Unilateral Acute Respiratory Distress Syndrome with Contralateral Pulmonary Artery Agenesis: A Rare Scenario.

Unilateral pulmonary artery agenesis (UPAA) is a rare condition where the patient may remain asymptomatic for a long period till adulthood. Presentation may be in the form of dyspnea, cough, hemoptysis, decreased exercise tolerance, and recurrent respiratory tract infections. Ventilation-perfusion mismatch and excessive blood flow to the normal lung may eventually lead to unilateral acute respiratory distress syndrome (ARDS). We present a case of a 40-year-old gentleman with nonresolving pneumonia who was diagnosed to have unilateral ARDS due to UPAA. Even though ARDS involves bilateral lung, unilateral ARDS which does not show resolution with lung protective strategies should always raise the suspicion of a rare disease like UPAA among clinicians. To date, there is no specific prescribed treatment for UPAA.

INTRODUCTION

Unilateral pulmonary artery agenesis (UPAA) is a rare condition affecting about 1:200,000 adults.[1] It is more common on the right side and has nonspecific symptoms of shortness of breath (SOB), exercise intolerance, frequent respiratory infections, and hemoptysis.[234] Chest roentgenogram (CXR) may show a reduced size of the affected hemithorax with contralateral hyperinflation, mediastinal shift to the diseased side with the absence of pulmonary arterial markings on the affected side.[5] Such asymmetry in the lung aeration should raise the possibility of UPAA even in asymptomatic patients.[4] Unilateral acute respiratory distress syndrome (ARDS) due to UPAA, as in our case, has only been reported once in literature.[1] It may be associated with cardiovascular anomalies such as Fallot's tetralogy, cardiac septal defects, and coarctation of the aorta, which should also be looked for.[6]

CASE REPORT

A 40-year-old gentleman presented to the emergency with chief complaints of SOB, cough, and fever for about a week. He did not have any other any other known comorbidities. He had a history of dyspnea in the past also. On examination, his heart rate was 120 b.p.m., respiratory rate was 30–35 b.p.m., oxygen saturation (SpO2) was 90% on room air, and he was febrile with temperature of 100.2° F. There were decreased breath sounds on the right side and crepitations on the left side of the chest. He was administered noninvasive ventilation (NIV), and his SpO2 improved to 99%. Chest X-ray images showed extensive left-sided infiltrates, right-sided mediastinal shift, and loss of lung volume on the right side [Figure 1]. Subsequently, he was shifted to Intensive Care Unit, and as his chest X-ray images worsened despite NIV and broad-spectrum antibiotics, he was intubated and ventilated. His white blood cell count was 18,700 per uL and procalcitonin was 36.5 ng/mL. Arterial blood gas showed poor oxygenation and respiratory acidosis, eventually falling into category to ARDS, according to ratio of partial pressure of oxygen in arterial blood and fraction of inspired oxygen (PaO2-FiO2). Echocardiography revealed pulmonary arterial hypertension (PAH) and no other significant findings. Endotracheal tube aspirate showed Klebsiella pneumoniae, and he was administered the sensitive antibiotics. Ventilatory management of ARDS was done using 6 mL/kg of predicted body weight, keeping the plateau pressure goal of <30 cm H2O with applicable positive end-expiratory pressure. Due to nonresolution of the pulmonary infiltrates and PaO2-FiO2 despite lung protective ventilation, prone ventilation was done with adequate precautions. Prone position ventilation was administered for 16 h a day. Eventually, his oxygenation and CXR worsened. Due to this deterioration in spite of all possible lung protective ventilator measures and treatment, computerized tomography (CT) of the thorax and pulmonary angiography were done. It showed agenesis of the right pulmonary artery and hypoplasia of the right lung with hyperplastic left lung having nonhomogeneous infiltrates [Figures 2 and 3]. Three-dimensional thoracic angiogram also showed right pulmonary artery agenesis [Figures 4 and 5]. He was referred to a higher center for requirement of extracorporeal membrane oxygenation (ECMO) for the nonresolving ARDS, but due to financial restraints, the family was unable to take him to an ECMO center. He succumbed to his condition and expired despite multimodal treatment and management.

Figure 1

Chest X-ray showing nonhomogeneous opacities in the left lung, with mediastinal shift to right along with decreased hilar markings on the right side

Figure 2

Pulmonary angiogram showing agenesis of the right pulmonary artery

Figure 3

Computerized tomography thorax showing left-sided lung infiltrates

Figure 4

Three-dimensional reconstruction showing the absence of the right pulmonary artery. The white arrow depicts the origin of otherwise normal right pulmonary artery

Figure 5

Three-dimensional angiogram showing the absence of the right pulmonary artery. The left pulmonary artery and its branches are clearly visible

DISCUSSION

UPAA has no specific symptoms, and as many as 30% individuals may remain asymptomatic, making its diagnosis difficult.[7] It is due to a defect in the connection of the pulmonary trunk with the sixth aortic arch.[6] Pulmonary angiography is the gold standard for diagnosing UPAA.[8]

In our patient, the unilateral ARDS was unique and that was what made us look for possible rarer causes of unilateral ARDS. After the lung protective strategies failed to show any improvement, the CT pulmonary angiography (CTPA) was done which clinched the diagnosis of UPAA as the cause of unilateral ARDS. There has been only a single case report of unilateral ARDS due to UPAA reported in literature.[1] The presence of PAH can even lead to hemodynamic instability in cases of UPAA.[1] It has been postulated that pathogenesis of ARDS involves increased permeability of pulmonary endothelial barriers, excessive accumulation, and activity of leukocytes and platelets along with transendothelial migration of leukocytes. All these ultimately cause fluid leak and alveolar edema.[9] The unilateral ARDS in cases of UPAA may be due to the excessive blood flow and altered permeability of the pulmonary vasculature of the unaffected side. This may be responsible for the refractory hypoxemia in such patients, despite lung protective strategies, as the core issue of excessive perfusion to the unaffected side is not resolved by any of these measures. The unilateral ARDS in the unaffected left lung is explained by the excessive perfusion-induced leakage of edema fluid, leading to alveolar edema. In UPAA, the lung on the side of pulmonary agenesis is not affected by ARDS. It is the lung on the opposite side which gets more perfusion and has endothelial leak which develops ARDS.

Our case did not have any other cardiac anomalies apart from PAH, for which he was administered tablet sildenafil. The CTPA revealed development of collaterals providing the blood supply to the right diseased hypoplastic lung. Treatment options of UPAA involve embolization of the abnormal systemic to pulmonary collateral vessels in cases presenting with hemoptysis, and even in few cases, pneumonectomy of the affected lung may even be essential.[110]

In the case report of unilateral ARDS due to UPAA by Saladi et al., lung protective ventilator strategy was successfully implemented, and the patient recovered.[1]

However, in our case, the patient had severe unilateral ARDS, and lung protective strategy failed. We had used ventilation protocol as per ARDS network protocol.[11] In such a scenario, ECMO could have been efficacious but was unavailable at our center. ECMO has shown to be beneficial in cases of severe ARDS where conventional ventilation and prone positioning have failed and has shown a higher percentage of survival at 6 months.[12]

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

CONCLUSION

In cases of unilateral, nonresolving ARDS, UPAA should always be kept in mind and CTPA should be done as the gold standard investigation. What is more alarming in this disease is that the normal lung gets involved due to excessive perfusion and thus spells a worse prognosis. Patients may show a myriad of symptoms in UPAA and such conditions should be kept in mind in critical care settings. In cases of ARDS where conventional lung protective ventilation fails to improve oxygenation, transfer to ECMO center is advised.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.