Methods
angulation
We designed an open-source 3D printed needle guide to facilitate IP-CVC insertion. The 7.5-MHz linear probe HFL38 available on the M-Turbo® device (Sonosite, Bothewell, MA) was scanned with an EinScan Pro 2X device. Scanning process required two hours per model. We obtained the 3D mold of the probe. The needle guide made of poly lactic acid was wrapped around the digitalized probe using Autodesk Fusion 360. A dedicated needle-guiding railway was incorporated into the mold along the narrow side of the probe. The railway must allow adjustments in needle angulation, while also maintaining tightly the needle in the ultrasound beam. Finally, the needle guide was 3D printed on a Prusa I3mkiiiS printer (Prusa Research, Praha, CZ). Six needle guide iterations were tested before obtaining the perfect fit for the probe (Additional file We conducted a prospective, randomized study among residents and board-certified physicians from either ICU or emergency department to assess the needle guide in the setting of central venous puncture performed on inanimate manikin. All the participants had received a training in ultrasound-guided CVC insertion, but their proficiency was inhomogeneous. The participants were classified according on whether they had performed more or less than twenty CVCs insertion on patients. All participants were given a one-hour US-CVC lecture about US-guided IP and OOP approaches on simulator.Two simulators were used i) (the Blue Phantom II, CAE Healthcare St. Louis, MO) which allows internal jugular and subclavian puncture and ii) (the Gen II Femoral Vascular Access Ultrasound Training Model, CAE Healthcare St. Louis, MO) which permits femoral vein puncture. Blue fluid return confirmed venous puncture, whereas return of red fluid ruled in arterial puncture. Before the study, the participants were given a 10-min session to the needle guide and the simulators. Each operator performed needle puncture of the jugular, subclavian and femoral veins on the simulators, with three different techniques, assigned in random order: out-of-plane free hand (OP-FH), in-plane free hand (IP-FH) and in-plane with needle guide (IP-NG) (Additional file We recorded: success rate at first pass, number of needle redirections (and skin breaches) and duration of different parts of the puncture procedure (i) from skin contact to first skin puncture, (ii) from first skin puncture to successful venous puncture and (iii) from skin contact to successful venous return (entire puncture procedure). Uncomplicated puncture was defined as puncture (with venous return) performed in less than 120 s without arterial puncture.Data are expressed as median [1st and 3rd interquartile]. Success rates are compared using Chi-2 or Fisher exact test as required. The number of needle re-directions and the procedure time are compared using bilateral Wilcoxon matched pairs test. Significance is set for p less than 0.05.