. 2020 Mar 20;40(3):308–315. doi: 10.12122/j.issn.1673-4254.2020.03.02

2.

Subgroup analysis of the first-attempt success rate

Subgroup	No. of studies	No. of patients	RR (95%CI)Random Effects Model	Heterogeneity of subgroup I² (P-value)
Subgroup	No. of studies	SAX/LAX	RR (95%CI)Random Effects Model	Heterogeneity of subgroup I² (P-value)
LAX: Long-axis; SAX: Short-axis; OR: Operating room; SICU: Surgical intensive care unit; PACU: Post-anesthesia care unit; ED: Emergency department; HC: Hemodialysis center; RR: Relative risk; a: Favors short-axis; IJV: Internal jugular vein; SCV: Subclavian vein; AV: Axillary vein.
Vein	IJV^{[7, 8, 10, 11]}	195/198	1.20(0.99-1.46)	I²=29.2% (P=0.24)
	SCV^[6]	95/95	1.28(1.09-1.51)^a
	AV^[9]	43/43	1.70(1.19-2.43)^a
Operation department	OR^{[9, 10, 11]}	41/41	0.78(0.54-1.13)	I²=60.1% (P=0.06^c)
	OR or SICU^[7]	124/125	1.36(1.15-1.61)^a
	SICU^[6]	95/95	1.28(1.09-1.51)^a
	OR or PACU^[8]	73/75	1.34(1.03-1.75)^a
Basic characteristics of patients	No different^{[6, 8, 9, 10, 11]}	292/295	1.31(1.20-1.44)^a	I²=86.2% (P=0.007^c)
Basic characteristics of patients	Different^[7]	41/41	1.27(1.11-1.46)^a	I²=86.2% (P=0.007^c)
No. of operators	> 1^{[6, 8, 9, 10, 11]}	292/295	1.31(1.20-1.44)^a	I²=86.2% (P=0.007^c)
No. of operators	=1^[7]	41/41	1.27(1.11-1.46)^a	I²=86.2% (P=0.007^c)
No. of patients	≥100^{[6, 8]}	168/170	1.30(1.31-1.49)^a	I²=0% (P=0.76)
No. of patients	< 100^{[7, 9, 10, 11]}	165/166	1.24 (1.11-1.46)^a	I²=0% (P=0.76)
Publishing time	≥2015^{[6, 7, 8, 9, 10]}	284/286	1.27(1.06-1.53)^a	I²=0% (P=0.91)
Publishing time	< 2015^[11]	49/50	1.26(1.08-1.46)^a	I²=0% (P=0.91)