Study design
This cross-sectional, observational study used humans and was approved by the Research Ethics Committee from Fundação Hospitalar do Estado de Minas Gerais (FHEMIG) under Protocol Number 59842616.0.0000.5119.
Study settings and population
From November 2016 to April 2017, we enrolled 105 patients hospitalized in the Clinic, Gynecology, and Obstetrics wards at Santa Casa de Misericórdia de Barbacena—Minas Gerais Brazil.
Patients aged at least 18 years of either sex were included. Each indicated agreement to participate in the study by providing their signature or their guardian’s signature on the Informed Consent Form.
Excluded were patients with prior central venous access and those who did not agree to participate. Each patient was stable, without critical disease, and denied a prior central venous access.
Study protocol
Six 4th-year medical students without experience with US were selected from the Barbacena’s School of Medicine and SUPREMA-Faculty of Medical Sciences and Health of Juiz de Fora. They were given 4 h of theoretical–practical training in US coordinated by an intensivist and nephrologist with extensive experience in TTs and USGTs.
The training included four 60-min stages: (a) a theoretical exposition including TTs, the physical principles of US, and USGTs; (b) a practical demonstration of anatomical markers and positioning the transducer; (c) practical training in ultrasonographic visualization of vessels and simulation of puncture via TTs, using each other as models; and (d) four supervised examinations per student and completion of the report.
Ultrasonographic evaluations were performed using a Sonosite Fujifilm MTurbo portable US (Bothell, WA, USA) equipped with a linear transducer with a frequency between 6 and 13 MHz.
Patients were placed in dorsal decubitus at 0º, and the cervical region was exposed via contralateral rotation of the neck. The apex of the triangle, composed of the clavicle and the two borders of the sternocleidomastoid muscle, was determined. The pulse at the common carotid artery (CCA) was verified, and immediately lateral to that point, the site chosen for the TT was marked with a pen (Fig. 1).
The US evaluation began by positioning the transducer at the marked point. Then, puncture via a TT was simulated by positioning a flexible cotton-coated rod at the marked point (Fig. 2). The artifact caused by the slight compression of this puncture point was visualized on the US screen and an imaginary line between that point and the position of the patient’s ipsilateral nipple was drawn. This line corresponds to the path the needle would make in an actual puncture guided by anatomical landmarks. If this line passed through the IJV, it was understood that puncture via a TT would have been effective. If the traced line did not cross the vein path, the TT was deemed a failed attempt (Fig. 3). All exams and simulations were filmed and, shortly thereafter, they were analyzed by two physicians with extensive experience in both puncture techniques.
The evaluation was fully qualitative, and the following variables were obtained: IJV position relative to the CCA (medial, anteromedial, lateral, anterolateral, posterior, or anterior); visual estimation of the IJV caliber relative to the CCA (less than 50%, between 50 and 100%, 101 and 150%, 150 and 200%, or greater than 200%); probability of reaching the IJV via the TT relative to the relative size and position of the IJV (success or failure).
Data analysis
Sample size was calculated based on an assumption that more than 12% of the Western population presents significant anatomical variations of the great vessels of the neck, as reported in the literature [17]. Thus, for a power of 80%, with a confidence index of 95%, the minimum sample was 63 individuals [18].
Relationships between studied variables were determined using the Fisher exact test and the Chi square test. Differences were considered significant when p < 0.05. Accuracies and their confidence intervals were calculated. Statistical analysis was performed using Stata software, version 9.2 (StataCorp, College Station, TX, USA).