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

2000; Elsevier BV; Volume: 85; Issue: 6 Linguagem: Inglês

10.1093/bja/85.6.921

1471-6771

Ivan L Marples, Mike Heap, S K Suvarna, Gary Mills,

Congenital Heart Disease Studies

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 (RLIAS). Patient 1 was a 67-yr-old male with an atrial septal defect who became hypoxic and developed the rare sign of platypnoea following elective repair 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 pericardial effusion. Patient 3 was a 46-yr-old male with a PFO who developed hypoxia without platypnoea because of multiple pulmonary emboli following right hemicolectomy. These case reports illustrate the need to consider RLIAS as a cause of hypoxia of sudden onset. Early use of bubble contrast echocardiography is indicated. 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 (RLIAS). Patient 1 was a 67-yr-old male with an atrial septal defect who became hypoxic and developed the rare sign of platypnoea following elective repair 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 pericardial effusion. Patient 3 was a 46-yr-old male with a PFO who developed hypoxia without platypnoea because of multiple pulmonary emboli following right hemicolectomy. These case reports illustrate the need to consider RLIAS as a cause of hypoxia of sudden onset. Early use of bubble contrast echocardiography is indicated. Shunting of blood across a defect between the two sides of the heart is usually directed by the left-to-right pressure gradient. A large and persistent left-to-right shunt can increase pulmonary blood flow, which over months or years leads to microvascular changes, increased pulmonary vascular resistance and elevated pulmonary artery pressure. When the pulmonary arterial pressure approaches the systemic arterial pressure, the direction of the shunt reverses (the Eisenmenger syndrome). This chronic development of right-to-left shunt (RLIAS) is accompanied by electrocardiographic changes of atrial enlargement and right ventricular hypertrophy. Chest radiography reveals prominent pulmonary arteries.1Vongpatanasin W Brickner ME Hillis LD Lange RA The Eisenmenger syndrome in adults [Review].Ann Intern Med. 1998; 128: 745-755Crossref PubMed Scopus (242) Google Scholar In contrast, the adult patient with an asymptomatic inter-atrial defect may develop an acute RLIAS following a cardiac or respiratory insult. Acute RLIAS is a separate clinical entity from the Eisenmenger syndrome. Acute RLIAS is often overlooked as a cause of hypoxia2Al Khouzaie T Busser JR A rare cause of dyspnea and arterial hypoxemia.Chest. 1997; 112: 1681-1682Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar but early diagnosis can direct therapy and avoid unnecessary invasive investigations. The three cases reported here illustrate the need to consider RLIAS in the differential diagnosis and investigation of profound hypoxia. A 67-yr-old man presented for elective repair of an abdominal aortic aneurysm. He had a past history of hypertension, transient ischaemic attacks and a left hemiparesis from which he had made a full recovery. His exercise tolerance was good and a preoperative multiple uptake-gated acquisition scan demonstrated a left ventricular ejection fraction of 67%. Anaesthesia and surgery were uneventful. The perioperative cardiac index was 3–4 litres min−1 m−2 and pulmonary arterial pressures ranged between 28/8 and 52/24 mm Hg. He required admission to intensive care unit (ICU) 3 days postoperatively with hypoxia (Pao2=5 kPa) on room air, pulmonary oedema, blood pressure of 90/60 mm Hg and oliguria. He required tracheal intubation, positive pressure ventilation, diuretics and inotropes. His oxygenation improved, allowing tracheal extubation after 3 days but after 10 days his Pao2 was 5.65 kPa and Paco2 2.7 kPa on a Fio2 0.95. He also developed platypnoea; that is he was unable to sit upright because of severe breathlessness but he was less breathless when lying flat, particularly in the left lateral decubitus position. Initially the underlying cause of this patient's hypoxia was not clear. Transthoracic echocardiography (TTE) demonstrated good left ventricular function, mild mitral regurgitation and septal hypertrophy. A lung perfusion scintographic scan showed no evidence of pulmonary embolism. Thoracic computerized tomography