Persistent unexplained hypoxaemia can result from the presence of a Patent Foramen Ovale (PFO)

A quarter of young adults have a #PFO

Actually there is no deficiency of atrial septal tissue per se, in such cases

In the absence of left atrial dilation, the defect functions as a flap valve, only allowing right-to-left flow.

Normally, left atrial pressure exceeds right atrial pressure and no shunting occurs.

However, if right-sided pressures increase, right-to-left shunting and therefore potential hypoxaemia can occur.

Acutely, this may become evident in such patients

during #ventilator asynchrony

with maintenance of high positive end-expiratory pressures (PEEP) during mechanical ventilation

in #ARDS patients with acute cor pulmonale or with right ventricular systolic dysfunction, particularly as part of the right ventricular infarction syndrome.

The diagnosis should be considered in any intensive care patient in whom the degree of hypoxaemia appears disproportionate, and should be detectable by colour Doppler.

Management might include a counterintuitive decrease in positive end-expiratory pressure ( #PEEP )and the re-establishment of spontaneous ventilation.

#Hypoxia , #MechanicalVentilation , #ICU , #CriticalCare , #Anaesthesia , #IntensiveCare

Reference: AAGBI Core Topics in Anaesthesia 2015 , Echocardiography and Anaesthesia, Jonathan H. Rosser and Nicholas J. Morgan-Hughes