INTRODUCTION

TOP ABSTRACT INTRODUCTION DISCUSSION REFERENCES

Cardiopulmonary and neurological disorders are the most frequently reported causes of in-flight morbidity and mortality (1). However, considering the large number of airplane passengers with a variety of medical conditions, the incidence of fatal casualties is low (0.31 per million passengers, mass casualty deaths in aircraft crashes excluded) (2).

Pulmonary barotrauma may occur during rapid ascent in scuba divers, and is a well-established cause of arterial gas embolism (3). Only a few cases of pulmonary barotrauma during commercial flights have been reported (4, 5), and specific pre-existing lung pathologies such as large cysts seem to be responsible (5, 6). Bronchogenic cysts are the result of an abnormal bronchial development from the primitive ventral foregut, and are located either within the lung or in the mediastinum. They are often asymptomatic; however, emergencies may be caused by a sudden increase in the cyst size due to hemorrhage, infection, or rapid decompression (7, 8). We present the unusual case of a female with a previously asymptomatic giant intrapulmonary bronchogenic cyst who sustained fatal air embolism during a commercial air flight. This case highlights the pathophysiology of pulmonary barotrauma usually diagnosed in divers. Furthermore, it emphasizes the importance of preventive surgical resection of incidentally diagnosed large intrapulmonary cysts prior to exposure to even small changes in ambient pressure.

	CASE REPORT

A 40-yr-old nonsmoking Romanian female airplane passenger with no history of cardiac, pulmonary, or neurologic disease experienced sudden severe chest pain and dyspnea followed by loss of consciousness 10 min after the takeoff of an Airbus A 320 on its way from Bucharest to Toronto. Since the spontaneously breathing passenger remained unconscious, an unscheduled landing in Zurich was undertaken. On admission to our hospital, the comatose patient was breathing spontaneously, the blood pressure was 150/ 80 mm Hg, and the heart rate was regular at 100 bpm. Recurrent, generalized convulsive attacks were noted. The patient was intubated and mechanical ventilation was started. The pupils were equal in size, round, and reactive to light. Gag reflexes and deep tendon reflexes were absent. There was no reaction to pain. Babinski's sign was positive on both sides. The vestibulo-ocular reflex was absent. The funduscopy was normal. Examination of the skin revealed bluish-red reticular lesions (livedo reticularis) on the upper thorax and on the back of both hands (Figure 1, panel A). A chest radiograph (Figure 1, panel B) and a subsequent computed tomography (CT) scan (Figure 1, panel C) revealed an intrapulmonary thin-walled cyst measuring 7.3 cm × 6.6 cm × 11 cm in diameter in the left upper lobe. There was no evidence of pneumothorax or pneumomediastinum. The electrocardiogram showed S-T segment elevations consistent with an acute inferior myocardial infarction. Laboratory data (initial, i.e., 5 h after the event, and maximal values, respectively, range of normal in brackets) were as follows: total creatine kinase (CK) initial 113 U/L (< 150 U/L), maximal 2,069 U/L; MB isoenzyme of CK (CK-MB) mass initial 4.4 µg/L (< 4.7 µg/L), maximal 128.7 µg/L; lactate dehydrogenase (LDH) initial 412 U/L (< 420 U/L), maximal 889 U/L; aspartate aminotransferase (AST) initial 23 U/L (< 50 U/L), maximal 175 U/L. The remaining laboratory data were within normal range. A CT scan of the head showed mild diffuse brain edema.

View larger version (143K): [in this window] [in a new window]   View larger version (128K): [in this window] [in a new window]   View larger version (106K): [in this window] [in a new window]   View larger version (98K): [in this window] [in a new window]   Figure 1.   (Panel A) Livedo reticularis (mottling) of the back of the hand due to air embolism to the skin. (Panel B) Chest X-ray with a cyst compressing adjacent lung tissue. (Panel C) CT scan of the chest with a cystic intrapulmonary lesion crossed by a fibrous strand. (Panel D) Thin-walled, air-filled cyst containing vascular structures found at autopsy.

The diagnosis of air embolism to the upper body involving the brain, the heart, and the skin, attributable to the seated position of the patient during the flight, was made. Tears in the cyst wall from expansion of intracystic gas volume during the decompression phase of the flight were assumed to be the entry port of air. Hyperbaric oxygen treatment was considered; however, the patient was too critically ill to be transferred to a hyperbaric chamber. The patient was ventilated with 100% oxygen.

A repeated CT scan of the head 6 d after the initial study revealed a severe diffuse brain edema with multiple cerebral infarctions. The patient died on the eighth hospital day. A chest radiograph performed 6 mo earlier as a part of the screening exam required by the Canadian immigration authorities disclosed an intrapulmonary cyst with slightly smaller dimensions, as seen on admission.

The autopsy confirmed the presence of a bronchogenic intrapulmonary cyst with a smaller second cyst within (Figure 1, panel D). No communication to the tracheobronchial tree was found. Microscopic examination revealed the cyst wall to be lined with ciliated pseudostratified columnar epithelium with smooth muscle bundles, cartilaginous plates, and multiple dysplastic and partially ruptured vessels. Diffuse patchy myocardial (patent coronary vessels) and brain necroses were present.

