A simple, standard method to characterize pressure/flow performance of vascular access cannulas

Area of Science:

• Biomedical Engineering
• Medical Devices
• Fluid Dynamics

Background:

• Vascular access cannulas for extracorporeal life support (ECLS) are sized by French (Fr) units, offering insufficient data on pressure (P) and flow (Q) performance.
• Previous metrics, like the M number, were complex and required nomograms, limiting clinical applicability.

Purpose of the Study:

• To introduce and validate an easier, clinically relevant metric for assessing cannula performance in ECLS.
• To establish the "UM number" (flow at 100 mm Hg P) as a practical standard for cannula selection and performance evaluation.

Main Methods:

• A simulated ECLS circuit with a centrifugal pump, Tygon tubing, and reservoir was utilized.
• Seventy-four cannulas (arterial, venous, double lumen; 6-50 Fr) were tested using a 3 cP glycerol solution to mimic blood viscosity.
• Pressure and flow data were collected using a Biopac system and ultrasonic flow probe across the cannulas' performance range.

Main Results:

• The UM number effectively characterizes the pressure-flow relationship for various cannulas.
• This metric provides a straightforward method for selecting ECLS access cannulas based on desired performance parameters.
• The UM number aids in verifying if actual cannula flow aligns with expected performance during ECLS procedures.

Conclusions:

• The UM number offers a simplified and clinically useful metric for evaluating extracorporeal life support cannula performance.
• Adoption of the UM number can improve the selection process and in-situ monitoring of vascular access cannulas.
• This metric enhances the ability of clinicians to match cannula performance to patient needs in ECLS.