Author: Jason B Lee / Editor: Jason B Lee / Reviewer: Sarah Hickin-Yacoub, Caitriona Considine / Codes: CAP6, CAP7, HAP6, HAP8, ResC8, ResP1, ResP2, RP5, RP7, SLO1, SLO3, SLO6 / Published: 07/09/2020


A pneumothorax is a collection of gas in the pleural space that results in a variable amount of lung collapse on the affected side. By definition, spontaneous pneumothoraces occur in the absence of any trauma (including iatrogenic causes) to the chest wall. Primary spontaneous pneumothoraces occur in people with no underlying lung pathology. Secondary spontaneous pneumothoraces occur in patients with pre-existing lung parenchymal or pleural pathology (e.g. asthma, lung carcinoma).

Table 1 Recognised causes of a secondary pneumothorax*

Obstructive airway disease Asthma COPD
Lung and pleural malignancy
Infection Pneumonia (particularly pneumocystis jiroveci [formerly PCP]) TB
Suppurative lung disease Cystic Fibrosis Bronchiectasis Lung abscess
Interstitial lung disease Sarcoidosis Idiopathic Pulmonary Fibrosis Hypersensitivity pneumonitis Pneumoconiosis Catamenial

*This list is not considered comprehensive

NB: the British Thoracic Society automatically considers long term smokers aged over 50 years to have secondary pneumothoraces.

Table 2 Comparison table of primary and secondary pneumothoraces

Primary Secondary
Peak incidence age (years) 20 30 60 70
Male: Female ratio 6:1 3:1
Aetiology Ruptured sub-pleural bleb Various
Proportion of all spont. pnemothoraces 80 90% 10-20%
1 year recurrance rate (without pleurodesis) 25% Higher but dependant on underlying condition

Primary Spontaneous pneumothorax

The classic presentation is that of sudden onset of pleuritic chest pain and dyspnoea at rest. The symptoms do not correlate closely with the size of the pneumothorax [12]. In many cases the symptoms are mild and approximately half of patients will present after more than 2 days of symptoms [13].

Secondary Spontaneous pneumothorax

The symptoms are often more severe than those associated with a primary pneumothorax because lung function may already have been compromised by the underlying pathological process. The symptoms will vary depending on the cause e.g. fever, weight loss, night sweats but the primary complaint is that of breathlessness which is often out of proportion to the size of the pneumothorax radiologically.

Unlike symptoms, the examination findings in primary spontaneous pneumothoraces are affected by the size of the pneumothorax. A small pneumothorax can be impossible to identify on clinical examination.

If the pneumothorax is large then some of the following features may be present:

  • Tachycardia
  • Tachypnoea
  • Reduced breath sounds on the affected side
  • Reduced chest expansion on the affected side as the patient splints the chest wall
  • Hyper-resonance on the affected side
  • Decreased tactile / vocal fremitus on the affected side

The diagnosis is usually confirmed radiologically, following which specific information should be sought in order to guide management, advice and appropriate patient disposition/ follow-up:

Tension pneumothorax

If the pleural leak exerts a one-way valve effect then a tension pneumothorax can develop. This recognition and management of this complication is discussed later in the session.


The most useful investigation is the PA chest radiograph despite the fact that it tends to under-estimate the size of a pneumothorax by virtue of it being a 2-dimensional image of a 3-dimensional structure.

In 2010 the British Thoracic Society14, proposed a method for quantifying pneumothorax size on a PA radiograph by measuring the distance from the lung edge to the thoracic wall at the level of the hilum:

Distances <2cm are classified as small pneumothoraces

Distances >2 cm are classified as large pneumothoraces

The rationale for using 2 cm as the cut-off for indicating a large pneumothorax is that this approximates to the point at which up to half of the lung volume has been lost.

Learning Bite

Where to measure? When following the BTS guidelines, pneumothorax size should be determined (on a PA chest radiograph) by measuring the distance from the lung edge to the thoracic wall at the level of the hilum and not at the apex

The PA radiograph has a sensitivity of ~80-85% at identifying small pneumothoraces [17]. The diagnosis is made by the visualising the visceral pleura (lung edge) separated from the thoracic cage with no visible lung marking between the two. Small pleural effusions are sometimes seen.

