Barotrauma as aetiological cascade of fatal intrapulmonary plastic bronchitis in a post-Fontan child

Abstract

The role of barotrauma in the exaggeration of plastic bronchitis after Fontan circulation has yet to be examined. We aim to describe a case of a 4-year old post-Fontan circulation girl where barotrauma suffered during commercial air travel played a role in the aetiological cascade of plastic bronchitis.

INTRODUCTION

The incidence of plastic bronchitis in children after completion of Fontan circulation, though rare, carries a grave mortality risk of acute obstructive respiratory distress [1]. This acellular non-inflammatory cast formation has been hypothesized to be the result of chronic pulmonary venous congestion experienced in this population attributable largely to their suboptimal circulatory status [2]. The role of barotrauma in the exaggeration of plastic bronchitis has yet to be examined. Here we aim to describe a case of a 4-year old post-Fontan circulation girl who developed plastic bronchitis as a consequence of barotrauma suffered during commercial air travel. She was subsequently supported with extracorporeal circulation (ECMO).

REPORT

The patient presented at the emergency department with worsening respiratory distress accompanied with intermittent coughing, vomiting and increased lethargy over the previous 3 weeks. The day before presentation, she had just made a 2-h commercial passenger flight. She was noticed by her parents to have appeared unwell with worsening of respiratory symptoms the subsequent morning.

The medical history included a complex congenital cardiac defect, consisting of right isomerism, a common atrium, complete atrioventricular septal defect, double outlet right ventricle, transposition of great arteries, total anomalous pulmonary venous drainage to the left superior vena cava and asplenia. She had undergone a Fontan procedure (18-mm fenestrated extracardiac conduit) for single ventricular physiology 6 months before this presentation. She was on regular prophylactic penicillin coverage.

On presentation, the patient was in significant respiratory distress, with severe costal recession and tachypnoea at a respiratory rate of 65. She was also tachycardic and hypertensive with a heart rate of 165 beats/min and a blood pressure of 128/108 mmHg. Physical examination revealed a prolonged expiratory phase, bilateral crackles as well as subcutaneous emphysema. Investigations showed severe respiratory acidosis with hypoxaemia and hypercapnea (arterial blood case pH 7.22, pO2 46.6 mmHg, pCO2 61 mmHg) on initial presentation. Haematological investigations revealed only polycythaemia without leukocytosis. A chest X-ray (CXR; Fig. 1) was performed and revealed a pneumomediastinum with extensive subcutaneous emphysema in the neck region as well as diffuse interstitial opacities throughout both the lungs. Her oxygen saturation was maintained initially in the seventies with non-invasive ventilation, but subsequently desaturated down to mid 50s. Hence, continuous positive airway pressure was initiated and she was transferred to the intensive care unit (ICU) for further examinations.

Figure 1:

Top-left, clockwise: X-ray 1 (on presentation) revealing pneumomediastinum and extensive subcutaneous emphysema (block arrows). X-ray 2 (hours after ED presentation) showing newly developed right pneumothorax (arrow). X-ray 3 (second day in ICU) showing dense air-space opacification (*) in both upper lobes with focal collapse of left lung base. X-ray 4 (2 days after weaning off extracorporeal membrane oxygenation) with diffuse interstitial thickening bilaterally in otherwise clear lung fields.

Because of increasing drowsiness, she was intubated. Unfortunately, the treatment became arduous, with the development of hypotension with mean arterial pressures as low as 47 mmHg, which required extensive ionotropic support. Echocardiogram investigations were unremarkable, revealing an unobstructed Fontan pathway (fenestration was patent, with high velocity left-to-right flow) with preservation of cardiac function and slight dilation of the inferior vena cava. Hence, in an attempt to provide more optimal haemodynamic support, veno-arterial extracorporeal membrane oxygenation was initiated with a flow of 1 l/min, which maintained oxygen saturation around 80%.

In microbiological investigations, the girl tested negative for legionella, influenza, respiratory syncytial virus, mycoplasma pneumoniae and enterovirus. Initial treatment comprised extensive antibiotic coverage, including azithromycin, lincomycin and cefotaxime. Tamiflu was also administered.

The chest X-ray (Fig. 1) then revealed a newly developed right pneumothorax with subsequent development of dense bilateral consolidations. Urgent bronchoscopy was performed and a bronchial cast was extracted (Fig. 2). The histology demonstrated mucus cast admixed with inflammatory cells, including histocytes, lymphocytes, plasma cells and some neutrophils. Occasional clumps of gram positive cocci were seen. She was consequently treated with NaCl nebulizers and dornase alfa, which improved her respiratory function, followed by successful weaning off ECMO after a week of support. She was later extubated 3 days after weaning off ECMO and has since returned to her preadmission functional status. She had a second investigative catheterisation and was reported to be normal.

Figure 2:

Bronchial cast retrieved during emergent bronchoscopy.

