LETTER
Positive End-Expiratory Pressure and Shunting across Foramen Ovale
Mark D. Siegel, MD
1 April 1994 | Volume 120 Issue 7 | Page 620
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.
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Author and Article Information
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Yale University School of Medicine; New Haven, CT 06520
1. Cujec B, Polasek P, Mayers I, Johnson D. Positive end-expiratory pressure increases the right-to-left shunt in mechanically ventilated patients with patent foramen ovale. Ann Intern Med. 1993; 119:887-94.
2. Cross SJ, Thomson LF, Evans SA, Lee HS, Jennings KP. Inter- and intra-observer variability in detection of patent foramen ovale with contrast echocardiography. Eur Heart J. 1993; 14:388-90.
3. Suter PM, Fairley HB, Isenberg MD. Optimum end-expiratory airway pressure in patients with acute pulmonary failure. N Engl J Med. 1975; 292:284-9.
4. West JB. Pulmonary Pathophysiology—The Essentials. 3d ed. Baltimore: Williams & Wilkins; 1987;30.
5. Ravenscraft SA, Marinelli WA, Johnson T, Henke CA. Profound hypoxemia precipitated by positive-end-expiratory pressure: induction of an intracardiac shunt. Crit Care Med. 1992; 20:434-6.
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