Acute right-to-left inter-atrial shunt; an important cause of profound hypoxia

Three patients presented to our intensive care unit over a 3-yr period with profound hypoxia resulting from acute right-to-left inter-atrial shunt (RL IAS). Patient I was a 67-yr-old male with an atrial septal defect who becam e hypoxic and developed the rare sign of platypnoea following elective repa ir of an abdominal aortic aneurysm (breathlessness made worse when upright and relieved by lying flat). patient 2 was a 38-yr-old female who developed platypnoea and hypoxia secondary to a patent foramen ovale (PFO) and peric ardial effusion. Patient 3 was a 46-yr-old male with a PFO who developed hy poxia without platypnoea because of multiple pulmonary emboli following rig ht hemicolectomy. These case reports illustrate the need to consider RLIAS as a cause of hypoxia of sudden onset. Early use of bubble contrast echocar diography is indicated.