Assessing Validity of M-Mode Time-to-Turbulence "T2T" Echo Use to Confirm CVC Tip Position

1. Background:

The central venous catheter (CVC) is a vital tool in the intensive care unit. It is used to provide medications, fluids nutrition and assess central venous pressure. Common sites of insertion are internal jugular and subclavian vein. It is obligatory to confirm correct positioning of the CVC in the superior vena cava (SVC) at or before the junction with the right atrium before use. The incorrectly positioned catheter can lead to significant complications including arrhythmias and haemothorax. The most common method used to confirm correct CVC tip positioning is the chest x-ray (CXR). Frequent use of CXR in intensive care leads to repeated exposure to radiation and has implications for use of resources and cost. There have been multiple attempts to develop new methods to replace the CXR for confirmation of CVC tip position without increasing patient risk of radiation.

The use of ultrasound (US) has become routine practice to guide CVC insertion. It is well established that using ultrasound to assist in central venous catheter insertion reduces the incidence of complications (1). However ultrasound is currently not routinely used to confirm the correct position of the CVC tip.

The correct position for the CVC tip is widely accepted to be at or slightly above the SVC junction with the right atrium. CXR is the gold standard tool for assessing the correct tip position and is routinely requested after CVC insertion in the upper body veins. Several research studies have used varied US approaches to detect CVC positioning after subclavian (SC) and internal jugular (IJ) CVC placement.. Some studies focused on the direct US identification of the distal CVC tip near to or within the right atrium or the aberrant placement within an IJ or SC vein (2) (3) (4). Others indirectly identified venous insertion and distal CVC tip location near the right atrium by the rapid entry of turbulent flow into the right atrium after agitated saline or rapid saline flush of the distal CVC port. Delayed and weak turbulence suggests aberrant venous placement whereas complete lack of turbulence is concerning for arterial CVC placement (1) (5-11).The previous studies used a 2D substernal view to detect the turbulence in the right atrium. The time measurement had no set On and Set Off on the machine , which makes it hard to review or record. A great advantage of M-mode echocardiography is its high temporal resolution which enables simple and accurate measurement of the time and distance of any structure movement.(14). We are using M-Mode to measure a temporal change which makes it a more accurate measurement. The trigger time and the end point , i.e turbulence, can be recorded , reviewed and audited. 2. Rationale of the study:

In order to minimize the risk of radiation exposure and reduce resource use, we considered the use of Ultrasound to confirm the CVC tip position. We will assess the use of M-Mode in a novel way, we called Time to Turbulence (T2T), to determine the proximity of the CVC tip to the right atrium.