The present study aims to evaluate the effect of mechanical insufflation-exsufflation on airway mucus clearance among mechanically ventilated ICU patients. A parallel group randomized clinical trial will be conducted in a single mixed medical-surgical ICU of a tertiary hospital in Southern Brazil. Adult ICU patients with a length of mechanical ventilation >24 hours will be evaluated for eligibility. Patients will be randomized in a 1:1 ratio to receive respiratory physiotherapy using a mechanical insufflation-exsufflation device (intervention group) or standard respiratory physiotherapy without the use of the mechanical insufflation-exsufflation device (control group). The primary outcome is the amount of aspirated respiratory mucus (weight in grams) 5 minutes after the finish of respiratory physiotherapy.