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Clinical Investigations in Critical Care |

A New Oxygenation Index for Reflecting Intrapulmonary Shunting in Patients Undergoing Open-Heart Surgery*

Mohamad F. El-Khatib; Ghassan W. Jamaleddine
Author and Funding Information

*From the Departments of Anesthesiology (Dr. El-Khatib) and Medicine (Dr. Jamaleddine), School of Medicine, American University of Beirut, Beirut, Lebanon.

Correspondence to: Mohamad Khatib, PhD, Department of Anesthesiology, American University of Beirut, PO Box 11-0236, Riad El Solh, Beirut 1107 2020 Lebanon; e-mail: mk05@aub.edu.lb



Chest. 2004;125(2):592-596. doi:10.1378/chest.125.2.592
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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.

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