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Severe Hypoxemia Secondary to Pulmonary Embolization Treated Successfully with the Use of a CPAP (Continuous Positive Airway Pressure) Mask

1978; Elsevier BV; Volume: 74; Issue: 5 Linguagem: Inglês

10.1378/chest.74.5.588

1931-3543

David A. Orta, Natalie Tucker, Lawrence E. Green, Bruce M. Yergin, Gerald N. Olsen,

Airway Management and Intubation Techniques

We describe a patient who was admitted with acute onset of dyspnea and pleuritic chest pain. The patient was in acute hypoxic respiratory failure documented by arterial blood gas levels. The severe hypoxemia was refractory to 100 percent O2 administration. The cause of the patient's sudden deterioration was a pulmonary embolus documented by angiography. The patient was managed successfully with heparin therapy. A continuous positive airway pressure (CPAP) mask corrected the severe hypoxemia, which otherwise would have required a more invasive method of respiratory support. We describe a patient who was admitted with acute onset of dyspnea and pleuritic chest pain. The patient was in acute hypoxic respiratory failure documented by arterial blood gas levels. The severe hypoxemia was refractory to 100 percent O2 administration. The cause of the patient's sudden deterioration was a pulmonary embolus documented by angiography. The patient was managed successfully with heparin therapy. A continuous positive airway pressure (CPAP) mask corrected the severe hypoxemia, which otherwise would have required a more invasive method of respiratory support. It should be the goal of every physician to search for new techniques which reduce the cost of medical care and at the same time avoid the use of the more invasive techniques with their potential risks and added cost. The recent use of CPAP is a clear example of such new technique. The present literature is generous with examples of such situations in which the use of CPAP, applied by means of a face mask, avoided endotracheal intubation and mechanical ventilation both in children1Gregory G Kitterman J Phibbs RH et al.Treatment of the idiopathic respiratory-distress syndrome with continuous positive airways pressure.N Engl J Med. 1971; 284: 1333-1340Crossref PubMed Scopus (869) Google Scholar and in adults.2Greenbaum D Millen J Eross B et al.Continuous positive airway pressure without tracheal intubation in spontaneously breathing patients.Chest. 1976; 69: 615-620Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar, 4Taylor G Brenner W Summer W Severe viral pneumonia in young adults: Therapy with continuous positive airway pressure.Chest. 1976; 69: 722-728Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar, 7Civetta J Brons R Gabel J A simple and effective method of employing spontaneous positive-pressure ventilation.J Thorac Cardiovasc Surg. 1972; 63: 312-317PubMed Google Scholar Details of the actual mechanical setup,1Gregory G Kitterman J Phibbs RH et al.Treatment of the idiopathic respiratory-distress syndrome with continuous positive airways pressure.N Engl J Med. 1971; 284: 1333-1340Crossref PubMed Scopus (869) Google Scholar, 2Greenbaum D Millen J Eross B et al.Continuous positive airway pressure without tracheal intubation in spontaneously breathing patients.Chest. 1976; 69: 615-620Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar, 4Taylor G Brenner W Summer W Severe viral pneumonia in young adults: Therapy with continuous positive airway pressure.Chest. 1976; 69: 722-728Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar guidelines,3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar and indications8Gilbert R Keighley JF The arterial/alveolar oxygen tension ratio. An index of gas exchange applicable to varying inspired oxygen concentrations.Am Rev Respir Dis. 1974; 109: 142-144PubMed Google Scholar for the use of CPAP mask in adults with respiratory failure are also available. The purpose of this report is to illustrate yet another possible indication for this technique.Case ReportIn November 1975, a diagnosis of ovarian carcinoma, stage 3, was made in a 55-year-old woman. Treatment consisted of partial hysterectomy and bilateral salpingo-oophorectomy followed by adjuvant chemotherapy with methotrexate, cyclophosphamide and 5-fluorouracil for approximately 18 months.The patient was readmitted in September, 1977, with symptoms of pleuritic chest pain. She was in no obvious respiratory difficulty; however, chest x-ray films at the time revealed a left pleural effusion. Thoracocentesis and chest tube drainage revealed approximately 3,000 ml of serosanguineous fluid. Analysis of the pleural fluid documented the presence of