Background and Goal of Study: The lower superior vena cava (SVC) near the junction with the right atrium (RA) is considered the ideal location for the central venous catheter tip to ensure proper perioperative function and prevent injuries. We determined the catheter insertion depth with a new formula using the sternoclavicular joint and the carina as landmarks, with 1.5 cm safety margin. The accuracy of tip positioning with radiologic landmark based technique (R) and Peres' formula (P) was compared in this study using transoesophageal echocardiography. 
Materials and Methods: Real-time ultrasound guided central venous catheterization was done through the right internal jugular or subclavian vein. Patients were randomly assigned to either the P group (n=93) or the R group (n=95). The optimal catheter tip position was considered within 2 cm above and 1 cm below the RA/SVC junction. Catheter tip position, abutment, angle to the vascular wall and flow stream were evaluated on bicaval view.
Results and Discussion: Distance from skin insertion point to the RA/SVC junction and determined depth of catheter insertion were more strongly correlated in the R group (17.4 [1.2] cm and 16.7 [1.5] cm, r=0.821, P< 0.001) than in the P group (17.3 [1.2] cm and 16.4 [1.1] cm, r=0.517, P< 0.001), with z=3.96 (P< 0.001). More tips were correctly positioned in the R group than in the P group (74.2% vs 92.6%, P=0.001). Abutment, tip angle to the lateral wall >40°, and disrupted flow stream were comparable between the groups. 
Conclusion(s): The catheter tip was positioned more accurately with radiologic landmark based technique than Peres' formula.
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Transoesophageal echocardiographic evaluation of positioning of central venous catheter determined by Peres’ formula and radiologic landmark based technique