title: 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).
  
  
  METHODS
  Convenience sample with randomized application of PEEP.
  
  
  METHODS
  General intensive care unit of a university teaching hospital.
  
  
  METHODS
  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.
  
  
  METHODS
  Randomized application of PEEP (0 and 10 cm of H2O).
  
  
  METHODS
  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.affiliation: Royal University Hospital, University of Saskatchewan, Saskatoon, Canada.
authors.forename: B
authors.initials: B
authors.lastname: Cujec
authors.forename: P
authors.initials: P
authors.lastname: Polasek
authors.forename: I
authors.initials: I
authors.lastname: Mayers
authors.forename: D
authors.initials: D
authors.lastname: Johnson
mesh_terms: D000208:Acute Disease; D000328:Adult; D000368:Aged; D016009:Chi-Square Distribution; D003131:Combined Modality Therapy; D017548:Echocardiography, Transesophageal; D005260:Female; D006344:Heart Septal Defects, Atrial / Q000150:complications* / Q000000981:diagnostic imaging / Q000503:physiopathology; D006439:Hemodynamics; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D011175:Positive-Pressure Respiration; D011897:Random Allocation; D012121:Respiration, Artificial; D012131:Respiratory Insufficiency / Q000150:complications / Q000503:physiopathology* / Q000628:therapy*; D013318:Stroke Volume
chemical_list: D010100:Oxygen