Fluid flow during percutaneous drainage procedures: an in vitro study of the effects of fluid viscosity, catheter size, and adjunctive urokinase.

OBJECTIVE: An in vitro study was performed to determine the range of flow times of different bodily fluids through catheters of different diameters and to test the hypothesis that urokinase might decrease the viscosity of purulent material.
MATERIALS AND METHODS: A standard viscometer was used to measure the viscosities of water, blood, pseudocyst fluid, purulent material, and purulent material with admixed urokinase. For each fluid, Poiseuille's law was used to calculate the kinematic viscosity, from which theoretical drainage times through seven different sizes of catheters were calculated. These theoretical times were compared with the actual measured values to verify that flow was according to Poiseuille's law.
RESULTS: The calculated kinematic viscosities (in 10(-6) stokes) were as follows: water, 0.695 +/- 0.006; pseudocyst fluid, 2.185 +/- 0.008; blood, 3.001 +/- 0.049; abscess fluid without urokinase, 5.729 +/- 0.064; and abscess fluid with urokinase, 4.416 +/- 0.070. The viscosity of abscess fluid decreased by 23% with the addition of urokinase. Drainage time was considerably shorter with larger catheters.
CONCLUSION: Flow of various bodily fluids, including pus, is according to Poiseuille's law, confirming that for more viscous fluid, larger catheters provide more rapid drainage. Urokinase decreases viscosity of purulent material and increases flow for all sizes of catheters.