adenocarcinoma, metastatic to the pleural space. This was followed by instillation of intrapleural tetracycline. The patient was discharged on Oct 3, 1977, in good condition.She was readmitted ten days later because of reaccumulation of the left pleural effusion and again no respiratory distress was noted. Chest tube drainage was initiated, followed by intrapleural instillation of blenoxane and chemotherapy with doxorubicin and vincristine. The patient was discharged in good condition five days later after removal of the chest tube.She was readmitted the same afternoon with sudden onset of dyspnea and pleuritic chest pain, which awoke her from her nap. Physical examination revealed a 55-year-old cyanotic white woman in obvious respiratory distress. Vital signs were as follows: blood pressure 110/70 mm Hg, pulse rate 120/min and regular, respiration rate 30–40/min and shallow, and temperature of 36.40°C (97.6°F). No jugular venous distention was present. Cardiovascular examination revealed no murmurs or gallops. Examination of the chest revealed only the previously noted dullness to percussion at the base of the left hemithorax with absent breath sounds and absent vocal fremitus. Arterial blood gas levels with the patient breathing room air were as follows: PaO2 27 mm Hg; PaCO2 28 mm Hg; pH 7.50; and on 100 percent oxygen the PaO2 rose to 60 mm Hg. An electrocardiogram showed sinus tachycardia. Chest x-ray film revealed opacification of the left hemidiaphragm by the previously documented pleural effusion. Pulmonary embolization was documented by angiography (Fig 1).The patient was started on heparin therapy and on CPAP, with the use of a face mask (Bird mask No. 4343-S) on 5cm H2O pressure, and .60 FIo2. Her condition improved dramatically, with the arterial blood gas levels on the above regimen showing marked improvement (Fig 2). By the fourth day of hospitalization, the patient no longer required the use of CPAP, and arterial blood gas measurements obtained on a Venturi mask at an FIo2 of .28 were as follows: PaO2 75 mm Hg; PaCO2 30 mm Hg; and pH 7.47. The patient was discharged on sodium warfarin (Coumadin) therapy, and chemotherapy was reinstituted.Figure 2Values for a/A ratio plotted against FIo2 requirements and hospital days. Solid line illustrates a/A ratio. Broken line represents FIo2 requirements. Duration of CPAP therapy is illustrated opposite hospital days.View Large Image Figure ViewerDownload (PPT)DiscussionThe cause of arterial hypoxemia in pulmonary embolization often remains obscure. The decreased arterial Po2 has been variously ascribed to different physiologic entities: a) diffusion impairment in areas with high blood flow and, therefore, reduced transit time;6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar, 10West BJ Ventilation-perfusion relationships (state of the art).Am Rev Respir Dis. 1977; 116: 919-943PubMed Google Scholar b) opening of potential pulmonary arteriovenous anastomoses as a consequence of the high pulmonary pressure;11Tobin CE Arteriovenous shunts in the peripheral pulmonary circulation in the human lung.Thorax. 1966; 21: 197Crossref PubMed Scopus (79) Google Scholar c) decrease in mean ventilation-perfusion ratio of the perfused, nonembolized area;10West BJ Ventilation-perfusion relationships (state of the art).Am Rev Respir Dis. 1977; 116: 919-943PubMed Google Scholar d) right-to-left shunting of a fraction of the cardiac output secondary to atelectasis,14Bendixen HH Hedley-Whyte J Laver MB Impaired oxygenation in surgical patients during general anesthesia with controlled ventilation: A concept of atelectasis.N Engl J Med. 1963; 269: 991Crossref PubMed Scopus (466) Google Scholar pneumoconstriction,15Nadel JA Colebatch HJH Olsen CR Location and mechanism of airway constriction after barium sulfate microembolism.J Appl Physiol. 1964; 19: 387Crossref PubMed Scopus (71) Google Scholar or pulmonary edema.16Said SI Longacher JW Davis RK et al.Pulmonary gas exchange during induction of pulmonary edema in anesthetized dogs.J Appl Physiol. 1964; 19: 403PubMed Google ScholarThe lack of correlation between the mean pulmonary artery pressure and the percentage of the cardiac output shunted weighs against the presence of arteriovenous anastomoses as the cause of arterial hypoxemia.6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar The decrease in mean ventilation-perfusion ratio of the perfused, nonembolized areas has been demonstrated only in experimental animals with experimentally induced pulmonary embolization.11Tobin CE Arteriovenous shunts in the peripheral pulmonary circulation in the human lung.Thorax. 