Relationship between Arterial and Peak Expired Carbon Dioxide Pressure during Anesthesia and Factors Influencing the Difference

Abstract

To determine how closely peak expired P[partial pressure]CO2 measured by mass spectrometry reflects arterial PCO2 during anesthesia and what variables contribute to a difference between the 2 measurements, peak expired CO2, arterial PCO2 and other physiologic variables were measured simultaneously. There was a significant correlation between peak expired and arterial PCO2 (P < 0.001). The difference between temperature-corrected arterial and peak expired PCO2 was related to the presence or absence of lung disease, age, A.S.A. [American Society of Anesthesiologists] class, and systolic blood pressure. No significant relationship was seen between the temperature-corrected difference and duration of anesthesia, diastolic pressure, expired O2 concentration, or anesthetic agent. Mean temperature-corrected arterial PCO2 exceeded mean peak expired PCO2 by 1.7 torr in all patients, 0.8 torr in patients without lung disease, and 3.3 torr in patients with lung disease. In patients in whom > 1 arterial sample was obtained, initial differences correlated significantly with subsequent differences (P < 0.001).