Table 4.

Sensitivity Analyses: The effect of potential biases on primary outcomes of adjuvant intrathecal meperidine. ^aExcluded high or unclear risk; ^bExcluded with unclear information; ASA, Physical status classification of American Society of Anesthesiologists; CI, confidence interval; G, gauge; LA, local anaesthetics; N/A, not applicable; RR, relative risk; y/o, years old.

Potential bias or limitations excluded	No. of studies	Overall incidence of shivering				Incidence of need for rescue analgesics				Incidence of nausea				Incidence of vomiting
		RR	95% CI	I 2	P	RR	95% CI	I 2	P	RR	95% CI	I 2	P	RR	95% CI	I 2	P
Overall	28	0.31	0.24–0.40	42%	<0.00001	0.27	0.12–0.64	0%	0.003	1.84	1.29–2.64	23%	0.0009	2.23	1.23–4.02	19%	0.008
RCT quality a
Selection bias16,25,27,29,33,42–46,49–51,53–56,58	18	0.28	0.20–0.40	54%	<0.00001	0.26	0.10–0.66	0%	0.005	2.15	1.27–3.63	24%	0.004	2.91	1.60–5.28	0%	0.0005
Performance bias30,33,50,51,54	23	0.31	0.23–0.40	37%	<0.00001	0.27	0.12–0.64	0%	0.003	2.1	1.30–3.38	41%	0.002	2.26	1.17–4.38	27%	0.02
Detection bias32,33,42–44,49–55,59	15	0.32	0.22–0.46	48%	<0.00001	0.27	0.11–0.65	0%	0.004	4.18	1.06–16.55	69%	0.04	3.32	1.04–10.66	54%	0.04
Attrition bias28,45	26	0.31	0.24–0.41	45%	<0.00001	0.26	0.10–0.66	0%	0.005	1.71	1.22–2.39	18%	0.002	2.23	1.23–4.02	19%	0.008
Other bias26,28,31,42,43,46,47,49,59	19	0.3	0.19–0.47	58%	<0.00001	0.3	0.12–0.72	0%	0.008	2.45	1.39–4.34	44%	0.002	2.65	1.04–6.72	42%	0.03
Participants b
ASA III16,33,44,45,47,54,55	21	0.33	0.25–0.42	43%	<0.00001	0.26	0.10–0.66	0%	0.005	1.85	1.22–2.81	32%	0.004	2.38	1.13–4.98	37%	0.02
Age ≥ 65 y/o16,26,44,47,51,52,54,55	20	0.29	0.21–0.40	41%	<0.00001	0.27	0.12–0.64	0%	0.003	2.04	1.29–3.23	40%	0.002	2.33	1.23–4.52	28%	0.01
Technique b
No bupivacaine16,29,33,47,49,55,58	21	0.32	0.24–0.43	46%	<0.00001	0.27	0.12–0.64	0%	0.003	1.94	1.35–2.77	8%	0.0003	2.98	1.61–5.52	0%	0.0005
LA contain other drugs52,57,58	25	0.29	0.22–0.39	39%	<0.00001	0.27	0.12–0.64	0%	0.003	1.84	1.37–2.47	0%	<0.0001	2.93	1.69–5.09	0%	0.0001
Needle size ≤ 24 G16,28,30,33,42,43,49,50,52,54	18	0.36	0.27–0.46	35%	<0.00001	0.21	0.07–0.67	25%	0.008	2.38	1.28–4.44	58%	0.006	2.44	1.19–5.01	35%	0.01
No prehydration16,45,51,54	24	0.29	0.22–0.39	45%	<0.00001	0.16	0.03–0.97	51%	0.05	1.85	1.23–2.79	32%	0.003	2.23	1.23–4.02	19%	0.008
No drapes26,31–33,42,43,45,47,49–55,58	13	0.3	0.21–0.44	50%	<0.00001	0.29	0.11–0.77	0%	0.01	3.75	1.37–10.21	59%	0.01	3.05	1.65–5.64	0%	0.0004
No warm prehydretion16,28,31–33,42–45,47,49–54,56,58	10	0.32	0.22–0.47	62%	<0.00001	0.29	0.10–0.80	NA	0.02	4.87	0.9–26.34	70%	0.07	2.97	1.64–5.38	0%	0.003