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Positive End-Expiratory Pressure and Shunting across Foramen Ovale
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TO THE EDITOR:
The study by Cujec and colleagues [1], showing that positive end-expiratory pressure (PEEP) increased right-to-left shunting in patients with a patent foramen ovale, raises several questions. First, did the echocardiographers know whether the patients were receiving PEEP? The interpretation of contrast echocardiograms is potentially subjective [2], and a nonblinded study is open to bias. Second, did the patients with and without a patent foramen ovale have similar functional residual capacities? The ability of PEEP to improve oxygen delivery varies among patients and correlates well with lower initial functional residual capacity [3]; therefore, this variable should have been controlled. Finally, how did the shunt increase in the patent foramen ovale group when the arterial and mixed venous oxygen remained the same [4]? More data on the arterial oxygenation of individual patients might clarify this paradox.
As the authors note, several case reports [5] offer persuasive evidence that PEEP can worsen oxygenation in some patients with a patent foramen ovale. The ability of PEEP to recruit atelectatic alveoli in severe acute respiratory distress syndrome, however, may outweigh the potential detrimental effects of intracardiac shunting. The circumstances during which PEEP is a liability need to be better defined.
Mark D. Siegel, MD
Yale University School of Medicine; New Haven, CT 06520
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
- Copyright ©2004 by the American College of Physicians
