This is a single-factor experimental study conducted in simulation with a quantitative approach, developed at the Advanced Center for Clinical Simulation and Technological Innovation of the Universidad del Rosario in Bogota, Colombia. Specialists in emergency medicine with experience in ultrasound-guided vascular access were recruited to perform the punctures using visualization techniques in one and two planes. The call was kept open until 10 specialists who met the inclusion criteria were recruited and subsequently agreed to participate under informed consent. Based on previous studies, cannulation success in the first attempt was estimated at 90% for the biplane technique and 50% for the in-plane and out-of-plane techniques [1], requiring 60 procedures (20 for each technique) to achieve a power of 80% and an α error of 0.05, allowing detection of the difference between the ultrasound windows and the outcomes under study. The arcosine approximation was used, employing the Granmo application version 7.12 April 2012.

Prior to each set of three events, a random assignment of the three ultrasound planes was conducted to determine which one would be used. The randomization was performed using the statistical package R Core Team 4.2.2.

The procedure was performed on a simulated model for central vascular accesses, CentraLineMan® System CML 50, which had external anatomical landmarks include clavicle, sternal notch, sternal and clavicular heads of the sternocleidomastoid muscle, manubrium, and lateral border of the first rib. The model was placed at a distance of 1.2 cm from the skin to the vessel at the lower third of the neck. A right jugular vein with a diameter of 1 cm and a right carotid artery located 7 mm away from the vein were used. The procedure utilized an adult central venous access device, Certofix® Duo S 720, with an 18G × 2 ¾" needle, 0.89 mm diameter guide, and a length of 50 cm (Fig. 1).

Ultrasound planes for vascular access. A Biplane, B Out-of-plane, C In-plane

Sociodemographic variables such as age and sex, experience-related variables, and procedure-related variables (time to window, time for internal jugular vein puncture, puncture success, posterior wall puncture, puncture success, redirection, and the number of punctures) were included.

The study was conducted in a controlled environment at a university simulation center. To ensure that participants were able to familiarize themselves with the ultrasound machine without becoming familiar with the characteristics of the actual target vessel, a different simulated model of the central venous access (Blue PhantomTM Central Venous Access) was used during the 15-min equipment familiarization period. This was done prior to the procedure, after each participant received a 6-min video explanation of the in-plane, out-of-plane, and biplane central venous access techniques. A researcher was present during this time to clarify any doubts about the operation of the ultrasound machine.

To perform the ultrasound windows, the Butterfly iQ + (pocket ultrasound scanner, reference 900-20006-01) was connected to an iPad Pro (9.7 inches) using the Butterfly Network V2.12.1 software, configured in the vascular access preset, with a depth of 3 cm and a gain of 90%. The participant could make adjustments considered pertinent to obtain real-time visualization of the best ultrasound window of the vessel to be cannulated.

The data were recorded immediately and stored digitally on university servers provided for this purpose (SharePoint-Office 365 license Universidad del Rosario), which only researchers had access to.

Categorical variables, such as gender, ultrasound plane, puncture success, cannulation success, redirection, and posterior wall puncture, were described using absolute and relative frequencies. Continuous variables, such as age, years of experience, specific experience, time to window, and time to vessel, were described using means and standard deviations or medians and interquartile ranges, depending on the distribution of the data. The normality of the data was explored using Shapiro–Wilk test.

To determine whether there were significant differences in proportions between the different ultrasound planes (biplane, in-plane, and out-of-plane), the success of cannulation, the success of puncture and posterior wall puncture, and the need to redirect the needle, Fisher's exact test was performed. To determine whether there were significant differences in medians (according to normality) between the different ultrasound planes and the time to window, time to vessel, and number of punctures, the Kruskal–Wallis test was applied. For cannulation time, the one-factor ANOVA test was used after checking the assumptions. Post hoc tests were used to further explore significant differences. A statistical significance level of 0.05% and a 95% confidence interval were used for all tests. The statistical analysis was performed using Jamovi software version 2.2.5.