Effects of vein width and depth on ultrasound-guided peripheral intravenous success rates.

BACKGROUND Increasing numbers of operators are learning to use ultrasound to guide peripheral intravenous (i.v.) catheter insertion in patients with difficult access. Unfortunately, failed cutaneous punctures are common. Some veins seen on ultrasound may be better choices than others. OBJECTIVES To estimate the effects of vein width and depth on the probability of success in ultrasound-guided i.v. catheter insertion. METHODS We prospectively collected data from attempts at ultrasound-guided venous catheter insertion between the antecubital fossa and mid-humerus. Each ultrasound machine's ruler function was used to determine depth from the skin to the closest vein edge and that vein's largest diameter. Success was defined as being able to freely withdraw blood or inject saline after the first skin puncture, considering each encounter independently. We calculated relative success rates, confidence intervals, and p values using reference groups selected by histogram analysis. RESULTS Thirty-five operators recorded 180 encounters; 100 (56%) were successful on the first skin puncture, and 152 (84%) were eventually successful. Success rates were not linearly related to vein width or depth. Success rates were higher for veins with diameter > or = 0.4 cm vs. those < 0.4 cm (63% [78/124] vs. 39% [22/56], relative success 1.6 [95% confidence interval (CI) 1.1-2.3], p = 0.005) and for veins of depth 0.3-1.5 cm vs. veins of depth < 0.3 or > 1.5 cm (58% [96/165] vs. 27% [4/15], relative success 2.2 [95% CI 0.9-5.1], p = 0.04). CONCLUSION Success rates are higher in larger veins (> or = 0.4 cm) and veins at moderate depth (0.3-1.5 cm).