Table 1

Relevant paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study weaknesses
Philbeck et al, 2009, USA	10 Healthy volunteers undergoing IO infusion into proximal humerus Incremental doses of 20 mg lidocaine injected via IO needle before flushing. Flush followed by further 40 mg lidocaine before commencing infusion. Pain scores recorded during infusion	Open-label trial	Pain on IO insertion (10-point VAS)	Mean 3.9 (±1.5)	Conference abstract only; small numbers; healthy volunteers; sponsored by device manufacturer
Philbeck et al, 2009, USA		Open-label trial	Pain during infusion (10-point VAS)	Mean 2.0 (±1.2) after 20 mg initial bolus; no pain after 40 mg initial bolus
Philbeck et al, 2010, USA	Part 1: 10 healthy volunteers undergoing bilateral tibial IO access. Left tibial IO had 40 mg 2% lidocaine injected, followed by 10 ml saline flush and a further 20 mg lidocaine. The right tibial IO had 80 mg 2% lidocaine injected, followed by 10 ml saline flush and 20 mg lidocaine Part 2: 5 of the volunteers, plus an additional 6 had a proximal right humerus IO needle then 40 mg 2% lidocaine injected, followed by 10 ml saline flush and 20 mg lidocaine and then saline infusion at increasing pressures	Open-label trial	Mean pain during IO insertion	Tibia 4.4 (±2.6) left; 3.6 (±2.3) right Humerus 3.0 (±1.5)	Healthy volunteers; 5 took part in both parts, so may have become ‘habituated’ to IO access. 1 new volunteer to part 2 withdrew after IO insertion because of excess pain; sponsored by manufacturer
			Mean pain score during initial flush	Tibia 6.8 (±2.9) left; 7.9 (±2.8) right Humerus 4.6 (±2.9)
			Peak pain during infusion	Tibia 2.9, humerus 1.4 (also 8/10 in tibia study needed an additional lidocaine injection to the right tibia to keep infusion pain below 5)

IO, intraosseous; VAS visual analogue scale.