revealed non-specific bilateral shadowing of the lung fields consistent with adult respiratory distress syndrome (ARDS) or infection. Despite antibiotic therapy followed by a trial of prednisolone 70 mg day−1 for possible ARDS, he continued to deteriorate and required reintubation and positive pressure ventilation. A pulmonary artery flotation catheter demonstrated a cardiac index of 2.1 litres min−1 m−2, mean right atrial pressure of 8 mm Hg, mean pulmonary arterial pressure of 37 mm Hg and pulmonary artery occlusion pressure of 3 mm Hg. During inspired nitric oxide therapy at 20 p.p.m. the cardiac index increased to 3.8 litres min−1 m−2, the mean right atrial pressure was 4 mm Hg, mean pulmonary arterial pressure 34 mm Hg and pulmonary artery occlusion pressure 5 mm Hg. The Pao2 increased from 10.5 to 24.5 kPa on a Fio2 1.0. A cardiology opinion was sought concerning the possibility of an inter-atrial shunt, but this diagnosis was thought to be excluded by the absence of a persistent right-to-left pressure gradient; right atrial pressure range of 4–8 mm Hg with a pulmonary artery occlusion pressure range of 3–5 mm Hg. However, an inter-atrial defect was discovered fortuitously during pulmonary angiography when a catheter passed from the right atrium into the left atrium. Bubble contrast transoesophageal echocardiogram (TOE) demonstrated RLIAS with severe impairment of right ventricular function (Fig. 1). The patient became septicaemic and died on the 26th postoperative day. Post-mortem examination revealed a secundum ASD, absent superior vena cava and anomalous venous drainage via a dilated coronary sinus. The right ventricle appeared normal and the lungs were oedematous. On histological examination, there was mild pulmonary fibrosis but no features of ARDS, organizing pneumonia, or pulmonary hypertension. A 38-yr-old woman presented with platypnoea and cyanosis that developed over a period of 4 days. Sitting upright exacerbated her breathlessness and she was more comfortable when lying flat despite being profoundly hypoxic. She had a past history of chronic renal impairment and aortic incompetence. At presentation she was an inpatient recuperating from an episode of infective endocarditis and gastrointestinal bleeding for which she had required treatment in the ICU. On physical examination she was apyrexial, heart rate 110 beats min−1, arterial pressure 120/80 mm Hg and the jugular venous pressure was not elevated. An aortic murmur was present, but unchanged from previous examinations; respiratory rate was 20 b.p.m. and chest auscultation was normal. Arterial blood gases on a Fio2 0.6 were: pH 7.6, Pao2 5.6 kPa, Paco2 3.8 kPa, base excess 6.3 mmol litre−1. A chest radiograph showed a small right pleural effusion. Lung perfusion scintographic scan demonstrated a single segment perfusion defect in the right mid-zone. A preliminary diagnosis of pulmonary embolism was made but the decision to anticoagulate was deferred until a pulmonary angiogram could be performed in view of her recent history of gastrointestinal haemorrhage. During pulmonary angiography, the catheter passed through a patent foramen ovale into the left atrium and left upper lobe pulmonary vein. Radio-opaque dye flowed from the right to the left atrium. Pulmonary arteriography demonstrated no emboli. Mean pulmonary arterial pressure was 12 mm Hg and mean right atrial pressure was 13 mm Hg compared with 8 mm Hg in the left atrium. Right atrial Po2 was 2.8 kPa and the left atrial Po2 was 5.5 kPa. Transthoracic echocardiogram revealed a right-sided pericardial effusion, 4.5 cm in depth, compressing the right ventricle. Left ventricular function was good. Pericardial tap brought immediate relief of the patient's hypoxia; the Pao2 rising from 5.8 to 30.4 kPa, on oxygen 10 litres min−1 by facemask. A 46-yr-old man presented with breathlessness 4 days after right hemicolectomy for caecal carcinoma. Axillary temperature was 38.5°C, he had a sinus tachycardia 135 beat min−1, arterial pressure 90/60 mm Hg and a respiratory rate of 32 breath min−1. Pao2 was 4.1 kPa and Paco2 4.2 kPa on room air. Oxygen at maximum flow via a facemask did not improve his hypoxia and he was transferred to ICU. Fio2 0.9 with CPAP 5 cm H2O produced a Pao2 7.5 kPa. The patient was not distressed despite his hypoxia and was able to tolerate lying flat for a