The following are recognised as potential mimics of pneumothoraces [19]:

  • Medial border of the scapula
  • The outline of the oxygen reservoir bag or associated tubing
  • Clothing
  • Bedsheets
  • Companion shadows (visible subcostal groove usually ribs 1 and 2)
  • Skin folds
  • Post-pleurectomy scarring/suture material

The presence of lung markings beyond the line in question, repeating the films with possible artefacts removed or comparison to previous films usually clarifies the situation.


CT is considered the gold standard at identification of a pneumothorax and is particularly valuable when radiographs are difficult to interpret or specific drain placement is required eg bullous lung disease, loculated pneumothoraces, surgical emphysema.


Ultrasound show promise with reports of sensitivities at identifying pneumothoraces in trauma and post procedure (eg lung biopsy) patients of ~95%20. However, it is highly user dependent and for patients with suspected spontaneous pneumothoraces, radiography has the advantage of identifying unexpected causes of pleuritic pain eg infection, carcinoma. Having said this, with the increasing use of ultrasound in Emergency Medicine, in the hands of an experienced user it can now reliably detect pneumothorax better than an anteroposterior chest radiograph.

Find out more: Sonographic diagnosis of pneumothorax

Arterial blood gases

Arterial gas monitoring may demonstrate hypoxia [21] but the information gained is unlikely to alter the management plan. Their main use is when administering supplemental oxygen to patients with pneumothoraces secondary to COPD.

Management depends upon whether the patient is symptomatic, whether the pneumo-thorax is primary or secondary, and its size on the PA radiograph. The guidance below is based upon the BTS guidelines (2010). Different guidelines have been adopted by other international bodies22.

Learning Bite

Supplemental oxygen: A pneumothorax will resolve up to 4 times faster if high flow oxygen is administered

Symptomatic patients and those admitted for observation should have high flow oxygen administered (15l/min via a non re-breathe mask with a reservoir). Compared to breathing room air, a pneumothorax will resolve 4 times faster if the patient is on high flow oxygen [23]. For patients with COPD, fixed concentration oxygen should be administered.

Entonox diffuses into air spaces and can convert an uncomplicated pneumothorax into a tension pneumothorax. Its use as an analgesic is contraindicated in this setting.

Minimal Symptoms

Patients with small spontaneous primary pneumothoraces and minimal symptoms (80% of whom will have no ongoing air leak) can be discharged with written advice and organised follow-up. Without supplemental oxygenation, spontaneous pneumothoraces resolve at a rate of approximately 2% of the hemi-thorax volume per day [24,25]. A 1cm pneumothorax (~25% pneumothorax) would be expected to fully resolve in approximately 12 days. A 2cm pneumothorax (~30-50% pneumothorax) may take 3-4 weeks to fully resolve.

Patients with spontaneous secondary pneumothoraces less than 1cm in size and minimal symptoms do not require drainage in the ED but should be admitted for observation and supplemental oxygenation.

Learning Bite

Secondary spontaneous pneumothoraces

  • Never discharge a patient from the ED with a diagnosis of a secondary pneumothorax.
  • As a minimum, supplemental oxygen and a 24 hour observation period is recommended.

Symptomatic patients

Symptomatic patients and those with large pneumothoraces, whether primary or secondary, require intervention.

There are two diagrams depicting the recommended treatment algorithm for a primary and secondary spontaneous pneumothorax, these are available to download at the end of this module.

Diagram 1 Primary spontaneous pneumothoraces

Diagram 2 Secondary spontaneous pneumothoraces

Pneumothorax diagram 2

Simple (needle) aspiration

Needle aspiration is technique that describes aspiration of air via the chest wall without insertion of a chest drain (thoracostomy tube). Overall, for primary spontaneous pneumothoraces, the initial success rate of the procedure is no different to that of chest drainage [26] (60-70%). Successful aspiration is associated with a much higher likelihood of discharge than chest drain insertion and fewer complications have been reported [27]. Following successful aspiration, patients with primary pneumothoraces should have a short period of observation in the Emergency Department before discharge. Recurrence rates are similar at 7 days and 1 year compared to thoracostomy tube insertion [24].

The BTS guidelines recommend use of a cannula no greater than 16G in diameter for aspiration though evidence that larger cannulae are more likely to cause a persistent pleural leakis limited. It should be remembered that narrower cannulae are also shorter and may not be long enough to reach the thoracic cavity in larger patients.