1966; 21: 197Crossref PubMed Scopus (79) Google Scholar, 12Dantzker DR, Wagner PD, Tornabene V, et al: Gas exchange after pulmonary thromboembolization in dogs. Circ Res (in press), 1977.Google Scholar Wilson et al6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar demonstrated the persistence of shunting for several weeks after the pulmonary embolus, making pulmonary edema an unlikely cause. Furthermore, the authors6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar failed to document a significant obstructive ventilatory defect in patients with pulmonary embolization, raising the question whether bronchoconstriction was a major contributing cause of the hypoxemia being observed. The high incidence of discoid atelectasis17Stein GN Chen JT et al.The importance of chest roentgenography on the diagnosis of pulmonary embolism.Am J Roentgenol. 1959; 81: 225Google Scholar, 18Fleischner F Hampton AO Castleman B Linear shadows in the lung (interlobar pleuritis, atelectasis and healed infarction).Am J Roentgenol. 1941; 46: 610-618Google Scholar observed on chest x-ray films after pulmonary embolus and the presence of roentgenographic evidence suggesting microatelectasis,17Stein GN Chen JT et al.The importance of chest roentgenography on the diagnosis of pulmonary embolism.Am J Roentgenol. 1959; 81: 225Google Scholar, 19Talbot S Worthington BS Roebuck EJ Radiographic signs of pulmonary embolus and pulmonary infarction.Thorax. 1973; 28: 198Crossref PubMed Scopus (13) Google Scholar, 20Moses DC Silver TM Bookstein JJ The complimentary roles of chest radiology, lung scanning, and selective pulmonary angiography in the diagnosis of pulmonary embolism.Circulation. 1974; 49: 179Crossref PubMed Scopus (92) Google Scholar ie, loss of volume and elevated hemidiaphragms suggested to Wilson et al6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar that atelectasis was the major cause of the arterial hypoxemia seen in pulmonary thromboembolism.In order for the shuntlike effect to appear, perfusion would have to be preserved or restored in the areas of atelectasis. Wessler et al13Wessler D Freiman D Ballon JD et al.Experimental pulmonary embolism with serum-induced thrombi.Am J Pathol. 1961; 38: 89PubMed Google Scholar demonstrated persistence of blood flow after releasing a large thrombus from a segment of the inferior vena cava by injecting radioactive microspheres and later measuring the radioactivity. Pulmonary emboli that only partially occlude flow may cause alterations in surface-active properties enough to cause atelectasis. It is possible that spontaneous fibrinolysis with clearing of some emboli occurs faster than restoration of surface-active properties of the alveoli in the embolized regions.The use of CPAP in hypoxemic respiratory failure secondary to pulmonary embolization seems a logical supplement to the treatment of this condition, if, indeed, the arterial hypoxemia is due to venous admixture secondary to low V˙/Q˙ ratios in areas of unstable alveoli which would lead to a loss of functional residual capacity. In matching ventilation to perfusion in disease states, the method of delivering ventilation becomes important. With CPAP, functional residual capacity increases,5Ashbaugh D Effects of ventilatory methods and patterns on physiologic shunt.Surgery. 1970; 68: 99-104PubMed Google Scholar, 7Civetta J Brons R Gabel J A simple and effective method of employing spontaneous positive-pressure ventilation.J Thorac Cardiovasc Surg. 1972; 63: 312-317PubMed Google Scholar and areas that are perfused but poorly ventilated become reexpanded. Another advantage is that patients on whom CPAP therapy is used and mechanical ventilation plus PEEP (positive-end-expiratory pressure) is avoided, have a smaller impairment of venous return and a smaller reduction in cardiac output.2Greenbaum D Millen J Eross B et al.Continuous positive airway pressure without tracheal intubation in spontaneously breathing patients.Chest. 1976; 69: 615-620Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 7Civetta J Brons R Gabel J A simple and effective method of employing spontaneous positive-pressure ventilation.J Thorac Cardiovasc Surg. 1972; 63: 312-317PubMed Google ScholarIn our patient, we successfully reversed the profound hypoxemia with the use of a CPAP mask. We documented in the first three days of hospitalization a progressive decrement in FIo2 requirement, with a marked improvement in arterial oxygen tension along with a trend to normalization of the a/A ratio (Fig 2).Of all the proposed etiologies for the arterial hypoxemia in pulmonary embolization, our patient's response to CPAP therapy supports the concept of venous admixture occurring possibly secondary