The risk of developing spontaneous pneumothrax for air passengers depends on his or her history of lung disease and similar respiratory problems. There were cases of pilots and deep sea divers developing this problem due air pressure changes into lung cavities or blebs (blisters) in weakened areas of the lungs. Air may flow from lungs into the thoracic cavity and vice versa when air pressure changes.
When blebs rupture, air enters from the lungs into the pleural space and thoracic cavity. If air was trapped in the pleural spaces due to previous history of pneumothorax, it will then expand against the lower pressure in the lungs when the cabin pressure is lowered to about ¾ that of the normal atmospheric pressure. This may cause the lungs to collapse at certain areas.
Medical scientists are unable to evaluate the risk with certainty because they have little data to work on due to limited studies on air passengers who faced this problem. Passengers who have history of spontaneous pneumothorax previously are advised to have their lung strength and functions tested by their own respiratory physician before they fly.
Mechanism of Respiration
Before we answer or discuss this problem whether or not pilots and air passengers could develop spontaneous pneumothorax in detail, we need to understand the physiology and pathology of respiration, and how pneumothorax come about.
Gasses are able to move in and out of the lungs through muscular energy exerted on the thorax and changes between intrathoracic and atmospheric pressures. The pressure within the lungs and thorax must be less than atmospheric pressure for inspiration to occur; air then flows from an area of higher pressure to one of lower pressure. As the diaphragm and intercostal muscles work to increase the size of the thorax, intrathoracic pressure decreases below atmospheric pressure and air moves into the lungs. During exhalation, the inspiratory muscles relax, and the elastic recoil of the lung tissues, combined with a rise in intrathoracic pressure, causes air to move out of the lungs
What is Pneumothorax?
Pneumothorax is the presence of air in the pleural cavity or thorax, causing the lung(s) to collapse. Usually the air pressure between the pleura is lower than the pressure inside the lungs. If air gets inside this space, the pressure between the pleura becomes greater than the pressure in the lungs. This causes the lungs to collapse either completely or partly. Partial or complete lung collapse causes immediate, severe shortness of breath.
A pneumothorax may occur for no apparent reason. Sometimes it occurs because a rupture develops in a small, weakened area of the lung that leaks air into the pleura, most often in older people who have lung disease such as emphysema, cystic fibrosis, Langerhans cell granulomatosis, sarcoidosis, lung abscess, tuberculosis, and pneumocystis pneumonia.
Causes and Risk Factors
Primary spontaneous pneumothorax is a common clinical problem and its incidence is thought to be increasing. This may be a spontaneous occurrence without a preceding event, or it may be due to a penetrating chest injury or a traumatic causing air to enter into the pleural cavity. It may even be iatrogenic in origin, meaning, caused by a doctor during surgical or medical treatment such as inserting a subclavian central line into the chest. Sometimes this happens in chest surgery when it could be dangerous due to underlying lung disease, although the leak may be sealed by filling the space with a talc mixture or giving the drug doxycycline through a chest tube that is draining air from the space. Other causes of iatrogenic pneumothorax may be postoperative complication, mechanical ventilation, and thoracentesis (also known as pleural tap to remove fluid or air from the pleural space for diagnostic or therapeutic purposes, central venous cannulation.
With the advent of increasing diagnostic and therapeutic procedures iatrogenic pneumothorax is becoming very common. In such case it is categorized as a subdivision of traumatic pneumothorax.
Spontaneous pneumothorax that occurs naturally is further subdivided into primary spontaneous pneumothorax and secondary pneumothorax. Whatever the classification, pneumothorax in apparently healthy individuals is a relatively common disease, particularly in those in their second and third decades of life. Spontaneous pneumothorax is primarily a disease of young people and is predominant in males. Studies also showed that pneumothorax is common in young people in their second and third decade of life. Tall men who are younger than 40 are most at risk for developing a pneumothora
Primary spontaneous pneumothorax is usually caused by the rupture of the subpleural bleb (bulla or blister in the lungs). They are usually multiple and mostly occur at base or apices of the lungs.
Secondary spontaneous pneumothorax is caused by an underlying lung disease. The disease that is associated the most with secondary spontaneous pneumothorax is chronic obstructive pulmonary disease (COPD). COPD patients tend to be middle aged or elderly while emphysema is the commonest cause of pneumothorax above the age of 40, especially among smokers. It is well established that smoking increases the risk of contracting first pneumothorax especially if they already have a history of COPD Secondary spontaneous pneumothorax is an important complication of pulmonary tuberculosis in which the lung cavities or blebs rupturing in to pleural space causing air to enter from the lungs into the pleural cavity.
