthesia induction, Time 2 start recording the time of coughing after opioid injection