Pneumothorax is characterized by the presence of air in the pleural cavity. Spontaneous pneumothorax [SP] occurs without obvious cause and commonly affects young, healthy, men. These young men typically fit a profile of being both tall and thin, and most are quite healthy. Because this demographic includes the majority of aviation personnel, the pilot population is especially vulnerable to pneumothorax episodes. The physical effects of altitude can greatly aggravate an existing pneumothorax and can even bring about an attack in an already predisposed person. Several methods of treatment are available, ranging from bed rest to thoracic surgery. Bilateral parietal pleurectomy is the most effective means of preventing recurrence of SP attacks and is recommended for affected individuals who desire to begin or continue a flying career.

Pneumothorax is defined as the presence of air in the intra-pleural space, the area between the visceral and parietal pleurae. The visceral pleura coats the lung, and the parietal pleura covers the chest wall. Under normal conditions, the two are held in close contact by the negative intrapleural pressure and are allowed to slide (accommodating the lung’s elasticity) by the presence of the pleural fluid. The phenomenon known as pneumothorax is divided into three categories: artificial, traumatic, and spontaneous. Artificial pneumothorax refers to the historical medical treatment for tuberculosis, and traumatic pneumothoraces are caused by sudden trauma to the chest (gunshot wound, automobile accident, etc.). Spontaneous pneumothorax is either without apparent cause or can be caused by pre-existing lung disease.

Spontaneous pneumothorax [SP] is a relatively common condition among the general population and is often considered benign, as it usually heals automatically. One source cites the rate of SP occurrence as 4.7 per 100,000 per year. Among other groups considered at high risk, namely college students and military personnel, the incidence rates can be as high as 47 per 100,000. Voge and Anthracite argue that one of every 500 young men has a history of spontaneous pneumothorax. These numbers are most likely understated, however, due to the fact that many victims do not consult a physician because their symptoms are not of such severity that they seek medical attention.

Although SPs heal automatically without treatment, recurrence is likely. Following the first attack, SP recurrence probability is as high as 30%; it can be as high as 80% following the third attack.

Most SP attacks (75%) occur during periods of light physical activity or during sleep and seem unrelated to stress. Studies suggest that strenuous physical activity does not increase one’s susceptibility to SP.

The most common cause of idiopathic (non disease) spontaneous pneumothorax is the rupture of a sub pleural bleb or bulla (blister) on the lung, usually located at the lung’s apex. These blebs and bullae are common among the general population, and when patients are examined by physicians, they are usually noted as being present on both lungs. Patients exhibiting such blebs traditionally have no history of lung disease.

SP does not choose its victims at random. The stereotypical SP patient is a young, tall, thin male with no history of medical problems. The predominance of SP in men is overwhelming; SP affects 5-10 times as many males as females. The peak age group is 20-29 years of age, and many studies indicate much higher susceptibility among smokers, though some studies dispute this claim. The harmful ingredients in tobacco smoke may irritate the pleura and therefore increase the likelihood of a rupture or tear in the pleural membrane. The reason for the high incidence of spontaneous pneumothorax among tall males is not completely understood. However, many feel that the morphology and physiology of tall men is such that they have an inherent defect in their structure which is manifested by a lengthened chest cavity and lung. This structure makes the lung apex more vulnerable to gravitational and other stresses which may cause bleb formation and a subsequent spontaneous collapse of the lung. In addition to body structure, other risk factors for the development of SP are pre-existing lung disease, the presence of sub pleural blebs, and forceful coughing. When evaluating patients reporting chest pain, one must always consider SP if the patients are tall, thin, young men with a positive smoking history.

Spontaneous pneumothorax may be either partial or total, and it may be bilateral or isolated to one side. The presence of air in the pleural space causes a reduced lung volume and therefore reduced oxygen diffusing capacity. Hence arterial blood saturation is restricted. The degree of this reduction in saturation varies with the amount of lung collapse. A collapse of 50% or more of the lung leads to a consistent fall in arterial blood oxygen [O₂] saturation. This condition leads to hypoxemia.

The greatest danger with SP is a simultaneous bilateral pneumothorax. Bilateral SPs are rare and occur in approximately 2.5% of patients. This condition is potentially fatal due to low blood oxygenation, but the mortality rate associated with SP is less than 1%.