	DISCUSSION

TOP ABSTRACT INTRODUCTION DISCUSSION REFERENCES

The characteristic pattern of livedo reticularis, a patchy cutaneous venodilatation that develops distal to arteriolar occlusion, cerebral infarction, and myocardial injury is identical to the symptoms and physical findings as reported in the literature in response to mechanical ventilation in patients with adult respiratory distress syndrome and is highly suggestive of systemic air embolism (9). There is circumstantial evidence that the bronchogenic cyst was the origin of air entry into the systemic circulation in our patient.

At cruising altitudes of 30,000 to 35,000 ft, the modern Airbus A 320 passenger aircraft is pressurized to maintain a cabin pressure equivalent to an altitude of 8,000 ft. The corresponding pressure drop inside the passenger cabin during the climb of the aircraft is from 760 mm Hg at sea level (Bucharest) to 560 mm Hg at cruising altitude (10). Assuming the vestigial communication between the bronchial tree and the cyst was obliterated, the decrease in ambient pressure during the climb of the aircraft resulted in an expansion of the cyst volume (as evidenced in our case) up to one-third (Boyle-Mariotte's law: P × V = constant), depending on the compliance of the cyst, subsequent tears of the wall, and discharge of intracystic air into the surrounding vessels.

Barotrauma lung injury in commercial aviation is rare, since the cabin pressure of modern airplanes decreases only to a pressure equivalent to the ambient pressure at 7,000-9,000 ft above sea level at a rate of 1,500-2,000 ft/min with no sudden pressure fluctuation. A few cases of pneumothorax (4, 5) and one case of air embolism (6) due to pulmonary barotrauma have been reported in commercial aviation. Air-filled pulmonary cysts represent a potential source of barotrauma injury (5, 6, 11). Bronchogenic cysts are closed sacs that result from abnormal budding during the early development of the foregut. The fluid-filled mediastinal bronchogenic cysts (80%) rarely communicate with the tracheobronchial tree. In contrast, intrapulmonary bronchogenic cysts (20%) arise later during gestation and often communicate with the distal bronchial tree, making them more likely to cause complications (12). The development of a large, air-filled cyst may be due to a "stopcock valve mechanism" that allows air to enter but not to escape from the cyst. Identification of the bronchial connection is difficult, and determination of its anatomical location is usually not possible. Symptoms mainly result from compression of the adjacent structures by the expanding cyst. Infection is the most common complication. Rare complications reported in adults include compression of pulmonary or coronary arteries (13, 14), superior vena cava obstruction (15), pericardial tamponade (16), obstructive emphysema (17), unilateral ventilation- perfusion defect (18), pleural effusion (19), hemoptysis (20), pneumothorax (21), and malignancy (22). Air embolism as a complication of intrapulmonary bronchogenic cysts has been reported in scuba divers (11), in two men who underwent decompression after construction work in a pressurized tunnel (25), and in an airplane passenger (6). Hyperbaric oxygen therapy is the most effective treatment if started immediately after acute air embolism (26). Some case reports with a favorable outcome support the application of hyperbaric oxygen therapy even after a considerable time delay (27).

In general, pulmonary barotrauma results in pneumothorax, pneumomediastinum, or air embolism and represents a typical hazard in divers. Breath-holding during the ascent, or local obstructive lung pathology, may result in rupture of alveoli as the volume of the enclosed air space increases. Experimentation in unchilled cadavers and dogs has shown that a pressure differential of 80 mm Hg is necessary to cause alveolar rupture (28). With a tightly sealed gas space within the lung, a pressure difference of 80 mm Hg can develop during a diving ascent of 3 ft or during an airplane climb to 3,000 ft from sea level. This explains the different frequencies of pulmonary barotrauma in diving and aviation. Because of the relatively low pressure changes in modern, pressurized airplane cabins, pre-existing lung pathology is considered a necessary cofactor in altitude-induced pulmonary barotrauma (4). Bronchogenic cysts are found incidentally on chest radiographs and at necropsy in adults. Available reported series of complications were thought to reflect a significant selection bias in favor of symptomatic individuals (29, 30). However, more recent reports recommend the resection of all asymptomatic bronchogenic cysts diagnosed in adults because of the unpredictable long-term prognosis and the fact that a majority will ultimately become symptomatic (7, 8, 31). Since dysplastic embryonal vessels are part of the cyst wall, they may be the source of fatal air embolism. Patients should therefore abstain from activities leading to considerable changes in ambient pressure, such as flying in airplanes, diving, or ascending to high altitudes by cable car. Video-assisted thoracoscopic surgery as a minimal invasive procedure facilitates the decision in favor of a surgical intervention even in an asymptomatic, healthy person (32).

Although many medical conditions are aggravated by factors in the airplane cabin environment, such as hypobaric hypoxia, low humidity, turbulence, and immobility, the incidence of in-flight medical emergencies reported to the International Air Transport Association is low (1 per 10,000 passengers, 0.31 deaths per million passengers), and is usually due to cardiac-related events in otherwise healthy middle-aged men (1, 2). In 1996 the estimated number of commercial airline passengers was 375 million. This growing mass of commercial air travelers may result in significant morbidity and mortality in the future, even though the percentage incidence of in-flight medical emergencies remains low.

However, in view of the huge costs and the minimal benefit, rigorous screening for pre-existing lung pathologies in the growing mass of commercial air travelers is neither reasonable nor practicable. Pre-flight screening may only be indicated in ill individuals (33).