29.3% of bacteremias in intensive care units (ICU) are linked to vascular devices, including 7.7% to arterial catheters, with an influence on both morbility and mortality. It is now accepted that biofilm as a role on bacterial development on inner surface of vascular devices but there is yet a lack of clinical relevant data documenting a causal relation between biofilm formation and bacteremias. The investigators assume that a better structural and microbiological characterization of arterial catheter biofilm in ICU patients could help preventing bacteremias or have a more specific treatment when it appears.