to microatelectasis. We further suggest the use of CPAP mask as an adjunctive modality of therapy in the treatment of hypoxemic respiratory failure secondary to pulmonary embolization, provided the necessary guidelines3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar and criteria3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar for the selection of these patients are met. It should be the goal of every physician to search for new techniques which reduce the cost of medical care and at the same time avoid the use of the more invasive techniques with their potential risks and added cost. The recent use of CPAP is a clear example of such new technique. The present literature is generous with examples of such situations in which the use of CPAP, applied by means of a face mask, avoided endotracheal intubation and mechanical ventilation both in children1Gregory G Kitterman J Phibbs RH et al.Treatment of the idiopathic respiratory-distress syndrome with continuous positive airways pressure.N Engl J Med. 1971; 284: 1333-1340Crossref PubMed Scopus (869) Google Scholar and in adults.2Greenbaum D Millen J Eross B et al.Continuous positive airway pressure without tracheal intubation in spontaneously breathing patients.Chest. 1976; 69: 615-620Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar, 4Taylor G Brenner W Summer W Severe viral pneumonia in young adults: Therapy with continuous positive airway pressure.Chest. 1976; 69: 722-728Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar, 7Civetta J Brons R Gabel J A simple and effective method of employing spontaneous positive-pressure ventilation.J Thorac Cardiovasc Surg. 1972; 63: 312-317PubMed Google Scholar Details of the actual mechanical setup,1Gregory G Kitterman J Phibbs RH et al.Treatment of the idiopathic respiratory-distress syndrome with continuous positive airways pressure.N Engl J Med. 1971; 284: 1333-1340Crossref PubMed Scopus (869) Google Scholar, 2Greenbaum D Millen J Eross B et al.Continuous positive airway pressure without tracheal intubation in spontaneously breathing patients.Chest. 1976; 69: 615-620Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar, 4Taylor G Brenner W Summer W Severe viral pneumonia in young adults: Therapy with continuous positive airway pressure.Chest. 1976; 69: 722-728Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar guidelines,3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar and indications8Gilbert R Keighley JF The arterial/alveolar oxygen tension ratio. An index of gas exchange applicable to varying inspired oxygen concentrations.Am Rev Respir Dis. 1974; 109: 142-144PubMed Google Scholar for the use of CPAP mask in adults with respiratory failure are also available. The purpose of this report is to illustrate yet another possible indication for this technique. Case ReportIn November 1975, a diagnosis of ovarian carcinoma, stage 3, was made in a 55-year-old woman. Treatment consisted of partial hysterectomy and bilateral salpingo-oophorectomy followed by adjuvant chemotherapy with methotrexate, cyclophosphamide and 5-fluorouracil for approximately 18 months.The patient was readmitted in September, 1977, with symptoms of pleuritic chest pain. She was in no obvious respiratory difficulty; however, chest x-ray films at the time revealed a left pleural effusion. Thoracocentesis and chest tube drainage revealed approximately 3,000 ml of serosanguineous fluid. Analysis of the pleural fluid documented the presence of adenocarcinoma, metastatic to the pleural space. This was followed by instillation of intrapleural tetracycline. The patient was discharged on Oct 3, 1977, in good condition.She was readmitted ten days later because of reaccumulation of the left pleural effusion and again no respiratory distress was noted. Chest tube drainage was initiated, followed by intrapleural instillation of blenoxane and chemotherapy with doxorubicin and vincristine. The patient was discharged in good condition five days later after removal of the chest tube.She was readmitted the same afternoon with sudden onset of dyspnea and pleuritic chest pain, which awoke her from her nap. Physical examination revealed a 55-year-old cyanotic white woman in obvious respiratory distress. Vital signs were as follows: blood pressure 110/70 mm Hg, pulse rate 120/min and regular, respiration rate 30–40/min and shallow, and temperature of 36.40°C (97.6°F). No jugular venous distention was present. Cardiovascular examination revealed no murmurs or gallops. Examination of the chest revealed only the previously noted dullness to percussion at the base of the left hemithorax with absent breath sounds and absent