Altitude and air pressure with the plane’s cabin pressure differential is one can put a passenger at risk of developing spontaneous pneumothorax. Normally all airplanes are pressurized to maintain a comfortable living environment for human beings. Off course, if it were possible, a plane would be pressurized to ground level pressure but this is not practical, as the fuselage of a plane would have to be incredibly strong. Therefore, modern airliners are only pressurized to an altitude of around 2400 metres (8000 feet). Thus pressure inside the cabin at this altitude is 0.7230 atmospheres, equivalent to 549.5 mm Hg. This give a cabin pressure differential against the outside (at 13,100 metres = 0.1703 atmosphere = 129.4 mm Hg), equals to 549.5-129.4 = 420.1 mm Hg or 8.13 psi (pounds per square inch). 1 psi = 51.7 mm Hg.
So even if a Boeing 777 flies at 13100 metres (43,000 feet) as its actual cruising altitude, passengers are only experiencing an altitude of only 8000 feet in the passenger cabin!
The standard set for pressurization is SAE ARP1270. This standard sets down the guidelines for operation of the pressurization systems of aircraft cabins and is the standard recognized by the FAA and JAA. The most important factor in this standard is that: the compartments to be occupied must be equipped to provide a cabin altitude pressure of not more than 8000 feet (2440 m) at the maximum operating altitude in normal conditions. This is inevitably a compromise between the ideal position (but not feasible in terms of cost and engineering) of maintaining sea level pressure while flying at over 30,000 ft and unacceptably risky exposures.
It is worth noting that this maximum cabin altitude standard has been developed over the passenger aircraft routinely operate at lower cabin altitudes. It is based on data derived from the tests of hypoxia on healthy young males. This is obviously not a representative sample of the current traveling population and risks are greater for the elderly and those suffering from certain medical conditions, such as chronic obstructive pulmonary disease (COPD), in addition to anyone who has recently spent time diving to depth under water. The risk would also depend on the duration of the flight.
At 8000 ft, it is possible for some people to experience mild hypoxia, the symptoms of which include impaired mental performance, reduced exercise capacity, fatigue. Some individuals suffer mild hyperventilation, headache, insomnia or digestive dysfunction. The effects are not great, and would not necessarily be of significance in most cases, although accident risk could increase. It can also be speculated that fatigue resulting from hypoxia would discourage exercise. Anyway, hardly any passenger exercise in the cabin, and therefore, this increases the risk of Deep Vein Thrombosis (DVT). Conversely, exercising to avoid DVT might increase the risk or effects of hypoxia (deficient in oxygen), and this is made worse if the lungs are partially collapsed due to pneumothorax. It is the case of either the devil or the deep blue sea?
The reduction of applied external pressure also leads to the air trapped in the body cavities to expand (by 38% at 8000 ft cabin altitude). The cavities of concern are the ears, sinuses, stomach, intestines and lungs (and, for some people, teeth and eyes). This gas expansion can cause discomfort for the occupant (for example, ears popping) but in some susceptible cases it can also present a health risk. Not only is the absolute pressure important but also the rate of change of pressure. This is particularly so for the ears, in which rapid changes in pressure can cause damage. This section of the report will deal with both aspects of reduced cabin pressure.
In addition to the maximum cabin altitude, the SAE standard also relates to the rates of change the aircraft cabin altitude as the aircraft ascends and descends. The rate of change of pressure is an important part of both comfort and safety, particularly for the ears. In practice, the rate of change in passenger aircraft should not be a problem except for some babies and young children. Susceptible individuals may experience discomfort on descent and need to clear their ears. There are some indications of a trend towards more rapid ascent /descent in newer aircraft, so that more time is spent a cruising altitude. The effects of any such trend should be monitored.
Pilots and Air Passengers
Pilots are affected because of reduced air pressure, while divers suffer because of increased pressure. Increase in pressure in lungs may lead to barotrauma, one of which is the air sacs may burst causing air to leak from the lungs into the plural spaces. When the diver surfaces, the air trapped at a higher pressure between the pleural spaces outside the lungs then expands against the relatively lower atmospheric pressure in the lungs. This causes the lungs to be pushed inwards and collapse. This event is more pronounced if a deep sea diver emerges from the sea and immediately gets into a plane that is going to fly at high altitude. The pressure difference between the deep sea and high altitude in the atmosphere is even greater, increasing his risk of a pneumothorax. Even for pilots who ascend from normal sea-level air pressure to cruising heights of 43,000 feet, there were reported cases of pneumothorax among them, especially those with fragile lungs.
