Pulmonary oxygen transfer deficits of diabetic origin in patients undergoing coronary artery bypass grafting

The objective of this study was to determine the effects of a diabetic disposition on pulmonary gas exchange by examining 72 patients who underwent coronary artery bypass grafting (CABG), using the arterial/alveolar oxygen tension ratio (a/a)Po ₂] as a criterion. Patients were divided into a diabetic (DM) group and a nondiabetic (non-DM) group. The postoperative blood gases and hemodynamic data measured when the blood glucose level was at a maximum on the day of CABG were used as the postoperative pulmonary gas exchange indices, and the physicians who managed these patients were unaware of this study. The preoperative (a/a)Po ₂ ratio was 0.66±0.03 (SE) in the DM group and 0.78±0.02 in the non-DM group (P<0.01), while the postoperative ratios were 0.42±0.03 and 0.52±0.03, respectively (P=0.01). The correlation coefficient (r) for regression analysis of the relation between the postoperative Pao ₂/Fio ₂ ratio and the postoperative (a/a)Po ₂ ratio was 0.99 in the DM group (P<0.01) and 0.88 in the non-DM group (P<0.01). The r values of the relation between (a/a)Po ₂ and (a-a)Po ₂ were –0.68 (P<0.00) and –0.84 (P<0.01), while those for the respiratory index were –0.87 (P<0.01), and –0.93 (P<0.01), respectively. Thus, pulmonary oxygen transfer was compromised before and after CABG in the DM group compared to the non-DM group. Moreover, the Pao ₂/Fio ₂, being the simplest pulmonary gas exchange index to calculate, was a reliable substitute for the (a/a)Po ₂ ratio during the early postoperative management of CABG patients.