vocal fremitus. Arterial blood gas levels with the patient breathing room air were as follows: PaO2 27 mm Hg; PaCO2 28 mm Hg; pH 7.50; and on 100 percent oxygen the PaO2 rose to 60 mm Hg. An electrocardiogram showed sinus tachycardia. Chest x-ray film revealed opacification of the left hemidiaphragm by the previously documented pleural effusion. Pulmonary embolization was documented by angiography (Fig 1).The patient was started on heparin therapy and on CPAP, with the use of a face mask (Bird mask No. 4343-S) on 5cm H2O pressure, and .60 FIo2. Her condition improved dramatically, with the arterial blood gas levels on the above regimen showing marked improvement (Fig 2). By the fourth day of hospitalization, the patient no longer required the use of CPAP, and arterial blood gas measurements obtained on a Venturi mask at an FIo2 of .28 were as follows: PaO2 75 mm Hg; PaCO2 30 mm Hg; and pH 7.47. The patient was discharged on sodium warfarin (Coumadin) therapy, and chemotherapy was reinstituted. In November 1975, a diagnosis of ovarian carcinoma, stage 3, was made in a 55-year-old woman. Treatment consisted of partial hysterectomy and bilateral salpingo-oophorectomy followed by adjuvant chemotherapy with methotrexate, cyclophosphamide and 5-fluorouracil for approximately 18 months. The patient was readmitted in September, 1977, with symptoms of pleuritic chest pain. She was in no obvious respiratory difficulty; however, chest x-ray films at the time revealed a left pleural effusion. Thoracocentesis and chest tube drainage revealed approximately 3,000 ml of serosanguineous fluid. Analysis of the pleural fluid documented the presence of adenocarcinoma, metastatic to the pleural space. This was followed by instillation of intrapleural tetracycline. The patient was discharged on Oct 3, 1977, in good condition. She was readmitted ten days later because of reaccumulation of the left pleural effusion and again no respiratory distress was noted. Chest tube drainage was initiated, followed by intrapleural instillation of blenoxane and chemotherapy with doxorubicin and vincristine. The patient was discharged in good condition five days later after removal of the chest tube. She was readmitted the same afternoon with sudden onset of dyspnea and pleuritic chest pain, which awoke her from her nap. Physical examination revealed a 55-year-old cyanotic white woman in obvious respiratory distress. Vital signs were as follows: blood pressure 110/70 mm Hg, pulse rate 120/min and regular, respiration rate 30–40/min and shallow, and temperature of 36.40°C (97.6°F). No jugular venous distention was present. Cardiovascular examination revealed no murmurs or gallops. Examination of the chest revealed only the previously noted dullness to percussion at the base of the left hemithorax with absent breath sounds and absent vocal fremitus. Arterial blood gas levels with the patient breathing room air were as follows: PaO2 27 mm Hg; PaCO2 28 mm Hg; pH 7.50; and on 100 percent oxygen the PaO2 rose to 60 mm Hg. An electrocardiogram showed sinus tachycardia. Chest x-ray film revealed opacification of the left hemidiaphragm by the previously documented pleural effusion. Pulmonary embolization was documented by angiography (Fig 1). The patient was started on heparin therapy and on CPAP, with the use of a face mask (Bird mask No. 4343-S) on 5cm H2O pressure, and .60 FIo2. Her condition improved dramatically, with the arterial blood gas levels on the above regimen showing marked improvement (Fig 2). By the fourth day of hospitalization, the patient no longer required the use of CPAP, and arterial blood gas measurements obtained on a Venturi mask at an FIo2 of .28 were as follows: PaO2 75 mm Hg; PaCO2 30 mm Hg; and pH 7.47. The patient was discharged on sodium warfarin (Coumadin) therapy, and chemotherapy was reinstituted. DiscussionThe cause of arterial hypoxemia in pulmonary embolization often remains obscure. The decreased arterial Po2 has been variously ascribed to different physiologic entities: a) diffusion impairment in areas with high blood flow and, therefore, reduced transit time;6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar, 10West BJ Ventilation-perfusion relationships (state of the art).Am Rev Respir Dis. 1977; 116: 919-943PubMed Google Scholar b) opening of potential pulmonary arteriovenous anastomoses as a consequence of the high pulmonary pressure;11Tobin CE Arteriovenous shunts in the peripheral pulmonary circulation in the human lung.Thorax. 