The critically ill patient is a challenge for the health professionals, not only for the management of their underlying disease, but also due to the consequences of prolonged bed-rest, the requirement of ventilatory support, the metabolic issues, and the secondary effects of the pharmacological management, influencing the occurrence of respiratory and systemic complications. With the aim of describing the effects of pulmonary rehabilitation in the critical patient, a scientific literature review was carried out including the following topics: pathophysiological changes, effects on the pulmonary function, and prevention of muscular disorders. In conclusion, the patients in critical state need, not only a suitable treatment for the resolution of their underlying disease, but also require an intervention for pulmonary, as well as an intrinsically muscular, rehabilitation, that leads to a total or partial recovery of the complications of the ICU stay.