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

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.

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.

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.

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