Over the past two decades, continuous monitoring of end tidal carbon dioxide (etCO2) using capnography has become the American Society of Anesthesiologists (ASA) standard of care for continuous ventilation monitoring in patients undergoing general anesthesia in hospital operating rooms. In this setting, a review of a closed claims database concluded that capnography along with pulse oximetry monitoring could have prevented 93% of adverse respiratory events.1
Conventional capnography technology is associated with a number of drawbacks that have traditionally limited its use to the operating room. The development of innovative technology has made bedside capnography possible, and it is now rapidly becoming the standard of care for ventilation monitoring of non-intubated patients. Outside of the operating room, capnography addresses the specific needs of patients who are not intubated, who may alternate mouth/nose breathing, and who may be receiving supplemental oxygen. Growth in the use of capnography outside of the operating room can be attributed to increased attention to respiratory risk associated with opioid pain control therapy, as well as a growing recognition of the safety advantages of capnography for ventilation monitoring of patients receiving deep or moderate sedation.2
Capnography provides continuous, real-time, non-invasive measurement of etCO2, producing a waveform, or capnogram, that indicates changes in CO2 concentration throughout respiration. This enables measurement of the quality of breathing and exchange of O2 and CO2 during the respiratory cycle, beyond what is provided by pulse oximetry.
Accumulating evidence demonstrates that capnography is more accurate than traditional methods – pulse oximetry and visual inspection – for detecting alveolar hypoventilation and preventing hypoxemia during procedural sedation and patient-controlled analgesia (PCA).8,10,17,18,21,22
The best measure of adequate ventilation is the carbon dioxide tension of an arterial blood sample, which would not be practical due to the invasive nature of arterial blood sampling and the need for frequent sampling. However, the tension of carbon dioxide in expired gas, particularly at the end of a tidal expiration, closely approximates the tension in arterial blood. While normal PaCO2 is ~40 mm Hg, normal etCO2 is ~35–38 mm Hg.
source: smart capnography