PFO
Scenario: 88 year old female admitted to hospital after Non-Q wave MI. Patient required intubation during cardiac catheterization due to oversedation but pre procedure ABG was normal. Patient continue to have refractory hypoxemia. Workup for PE is negative with essentially normal chest CT. No infiltrates noted either. CXR is essentially normal too. Cardiac index is 2.7. Hpoxemia gets worse as PEEP was increased to counter hypoxemia. There is no auto-PEEP detected. Lactic acid and other workup is normal. Cardiac enzymes are actually improving. Regular Transthoracic Echo is normal. In short, you have a patient with stable labs and hemodynamics but with only refractory hypoxemia getting worse with increasing ventilator pressure.
Answer: Patent foramen ovale causing right to left shunt and worsening due to high right sided pressure from high PEEP. Patent foramen ovale is present in about 15% of the population. It get worse with age, usually from a mean of 3.4 mm in the first decade to 5.8 mm in the 10th decade of life. Any increase pressure on right side of heart may make it worse. Diagnosis can be made by bubble study during echocardiogram.
Bubble (contrast) study: After obtaining visualization of the atrial septum on echocardiography (transthoracic or transesophageal), a bolus of agitated saline is injected intravenously. Microbubbles will appear first in the right atrium. If the bubbles appear in the left atrium within 3 cardiac cycles of their appearance in the right atrium, the test is subjected to be call positive.
Treatment is closure of PFO surgically or by device. Or decreasing right sided pressure by IV nitro, diuresis and decreasing ventilator pressure till permanent solution can be intervened.
