  A hydrodynamic model is proposed to describe one of the most critical
problems in intensive medical care units: the formation of biofilms inside
central venous catheters. The incorporation of approximate solutions for the
flow-limited diffusion equation leads to the conclusion that biofilms grow on
the internal catheter wall due to the counter-stream diffusion of blood through
a very thin layer close to the wall. This biological deposition is the first
necessary step for the subsequent bacteria colonization.
