Randomized, double-blind clinical trial to compare the efficacy of catheter sealing with saline, compared to low-dose heparin. 3,450 patients hospitalized at the Hospital Residencia Sant Camil, in Catalonia (Spain), will be randomized to each branch of study. The primary outcome will be the percentage of catheters removed due to obstruction in each branch of study. As secondary outcomes, the number of catheter-associated phlebitis, catheter-associated bacetrihemia, extravasation, and catheter loss will be measured. For the primary outcome, a superiority analysis will be carried out in terms of the percentage of obstructed catheters in each branch of the study.