Needle aspiration is less likely to succeed for secondary pneumothoraces [15] and is only recommended in this setting if the patient has a small pneumothorax (1-2cm in size) and minimal symptoms. Following successful aspiration, patients with secondary pneumothoraces should be admitted for observation.

Table 5 describes a method of needle aspiration. Identification of the the 2nd intercostal space is achieved by locating the end of the 2nd rib mediall where it attaches at the manubriosternal angle. The ribspace below the 2nd rib is the 2nd intercostal space.

Photo 1 Insertion point for needle aspiration


Table 4 Needle aspiration of a spontaneous pneumothorax

  • Inform the patient about the planned procedure and obtain written consent
  • Position the patient in a slightly reclined position
  • Identify the insertion point (mid-clavicular line in the 2nd intercostal space) and mark with a pen
  • Put on a gown and sterile gloves, clean the area with anti-septic solution and apply drapes
  • Using an aseptic technique, infiltrate a few mls of 1% lidocaine subcutaneously
  • Insert a 14g cannula (attached to a 10ml syringe containing sterile normal saline) through the chest wall at the insertion point, in a horizontal plane
  • Aspiration of air confirms correct placement
  • Remove the trochar
  • Attach the cannula to a short connecting piece of tubing and a 3-way connector
  • Aspirate via a 50 ml syringe, turn the tap and dispel the air into the atmosphere.
  • Turn the tap again and aspirate another 50mls form the pleural cavity
  • Continue until the patient coughs or 2.5 litres have been aspirated.
  • Repeat the chest radiograph.
  • Repeat the aspiration if necessary (follow BTS guidelines)
  • If the procedure is successful, the cannula should be removed and a small occlusive dressing placed over the insertion site
  • If the procedure is unsuccessful, the cannula should be removed and a thoracostomy tube inserted

Simple (Needle) Aspiration

Authors observations:

  • Failure to attach the cannula to a connecting piece increases the likelihood of tube kinking or accidental removal
  • A minimum of 2 persons are required for this procedure, one to manually secure the cannula and turn the connector, the other to perform the aspiration
  • This is a time consuming procedure (50 times x 50 mls), particularly if it needs to be repeated, but success rates are relatively high
  • Beware turning the tap the wrong way and inserting air into the pleural cavity!
  • The syringe gets very warm from the friction and increasing effort is required with each aspiration

Intercostal chest drain (thoracostomy tube)

Traditionally, the treatment for a large pneumothorax has been the insertion of a large (e.g 28FG) drain through an incision in the chest wall.

Photo 2 large chest drain


In the last decade there has been a move toward inserting smaller drains percutaneously. Small drains (e.g 8-12FG) have been shown to be associated with fewer complications (particularly subcutaneous emphysema) without prolonging time to resolution [29]

Photo 3 Seldinger drain kit


Small drains may be associated with a higher failure rate when draining very large pneumothoraces but currently this evidence is limited. In obese patients the Seldinger technique may not be technically possible as the needle may be too short to traverse the chest wall. Whichever technique is used the landmarks are the same. Insertion in the safe triangle (picture) attempts to avoid injury to the long thoracic nerve and lateral thoracic artery, which sit in the mid-axillary line.

This triangle is formed by the anterior border of latissimus dorsi posteriorly, the lateral aspect of pectoralis major anteriorly, and the 6th rib inferiorly forming an apex below the axilla. In young, thin males the nipple will lie in the 5th intercostal space. Insertion of the drain just above the underlying rib minimises the risk of injury to the intercostal bundle.

Photo 4 The safe triangle


Both techniques are low risk in experienced hands. However, the National Patient Safety Agency [30] has issued specific recommendations following reports of 12 deaths and 15 cases of serious harm associated with drain insertion between 2005 and 2008.

Recognised complications include:

  • Failure
  • False passage (subcutaneous)
  • Intra-peritoneal placement with liver or splenic injury
  • Surgical Emphysema
  • Empyema
  • Haemothorax (intercostal or lateral thoracic artery injury)
  • Intercostal nerve injury
  • Long thoracic nerve injury
  • Lung laceration
  • Tube blockage
  • Myocardial injury

Learning Bite

Chest drain insertion is potentially dangerous, 27 cases of death or serious harm were reported as a result of chest drain insertion in the UK between 2005 and 2008. This is probably a conservative figure. This procedure should only be performed by a person trained and signed off as competent to do so

A method of inserting a drain using a Seldinger technique is described in table 5 and the contents of one commercial kit are shown below.

