Echocardiography With Bubble Test for Tip Location of Central Venous Catheters

The goal of this prospective observational study is to test the accuracy of the transthoracic echocardiography with bubble test to verify the location of the tip of the central venous catheter in patients undergoing cardiac surgery procedures. The main questions it aims to answer are:

1. Is there a difference in time elapsed between the injection of a saline solution (echogenic contrast) through a central venous catheter and the visualization of micro bubbles in right atrium ("push to bubbles" time) with transthoracic echocardiography, when the catheter tip is placed in four different positions identified by transesophageal echocardiography?
2. Is there a difference in time for the right atrium to be completely filled by bubbles after saline injection in a central venous catheter with the tip placed in four different positions identified by transesophageal echocardiography?
3. In what percentage of patients the acoustic window is good enough to evaluate "push to bubbles" time?
4. Is there a difference in "push to bubbles" time between different echocardiographic projections?
5. Is the bubbles flow laminar or turbulent in the four different positions?
6. Is there a relation between "push to bubble" time and heart rate, blood pressure, pulmonary artery pressure, central venous pressure and cardiac output measured through a pulmonary artery catheter?

Participants will require simultaneously a central venous catheter and an intraoperative transesophageal echocardiography.

The placement of central vascular access devices (VADs), with cervical-thoracic or femoral insertion (such as CICC, Central Inserted Central Catheter, and FICC, Femoral Inserted Central Catheter), as well as peripheral insertion (PICC, Peripherally Inserted Central Catheter), is a common procedure for patients admitted to the Intensive Care Unit and for patients undergoing major surgery or prolonged infusion therapy.

To reduce the incidence of complications related to improper positioning of the central venous catheter, the tip should be positioned in the lower part of the superior vena cava or in the upper part of the right atrium near the cavo-atrial junction, identified by the crista terminalis.

Among the methods used to verify the correct tip placement, the intracavitary ECG method is strongly recommended by various international guidelines, and its use has been widely validated in terms of safety, efficacy, and accuracy. However, the intracavitary ECG method, based on the principle that the appearance of a high P-wave indicates the proximity of the tip to the cavo-atrial junction, has limitations when it comes to patients with non-sinus rhythm. Recent studies are validating the use of modified intracavitary ECG in patients with atrial fibrillation, but in other cases where a P-wave is not visible, the method is not applicable.

Various methods for ultrasound-guided placement and confirmation of the final tip position have been developed, also because the chest X-ray performed at the patient's bedside has proven to be a less accurate method due to the lack of definite findings of the cavo-atrial junction.

Transesophageal echocardiography (TEE), while being the method of choice as it allows direct visualization of the cavo-atrial junction and, therefore, the real position of both the guidewire and the tip of the catheter at the end of placement, remains an invasive method that is difficult to perform outside of cardiac operating rooms.

Transthoracic echocardiography may allow for the direct visualization of the tip of the VAD inside the heart chambers or indirectly assessing the tip's position by injecting echogenic contrast. Echogenic contrast refers to a rapid bolus of 5-20 ml of 0.9% saline solution, with or without the addition of 1 ml of air, vigorously shaken to create micro bubbles that can be easily visualized during the echocardiographic exam. The bolus is injected into the VAD once it has been positioned, and the micro bubbles are visualized in the right atrium, using transthoracic echocardiography. In nearly all studies, the VAD is considered in the correct position if the micro bubbles appear in the atrium within 2 seconds of injection ("push to bubble" time); otherwise, it is not considered correctly positioned if the bubbles appear after 2 seconds, but in one study, the adequate time was considered to be less than 500 ms. In almost all echocardiography studies, however, the reference method used to evaluate and confirm the VAD tip position has been chest radiography, which has been proven to be a less accurate method; moreover, literature shows significant variations in the indicative times for the visualization of micro bubbles that suggest incorrect position (range 0.5-2 seconds).

In this context, it could be useful to determine accurately if different "push to bubble" times are indicative for different positions of the VAD tip. For this purpose, the echogenic contrast (10 ml of 0,9% saline solution with the addition of 1 ml of air vigorously shaken to create micro bubbles) will be injected in the distal lumen of a VAD, whose tip is positioned in four different points, identified with using transesophageal echocardiography and the time from the contrast injection to the visualization of the bubbles in right atrium will be recorded using transthoracic echocardiography.

The four positions in which the catheter tip will be placed are: right atrium, cavo-atrial junction (CAJ), at 4 centimeters proximal to the CAJ in superior vena cava and at 8 centimeters to the CAJ. The catheter tip positions in right atrium and at CAJ will be directly evaluated using 2D and 3D transesophageal echocardiography, the other positions will be obtained moving the catheter back 4 and 8 centimeters from the CAJ. The transthoracic echocardiography will be carried out always by the same cardiologist trained in echocardiography unaware of the purpose of the study. The time measurements will be carried out always by the same cardiac anaesthesiologist, trained in echocardiography, unaware of the different catheter tip positions.

Eligibility Criteria:
Inclusion Criteria:

* age \> 18 years
* written informed consent from the patient
* intra-operative need for a central venous catheterization via the supra/infra clavicular right veins (centrally inserted central catheter, CICC)
* indication to intra-operative Trans Esophageal Ultrasound (TEE) based on American Society of Anesthesiologists (ASA)

Exclusion Criteria:

* contraindications to TEE based on American Society of Anesthesiologists (ASA) recommendations (esophageal or gastric diseases or previous surgery)
* emergency procedures
* central VAD already placed
* need for a CICC via supra/infra clavicular left veins
* need for a femorally inserted central catheter (FICC)
* need for a peripherally inserted central catheter (PICC)
* tricuspid valve regurgitation
* hemodynamic instability/ presence of an intra-aortic ballon pump (IABP)
* absence of septal atrial defect