Persons experiencing SP may be completely incapacitated or they may be asymptomatic, depending on the extent of lung collapse and other factors. The most common symptom of SP is sharp, knife-like pain in the upper chest or shoulder which is aggravated by breathing (Green, Johnston, 1974). This pain is characterized by its sudden onset. In Voge and Anthracite’s study, 89% reported pain associated with their SP and 61% reported some degree of dyspnea, or difficulty breathing (1986). Patients typically feel unable to inhale a full breath, and their attempts to do so can result in further lung damage. Another less common symptom of SP is a non-productive cough, and some physicians may note decreased breath sounds on the affected side. Spontaneous pneumothorax is not associated with elevated body temperature.

Symptoms of pneumothorax can be severe and life threatening in up to 10% of cases, whereas 7% of patients report no symptoms whatsoever. In young and healthy victims, even total collapse of a lung may fail to yield severe symptoms. Even with simultaneous bilateral pneumothorax, the patient may be asymptomatic, or the condition may be so severe as to cause sudden death.

SP patients reporting the aforementioned symptoms are often misdiagnosed as suffering from influenza, acute upper respiratory infection, or myocardial infarction. Confirmation of a pneumothorax is done via a chest x-ray.

In many cases of untreated SP, sharp pain abates within days and all symptoms disappear even before full re-expansion of the lung has occurred. Full re-expansion in less than two weeks is rare.

Spontaneous pneumothorax is a concern in the aviation community because SP can cause sudden and total incapacitation of a crewmember. Though most cases are not reported as being debilitating, the sudden chest pain and dyspnea can be severely distracting. Also, hypoxia associated with the pneumothorax can further aggravate the existing hypoxic effects of altitude.

The aviation community and the armed forces in particular are more susceptible to incidences of SP than the general population due to their demographics; the aviation world is comprised primarily of young, healthy males. Furthermore, it is hypothesized that positive pressure breathing, oxygen breathing, and G stresses may make the lungs more susceptible to an SP.

A pneumothorax will worsen as ambient pressure decreases, such as at altitude. Boyle’s Law states that the volume of air will expand as the surrounding ambient pressure decreases. Therefore, gas trapped in the pleural space will expand at altitude causing further compression of the lung and decreased O₂ saturation. For this reason, continued flight or flight after suffering an SP on the ground is extremely dangerous.

Some studies also indicate that decreased ambient pressure may precipitate an attack in a predisposed individual (one exhibiting blebs on or near the lung apex). Previously demonstrated small apical blebs and bullae increased markedly in size when the patient was subjected to decreasing atmospheric pressure in a hypobaric chamber. This phenomenon is due to Boyle’s Law and only applies when the air trapped within the blister is isolated. If the bleb is sufficiently connected to the tracheobronchial tree, a sudden change in ambient pressure will not pose a problem. Only if the air pocket is isolated will it rupture when exposed to a decrease in atmospheric pressure and thereby cause a pneumothorax.

Although persons in flight would theoretically be more likely to sustain a pneumothorax, data does not necessarily demonstrate this. One study reported that only 12% of aircrew pneumothoraces occurred while in flight or in an altitude chamber. However, because so many aircraft accidents are labelled as "cause undetermined" or "human error," it is impossible to know if SP may have played a role in more military and civilian fatal air accidents. For this reason, trained aircrews who suffer a SP must be grounded until they have received adequate treatment.

The most significant complication associated with pneumothorax is the high incidence of recurrence. The recurrence rate without treatment is between 7-33% on the same side and 10-20% for the opposite or unaffected side. Most SPs recur within the first year . However, the problem may reappear many years later. Medical treatment for spontaneous pneumothorax can be conservative or surgical, depending on the degree of collapse and the patient’s level of distress. Surgery is usually required when the lung fails to re-expand after 3-10 days or if the pneumothorax is bilateral. Surgery is often used for treatment of a recurrent SP. There is no consensus as to whether conservative or surgical treatment is better for non-aviation persons, but surgery is the only option for aircrews who wish to continue in service.

Conservative treatment for SP includes bed rest and/or needle aspiration (thoracocentesis) to remove the trapped air from the pleura. Although the lung will normally re-expand spontaneously, removal of the pleural air causes instant re-expansion. In more severe cases, a chest tube is inserted to evacuate the air in the pleural space and maintain the negative pressure under suction until the rip or tear is healed. If the lung collapse is less than 20%, bed rest and observation alone is usually sufficient. The patient is monitored for skin colour, breathing difficulty, breath sounds, and pain level. 100% oxygen is administered to maintain arterial blood saturation at optimum levels. If the collapse is greater than 20% but the patient is in no apparent distress, a catheter is inserted to removed the air pocket. If the lung collapse is complete (100%) or the patient is in respiratory distress, a chest tube is inserted. Bed rest and observation alone are normally sufficient to allow a SP to heal. Left untreated, severe pain normally ceases within a day and dyspnea within several days. Full re-expansion can take 2-4 weeks for a small to moderate pneumothorax. Large SPs can take 2-3 months to fully re-inflate without any intervention. The average re-expansion rate is 1.25% per day.