What actually happens is that if the lungs are fragile with holes in the air sac, air in the lungs will leak from the lungs into the pleural or thoracic cavity where the pressure is lower, and gets trapped there. When the pilot ascends, the decrease in cockpit or cabin pressure to about three-quarter the normal, will cause the trapped air to push the lungs inwards where the pressure is reduced, resulting in the lungs collapsing.
Deep Sea Divers
In the case of deep sea divers, the increased pressure will cause the air in the lungs to be forced into the pleural cavity through weakened areas in the lungs. When he ascends to the surface the trapped air at increased pressure will tend o flow into a region of near normal atmospheric pressure, causing the lungs also to collapse. The result is the same either way. If the sea diver, now gets into a plane, and climbs to high altitudes, it will aggravate the problem even more.
Albeit the incidence of pneumothorax among pilots is relatively rare, there are reported increases in the number of cases. The same incidence rate applies for deep sea divers.
To diagnose a pneumothorax, physicians perform a physical examination and listen for abnormal breathing sounds using a stethoscope. A chest X-ray can reveal the air pocket and the collapsed lung outlined by the thin inner pleural layer. It can show if the trachea (the large airway at the front of the neck) is being pushed to one side because of a collapsed lung.
A small pneumothorax that develops without any apparent cause usually does not require treatment. There are no serious breathing problems, and the lung absorbs the air again in two to three days. If the pneumothorax is larger, it may take two to four weeks to absorb the air. In this case, the pneumothorax is usually removed by inserting a tube into the lung as already described.
Sometimes pneumothorax occurs during diving or high-altitude flying, probably as a result of air pressure changes in the lungs. If a person has recurring pneumothorax or is at high risk (divers and airline pilots, for example), surgery may be done the first time a pneumothorax happens. Usually the surgery repairs the leaking areas of the lung and firmly attaches the inner layer of pleura to the outer layer.
Regardless of the aetiology (causes), the aim of treatment of pneumothorax is to eliminate the collection of air from the pleural cavity. Invasive method to manage penemothorax includes the insertion of inter-costal (between the ribs) chest tube drainage (ICTD). This is the most commonly used treatment modality for pneumothorax but requires significant expertise and hospitalization. Needle aspiration provides a simple and easy alternative that can be performed on out-patient basis in a hospital environment. The aspiration is normally carried out in the second inter-costal space in the mid-clavicular line (vertical line crossing through the collar bone), or the fourth inter-costal space in the anterior axillary line. The site was infiltrated with lignocaine, a local anasthetic. An 18 G intravenous (IV) cannula was inserted into the pleural cavity.
The needle was withdrawn and three-way stopcock was connected to the IV cannula. A 50 cc syringe and IV tubing with its end under water seal. This procedure has been recommended for initial management of symptomatic spontaneous pneumothorax by the British Thoracic Society. The American College of Chest Physicians guidelines for management of pneumothorax did not recommend simple aspiration for any type of pneumothorax; a suggestion that has been questioned.
For this controversial reason, it may not be recommended that a chest tube insertion be done on a passenger in an air plane, even if there is a medical doctor on board. The doctor, especially a general practitioner, may not be familiar or inexperienced in the procedure. Doctors practicing family or general medicine may not be familiar with specialized procedures of intercostal chest tube drainage (ICTD) which is best left to a thoracic surgeon, trained in thoracotomy or thoracoscopy or an emergency physician trained in emergency medicine. Similarly, even if there are other medical specialists on board, they too may only be familiar and competent in their areas of expertise. So not all doctors may be able to handle this situation even in an emergency especially inside an airplane cabin where there is no surgical facilities.
Let’s look at some air pressure data before discussing further.
Air pressure at sea level = 760 mm (29.92 inch) of Hg Density = 100 %
At 8000 feet the air pressure drops to 22.22 inch (564.4 mm) of Hg and density drops to 78 .6 % (74.26 %) depending on temperature, humidity.
Increase Cabin Pressure?
