Abstract: Altogether 13 studies enrolling 2341 participants (and involving 2360 procedures) fulfilled the inclusion criteria. The quality of evidence was very low (subclavian vein N = 3) or low (subclavian vein N = 4, femoral vein N = 2) for most outcomes, moderate for one outcome (femoral vein) and high at best for two outcomes (subclavian vein N = 1, femoral vein N = 1). Most of the trials had unclear risk of bias across the six domains, and heterogeneity among the studies was significant. For the subclavian vein (nine studies, 2030 participants, 2049 procedures), two-dimensional ultrasound reduced the risk of inadvertent arterial puncture (three trials, 498 participants, risk ratio (RR) 0.21, 95% confidence interval (CI) 0.06 to 0.82; P value 0.02, I² = 0%) and haematoma formation (three trials, 498 participants, RR 0.26, 95% CI 0.09 to 0.76; P value 0.01, I² = 0%). No evidence was found of a difference in total or other complications (together, US, USD), overall (together, US, USD), number of attempts until success (US) or first-time (US) success rates or time taken to insert the catheter (US). For the femoral vein, fewer data were available for analysis (four studies, 311 participants, 311 procedures). No evidence was found of a difference in inadvertent arterial puncture or other complications. However, success on the first attempt was more likely with ultrasound (three trials, 224 participants, RR 1.73, 95% CI 1.34 to 2.22; P value < 0.0001, I² = 31%), and a small increase in the overall success rate was noted (RR 1.11, 95% CI 1.00 to 1.23; P value 0.06, I² = 50%). No data on mortality or participant-reported outcomes were provided. On the basis of available data, we conclude that two-dimensional ultrasound offers small gains in safety and quality when compared with an anatomical landmark technique for subclavian (arterial puncture, haematoma formation) or femoral vein (success on the first attempt) cannulation for central vein catheterization. Data on insertion by inexperienced or experienced users, or on patients at high risk for complications, are lacking. The results for Doppler ultrasound techniques versus anatomical landmark techniques are uncertain.

Plain-language summary: This Cochrane systematic review compared landmark techniques versus ultrasound guidance. The evidence is current to´January 2013. We included in the review 13 studies enrolling 2341 participants (and involving 2360 procedures). The studies were varied, and their quality was not high. We reran the search in August 2014. We will deal with any studies of interest when we update the review. Nevertheless, ultrasound offered some benefits, as it reduced the risk of arterial puncture and severe bruising in subclavian vein catheterization. Fewer data were available for femoral vein catheterization, but success rates seemed to be higher with ultrasound. No evidence showed a significant difference in complication rates or in time taken to cannulate at either site. On the basis of available data, we conclude that two-dimensional ultrasound offers small advantages in safety and quality when compared with an anatomical landmark technique for subclavian vein (reduced arterial puncture and haematoma formation) or femoral vein (reduced success on the first attempt) cannulation for central vein catheterization, but these findings do not necessarily hold for all groups of ultrasound users or for patients at high risk for complications. The results for Doppler ultrasound techniques versus anatomical landmark techniques are uncertain.