Photo 5 Seldinger drain kit contents


Table 5 Seldinger technique for insertion of a thoracostomy tube

  • Inform the patient about the planned procedure and obtain written consent
  • Position the patient reclined at approximately 45 degrees with their hand placed behind their head
  • Identify the insertion point (just anterior to the mid-axillary line in the 5th intercostal space) and mark the with a pen
  • Put on a gown and sterile gloves, clean the area with anti-septic solution and apply drapes
  • Using an aseptic technique, infiltrate 1% lidocaine* subcutaneously and down to the pleura
  • Insert the needle form the drain kit (attached to the provided syringe) slowly through the chest wall, just above the underlying rib, in a horizontal plane
  • Stop advancing the aspiration needle when aspiration of air confirms correct placement
  • Thread the guidewire through the needle
  • Remove the aspiration needle
  • Gently dilate the track with the dilators provided (sometimes a small nick needs to be made in the skin with a scalpel to facilitate this)
  • Feed the drain over the guide wire (usually to about 12 cm in adults)
  • Remove the guidewire and the tube obturator
  • Fogging of the tube suggests correct placement
  • Connect the tube to an underwater drainage system (below the level of the patient). An assistant should hold the drain at this stage to prevent the drain coming out before suturing
  • Bubbling on patient coughing and a fluid swing confirms drain placement
  • Secure with a stay suture (BTS guidance)
  • Place a clear dressing over the insertion site
  • Secure the drain to the chest wall with an omental tag (BTS guidance)
  • Repeat the chest radiograph

Authors observations:

Holding the dilators close to the chest wall should prevent excessive force of insertion or a sudden give. These are solid objects and on the left side the apex of the heart lies close to the insertion point!

*Maximum 0.3mls/kg of 1% lidocaine

Referral to a respiratory specialist

The BTS recommends that any patient requiring admission be reviewed by a respiratory physician within 24 hours.

Chest drain suction

The routine use of suction is not recommended.

Chest drain suction (high volume, low pressure) should be considered when lung re-expansion has not occurred 48 hours after chest drain insertion, which is suggestive of an ongoing air leak. Earlier application of suction is not recommended because of concerns over precipitating re-expansion pulmonary oedema, which conveys a significant mortality risk [36]. The lung capillaries become leaky following a pneumothorax and application of additional mechanical stresses can result in oedema. There is often no ongoing air leak in spontaneous pneumothoraces and lower mechanical stresses will be caused by aspiration or thoracostomy tube insertion without suction. Re-expansion pulmonary oedema is more common in patients under 30 years old, those with late presentation of a pneumothorax and those with large pneumothoraces [37].

Referral to a cardiothoracic surgeon

The following criteria are accepted as indications for seeking a cardiothoracic opinion

  • Second ipsilateral pneumothorax
  • First contra-lateral pneumothorax
  • Bilateral spontaneous pneumothorax
  • Persistent air leak or failure of lung re-expansion 5 days after chest drain insertion
  • Spontaneous haemothorax
  • Professions at risk (e.g. pilots, divers)
  • Pregnancy

The risk of pneumothorax recurrence increases in pregnancy and conveys a significant risk to both the mother and foetus.

Most air leaks will resolve after 2 weeks but the risk of infection of prolonged drainage may outweigh the low morbidity rate associated with surgical intervention, which has the added benefit of significantly reducing the future recurrence rate.

Surgical options include:

Open thoracotomy, resection of pleural blebs and pleurectomy

This is considered the gold standard at preventing recurrences with a failure rate of less than 1%

Open thoracotomy, resection of pleural blebs and pleural abrasion/ pleurodesis

The recurrence rate is approximately 2%.

Video assisted thorascopic surgery (VATS)

This technique is becoming increasingly popular as it is associated with a shorter hospital stay and less postoperative pain. The recurrence rates of >5% mean that it cannot be recommended in patients wishing to dive.

Chemical Pleurodesis is an option for patients that refuse surgery or are considered poor surgical candidates. Tetracycline or talc can be administered via the chest drain. The failure rate is approximately 10%.

