Positive end-expiratory pressure increases the right-to-left shunt in mechanically ventilated patients with patent foramen ovale.

Abstract

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.

• Authors: B Cujec, P Polasek, I Mayers, D Johnson
• Journal: Annals of internal medicine (Ann Intern Med) Vol. 119 Issue 9 Pg. 887-94 (Nov 01 1993) ISSN: 0003-4819 [Print] United States
• PMID: 8215000 (Publication Type: Comparative Study, Journal Article)

Chemical References

• Oxygen

Topics

• Acute Disease
• Adult
• Aged
• Chi-Square Distribution
• Combined Modality Therapy
• Echocardiography, Transesophageal
• Female
• Heart Septal Defects, Atrial (complications, diagnostic imaging, physiopathology)
• Hemodynamics
• Humans
• Least-Squares Analysis
• Male
• Middle Aged
• Oxygen (blood)
• Positive-Pressure Respiration
• Random Allocation
• Respiration, Artificial
• Respiratory Insufficiency (complications, physiopathology, therapy)
• Stroke Volume