BEIJING—Horizontal loops in catheter tubing can reduce flow rate by nearly two-thirds, a study has shown.

Investigators analyzed water flow through Foley catheters of different diameters with or without horizontal or vertical loops. They found the greatest reduction in flow, of 61.6%, with looped horizontal tubing.

Loops in catheter tubing are anecdotally known to be common in clinical practice, but at this point there is little caregivers or patients can do other than to visually check and straighten out the loops, according to lead investigator Jerry Blaivas, MD, of the State University of New York (SUNY) Downstate Medical Center in Brooklyn.

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“The real solution is better catheter/tubing design,” Dr. Blaivas told Renal & Urology News after presenting the study results at the International Continence Society’s 2012 annual meeting. “Our next steps are to find out how much of a clinical problem this is by checking residual urine in patients with catheters in hospital in-patients and to look into better methods of insuring low pressure drainage through the entire catheter-tubing-drainage system.”

To start looking into this vexing problem, Dr. Blaivas teamed up with three other investigators from SUNY and the Weill Cornell Medical College in New York.

They coupled 14, 16, 18 and 20 Fr silicone/latex Foley catheters to 21 7/8 inches of polyvinyl chloride (PVC) tubing that was 1.5 inches in diameter, using bushings and petroleum jelly to obtain a water-tight seal. They paired the catheter-tubing combination to PVC tubing that was 10, 30, 50 and 70 cm in length. They then filled the tubing with water, hung the apparatus over a Urocap III flow meter and let the water drain for 20 seconds.

The team tested four configurations of tubing with each of the four sizes of Foley catheter: vertical without loops, vertical with two loops that were each eight inches in diameter, horizontal without loops and horizontal with two loops. The investigators repeated the flow test five times for each configuration.

The horizontal looped configuration caused the greatest flow reduction. There was an average 61.6% flow reduction compared to the vertical unlooped configuration and a 53.6% reduction compared to vertical looped tubing.

The investigators believe that in the clinical setting, with a closed system and a drainage bag, the resistance and hence flow impedance would be even greater.