Follow up

Patients discharged from the Emergency Department following a spontaneous pneumothorax should ideally be reviewed by a respiratory physician after 2 weeks. In practice, it may be impossible to access specialist clinics in the recommended timeframe. If this is the case, then the patient should be advised to initially return to the Emergency Department for a repeat chest radiograph and senior doctor review at 2 weeks, pending specialist review. Most patients with spontaneous pneumothoraces that have resolved need no further follow up. If the pneumothorax is recurrent or the patient has a high risk vocation, referral for a cardiothoracic outpatient appointment is appropriate.


All patients discharged following a pneumothorax should be given verbal and written advice to immediately return to the Emergency Department if they develop breathlessness. Smokers they should be advised to quit and seek assistance from the GP to successfully achieve this. Men who smoke more than 20 cigarettes a day have 100 times the risk of developing a pneumothorax compared to men that don’t smoke


Changes in atmospheric pressure can rapidly convert simple pneumothoraces to tension pneumothoraces with catastrophic consequences. The BTS Air Travel Working Party [38] recommends that patients should be advised to avoid flying for at least a week after a chest radiograph has confirmed complete resolution of their spontaneous pneumothorax, or until they have recovered from a definitive surgical procedure aimed to prevent pneumothorax recurrence. The previous advice to avoid flying for 6 weeks is not supported by existing evidence. It is advised that 2 weeks have elapsed following confirmed resolution if the pneumothorax was traumatic in origin, which corresponds to the advice issued by the UK civil aviation authority.


The British Thoracic Society Fitness to Dive Group39 recommends that underwater diving should be permanently avoided after a pneumothorax, unless the patient has had bilateral open surgical pleurectomy.

Key Learning Points

  • Smoking is strongly associated with pneumothorax recurrence [B]
  • Breathless patients require intervention regardless of pneumothorax size [C]
  • All patients with secondary pneumothoraces require admission [C]
  • Oxygen should be applied to all patients with a pneumothorax if they are breathless or require admission [B]
  • Simple (needle) aspiration should be considered the first-line treatment for primary spontaneous pneumothoraces that require intervention [A]
  • Simple (needle) aspiration should be only be used for secondary pneumothoraces when the pneumothroax is small (1-2cm) and the patient is not breathless [B]
  • Small drains are as effective as large drains in treating spontaneous pneumothoraces and their use is preferred [B]
  • Patients should not fly until a week has elapsed since complete resolution of the pneumothorax has been demonstrated on a chest radiograph [C]
  • Patients should never dive after a pneumothorax unless bilateral surgical pleurectomy has been performed [C]

27 cases of death or serious harm were reported to the National Patient Safety Agency as a result of chest drain insertion in the UK between 2005 and 2008. This is probably a conservative figure.


