This prospective, observational, clinical trial was approved by the Institutional Review Board of Dongsan Medical Center (no. 2016-09-009). The study protocol was registered at clinicaltrials.gov (NCT03116724; https://register.clinicaltrials.gov/prs/app/action/SelectProtocol?sid=S0006WY1&selectaction=Edit&uid=U00032RV&ts=2&cx=-8q8uk6, 17/04/2017) before enrolment of subjects. This study was performed in accordance with the Declaration of Helsinki 2013 and written informed consent was obtained from all patients. Patients were enrolled between April 2017 and August 2017. Adult patients (age > 18) scheduled for elective open-heart surgery, requiring central venous catheterization through the right internal jugular vein and TEE, were screened for eligibility in the study. The exclusion criteria were patients who had to receive central venous catheterization at another site, such as the left internal jugular vein, subclavian vein, or femoral vein, for any reason. After we obtained informed consent from the patients, we recorded the patients’ characteristics, including age, sex, height, weight, and body mass index (BMI).
First, we defined the optimal insertion depth of the central venous catheter (CVC) as 2 cm above the crista terminalis from a review of previous studies and clinical meaning. Additionally, we defined the optimal zone for the position of the tip of the CVC as 1 cm above the crista terminalis to 3 cm above it in the study. Anesthesia and surgical techniques were performed in a standardized manner regarding the routine practice in our institute during the trial. All patients arrived in the operating room without any premedication. Patient monitoring, including electrocardiography, peripheral oxygen saturation, noninvasive blood pressure, and bispectral index began before the induction of anesthesia. After indwelling the radial artery catheter under local anesthesia with 1% lidocaine injection, general anesthesia was induced with 0.15 mg/kg midazolam, and continuous intravenous infusion of remifentanil was performed using a target concentration infusion (TCI) system. After loss of patient consciousness, 0.8 mg/kg rocuronium was intravenously administered for muscle relaxation while the patients’ lungs were manually ventilated with 100% oxygen and sevoflurane. After tracheal intubation, mechanical ventilation was applied. Maintenance of anesthesia was provided with sevoflurane and continuous infusion of remifentanil. Next, a multi-plane probe (6VT-D/8.0–3.0 MHz, GE Healthcare Technologies, Wauwatosa, WI) for TEE was inserted into the patient’s esophagus at the mid-esophageal level for intraoperative cardiac monitoring, and a bicaval view was obtained with control of the probe.
For central venous catheterization through the right jugular vein, patients were placed in the 8° Trendelenburg position by tilting the operating table and the patient’s head was turned approximately 30–40° after a standard pillow was placed under the patient’s right shoulder. After sterile preparation and draping of the right jugular site, an investigator inserted an introducer needle into the sterilized area to puncture the right internal jugular vein under real-time ultrasound guidance with an ultrasound machine (Vivid™ S70, GE Healthcare Technologies, Wauwatosa, WI) equipped with a linear array probe (9L-D/10.0-2.4 MHz, GE Healthcare Technologies, Wauwatosa, WI). The puncture site was located at the level of the crease of the cricoid cartilage in all patients. Catheterization was performed with a 7 Fr. triple lumen catheter (Presep®, Edwards Lifescience, Irvine, CA) by the modified Seldinger maneuver after fresh dark blood was smoothly aspirated into the syringe, which was attached to the introducer needle. In the process of placing the central venous catheter through the right internal jugular vein while removing the guidewire, the catheter tip was first placed at the superior edge of the crista terminalis under a bicaval view of real-time transesophageal echocardiography 19,23. The TEE examination was performed by one board-certified cardiothoracic anesthesiologist. If the catheter tip was not clearly visible, the position of the tip was confirmed by injecting fluid into the distal lumen and observing the microbubble (Fig. 1) 19,24,25. The length of the inserted part of the catheter from the skin was checked when it was finally confirmed that the catheter tip was placed at the superior edge of the crista terminalis by TEE. Next, the catheter was drawn by 2 cm to move the catheter tip to the optimal position, which was defined as 2 cm above the crista terminals in our study. The practitioner fixed the catheter by anchoring it at the skin, and a sterile dressing was placed. The final insertion length was recorded as the optimal depth for each patient. Then, anesthesia and surgery proceeded in line with routine practices in our institute.
The primary end point was the optimal insertion depth, and we placed the catheter tip 2 cm above the superior edge of the crista terminalis using real-time TEE. The secondary endpoint was a new simple formula with the most correlated patient parameters to calculate the accuracy of the new formula and some previous guidelines for placing the tip of the inserted catheter within the newly proposed optimal zone (from 1 cm above to 3 cm above the edge of the crista terminalis) in the present study and to compare the accuracy rate between our new formula and the previous guidelines in terms of the placement of the central venous catheter within the optimal zone. Additionally, we evaluated the vertical distance from the catheter tip to the carina in the postoperative chest X-ray (Fig. 2).
When we reviewed the results of the previous study by Ahn et al. 19, the central venous catheter according to Peres’ formula was located in the optimal zone, which was newly proposed by us in the present study (from 3 cm above the upper margin of the crista terminalis to 1 cm above it), in approximately 57% of patients in their study. Considering that our new formula based on the data of the present study could guide the tip of the central catheter within the newly proposed optimal zone in a higher percentage by 20% than Peres’ formula in our study population, a total of 85 patients were required. Considering an ~ 5% drop-out rate, a total of 89 subjects were needed.
Statistical analyses
Categorical data are presented as numbers. Continuous data are presented as the mean and standard deviation (SD). Pearson’s correlation test was used to assess correlations between the real-measured optimal depth for the central venous catheter through the right internal jugular vein and the patient characteristics, including age, sex, height, weight, and BMI. In addition, we made a new simple formula for the optimal depth using the most correlated variable with the real-measured optimal depth. We calculated the predictability of a new formula for the placement of the central venous catheter within the optimal zone, which was newly proposed by us in our study population. Additionally, we calculated the predictability of some formulas or guidelines, including Peres’ formula. The previous formula and guidelines included ‘height(cm)/10’ by Peres 7, ‘height(cm)/10–1’ by Czepizak et al. 8, ‘height(cm)/10–1.3’ by Lum et al. 9, a fixed depth of 15 cm by Kim et al. 10, or ‘to the carina 11. We compared the predictability of the optimal depth between our new formula and the previous formula or guidelines including Peres’ formula, by using generalized estimating equation (GEE) analysis and a post- hoc test with Bonferroni correction. All data were analyzed using SPSS 21.0 (SPSS Inc. Chicago, IL, USA) and SAS 9.4 (SAS Institute Inc. Cary, NC, USA). A P-value less than 0.05 was considered statistically significant. The 95% confidence interval was calculated for adequate values.