The peaked p wave reaches its maximum height as the PICC reaches the cavo-Atrial junction. As the PICC reaches the pericardial reflection, the p wave starts to become more peaked.

Schematic diagram showing how the intra-cavity ECG changes as the peripherally inserted central catheter (PICC) is inserted down the superior vena cava, through the cavo-atrial junction, and into the right atrium.

The electro-magnetic positioning system assists with initial placement of the catheter tip in the superior vena cava, after which the ECG system can be used to guide the final position relative to the cavo-atrial junction. The sensor, which is calibrated before insertion, contains an array of 3-axis magnetic sensor microchips, and provides magnetic field information that is used to triangulate the three-dimensional position and orientation of the stylet relative to the sensor. The electro-magnetic positioning system consists of a magnet-tipped stylet that is inserted through the PICC and left level with the tip, and a sensor that is placed over the chest wall. One manufacturer has recently developed a system that combines intra-cavity ECG with an electro-magnetic positioning system (Sherlock 3CG Tip Confirmation System Bard Access Systems, Salt Lake City, UT, USA), Fig. This method relies on the ability to position the catheter tip ‘blindly’ in the superior vena cava, before advancing using the ECG to guide depth. If the catheter tip is advanced further, the p wave becomes biphasic, which is thought to correspond to entry into the right atrium. One technology that is better suited to bedside insertion is the use of intra-cavity ECG, in which the catheter is inserted until the tip is positioned at the point of maximum p wave this is thought to correspond anatomically to the cavo-atrial junction 2. However, X-ray fluoroscopy is an expensive resource, and impractical in critically ill patients. We have previously shown that this method of catheter tip positioning may result in malposition rates of 42–76%, with a higher malposition rate in critically ill patients than in the general hospital population 1.Ī number of techniques exist to reduce the incidence of catheter tip malposition, including X-ray fluoroscopy. This ‘blind’ method commonly uses a combination of anthropometric measurements and operator experience to guide catheter length. Peripherally inserted central catheters are frequently positioned ‘blindly’ in the central circulation, with a post-insertion chest radiograph used to confirm the position of the catheter tip. They are frequently used for infusions that are irritant to the vascular endothelium, and are often left in position for several weeks or months it is therefore vital that the tip of the PICC is in an adequate position within the central circulation. Peripherally inserted central catheters (PICCs) are increasingly being used to provide access to the central venous circulation. These malposition rates are significantly lower than our own historical data, which used a ‘blind’ anthropometric technique to guide peripherally inserted central catheter insertion. When an adequate position was defined as mid/low superior vena cava, cavo-atrial junction or high right atrium (≤ 2 cm from cavo-atrial junction), 49 (20.5% 95% CI 16–26%) catheters were malpositioned. When an adequate position was defined as low superior vena cava or cavo-atrial junction, 134 catheters (56.1% 95% CI 50–62%) were malpositioned. A total of 239 catheters positioned using the Sherlock 3CG Tip Positioning System were analysed. In this observational study, we investigated how the Sherlock 3CG Tip Positioning System would affect peripherally inserted central catheter malposition rates, defined using a post-insertion chest radiograph, in critically ill patients.

Recently, a new technology has been introduced (Sherlock 3CG Tip Positioning System) that uses an electro-magnetic system to guide positioning in the superior vena cava, and then intra-cavity ECG to guide positioning at the cavo-atrial junction. Peripherally inserted central catheters are often positioned blindly in the central circulation, and this may result in high malposition rates, especially in critically ill patients.

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