Tissue perfusion, oxygenation and temperature of the assessed area will be made with the system Periflux 5000, composed of 2 units of Laser Doppler Flowmetry (LDF): PeriFlux 5001, which includes the laser source; and PeriFlux 5002, which provides temperature and tissue oxygenation measurements. The information of both instruments will be collected and integrated into a software that allows the simultaneous measurement of all signals. Tissue oxygenation will be measured by transcutaneous oximetry (TcpO2), a noninvasive procedure that reflects the amount of oxygen diffuses into the capillaries through the epidermis. This process depends on the state of respiratory oxygenation, the oxygen carrying capacity of blood and the overall circulatory condition. Any deterioration in any of these three members, immediately affect the skin tissue perfusion, which allows to evaluate how these factors affect the PU risk. It is measured by an electrode that heats the underlying tissue to create a local hyperemia that intensifies blood perfusion and, consecuently, oxygen pressure increases. The heat dissolves the lipid structure of the keratinized layers of the epidermis, allowing the skin permeability to gas diffusion.