Study objectives: To assess the reliability of new and traditional oxygenation measurements in reflecting intrapulmonary shunt.
Design: Prospective study.
Setting: Cardiac surgery unit at a university hospital.
Patients: Fifty-five patients undergoing coronary artery bypass grafting.
Measurements and results: Simultaneous blood samples were collected from an indwelling arterial line and a catheter for determination of blood gases. Standard accepted formulas were utilized to measure a new oxygenation index: Pao2/fraction of inspired oxygen (Fio2) × mean airway pressure (Paw). The standard formulas used were the oxygenation ratio (Pao2/Fio2), Pao2/alveolar partial oxygen pressure (Pao2), alveolar-arterial oxygen tension gradient (P[A-a]O2), and intrapulmonary shunt (venous admixture [Qsp/Qt]). There were significant negative (p < 0.05) correlations between the Pao2/(Fio2 × Paw) and Qsp/Qt (r = − 0.85), between the Pao2/Fio2 and Qsp/Qt (r = − 0.74), and between the Pao2/Pao2 and Qsp/Qt (r = − 0.71). There was a significant positive (p < 0.05) correlation between the P(A-a)O2 gradient and Qsp/Qt (r = 0.66). However, the correlation was strongest between the Pao2/(Fio2 × Paw) and Qsp/Qt.
Conclusion: In this group of patients, Pao2/(Fio2 × Paw) might be more reliable than other oxygenation measurements in reflecting intrapulmonary shunt.