1. Complications.

Level	Number of participants			Overall complications			Swelling or haematoma			Pain			Nerve injury			Arterial puncture			Catheter dislocation
	USG		LM	USG		LM	USG		LM	USG		LM	USG		LM	USG		LM	USG		LM
Difficult
Costantino 2005	39		21	0		2 (9.5)	0		2 (9.5)	NS		NS	NS		NS	NS		NS	NS		NS
Stein 2009	28		31	0		0	0		0	NS		NS	0		0	0		0	NS		NS
İsmailoğlu 2015	30		30	9 (30.0)		14 (46.7)	NS		NS	NS		NS	NS		NS	NS		NS	NS		NS
McCarthy 2016A	98		94	4 (4.1)		5 (5.3)	2 (2.0)		3 (3.2)	NS		NS	1 (1.0)		1 (1.1)	1 (1.0)		1 (1.1)	NS		NS
Nishizawa 2020	30		30	3 (10.0)		4 (13.3)	3 (10.0)		4 (13.3)	NS		NS	NS		NS	NS		NS	NS		NS
Moderate
McCarthy 2016B	202		199	11 (5.4)		13* (6.5)	8 (4.0)		13 (6.5)	NS		NS	2 (1.0)		2 (1.0)	1 (0.5)		0	NS		NS
Easy
McCarthy 2016C	305		291	13 (4.3)		5 (1.7)	12 (3.9)		5 (1.7)	NS		NS	1 (0.3)		0	0		0	NS		NS
No restriction of difficulty
Glasin 2020	45		45	5 (11.1)		6† (13.3)	0		1 (2.2)	5 (11.1)		6 (13.3)	NS		NS	NS		NS	NS		NS
Skulec 2019	D	S	100	D	S	26 (26.0)	D	S	10 (10.0)	D	S	16 (16.0)	D	S	NS	D	S	0	D	S	0
	100	100		13 (13.0)	7 (7.0)		8 (8.0)	3 (3.0)		4 (4.0)	3 (3.0)		NS	NS		0	1 (1.0)		1 (1.0)	0
Total
	977		841	65		75	36		38	12		22	4		3	3		1	1		0

Values are n (%)

USG: ultrasound guidance, LM: landmark method, NS: not specified, D: dynamic guidance, S: static guidance

*Two participants had complications of both swelling and nerve injury.
^†One participant had complications of both swelling and pain.