Does Size Matter? Measured and Modeled Effects of Suprapubic Catheter Size on Urinary Flow.

OBJECTIVE: To quantify the effects of catheter size and urinary sediment on catheter drainage, and to determine the French size at which catheter upsizing yields a diminished marginal return in flow.

MATERIALS AND METHODS: Latex Foley catheters (12-26 French [Fr]) were connected to a simulated bladder. Passive drainage times of 450 mL water were measured over 5 successive trials for each catheter size. The effect of sediment was modeled by adding 2g of infant rice cereal to the water. Measurements were repeated in half-length catheters to assess the effect of catheter length. A computational model of resistance was compared to measured data. Percent differences in catheter resistance based on measured catheter dimensions were determined.

RESULTS: Catheter resistance significantly decreased (P < .001) with increasing catheter size. All catheter sizes had significantly faster (P < .001) drainage times after being shortened, except for the 16 Fr catheter. All catheter sizes exhibited significantly prolonged (P < .001) drainage times after the addition of sediment, except for the 16 Fr catheter. Beyond 18 Fr, larger catheter sizes provided diminishing marginal returns in flow; upsizing from 18 Fr to 20 Fr reduced measured resistance by 19%, which was the lowest improvement in resistance between 2 catheter sizes. The coefficient of determination (R2 ) between measured and modeled resistances was 0.9754, confirming that the model of catheter performance was accurate.

CONCLUSION: Marginal improvement in urine flow occurs with catheter upsizing after 18 Fr; however, shortening catheter lengths may serve as another means of improving flow.