Continuous capnography should be used on patients admitted to post-anaesthesia care units (PACUs) with endotracheal tubes, but this monitoring is not always performed. Optimized ventilation in the PACU could be part of the global standards of practice to maintain the benefits of perioperative ventilation. The main objective was to study the rate of patients with alveolar hypoventilation before tracheal extubation or Laryngeal Mask Airway (LMA) removal upon the measurement of continuous capnography. In this prospective, parallel-group, randomized controlled study, we enrolled adult patients admitted to the PACU after general anaesthesia with an endotracheal tube or LMA in place. Patients were randomly assigned to two groups: in the Capno + group, nurses managed the patients with access to the capnometer and end-tidal carbon dioxide pressure (PETCO) measurements; in the Capno- group, nurses monitored the patients without seeing PETCO measurements. The primary outcome was the percentage of patients with PETCO measurements above 45 mm Hg during the minute before extubation. Secondary endpoints included the delay in recovering spontaneous breathing, rate of hypoxemia, delay before extubation, and length of stay in the PACU. Forty-eight patients were randomized into the two groups. The percentage of patients with PETCO > 45 mm Hg the minute before extubation was significantly decreased in the Capno + group (83.3% versus 54,1% in the Capno- and Capno + groups respectively, p = 0.029). There were no significant differences concerning secondary endpoints. The use of PETCO monitoring improves patient safety by decreasing the incidence of CO retention during recovery from general anaesthesia. This study suggests that this monitoring should be integrated in the PACU. The risk of hypoxemia can also be prevented through the early recognition of apnoea.Clinical Trial registry: clinicaltrial.gov. identifier: NCT03370081.< Réduire