The Need of Slanted Side Holes for Venous Cannulae

Joong Yull Park

doi:10.1155/2012/854938

Abstract

Well-designed cannulae must allow good flow rate and minimize nonphysiologic load. Venous cannulae generally have side holes to prevent the rupture of blood vessel during perfusion. Optimizing side hole angle will yield more efficient and safe venous cannulae. A numerical modeling was used to study the effect of the angle (0°–45°) and number (0–12) of side holes on the performance of cannulae. By only slanting the side holes, it increases the flow rate up to 6% (in our models). In addition, it was found that increasing the number of side holes reduces the shear rate up to 12% (in our models). A new parameter called “penetration depth” was introduced to describe the interfering effect of stream jets from side holes, and the result showed that the 45°-slanted side holes caused minimum interfering for the flow in cannula. Our quantitative hemodynamic analysis study provides important guidelines for venous cannulae design.

Highlights

Cannula is one of the most primary tools for cardiac surgery, especially when the extracorporeal blood circulatory device is expected
This is important in consideration of (1) that minimizing buffer volume for venous reservoir is required for better clinical outcome and (2) that a low central venous pressure limits an active control of blood flow rate for extracorporeal devices
The flow from side holes disturbed the main stream in the center of cannula, and the minimization of such disturbance should be achieved in new designs of venous cannulae

Summary

Introduction

Cannula is one of the most primary tools for cardiac surgery, especially when the extracorporeal blood circulatory device is expected. A special care should be given in design of venous cannulae because, as opposed to arterial cannulae, they generally have side holes to improve hydraulic performance in suction of blood. This is important in consideration of (1) that minimizing buffer volume for venous reservoir is required for better clinical outcome and (2) that a low central venous pressure limits an active control of blood flow rate for extracorporeal devices. For the evaluation of performance of cannulae, the “Mnumber” (or “catheter number”) has been widely used [2]; the M-number is a single dimensionless number that is based on a Reynolds friction factor correlation and describes the pressure-flow relationship in a cannula. Without deep understanding and close observation on the local flow in cannula, it is hardly possible to design and evaluate the cannulae appropriately

Methods

Results

Conclusion