Arterial Blood Gases after Coronary Artery Bypass Surgery

Coronary artery bypass graft (CABG) surgery adversely affects arterial blood gas (ABC) determinations. The purposes of this study were to assess serial changes in ABCs following bypass surgery and identify factors that may influence these changes. Room air ABCs were obtained preoperatively and on days 1, 2, 4, 6, and 8 postoperatively on 125 patients undergoing bypass surgery. Fifty-five patients (saphenous vein grafting [SVG] group) had only SVG grafting while 70 (internal mammary artery [IMA] group) received one (60 patients) or two (10 patients) IMA grafts in addition to the SVG grafts and were subjected to pleurotomy. The mean preoperative values (± SD) were as follows: PaO2, 75.1 ± 7.7 mm Hg, P(A-a)O2, 20.9 ±7.5 mm Hg; PaCO2, 33.6 ± 4.1 mm Hg; pH, 7.43 ± 0.04; hemoglobin, 14.8 ± 1.4 g/dl; and hematocrit, 44.2 ± 3.9 percent. There was a large decrease in the PaO2 postoperatively. The nadir for the PaO2 (55.7 ± 6.6 mm Hg) occurred on the second postoperative day. Eight days postoperatively, there were still significant abnormalities; the PaO2 was 65.7 ± 7.3 mm Hg, the P(A-a)O2 was 33.2 ± 8.8 mm Hg; the hemoglobin was 10.5 ± 1.4 g/dl; and the hematocrit was 31.7 ± 4.0 percent. The decrease in the PaO2 was particularly noteworthy given the large decrease in the hemoglobin and hematocrit. The changes in the PaO2 were not significantly correlated with the age, number of grafts, pump time, length of anesthesia, or endotracheal intubation or smoking history. Immediately postoperatively, changes were similar in both groups (p>0.05); on the second postoperative day, the PaO2 had decreased 26.9 percent in the SVC group and 25.5 percent in the IMA group. However, the postoperative abnormalities resolved more slowly in the IMA group (p