A new oxygenation index for reflecting intrapulmonary shunting in patients undergoing open-heart surgery

Chest. 2004 Feb;125(2):592-6. doi: 10.1378/chest.125.2.592.


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: PaO(2)/fraction of inspired oxygen (FIO(2)) x mean airway pressure (Paw). The standard formulas used were the oxygenation ratio (PaO(2)/FIO(2)), PaO(2)/alveolar partial oxygen pressure (PAO(2)), alveolar-arterial oxygen tension gradient (P[A-a]O(2)), and intrapulmonary shunt (venous admixture [Qsp/Qt]). There were significant negative (p < 0.05) correlations between the PaO(2)/(FIO(2) x Paw) and Qsp/Qt (r = - 0.85), between the PaO(2)/FIO(2) and Qsp/Qt (r = - 0.74), and between the PaO(2)/PAO(2) and Qsp/Qt (r = - 0.71). There was a significant positive (p < 0.05) correlation between the P(A-a)O(2) gradient and Qsp/Qt (r = 0.66). However, the correlation was strongest between the PaO(2)/(FIO(2) x Paw) and Qsp/Qt.

Conclusion: In this group of patients, PaO(2)/(FIO(2) x Paw) might be more reliable than other oxygenation measurements in reflecting intrapulmonary shunt.

Publication types

  • Comparative Study

MeSH terms

  • Adaptation, Physiological
  • Aged
  • Blood Gas Analysis
  • Carbon Dioxide / blood*
  • Coronary Artery Bypass / methods*
  • Coronary Disease / diagnosis
  • Coronary Disease / surgery*
  • Female
  • Follow-Up Studies
  • Hospitals, University
  • Humans
  • Male
  • Middle Aged
  • Monitoring, Intraoperative
  • Oximetry
  • Positive-Pressure Respiration*
  • Postoperative Care / methods
  • Probability
  • Prospective Studies
  • Pulmonary Circulation / physiology*
  • Pulmonary Gas Exchange / physiology*
  • Respiratory Function Tests
  • Risk Assessment
  • Sensitivity and Specificity
  • Severity of Illness Index


  • Carbon Dioxide