Although effective in terms of SP healing, conservative treatment does not address the problem of recurrence. Voge and Anthracite report that recurrence rates after the first episode are between 10-60% for patients with conservative treatment. After the second attack, the recurrence rate is 17-80%, and following the third and fourth, 80-100%. For these reasons, conservative therapy is considered unacceptable in the aviation community.

The first surgical treatment alternative for pneumothorax is pleurodesis. Normally performed as pleuroscopy, pleurodesis induces intrathoracic inflammation that causes the lung to fuse to the thoracic wall (chest wall), which obliterates the pleural space. Without a space to become lodged, the problem of air in the pleural space is eliminated. Pleurodesis can be done mechanically or chemically. Many prefer mechanical pleurodesis because it is less painful and more effective. It also has a decreased rate of complications. Chemical pleurodesis involves the insertion of a foreign substance into the pleural cavity which causes the desired irritation. Talc and silver nitrate are the most commonly used substances, but their use may cause appreciable disability and may fail to prevent recurrence. There is often insufficient adhesion, or the adhesion occurs in the wrong area of the lung, and therefore chemical pleurodesis cannot be guaranteed to prevent SP recurrences. Recurrence rates following chemical or mechanical pleurodesis may be as high as 30%. During the 1980s, however, some aviation institutions such as the British Royal Air Force were actively using chemical pleurodesis with silver nitrate as a surgical treatment for SP because it is less invasive than its surgical alternatives.

Most thoracic surgeons have abandoned pleurodesis in favour of a procedure known as parietal pleurectomy due to its lower SP recurrence rates. The goal of any surgical solution for SP is the removal of the causative lesion (bleb) on the lung or the elimination of the pleural space altogether. Parietal pleurectomy creates a uniform inflammatory surface with secondary adhesions of the lung to the endothoracic fascia (sheet of fibrous tissue) along the chest wall. The procedure may be completed via a large thoracotomy or median sternotomy or by a small lateral incision in the fifth or sixth intercostal space (Voge, Anthracite, 1986). The procedure involves the complete removal or oversewing of the pulmonary blebs and as complete as possible stripping of the parietal pleura. The procedure is well tolerated by patients and yields excellent long-term results.

Parietal pleurectomy is preferred to pleurodesis as a treatment for aircrews due to its increased effectiveness at preventing recurrence. The procedure is sometimes even performed on non-SP patients who demonstrate significant bleb formation and are therefore at risk for developing an SP episode in the future. As a preventative measure, the procedure should be done bilaterally, since the 10-20% contralateral recurrence rate is considered unacceptable in military aviation.

The mortality rates for thoracotomy and pleurectomy are no higher than with chemical pleurodesis, and the incidence of post-operative complication is considered low (4%). Aircrews treated with thoracotomy can often return to normal flying duties within three months of the operation and require no follow up.

In recent years, thoroscopic surgery has been attempted, but long term results are still unknown.

Spontaneous pneumothorax is presently disqualifying for an FAA medical certificate of any class unless the situation has been resolved radiographically and there is no underlying lung disease involved. Although the FAA has denied certificates on the basis of SP recurrence without treatment, this stance by the FAA is considered insufficient due to the very high likelihood of a future SP and the subsequent hazard to the airman and the general public.

Both the US Army and the US Navy classify spontaneous pneumothorax as disqualifying for flight duty. Airman are removed from the flight program or denied entry if an attack has occurred within the three year period preceding the medical exam unless it has been surgically corrected with a good prognosis. The United States Air Force is stricter; any history of SP is disqualifying for entry into the flight program. Retention in the USAF program is possible following a single isolated SP episode with full recovery or following successful surgical intervention with six months of grounded observation including hypobaric altitude chamber tests.

NASA currently has the strictest medical guidelines with regard to SP. Entry into the aerospace program is possible if the SP has been surgically corrected and no recurrence has been demonstrated within five years. For retention in the program, the condition must be corrected surgically with six months of observation and no incidence of recurrence.

Because of the risks associated with the operation of high speed, single-pilot aircraft, the military guidelines regarding SP appear adequate. The success of pleurectomy also appears to satisfactorily eliminate the danger of SP in flight. Military and civilian pilots should be made aware of this relatively common condition so that they will seek prompt medical attention in the event of a SP episode. They also must recognize the risk of ascent with an existing SP condition. The results of a bad decision can be life threatening not only to the crewmember but to the general population.