Progress of end-tidal carbon dioxide monitoring in non-intubated patients

End-tidal carbon dioxide (ETCO₂) monitoring is an important tool for assessing respiratory and circulatory status of patients. It has become an integral component of perioperative anesthesia care in patients undergoing general anesthesia with endotracheal intubation. ETCO₂ monitoring can also benefit non-intubated patients. This review covers the basics of ETCO₂ and methods of partial pressure of ETCO₂ (PETCO₂) monitoring and focuses on the literature regarding PETCO₂ monitoring for non-intubated patients. Most studies explored the superiority of PETCO₂ monitoring in patients under sedation outside operating room, while others investigated the potential advantages of PETCO₂ monitoring in other scenarios such as post-anesthesia care unit, cardiopulmonary resuscitation, and patient-controlled analgesia. As carbon dioxide detection technology and sampling circuits continue to improve, PETCO2 monitoring is expected to be used in more medical scenarios.