Postcardiopulmonary bypass hypoxemia: A prospective study on incidence, risk factors, and clinical significance

Objective:To evaluate the clinical significance of low arterial oxygen tens ion-inspired oxygen concentration (PaO2F1O2) ratio, as a measure of hypoxem ia, in the early period after cardiac surgery with cardiopulmonary bypass ( CPB); and to evaluate the preoperative, intraoperative, and postoperative f actors contributing to the development of hypoxemia within the first 24 hou rs after cardiac surgery with CPB. Design: Prospective observational study. Setting: University hospital. Participants: Patients who underwent elective or emergency cardiac surgery with CPB (n = 466). Interventions: Preoperative clinical and laboratory data were recorded, as were intraoperative and postoperative data regarding the PaO2-F1O2 ratio, f luid and drug therapy, and chest radiograph. Data analysis evaluated hypoxe mia as depicted by the PaO2-F1O2 ratios at 1, 6, and 12 hours after surgery . Thereafter, the effect of the PaO2-F1O2 ratios on time to extubation, lun g injury, and length of hospital stay was evaluated. The risk factors were analyzed in 3 separate periods: preoperative, intraoperative, and postopera tive. Univariate and multivariate analyses were performed on each period se parately. All data were analyzed in 2 consecutive steps: univariate analysi s and multivariate analysis. Measurements and Main Results: PaO2-F1O2 ratios after CPB were significantl y lower compared with baseline values. Six patients (1.32%) met the clinica l criteria compatible with acute lung injury. All 6 patients had prompt rec overy. Significant risk factors for hypoxemia were age, obesity, reduced ca rdiac function, previous myocardial infarction, emergency surgery, baseline chest radiograph with alveolar edema, high creatinine level, prolonged CPB time, decreased baseline Pa02-FI02, use of dopamine after discontinuation of CPB, coronary artery bypass grafting, use of left internal mammary arter y, higher pump flow requirement during CPB, increased level of hemoglobin o r total protein content, persistent hypothermia 2 and 6 hours after surgery , requirement for reexploration, event requiring reintubation, and chest ra diograph with alveolar edema 1 hour after surgery. Six hours after surgery, a lower PaO2-F1O2 ratio correlated significantly with time to extubation a nd lung injury. Conclusions:This study shows that despite improvements in the technique of CPB, hypoxemia depicted by low PaO2-F1O2 ratios is common in patients after CPB. It is short lived, however, and has minimal effect on the postoperati ve clinical course of these patients. Copyright (C) 2000 by WB. Saunders Co mpany.