pulmonary angiogram. Pulmonary angiogram revealed a large embolus in the left-upper lobe pulmonary artery with smaller emboli in the right middle lobe pulmonary artery and right pulmonary vessels peripherally. The catheter passed from the right atrium to the left atrium. Mean right atrial pressure was 13 mm Hg, left atrial pressure 11 mm Hg and mean pulmonary arterial pressure 27 mm Hg. Left pulmonary venous Po2 was 32.3 kPa but the radial arterial Pao2 was 6.24 kPa. A Greenfield inferior vena cava filter was deployed with its base at the level of the L3-L4 disc space. A bolus of tissue plasminogen activator 5 mg i.v. plus an infusion of 5 mg h−1 was instituted. The patient's oxygenation improved over the next 3 days and thereafter his recovery was uneventful. Acute RLIAS is a rare but important cause of profound hypoxia. The pathophysiology of acute RLIAS arises from an inter-atrial defect coupled with a secondary cardiac or pulmonary insult. Patent foramen ovale, which occurs in approximately 30% of the adult population,3Fawcett E Blachford JV The frequency of an opening between the right and left auricles at the seat of the foetal foramen ovale.J Anat Physiol. 1901; 35: 67-70Google Scholar is present in the majority of reported cases of acute RLIAS. ASD is present in the remainder. A rise in right atrial pressure above left atrial pressure may precipitate RLIAS. This can be the result of obstruction of pulmonary blood flow by pulmonary embolus4Estagnasié P Djedaïni K Le Bourdellès G Coste F Dreyfuss D Atrial septal aneurysm plus a patent foramen ovale.Chest. 1996; 110: 846-848Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar (Patient 3), increased transmural pressures in asthma,5Robert R Ferrandis J Malin F Herpin D Pourrat O Enhancement of hypoxemia by right-to-left shunting in severe asthma.Intensive Care Med. 1994; 20: 585-587Crossref PubMed Scopus (8) Google Scholar right ventricular hypokinesis following right ventricular infarction6Laham RJ Ho KKL Douglas PS et al.Right ventricular infarction complicated by acute right-to-left shunting.Am J Cardiol. 1994; 74: 824-826Abstract Full Text PDF PubMed Scopus (24) Google Scholar or coronary artery bypass grafting,7Rose GC Armstrong WF Mahomed Y Feigenbaum H Atrial level right to left intracardiac shunt associated with postoperative hypoxemia: demonstration with contrast two-dimensional echocardiography.J Am Coll Cardiol. 1985; 6: 920-922Crossref PubMed Scopus (14) Google Scholar or as a result of elevated Paco2 in hemidiaphragmatic paresis.8Farber HW Make B Physiologic closure of a symptomatic patent foramen ovale with oxygen therapy.Am Rev Respir Dis. 1985; 131: 181-183PubMed Google Scholar However, in similar cases right heart pressures can be normal, which indicates that other factors can induce RLIAS.4Estagnasié P Djedaïni K Le Bourdellès G Coste F Dreyfuss D Atrial septal aneurysm plus a patent foramen ovale.Chest. 1996; 110: 846-848Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar 9Brydon C Fawcett WJ Treasure T Clarke JT Pulmonary embolus and patent foramen ovale: a rare cause of refractory hypoxaemia.Br J Anaesth. 1993; 71: 298-300Crossref PubMed Scopus (10) Google Scholar 10Cox D Taylor J Nanda NC Refractory hypoxemia in right ventricular infarction from right-to-left shunting via a patent foramen ovale: efficacy of contrast transesophageal echocardiography.Am J Med. 1991; 91: 653-655Abstract Full Text PDF PubMed Scopus (20) Google Scholar Mechanical distortion of the heart can alter the relative positions of the atrial septum and the inferior vena cava (IVC) which then directs the flow of blood from the IVC towards the inter-atrial defect and into the left atrium. Mediastinal shift following lung resection is the most commonly reported cause of RLIAS.11van Rossum P Plokker HWM Ascoop CAPL Breathlessness and hypoxaemia in the upright position after right pneumonectomy.Eur Heart J. 1988; 9: 1230-1233Crossref PubMed Scopus (22) Google Scholar Other causes of distortion of cardiac anatomy with no apparent right-to-left pressure gradient include thoracic trauma,12Pacht ER Interatrial right-to-left shunting in the absence of elevated right-sided pressures after major trauma [letter].Chest. 1994; 105: 1614Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar rupture of the papillary muscles,13Ribichini F Conte R Lioi A Dellavalle A Ugliengo G Subacute tricuspid regurgitation with severe hypoxemia complicating blunt chest trauma.Chest. 