A person who has a history of spontaneous pneumothorax may feel fine under normal atmospheric pressure at sea level. But if he still has some air trapped in the thoracic cavity he may suffer another event of pneumothorax if he breathes rarified air, say even in the cabin which normally would not cause ill effects. This is because the residual air now tends to flow into the region of lower pressure in the lungs. If the lung cavity is already sealed, the back flow into the lungs cannot take place. So the air merely presses on the lungs, and causes them to become smaller or even collapse in some parts. Thus, if we increase the cabin pressure to normal atmospheric pressure as it were at sea level, this will inflate the lungs back to its normal volume. However, I am unsure if this will jeopardize the safety of the air-craft since the outside pressure at 43,000 feet, and the cabin pressure inside at 8,000 feet already generates a pressure difference of 420 mm Hg or 8.13 psi.
But if the cabin pressure is now brought higher to normal atmospheric pressure at 760 mm Hg, the pressure differential within it and outside will climb to an incredible 760 -129.4 = 630.6 mm Hg (12.2 psi) just because of one patient. The plane may just explode if the fuselage is not strong enough. I do not know for sure?
Since modern airliners are only pressurized to an altitude of around 2500 meters (8000 feet) without ill effect to the passengers. At this altitude, there is about 25% less oxygen than there is at sea level. However if this causes breathing difficulties to some patients with respiratory problems, another option is to supply pure oxygen to them instead of increasing the cabin pressure and endangering the aircraft or violating aviation laws.
Thus if the lungs have partially collapsed, and the patient experiences dyspnea (short of breath) breathing in pure oxygen from a face mask tightly sealed to the nasal and mouth region would probably be best approach. Supplying oxygen through a face mask is non-invasive, easy to administer, does not require much skill, and serves the primary aim of delivering oxygen to someone with partially collapsed lungs. Moreover, pure oxygen unlike air which contains 78 % insoluble nitrogen is easily absorbed into the blood even if it leaks from the lungs into the thoracic cavity. The aim is to push up the oxy-haemoglobin saturation level (SaO2) to about 97% if the cabin air pressure is too low This can normally be achieved with a partial oxygen pressure of around 100 mm (Hg pO2 100 mmHg). At 10,000 meters (33,000 feet), breathing pure oxygen is roughly equivalent to breathing air at sea level.
Tempting it may be, it may not be wise to force or increase the oxygen pressure to over 1 atmospheric pressure into the lungs in an attempt to inflate the lungs. Increasing the pressure within the lungs may cause more air or oxygen to seep into the pleural cavity if there are lung cavities (blebs) present. This should not be a problem if an individual has good strong lungs with no blebs in it, or has history of spontaneous pnemothorax. Any accumulation of gas in the pleural cavity will increase the pressure there, causing the lungs to be pushed inwards and collapse even more. The extent of the collapse depends on the pressure within the pleural cavity, which in turns depend on the amount of gas there.
It is best to breathe the oxygen under normal cabin pressure, and definitely not higher than atmospheric pressure. When air or oxygen tend to seeps into the thoracic cavity at a pressure higher than one atmospheric pressure. If the cabin pressure or the oxygen supplied is increased to more than one atmosphere, this will cause the lungs to collapse even more when the plane lands at normal atmosphere. This mechanism is similar to a deep sea diver ascending from the depths to the surface
The emergency first aid measure is to remain calm, and breathe in pure oxygen supplied from the cabin face mask normally until there is no shortness of breath. This is the best can be done during the emergency while the plane is still flying between 10,000 -13,000 metres (33,000 - 43,000 feet) The pilot should be informed, and the plane should be brought down very gradually so that the cabin pressure does not change rapidly. This will assist the patient to adapt slowly, and any remaining air or oxygen with the pleural cavity be allowed to dissolved back into the lungs while buying time during the descent. This is probably the best approach in this particular medical emergency while the patient is closely observed.
Difficulties in Research
The difficulty for scientists to study the risk of spontaneous pneumothorax developing in pilots, air passengers or deep sea divers and come with definitive conclusion is because:
· Not everybody flies
· Those who flies may not have history or are at risk of developing spontaneous pneumothorax
· Those who have, or with previous history of pneumothorax may not necessary fly, reducing the number available for study even further.
· Those who fly may not wish to be as subject of any study, or be a subject of any study or unethical medical experiment. All these limitations, reduces the number of subjects available to bare minimum.
Scientists hence have little data to work on. With limited cases among air-travelers reported in the literature, it is very difficult to make any firm conclusion. Passengers will have to take this risk on their own. It is best for them to see their own chest physicians for an evaluation based on their medical history and their current pulmonary health before traveling by air.
Dr JB Lim