1966; 21: 197Crossref PubMed Scopus (79) Google Scholar c) decrease in mean ventilation-perfusion ratio of the perfused, nonembolized area;10West BJ Ventilation-perfusion relationships (state of the art).Am Rev Respir Dis. 1977; 116: 919-943PubMed Google Scholar d) right-to-left shunting of a fraction of the cardiac output secondary to atelectasis,14Bendixen HH Hedley-Whyte J Laver MB Impaired oxygenation in surgical patients during general anesthesia with controlled ventilation: A concept of atelectasis.N Engl J Med. 1963; 269: 991Crossref PubMed Scopus (466) Google Scholar pneumoconstriction,15Nadel JA Colebatch HJH Olsen CR Location and mechanism of airway constriction after barium sulfate microembolism.J Appl Physiol. 1964; 19: 387Crossref PubMed Scopus (71) Google Scholar or pulmonary edema.16Said SI Longacher JW Davis RK et al.Pulmonary gas exchange during induction of pulmonary edema in anesthetized dogs.J Appl Physiol. 1964; 19: 403PubMed Google ScholarThe lack of correlation between the mean pulmonary artery pressure and the percentage of the cardiac output shunted weighs against the presence of arteriovenous anastomoses as the cause of arterial hypoxemia.6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar The decrease in mean ventilation-perfusion ratio of the perfused, nonembolized areas has been demonstrated only in experimental animals with experimentally induced pulmonary embolization.11Tobin CE Arteriovenous shunts in the peripheral pulmonary circulation in the human lung.Thorax. 1966; 21: 197Crossref PubMed Scopus (79) Google Scholar, 12Dantzker DR, Wagner PD, Tornabene V, et al: Gas exchange after pulmonary thromboembolization in dogs. Circ Res (in press), 1977.Google Scholar Wilson et al6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar demonstrated the persistence of shunting for several weeks after the pulmonary embolus, making pulmonary edema an unlikely cause. Furthermore, the authors6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar failed to document a significant obstructive ventilatory defect in patients with pulmonary embolization, raising the question whether bronchoconstriction was a major contributing cause of the hypoxemia being observed. The high incidence of discoid atelectasis17Stein GN Chen JT et al.The importance of chest roentgenography on the diagnosis of pulmonary embolism.Am J Roentgenol. 1959; 81: 225Google Scholar, 18Fleischner F Hampton AO Castleman B Linear shadows in the lung (interlobar pleuritis, atelectasis and healed infarction).Am J Roentgenol. 1941; 46: 610-618Google Scholar observed on chest x-ray films after pulmonary embolus and the presence of roentgenographic evidence suggesting microatelectasis,17Stein GN Chen JT et al.The importance of chest roentgenography on the diagnosis of pulmonary embolism.Am J Roentgenol. 1959; 81: 225Google Scholar, 19Talbot S Worthington BS Roebuck EJ Radiographic signs of pulmonary embolus and pulmonary infarction.Thorax. 1973; 28: 198Crossref PubMed Scopus (13) Google Scholar, 20Moses DC Silver TM Bookstein JJ The complimentary roles of chest radiology, lung scanning, and selective pulmonary angiography in the diagnosis of pulmonary embolism.Circulation. 1974; 49: 179Crossref PubMed Scopus (92) Google Scholar ie, loss of volume and elevated hemidiaphragms suggested to Wilson et al6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar that atelectasis was the major cause of the arterial hypoxemia seen in pulmonary thromboembolism.In order for the shuntlike effect to appear, perfusion would have to be preserved or restored in the areas of atelectasis. Wessler et al13Wessler D Freiman D Ballon JD et al.Experimental pulmonary embolism with serum-induced thrombi.Am J Pathol. 1961; 38: 89PubMed Google Scholar demonstrated persistence of blood flow after releasing a large thrombus from a segment of the inferior vena cava by injecting radioactive microspheres and later measuring the radioactivity. Pulmonary emboli that only partially occlude flow may cause alterations in surface-active properties enough to cause atelectasis. It is possible that spontaneous fibrinolysis with clearing of some emboli occurs faster than restoration of surface-active properties of the alveoli in the embolized regions.The use of CPAP in hypoxemic respiratory failure secondary to pulmonary embolization seems a logical supplement to the treatment of this condition, if, indeed, the arterial hypoxemia is due to venous admixture secondary to low V˙/Q˙ ratios in areas of unstable alveoli which would lead to a loss of functional residual capacity. In matching ventilation to perfusion in disease states, the method of delivering ventilation becomes important. With CPAP, functional residual capacity increases,5Ashbaugh D Effects of ventilatory methods and patterns on physiologic shunt.Surgery. 