1996; 109: 289-291Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar after tuberculosis,14Remy-Jardin M Remy J Wallaert B Right-to-left shunting through a patent foramen ovale without pulmonary hypertension.Chest. 1990; 97: 1250-1252Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar thoracic aortic aneurysm,15Laybourne KA Martin ET Cooper RAS Holman WL Platypnea and orthodeoxia: shunting associated with an aortic aneurysm.J Thorac Cardiovasc Surg. 1997; 113: 955-956Abstract Full Text Full Text PDF PubMed Scopus (56) Google Scholar pericardial effusion (Patient 2),16Klepper JI Seifert F Lawson WF et al.Intracardiac right-to-left shunting following cardiac surgery.Am Heart J. 1988; 116: 189-192Abstract Full Text PDF PubMed Scopus (10) Google Scholar and metastatic cardiac disease.17Gallerstein PE Belluscio RL Berger M Onseng F Jurado RA Right-to-left intracardiac shunt: a unique presentation with metastatic cardiac disease.J Am Coll Cardiol. 1984; 3: 865-867Crossref PubMed Scopus (18) Google Scholar The mechanism of RLIAS is unclear in cases of morbid obesity,18Collop NA Refractory hypoxaemia in a morbidly obese 28-year-old woman.Chest. 1996; 109: 1101-1102Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar cystic fibrosis,19Davidson A Chandrasekaran K Guida L Holsclaw DS Enhancement of hypoxemia by atrial shunting in cystic fibrosis.Chest. 1990; 98: 543-545Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar adult respiratory distress syndrome20Dewan NA Gayasaddin M Angelillo VA O'Donohue WJ Mohiuddin S Persistent hypoxemia due to patent foramen ovale in a patient with adult respiratory distress syndrome.Chest. 1986; 89: 611-613Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar and exposure to low atmospheric pressure.21Sorrentino M Resnekov L Patent foramen ovale associated with platypnea and orthodeoxia.Chest. 1991; 100: 1157-1158Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar 22Levine BD Grayburn PA Voyles WF Greene ER Roach RC Hackett PH Intracardiac shunting across a patent foramen ovale may exacerbate hypoxemia in high-altitude pulmonary edema.Ann Intern Med. 1991; 114: 569-570Crossref PubMed Scopus (37) Google Scholar Platypnoea is a sign that is strongly associated with RLIAS. This sign, first described in 1949 and given the name platypnoea in 1969, occurs in approximately one quarter of reported cases of acute RLIAS.23Burchell HB Helmolz HF Wood EH Reflex orthostatic dyspnea associated with pulmonary hypotension [Abstract].Am J Physiol. 1949; 159: 563-564Google Scholar 24Altman M Robin ED Platypnea (diffuse zone I phenomenon?).N Eng J Med. 1969; 281: 1347-1348Crossref PubMed Scopus (94) Google Scholar A corresponding postural change in oxygenation is known as orthodeoxia.25Robin ED Laham D Horn BR Theodore J Platypnea related to orthodeoxia caused by true vascular lung shunts.N Eng J Med. 1976; 294: 941-943Crossref PubMed Scopus (165) Google Scholar RLIAS is often diagnosed unexpectedly during investigation for other causes of acute hypoxia.26Schnabel TG Ratto O Kirby CK Johnson J Comroe JH Postural cyanosis and angina pectoris following pneumonectomy: relief by closure of an interatrial septal defect.J Thorac Surg. 1956; 32: 246-250Abstract Full Text PDF PubMed Google Scholar A pulmonary angiography catheter may pass through an inter-atrial defect, as occurred in our patients, but the angiogram may be reported as normal despite the presence of a significant RLIAS.4Estagnasié P Djedaïni K Le Bourdellès G Coste F Dreyfuss D Atrial septal aneurysm plus a patent foramen ovale.Chest. 1996; 110: 846-848Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar 13Ribichini F Conte R Lioi A Dellavalle A Ugliengo G Subacute tricuspid regurgitation with severe hypoxemia complicating blunt chest trauma.Chest. 1996; 109: 289-291Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar Lung perfusion scintigraphy indicates RLIAS when early activity is detected in the brain, myocardium and kidneys.27Dlabal PW Stutts BS Jenkins DW Harkleroad LE Stanford WT Cyanosis following right pneumonectomy: importance of patent foramen ovale.Chest. 