Evaluation of Partial Pressure of Arterial Oxygen in Obese Patients in Supine Position during General Anesthesia

Background: Anesthetists should measure the concentration of supplemental oxygen to determine whether patients’ partial pressure of arterial oxygen (PaO2) is correct during general anesthesia. However, the standard PaO2 value in obese patients in the supine position is unknown. We evaluated the PaO2 with respect to the Broca-Katsura obesity index. Materials and Methods: From January 2001 to December 2013, we evaluated 472 patients aged ≥16 years old that underwent general anesthesia in the supine position. The anesthetic charts of 472 patients with an American Society of Anesthesiologists physical status of I or II were retrospectively reviewed to investigate the PaO2. Results: In patients aged 16 to <65 years old, the PaO2 was 165.7 ± 25.6 mmHg at a Broca-Katsura index of <20%, 141.8 ± 26.9 mmHg at a Broca-Katsura index of 20% to <40%, 132.7 ± 22.7 mmHg at a Broca-Katsura index of 40% to <60%, and 111.7 ± 34.6 mmHg at a Broca-Katsura index of ≥60%. In patients aged 65 to <84 years old, the PaO2 was 152.1 ± 23.8 mmHg at a Broca-Katsura index of <20%, 130.6 ± 26.7 mmHg at a Broca-Katsura index of 20% to <40%, and 127.5 ± 11.3 mmHg at a Broca-Katsura index of 40% to <60%. Conclusion: With an increasing Broca-Katsura index, the PaO2 tended to decrease with age from 16 to <65 years old and 65 to <84 years old. Additionally, the PaO2 tended to decrease with age from 16 to <65 years at a BrocaKatsura index of 20% to <40%.