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