Arterial and End-Tidal Carbon Dioxide in Supine Obese Patients during General Anesthesia

Background: We investigated the differences between partial pressure of arterial carbon dioxide and end-tidal carbon dioxide (P(a-ET)CO2) with respect to the Broca-Katsura index (BKI), which is an obesity index, in obese patients during general anesthesia. Materials and Methods: From January 2003 to December 2013, we studied 601 patients aged 16 years old or over undergoing general anesthesia. Patients had American Society of Anesthesiology physical status I and II and we reviewed their anesthetic charts. The P(a-ET)CO2 with respect to the BKI divided patients into two groups: 16 to < 65 years old, and ≥ 65 years old, and compared the P(a-ET)CO2 values between the two groups. Results: In patients aged 16 to < 65 years old, the mean P(a-ET)CO2 was 2.2 ± 3.1 mmHg at BKI < 20%; 3.3 ± 3.1 mmHg at 20% < BKI < 40%; and 5.5 ± 5.0 mmHg at 40% < BKI < 60%. In patients aged ≥ 65 years old , the mean P(a-ET)CO2 was 3.2 ± 4.1 mmHg at BKI < 20%; 4.3 ± 3.6 mmHg at 20% to < 40%; and 4.4 ± 3.3 mmHg at 40% to < 60%. Conclusion: The P(a-ET)CO2 tends to increase in obese patients during general anesthesia with increasing BKI in patients aged 16 to < 65 years old.