DISCUSSION

Plastic bronchitis is a rare life-threatening entity characterized by recurrent formation of branching bronchial casts causing significant airway obstruction. The traditional classification involves dividing the casts on the basis of their histological subtypes [2]. Type 1 casts are composed of fibrinous stroma and eosinophilic infiltrate and is typically accompanied by surrounding inflamed respiratory epithelium. This was associated with chronic respiratory conditions including asthma, cystic fibrosis and allergic bronchopulmonary aspergillosis. Type 2 casts are found only in patients with congenital cyanotic heart disease and comprise acellular laminated mucin with an absence of inflammation in surrounding epithelium.

The Fontan procedure stands as the procedure most commonly associated with development of plastic bronchitis, its occurrence being repeatedly documented in existing literature [3]. However, the pathophysiology remains poorly understood. One of the existing hypotheses proposes the aetiology of mucus hypersecretion triggered by elevated pulmonary venous pressures [2]. It has also been hypothesized that the constant circulatory insufficiency in the Fontan circulation increases vulnerability to the breech of bronchial mucosal integrity, hence leading to proteinaceous fluid leakage into the airway, a mechanism similar to that behind protein-losing enteropathy. Other related causes of haemodynamic instability, including poor cardiac function [1], elevated central venous pressure and arrhythmias [2], have also been reviewed as possible triggers. An alternative theory describes the contribution of endobronchial lymphatic leakage that resulted in cast formation, caused by surgical trauma, adhesions or elevated central pressures. This has been supported by documented cases of non-recurrence following thoracic duct ligation [4].

In the case described earlier, the presentation and the clinical progression of the disease were in fair agreement with existing case reviews. However, we believe that this is the first case to date reviewing the role of barotrauma secondary to air travel in the manifestation of plastic bronchitis. Pulmonary barotrauma associated with commercial aviation is rare probably because of the cabin pressure within modern pressurized aeroplanes decreasing only to a pressure equivalent to that at 7000–9000 feet above sea level, with only gradual pressure fluctuations, therefore making pre-existing lung pathology a necessity for such an occurrence. Altitude-related pulmonary barotrauma has been scantily reviewed in present literature, with cases describing the rupture of pre-existing bronchogenic cysts leading to the development of pneumo-pericardium, pneumo-thorax and cerebral gas embolism [5]. The expansion and rupture of these cysts are a consequence of the expansion of intrathoracic air volume with the decreasing ambient pressure, according to Boyce's Law (pressure × volume = constant).

However, in view of the temporal relationship between air travel and prompt development of respiratory symptoms, it is postulated that the in-flight pressure fluctuations experienced by our patient may have resulted in alveolar rupture and subsequent air leakage into adjacent pulmonary vasculature. This along with localized air trapping that may further compress pulmonary vessels serve to further increase pulmonary venous pressures. Pulmonary venous congestion may, hence, have triggered the subsequent development of plastic bronchitis by mechanisms described earlier. However, it remains impossible to ascertain such causative relationships. The cavopulmonary connection was fenestrated, which suggests that the haemodynamics may have been suboptimal pre-cavopulmonary completion. Hence the development of casts may generally be a non-acute phenomenon. Hence, the plastic bronchitis may have been insidiously manifesting before the flight, exacerbating gas trapping by obstructing the airways and hence precipitating subsequent alveolar damage.

Aircraft cabins typically have a partial pressure of atmospheric oxygen (PiO₂) of 108–122 mmHg compared with that at sea level of 149 mmHg [5]. In persons with normal respiratory function, the resultant variations in oxygen saturation remain within the flat section of the oxygen dissociation curve. However, for patients with Fontan circulations with predictably greater vulnerability to environmental changes, the reflex pulmonary vasoconstriction would likely produce a more severe decrease in oxygen saturations, with pulmonary flow being solely dependent on systemic venous pressure. This hypobaric hypoxia would similarly induce a reflex increase in minute ventilation, heart rate and cardiac output, all of which may have contributed to the ensuing development of plastic bronchitis in the case described in this article.

However, it is important to acknowledge the possibility that the plastic bronchitis was an incidental finding and that the respiratory failure resulted solely from the reflex pulmonary vasoconstriction in response to in-flight variations of PiO₂, with the development of pneumomediastinum and subcutaneous emphysema as a result of her attempts to overcome the dyspnoea. The development of events was probably the trigger of the acute decompensation more than the cast bronchitis. Though many details are missing, especially related to the Fontan circulation before the event and transpulmonary gradient; though pivotal to describe the phenomenon; the fact that the Fontan was fenestrated does not necessarily mean that the haemodynamics was suboptimal as many surgeons performs this on a routine basis.

Although barotrauma is one possibility, pre-existent casts with pneomedistinum related to altered respiratory effort or cough or the impact of drying of secretions at an altitude altering the state of the cast are other potential explanations. The proposition of barotrauma is interesting, but only one of a range of possibilities. The main objective of this case discussion is to propose the possible increased risk of barotrauma, plastic bronchitis being a potential consequence, in patients with Fontan circulations. These patients would likely benefit from in-flight supplemental oxygen as well as from physical activity restrictions during air travel to reduce the extent of pulmonary vasoconstriction. At the same time, one has to be mindful that while air travel does expose such patients to risk, over-interpretation by potential travellers is a possible consequence, and therefore a better risk analysis of this patient ‘in particular’, rather than of cavopulmonary repair patients in general is also worthy of some thought.

Conflict of interest: none declared.