1970; 68: 99-104PubMed Google Scholar, 7Civetta J Brons R Gabel J A simple and effective method of employing spontaneous positive-pressure ventilation.J Thorac Cardiovasc Surg. 1972; 63: 312-317PubMed Google Scholar and areas that are perfused but poorly ventilated become reexpanded. Another advantage is that patients on whom CPAP therapy is used and mechanical ventilation plus PEEP (positive-end-expiratory pressure) is avoided, have a smaller impairment of venous return and a smaller reduction in cardiac output.2Greenbaum D Millen J Eross B et al.Continuous positive airway pressure without tracheal intubation in spontaneously breathing patients.Chest. 1976; 69: 615-620Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 7Civetta J Brons R Gabel J A simple and effective method of employing spontaneous positive-pressure ventilation.J Thorac Cardiovasc Surg. 1972; 63: 312-317PubMed Google ScholarIn our patient, we successfully reversed the profound hypoxemia with the use of a CPAP mask. We documented in the first three days of hospitalization a progressive decrement in FIo2 requirement, with a marked improvement in arterial oxygen tension along with a trend to normalization of the a/A ratio (Fig 2).Of all the proposed etiologies for the arterial hypoxemia in pulmonary embolization, our patient's response to CPAP therapy supports the concept of venous admixture occurring possibly secondary to microatelectasis. We further suggest the use of CPAP mask as an adjunctive modality of therapy in the treatment of hypoxemic respiratory failure secondary to pulmonary embolization, provided the necessary guidelines3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar and criteria3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar for the selection of these patients are met. The cause of arterial hypoxemia in pulmonary embolization often remains obscure. The decreased arterial Po2 has been variously ascribed to different physiologic entities: a) diffusion impairment in areas with high blood flow and, therefore, reduced transit time;6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar, 10West BJ Ventilation-perfusion relationships (state of the art).Am Rev Respir Dis. 1977; 116: 919-943PubMed Google Scholar b) opening of potential pulmonary arteriovenous anastomoses as a consequence of the high pulmonary pressure;11Tobin CE Arteriovenous shunts in the peripheral pulmonary circulation in the human lung.Thorax. 1966; 21: 197Crossref PubMed Scopus (79) Google Scholar c) decrease in mean ventilation-perfusion ratio of the perfused, nonembolized area;10West BJ Ventilation-perfusion relationships (state of the art).Am Rev Respir Dis. 1977; 116: 919-943PubMed Google Scholar d) right-to-left shunting of a fraction of the cardiac output secondary to atelectasis,14Bendixen HH Hedley-Whyte J Laver MB Impaired oxygenation in surgical patients during general anesthesia with controlled ventilation: A concept of atelectasis.N Engl J Med. 1963; 269: 991Crossref PubMed Scopus (466) Google Scholar pneumoconstriction,15Nadel JA Colebatch HJH Olsen CR Location and mechanism of airway constriction after barium sulfate microembolism.J Appl Physiol. 1964; 19: 387Crossref PubMed Scopus (71) Google Scholar or pulmonary edema.16Said SI Longacher JW Davis RK et al.Pulmonary gas exchange during induction of pulmonary edema in anesthetized dogs.J Appl Physiol. 1964; 19: 403PubMed Google Scholar The lack of correlation between the mean pulmonary artery pressure and the percentage of the cardiac output shunted weighs against the presence of arteriovenous anastomoses as the cause of arterial hypoxemia.6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar The decrease in mean ventilation-perfusion ratio of the perfused, nonembolized areas has been demonstrated only in experimental animals with experimentally induced pulmonary embolization.11Tobin CE Arteriovenous shunts in the peripheral pulmonary circulation in the human lung.Thorax. 1966; 21: 197Crossref PubMed Scopus (79) Google Scholar, 12Dantzker DR, Wagner PD, Tornabene V, et al: Gas exchange after pulmonary thromboembolization in dogs. Circ Res (in press), 1977.Google Scholar Wilson et al6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar demonstrated the persistence of shunting for several weeks after the pulmonary embolus, making pulmonary edema an unlikely cause. Furthermore, the authors6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar failed to document a significant obstructive ventilatory defect in patients with pulmonary embolization, raising the question whether bronchoconstriction was a major contributing cause of the hypoxemia being observed. The high incidence of discoid atelectasis17Stein GN Chen JT et al.The importance of chest roentgenography on the diagnosis of pulmonary embolism.Am J Roentgenol. 