Continuous monitoring of end-tidal carbon dioxide (PETCO2) is a long-established standard of care in the operating room (OR). Carbon dioxide can be useful to monitor the mechanically ventilated patient when used in conjunction with other monitors of the patient's clinical status. CO2 monitoring is affected by changes in metabolism or CO2 production, cardiovascular function, and respiratory function. Comparison of the gradient between arterial and end-tidal CO2 (PaCO2-PetCO2) can offer valuable information regarding a patient's clinical status. In newborns, the therapeutic administration of CO2 in the ventilator circuit has been used in the preoperative management of hypoplastic left heart syndrome. Volumetric capnography or volumetric CO2 (VCO2) is the measurement of CO2 as a function of volume as opposed to time. When CO2 production increases with constant minute ventilation, PaCO2 will increase. Alveolar minute ventilation can be used as a guide for predicting the PaCO2 that may result from adjusting ventilation parameters.

Anesthesiologists monitor their patients' breathing by listening to the lungs or auscultating over the trachea, counting the respiratory rate, watching chest movement and tidal volume, and employing pulse oximetry and capnography. This chapter focuses on issues related to capnography specific to anesthesia and the operating room. Capnography is the best monitor to identify complete disconnection of the breathing circuit. Exhaled tidal volume is a sensitive indicator of leaks and partial disconnects during mechanical ventilation. Capnography will continue to detect expired CO2 as long as the patient's exhaled tidal volume passes sidestream or mainstream sampling ports. Patients with chronic obstructive pulmonary disease or asthma exhibit typical capnograms with upsloping expired values brought about by the slow emptying of partially obstructed segments of the lungs. Intermittent PaCO2 determination has been used as a routine parameter for acid-base management during cardiopulmonary bypass (CPB).