Evidence-based decision making in ultrasound-guided central venous cannulation: choosing between the eye and the ear.

Central venous cannulation (CVC) traditionally has been guided by surface landmarks. There is a spectrum of established techniques and associated risks [1]. The rates of failure and complications vary from 10.1% to 19.4% and from 5.4% to 11.0%, respectively, depending on factors such as level of operator experience and type of lung ventilation [1]. A major reason for these observations is that nearly 10% of patients have abnormal venous anatomy, including complete absence of the central vein of interest [2]. Clearly, surface landmarks have major limitations. The ability to accurately locate the central vein before and/or during cannulation would not only enhance the conduct of CVC but also presumably reduce patient risk. The advent of vascular ultrasound-facilitated precise vein localization measurably improved the conduct of CVC (P b 0.05) [3]. Ultrasound-guided CVC minimized the impact of operator inexperience and was significantly cost-effective despite the initial setup costs [4,5]. There are, however, two types of ultrasound technologies available for CVC: audio-guided Doppler (relying on the ear) and B-mode ultrasound, which is also known as 2-dimensional ultrasound (relying on the eye because this technology generates a picture of the vein in real time). Both technologies have documented efficacy in CVC [3,4,6,7]. However, which technology is superior in the conduct of CVC? Is there evidence to guide a clinician’s choice? This question has been partially addressed in the metaanalysis of 18 clinical trials with a cumulative sample of 1646 subjects [7]. Compared with CVC by surface landmarks, CVC (adult internal jugular vein) with real-time, 2-dimensional ultrasound significantly lowered failure rate overall (relative risk 0.14) and on first attempt (relative risk 0.59). Three studies in infants all had similar findings (relative risk of 0.15). There was limited evidence favoring 2-dimensional ultrasound in adult CVC involving the subclavian or femoral veins.