1982; 81: 370-372Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar It has been advocated as the investigation of choice28Durand E Bussy E Gaillard JF Lung scintigraphy in postpneumonectomy dyspnea due to a right-to-left shunt.J Nucl Med. 1997; 38: 1812-1815PubMed Google Scholar but failed to detect RLIAS in our first and second patients and in several other reported cases.2Al Khouzaie T Busser JR A rare cause of dyspnea and arterial hypoxemia.Chest. 1997; 112: 1681-1682Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar 4Estagnasié P Djedaïni K Le Bourdellès G Coste F Dreyfuss D Atrial septal aneurysm plus a patent foramen ovale.Chest. 1996; 110: 846-848Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar 29Dexter L Atrial septal defect.Br Heart J. 1956; 18: 209-225Crossref PubMed Scopus (104) Google Scholar Injection of radiolabelled microaggregates into the arm has resulted in a normal perfusion scan whereas injection into the foot demonstrated shunt because of preferential flow from the IVC across the interatrial defect.30Thomas JD Tabakin BS Ittleman FP Atrial septal defect with right to left shunt despite normal pulmonary artery pressure.J Am Coll Cardiol. 1987; 9: 221-224Crossref PubMed Scopus (51) Google Scholar Bubble contrast echocardiography has the greatest sensitivity for detecting RLIAS and has the advantage that it is a relatively non-invasive technique that can be performed at the bedside.1Vongpatanasin W Brickner ME Hillis LD Lange RA The Eisenmenger syndrome in adults [Review].Ann Intern Med. 1998; 128: 745-755Crossref PubMed Scopus (242) Google Scholar 31Lynch JJ Schuchard GH Gross CM Wann LS Prevalence of right-to-left shunting in a healthy population: detection by Valsalva maneuver contrast echocardiography.Am J Cardiol. 1984; 53: 1478-1480Abstract Full Text PDF PubMed Scopus (284) Google Scholar 32Berry L Braude S Hogan J Refractory hypoxaemia after pneumonectomy: diagnosis by transoesophageal echocardiography.Thorax. 1992; 47: 60-61Crossref PubMed Scopus (14) Google Scholar A syringe filled with 9 ml saline and 1 ml air is agitated, macroscopic bubbles expelled and the remaining microbubble emulsion injected i.v. The test is positive if microbubbles are seen in the left atrium (Fig. 1) within two to three cycles of the initial appearance in the right atrium. Bubble contrast echocardiography has detected RLIAS as a first line investigation15Laybourne KA Martin ET Cooper RAS Holman WL Platypnea and orthodeoxia: shunting associated with an aortic aneurysm.J Thorac Cardiovasc Surg. 1997; 113: 955-956Abstract Full Text Full Text PDF PubMed Scopus (56) Google Scholar 22Levine BD Grayburn PA Voyles WF Greene ER Roach RC Hackett PH Intracardiac shunting across a patent foramen ovale may exacerbate hypoxemia in high-altitude pulmonary edema.Ann Intern Med. 1991; 114: 569-570Crossref PubMed Scopus (37) Google Scholar 33Vacek JL Foster J Quinton RR Savage PJ Right-to-left shunting after lobectomy through a patent foramen ovale.Ann Thorac Surg. 1985; 39: 576-578Abstract Full Text PDF PubMed Scopus (21) Google Scholar and when preceding pulmonary angiogram and lung perfusion scintigram have both been falsely negative.2Al Khouzaie T Busser JR A rare cause of dyspnea and arterial hypoxemia.Chest. 1997; 112: 1681-1682Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar 12Pacht ER Interatrial right-to-left shunting in the absence of elevated right-sided pressures after major trauma [letter].Chest. 1994; 105: 1614Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar 29Dexter L Atrial septal defect.Br Heart J. 1956; 18: 209-225Crossref PubMed Scopus (104) Google Scholar Injection of contrast via the leg may increase the sensitivity of the test as most shunting occurs via the IVC.34Strunk B Cheitlin MD Stulbarg MS Schiller NB Right-to-left interatrial shunting through a patent foramen ovale despite normal intracardiac pressures.Am J Cardiol. 1987; 60: 413-415Abstract Full Text PDF PubMed Scopus (101) Google Scholar RLIAS is exacerbated when intra-thoracic pressure is increased by PEEP in the artificially ventilated patient35Lemaire F Richalet JP Carlet J Brun-Buisson C MacLean C Postoperative hypoxemia due to opening of a patent foramen ovale confirmed by a right atrium-left atrium pressure gradient during mechanical ventilation.Anesthesiology. 1982; 57: 233-236Crossref PubMed Scopus (51) Google Scholar and during coughing or the Valsalva manoeuvre.31Lynch JJ Schuchard GH Gross CM Wann LS Prevalence of right-to-left shunting in a healthy population: detection by Valsalva maneuver contrast echocardiography.Am J Cardiol. 