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Positive End-Expiratory Pressure Increases the Right-to-Left Shunt in Mechanically Ventilated Patients with Patent Foramen Ovale

Bibiana Cujec, MD; Petr Polasek, MD; Irvin Mayers, MD; and David Johnson, MD
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From the Royal University Hospital, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 0X0 Canada. Requests for Reprints: Bibiana Cujec, MD, Division of Cardiology, Royal University Hospital, Saskatoon, Saskatchewan, Canada S7N OXO. Acknowledgments: The authors thank the staff of the Royal University Hospital Intensive Care Unit for their assistance in this project and Anita Zacharias and Helen Reid for preparing the manuscript.


Copyright 2004 by the American College of Physicians


Ann Intern Med. 1993;119(9):887-894. doi:10.7326/0003-4819-119-9-199311010-00004
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Objective: To determine the effect of the presence of a patent foramen ovale on the right-to-left shunt in patients with respiratory failure who receive positive end-expiratory pressure (PEEP).

Design: Convenience sample with randomized application of PEEP.

Setting: General intensive care unit of a university teaching hospital.

Patients: A total of 46 mechanically ventilated patients with respiratory failure requiring an inspired oxygen concentration of at least 50% and a PEEP of at least 5 cm of H2O.

Intervention: Randomized application of PEEP (0 and 10 cm of H2O).

Measurements: A patent foramen ovale was detected by saline contrast transesophageal echocardiography. The alveolar-to-arterial oxygen difference and the right-to-left shunt were calculated from arterial and venous blood gas sampling.

Results: In patients without a patent foramen ovale (n = 39), the alveolar-to-arterial oxygen difference and the shunt fraction decreased (50 mm Hg [95% CI, 21 to 67]and 0.05[CI, 0.03 to 0.07],respectively) after adding PEEP (10 cm of H2O). In patients with a patent foramen ovale (n = 7), minimal changes were noted in the alveolar-to-arterial oxygen difference (4 mm Hg, P > 0.2), but the shunt fraction increased (0.05, CI, 0 to 0.09). Adding PEEP (10 cm of H2O) increased the shunt fraction in 6 of 7 (86%) patients with a patent foramen ovale, whereas the shunt increased in only 7 of 39 (18%) patients without a patent foramen ovale (P < 0.007).

Conclusions: A patent foramen ovale was found in 7 of 46 patients (15%; CI, 6% to 29%) with acute respiratory failure. This condition is a common cause of lack of improvement in oxygenation with the addition of PEEP in the mechanically ventilated patient. In patients with a patent foramen ovale, the right-to-left shunt is usually increased by using PEEP.

Figures

Grahic Jump Location
Figure 1.
The changes after adding positive end-expiratory pressure (10 cm of H2O) in patients with and without a patent foramen ovale.leftrighthatched bar*P**P

Changes in the alveolar-to-arterial difference for oxygen ( ) and in shunting ( ) are shown in those patients with a patent foramen ovale ( ) and in those patients without a patent foramen ovale (white bar). Note that increases in shunting and increases in the alveolar-to-arterial difference for oxygen are represented by negative values and reflect more severe conditions. = 0.003; = 0.044.

Grahic Jump Location

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