  • Failure to identify the pneumothorax as secondary and thus following the wrong BTS management algorithm
  • Discharging a patient with a secondary pneumothorax from the ED
  • Belief that the absence of a hiss on attempted needle decompression excludes a tension pneumothorax
  • Use of excessive force when inserting track dilators and chest drains
  • Insertion of chest drains outside of the safe triangle
  • Failure to give patients advice on smoking cessation
  • Failure to advise patients against flying and diving
  • Failure to organise review of discharged patients
  1. Melton LJ, Hepper NG, Offord KP. Incidence of spontaneous pneumothorax in Olmsted County, Minnesota: 1950 to 1974. Am Rev Respir Dis 1979;120:1379-82.
  2. Gupta D, Hansell A, Nichols T, et al. Epidemiology of pneumothorax in England. Thorax 2000;55:666671
  3. Lasts anatomy: Regional and applied 1990;8th edition. London: Churchill Livingstone
  4. Lesur O, Delorme N, Frogamet JM, et al. Computed tomography in the aetiological assessment of idiopathic spontaneous pneumothorax. Chest1 990;98:3417
  5. Donahue DM, Wright CD, Viale G, et al. Resection of pulmonary blebs and pleurodesis for spontaneous pneumothorax. Chest 1993;104:17679.
  6. Bense L, Eklund G, Wiman LG. Smoking and the increased risk of contracting spontaneous pneumothorax. Chest. Dec 1987;92(6):1009-12
  7. Zbar B, Alvord WG, Glenn G, et al. Risk of renal and colonic neoplasms and spontaneous pneumothorax in the Birt-Hogg-Dube syndrome. Cancer Epidemiol Biomarkers Prev. Apr 2002;11(4):393-400]
  8. Byrnes TA, Breving JK, Yeoh CB. Pneumothorax in patients with acquired immunodeficiency syndrome. J Thorac Cardiovasc Surg 1989;98: 546550.
  9. Coker RJ, Moss F, Peters B, et al. Pneumothorax in patients with AIDS. Respir Med 1993; 87: 4347.
  10. Johnson MM. Catamenial pneumothorax and other thoracic manifestations of endometriosis Clin Chest Med. 2004 Jun;25(2):311-9.
  11. MacDuff A, Arnold T, Harvey J. BTS guidelines for the management of spontaneous pneumothorax. Thorax 2010;65(Suppl 2):ii18eii31. doi:10.1136/thx.2010.136
  12. C-H. Marquette, A. Marx, S. Leroy, et al. Simplified stepwise management of primaryspontaneous pneumothorax: a pilot study Eur Respir J 2006;27:470476
  13. Seow A, Kazerooni EA, Pernicano PG, et al. Comparison of upright inspiratory and expiratory chest radiographs for detecting pneumothoraces. Am J Roentgenol 1996;166:313-6.
  14. Connor AR, Morgan WE. Radiological review of pneumothorax. BMJ 2005;330:1493-1497
  15. Garofalo G, Busso M, Perotto F. Ultrasound diagnosis of pneumothorax. Radiol Med (Torino). May 29 2006.
  16. Norris RM, Jones JG, Bishop JM. Respiratory gas exchange in patients with spontaneous pneumothorax. Thorax 1968;23:42733
  17. Baumann MH, Strange C, Heffner JE et al. Management of spontaneous pneumothorax. An American College of Chest Physicians Delphi consensus statement. Chest 2001;119:590-602
  18. Northfield TC. Oxygen therapy for spontaneous pneumothorax. BMJ 1971;4:868
  19. Flint K, Al-Hillawi AH, Johnson NM. Conservative management of spontaneous pneumothorax. Lancet 1984;ii:6878
  20. Kelly AM, Loy J, Tsang AYL et al. Estimating the rate of re-expansion of spontaneous pneumothorax by a formula derived from computed tomography volumetry studies. Emerg Med J 2006;23:780-782
  21. AyedAK, Chandrasekaran C, Sukumar M. Aspiration versus tube drainage in primary spontaneous pneumothorax: a randomised study. Eur Respir J 2006;27:477-482
  22. Harvey J, Prescott RJ. Simple aspiration versus intercostal tube drainage for spontaneous pneumothorax in patients with normal lungs. BMJ 1994;309(6965):1338-1339
  23. Faruqi S, Gupta D, Aggarwal AN et al. The Indian Journal of Chest Diseases & Allied Sciences 2004;46:183-190
  24. Replace with: Akram AR, Hartung TK. Intercostal chest drains: a wake-up call from the National Patient Safety Agency rapid response report. Journal of Royal College of Physicians of Edinburgh 2009; 39: 117-20
  25. Leigh-Smith S, Harris T. Tension pneumothoraxtime for a re-think? Emerg Med J. Jan 2005;22(1):8-16
  26. Holloway VJ, Harris JK. Spontaneous pneumothorax: is it under tension? J Accid Emerg Med 2000;17:2223
  27. Barton, ed. Tension pneumothorax. Curr Opin Pulm Med 1999;5:26974
  28. Britten S , Palmer SH, Snow TM. Needle thoracocentesis in tension pneumothorax: insufficient cannula length and potential failure. Injury 1996;27:3212
  29. Mafhood S, Hix WR, Aaron BI, et al. Re-expansion pulmonary edema. Ann Thorac Surg 1988;45:3405
  30. Matsuura Y, Nomimura T, Nurikami H, et al. Clinical evidence of re-expansion pulmonary edema. Chest 1991;100:15626.
  31. Managing Passengers with Respiratory Disease Planning Air Travel revised Guideline
  32. British Thoracic Society guidelines on Respiratory Aspects of Fitness for DivingThorax 2003; 58:3-13
  33. Diagram 1 Recommended treatment for primary Spontaneous Pneumothorax
  34. Diagram 2 Recommended treatment for secondary Spontaneous Pneumothorax