1959; 81: 225Google Scholar, 18Fleischner F Hampton AO Castleman B Linear shadows in the lung (interlobar pleuritis, atelectasis and healed infarction).Am J Roentgenol. 1941; 46: 610-618Google Scholar observed on chest x-ray films after pulmonary embolus and the presence of roentgenographic evidence suggesting microatelectasis,17Stein GN Chen JT et al.The importance of chest roentgenography on the diagnosis of pulmonary embolism.Am J Roentgenol. 1959; 81: 225Google Scholar, 19Talbot S Worthington BS Roebuck EJ Radiographic signs of pulmonary embolus and pulmonary infarction.Thorax. 1973; 28: 198Crossref PubMed Scopus (13) Google Scholar, 20Moses DC Silver TM Bookstein JJ The complimentary roles of chest radiology, lung scanning, and selective pulmonary angiography in the diagnosis of pulmonary embolism.Circulation. 1974; 49: 179Crossref PubMed Scopus (92) Google Scholar ie, loss of volume and elevated hemidiaphragms suggested to Wilson et al6Wilson J Pierce A Johnson Jr, R et al.Hypoxemia in pulmonary embolism, a clinical study.J Clin Invest. 1971; 50: 481-491Crossref PubMed Google Scholar that atelectasis was the major cause of the arterial hypoxemia seen in pulmonary thromboembolism. In order for the shuntlike effect to appear, perfusion would have to be preserved or restored in the areas of atelectasis. Wessler et al13Wessler D Freiman D Ballon JD et al.Experimental pulmonary embolism with serum-induced thrombi.Am J Pathol. 1961; 38: 89PubMed Google Scholar demonstrated persistence of blood flow after releasing a large thrombus from a segment of the inferior vena cava by injecting radioactive microspheres and later measuring the radioactivity. Pulmonary emboli that only partially occlude flow may cause alterations in surface-active properties enough to cause atelectasis. It is possible that spontaneous fibrinolysis with clearing of some emboli occurs faster than restoration of surface-active properties of the alveoli in the embolized regions. The use of CPAP in hypoxemic respiratory failure secondary to pulmonary embolization seems a logical supplement to the treatment of this condition, if, indeed, the arterial hypoxemia is due to venous admixture secondary to low V˙/Q˙ ratios in areas of unstable alveoli which would lead to a loss of functional residual capacity. In matching ventilation to perfusion in disease states, the method of delivering ventilation becomes important. With CPAP, functional residual capacity increases,5Ashbaugh D Effects of ventilatory methods and patterns on physiologic shunt.Surgery. 1970; 68: 99-104PubMed Google Scholar, 7Civetta J Brons R Gabel J A simple and effective method of employing spontaneous positive-pressure ventilation.J Thorac Cardiovasc Surg. 1972; 63: 312-317PubMed Google Scholar and areas that are perfused but poorly ventilated become reexpanded. Another advantage is that patients on whom CPAP therapy is used and mechanical ventilation plus PEEP (positive-end-expiratory pressure) is avoided, have a smaller impairment of venous return and a smaller reduction in cardiac output.2Greenbaum D Millen J Eross B et al.Continuous positive airway pressure without tracheal intubation in spontaneously breathing patients.Chest. 1976; 69: 615-620Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 7Civetta J Brons R Gabel J A simple and effective method of employing spontaneous positive-pressure ventilation.J Thorac Cardiovasc Surg. 1972; 63: 312-317PubMed Google Scholar In our patient, we successfully reversed the profound hypoxemia with the use of a CPAP mask. We documented in the first three days of hospitalization a progressive decrement in FIo2 requirement, with a marked improvement in arterial oxygen tension along with a trend to normalization of the a/A ratio (Fig 2). Of all the proposed etiologies for the arterial hypoxemia in pulmonary embolization, our patient's response to CPAP therapy supports the concept of venous admixture occurring possibly secondary to microatelectasis. We further suggest the use of CPAP mask as an adjunctive modality of therapy in the treatment of hypoxemic respiratory failure secondary to pulmonary embolization, provided the necessary guidelines3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar and criteria3Garg G Hill G The use of spontaneous continuous positive airway pressure for reduction of intrapulmonary shunting in adults with acute respiratory failure.Canad Anaesth Soc J. 1975; 22: 284-290Crossref PubMed Scopus (9) Google Scholar for the selection of these patients are met.