Bronchopleural Fistula

Etiology

• A BPF is an abnormal communication between the bronchial tree and the pleural cavity. An alveolar-pleural fistula may also occur between the lung parenchyma and the pleural space (Figure 1, source).¹
• BPFs most commonly occur after lung resection, with the highest incidence associated with pneumonectomy, ranging from 1.5% to 4.5%, though up to 20% has been cited. The prevalence of BPF after lobectomy is low, ranging from 0.5% to 1%.^2,3
• Symptoms often develop within 2 weeks of lung resection.²
• Nonsurgical etiologies include infection, such as empyema, ruptured bullae or spontaneous pneumothorax, acute respiratory distress syndrome, penetrating chest trauma, and malignancy.^2,3
• Risk factors for postoperative BPFs can be broken down into patient and surgical factors (Table 1).²

Diagnosis

Clinical Presentation

• Postoperative BPF may be seen as a persistent air leak for more than 24 hours. A significant air leak may result in tension pneumothorax-physiology. Characterization of an air leak from a thoracostomy tube may aid in differentiating pathologies (Table 2).^3,4
• Signs of BPF in mechanically ventilated patients include loss of PEEP, hypoxia, and an increased inspiratory-to-expiratory volume difference, which can be directly measured on the ventilator to quantify the air leak.³
• If the diagnosis is delayed, patients may present with empyema, with severe cases eroding through the chest wall to form a pleural-cutaneous fistula.²

Diagnostic Imaging

• A chest x-ray will show hydropneumothorax/pneumothorax, possible tension pneumothorax (Figure 2, source).²
• Computed tomography (CT) imaging will similarly show hydropneumothorax/pneumothorax. It may demonstrate a likely etiology, such as large bullae, tumors, or cavitary lesions. A CT scan may localize the BPF in 55% of patients.^2,5
• Direct visualization of the BPF may be achieved through bronchoscopy by a mucosal defect, if large enough. For smaller defects, saline may help to localize air bubbles at the surgical site, or methylene blue may be instilled in the pleural space to then visualize on bronchoscopy (Figure 3, source).^2,6

Anesthetic Considerations

Induction and Airway Management

• Airway management in patients with BPF should focus on securing an airway that avoids positive-pressure ventilation through the fistula tract, which may worsen air leak and lead to tension pneumothorax. If infection or empyema is present, ventilation through the fistula tract may result in contamination of the healthy lungs.¹ 
• During induction, this can be achieved by maintaining spontaneous ventilation until the healthy lung is isolated using a double-lumen tube, single-lumen tube bronchial intubation, or bronchial blockers.¹ 
• If lung isolation results in intolerable shunt and hypoxia, passive oxygenation, continuous positive airway pressure, or positive end expiratory pressure can be applied to the affected lung, provided that pressures remain below the threshold for BPF opening. This can be monitored via air leak on the chest tube.¹

Ventilation Strategies

• When lung isolation cannot be achieved, ventilation of the affected lung should focus on reducing the driving pressure or flow through the fistula (F_BPF).
• F_BPF is proportional to the transpulmonary pressure, or pressure difference between the mean airway pressure and pleural pressure (P_PL). Therefore F_BPF can be reduced through strategies outlined in Figure 4, primarily by maintaining low mean airway pressure and limiting negative P_PL.³

• Permissive hypercapnia may be required because of these ventilatory strategies.
• Manipulating the P_PL via a chest tube can contribute to BPF healing. Postoperatively, placing a chest tube to water seal from suction has been cited to resolve persistent air leaks in 60% of patients. Sources have even suggested administering positive pressure via a chest tube to increase the P_PL, thereby decreasing the transpulmonary pressure gradient through the BPF. Care must be taken to avoid worsening a pneumothorax with positive pressure, however. During induction of anesthesia, the chest tube should be maintained on suction to counter accumulation of positive pressure delivered during induction.^1,3
• High-frequency jet ventilation (HFJV) has been used historically for large BPFs when surgical repair is not feasible, but it is now rarely used due to limited evidence and technical challenges. It was been shown that leak and entrained volumes vary widely with HFJV settings, worsening at frequencies <100 min^-1, with larger or more proximal fistulae, and with higher driving pressures, and that ventilator-displayed values are unreliable. Although leak was minimized only at very high frequencies (>200 min-1) with lower driving pressures, there is lack of confirmatory clinical data. Consequently, HFJV remains a historical or niche option rather than a routine strategy for BPF management.^1,3,7

Treatment

• Broad spectrum antibiotics should be initiated empirically until pleural studies are evaluated for underlying infection.² 
• Most BPF require surgical closure as spontaneous closure is rare. Surgical closure is most successful within 2 weeks of presentation from the initial surgery. It is often done through video-assisted thoracoscopy with debridement and reclosure of the stump and a vascularized flap of tissue (i.e., omentum) to aid in healing.²
• BPF refractory to surgical revision and complicated by recurrent infection may require an open window procedure such as the Eloesser flap or Calagett window, to create a permanent communication between the pleural space and the skin. This allows for continuous drainage and irrigation of the pleural space (Figure 5, source).² 
• For patients that are poor surgical candidates for BPF closure, temporary closure may be achieved via bronchoscopy. This may be done by application of occlusive material or endobronchial valves to seal small defects (less than 5 mm). For more proximal and larger (more than 8mm) defects in the central airway, airway stents, coils and even Amplatzer devices have been used.^2,3 
• Ultimately, venovenous extracorporeal membrane oxygenation may be used to rest the lungs and aid in BPF closure.³