1984; 53: 1478-1480Abstract Full Text PDF PubMed Scopus (284) Google Scholar Each of these manoeuvres can increase the likelihood of detecting RLIAS by echocardiography. Bubble contrast echocardiography is a safe technique widely reported in the investigation of chronic RLIAS, particularly in patients who are thought to have developed paradoxical embolism.36Meacham RR Headley AS Bronze MS Lewis JB Rester MM Impending paradoxical embolism [Review].Arch Intern Med. 1998; 158: 438-448Crossref PubMed Scopus (110) Google Scholar 37Ward R Jones D Haponik EF Paradoxical Embolism. An underrecognized problem.Chest. 1995; 108: 549-558Abstract Full Text Full Text PDF PubMed Scopus (121) Google Scholar Paradoxical embolism is not commonly associated with profound hypoxia as these patients present with systemic embolic phenomena. Patient 1 had a past history of cerebrovascular events and whether these were caused by paradoxical emboli is an interesting matter for conjecture. Treatment of RLIAS is treatment of the underlying cause and/or closure of the PFO or ASD. Successful closure of the inter-atrial defect is frequently reported38Wright LJ Burchell HB Kirklin JW Wood EH Congenital displacement of the tricuspid valve (Ebstein's malformation): report of a case with closure of an associated foramen ovale for the correction of right-to-left shunt.Proc Staff Meet Mayo Clin. 1954; 29: 278-284PubMed Google Scholar although some patients have died following its closure because of right heart failure.20Dewan NA Gayasaddin M Angelillo VA O'Donohue WJ Mohiuddin S Persistent hypoxemia due to patent foramen ovale in a patient with adult respiratory distress syndrome.Chest. 1986; 89: 611-613Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar 35Lemaire F Richalet JP Carlet J Brun-Buisson C MacLean C Postoperative hypoxemia due to opening of a patent foramen ovale confirmed by a right atrium-left atrium pressure gradient during mechanical ventilation.Anesthesiology. 1982; 57: 233-236Crossref PubMed Scopus (51) Google Scholar Temporary closure may be achieved with a balloon catheter10Cox D Taylor J Nanda NC Refractory hypoxemia in right ventricular infarction from right-to-left shunting via a patent foramen ovale: efficacy of contrast transesophageal echocardiography.Am J Med. 1991; 91: 653-655Abstract Full Text PDF PubMed Scopus (20) Google Scholar but definitive closure requires either open surgery or a percutaneous technique using an occlusive device.6Laham RJ Ho KKL Douglas PS et al.Right ventricular infarction complicated by acute right-to-left shunting.Am J Cardiol. 1994; 74: 824-826Abstract Full Text PDF PubMed Scopus (24) Google Scholar Patient 1 developed acute RLIAS and platypnoea. The nature of the precipitating cause remains uncertain. However, the raised perioperative pulmonary arterial pressures and the subsequent beneficial effect of nitric oxide suggests that pulmonary vasoconstriction was a contributing factor. The diagnosis of RLIAS was discounted because of the absence of a significant right-to-left pressure gradient between the atria. By the time RLIAS was diagnosed, the patient's condition precluded surgical closure of his ASD. The use of bubble contrast during the patient's first echocardiogram might have revealed the RLIAS early enough for surgery to be feasible. Patient 2 presented with platypnoea; as this is highly indicative of RLIAS, early use of bubble contrast echocardiography was indicated. A lung perfusion scintogram failed to detect it and was falsely positive for pulmonary embolism. RLIAS was discovered during pulmonary angiography when the catheter passed through a PFO. Early use of bubble contrast echocardiography might have saved the patient from these more invasive investigations. Patient 3 demonstrates that acute RLIAS can occur without platypnoea and without high pulmonary arterial pressures. In conclusion, the diagnosis of acute RLIAS should be considered in any patient with unexplained acute hypoxia particularly if platypnoea or orthodeoxia is present. Neither pulmonary hypertension nor a pressure gradient between the right and left atria need be present. Bubble contrast echocardiography is more sensitive in detecting RLIAS than more invasive techniques and should be performed early.