Air in the Pleural Cavity - Pneumothorax

Air is normally present in the lungs. On the other hand, the pleural cavities on the two sides (Right and left) formed by the two pleural membranes on the surface of the lungs are empty. The negative pressure in the pleural cavities keeps the lungs expanded with air. In some diseases of the lungs or due to injury to the pleural membrane, the air can enter the pleural cavity on either side. This condition is called ‘pneumothorax’ i.e. air the thorax – pleural cavity. (Pneumothorax is defined as presence of air in the pleural cavity, i.e. between the lung and the chest wall). Presence of air within the pleural space causes collapse of the lung.

 

TYPES OF PNEUMOTHORAX

 Pneumothorax is traditionally divided into primary and secondary varieties.  

1. Spontaneous pneumothorax which occurs in the absence of external trauma.

i)                    Primary spontaneous where the underlying lung is healthy.

ii)            Secondary spontaneous where the pneumothorax occurs as a complication of some underlying disease.

2. Traumatic:  It can result from injury from outside.

CAUSES OF PNEUMOTHORAX

1.      Primary spontaneous pneumothorax: It is caused by the rupture of sub pleural emphysematous blebs which may be congenital or acquired.  Recent studies have demonstrated such small emphysematous changes in up to 80% patients of spontaneous pneumothorax on CT scan.  Some risk factors identified for primary pneumothorax are:

• Tall and thin body habitus
• Smoking.  Risk may be as high as 100 times in heavy smokers (>20 cigarettes/day).
• Genetic and inherited factors like presence of HLA A2, B40 haplotype.
• Marfan’s syndrome
• Mitral valve prolapse
• Broad swings in atmospheric pressure, e.g., going on high altitude etc.
• Bronchial abnormalities like disproportionate bronchial anatomy.

2.      Secondary spontaneous pneumothorax: The incidence of secondary spontaneous pneumothorax is almost the same as that of primary spontaneous.  Tuberculosis and Chronic Obstructive Pulmonary Disease (COPD) are the common causes.  Almost every lung disease is known to be associated with pneumothorax.

Other known causes are:

• Infections.  Necrotizing pneumonias, lung abscess
• Interstitial lung disease.  Rheumatoid arthritis, Wegener’s granulomatosis, idiopathic pulmonary fibrosis etc.
• Occupational disease.  Silicosis, coal workers’ pneumoconiosis
• Neoplastic disorders.  Bronchogenic carcinoma, lymphangioleiomyomatosis
• Rare causes.  Pulmonary infarction, Bronchial asthma, Cystic fibrosis, Eosinophilic granuloma, Post-irradiation, etc.

3.      Traumatic Pneumothorax:  Trauma can result in pneumothorax in the following three ways viz.,

• Blunt injury to chest and abdomen
• Penetrating injuries to chest
• Iatrogenic, following procedures like pleural tap, pleural biopsy, needle aspirations from intrathoracic lesions, bronchoscopy and lung biopsies, endoscopy and sclerotherapy.

CLINICAL FEATURES

Symptoms:  Primary spontaneous pneumothorax usually develops suddenly.  It has no relation to heavy exertion as is usually believed.  Symptoms depend on the amount of air present in the pleural cavity.  If pneumothorax is small there may be no symptom and it may be detected by chance on routine chest x-ray.  Main symptoms are chest pain and dyspnea.  Chest pain is sharp, pleuritic, acute in onset and localized to the side of the pneumothorax.  Dyspnea is proportional to the amount of pneumothorax.  Secondary pneumothorax is usually more symptomatic because of the pre-existing compromised lung functions.

Tension Pneumothorax

This clinical syndrome associated with any sort of pneumothorax is a medical emergency and needs urgent recognition and attention.  It develops due to persistent air leak into the pleural cavity by a communication which opens up only during inspiration when pleural pressures rises, thus acting as a check valve.   Air accumulates with each successive breath and causes rising pressure in the pleural cavity thereby causing shift of mediastinum to the opposite side and pressure on great vessels.  There is decreased venous return to the heart and cardiac output falls leading to hypotension and cyanosis.

It commonly presents with sudden onset of shortness of breath or sudden increase in symptoms in a patient of pneumothorax. In addition, tachypnea, tachycardia, hypotension, cyanosis and pulsus paradoxus are usually present.

DIAGNOSIS

A high index of suspicion is required to diagnose pneumothorax in a given clinical setting.  Chest x-ray usually confirms the suspected pneumothorax.  It is also helpful in quantitating the pneumothorax. 

Chest CT scan is required to confirm a small pneumothorax and to see the condition of the underlying lung. Differentiation from a large bulla is at times very difficult on a plain chest x-ray.

TREATMENT

The treatment of pneumothorax is aimed at:

A.  Removal of air from pleural space, and

B.  Prevention of recurrence.

1. Removing air from pleural space

Pneumothorax needs aspiration if it is symptomatic, more than 20%, and if the underlying lung is diseased. Secondary spontaneous pneumothorax is better managed with intercostal tube drainage.

Intercostal tube drainage (ICTD) is required for all cases of:

       i)          Tension pneumothorax

ii)                  Secondary pneumothorax

iii)                Failed aspiration in primary pneumothorax

The tube should be kept under water seal or one way valve if available, should be used.  Once the lung expands, the tube should be clamped for 12-24 hours and a check x-ray should be done to exclude the recurrence before removing the tube.  Chest tube should be kept in situ for at least 24 hours after the lung has expanded and the air leak has ceased.  This is known to be associated with lesser recurrence rates than when ICTD is removed earlier.

Tension Pneumothorax needs immediate relief of tension.  It can be achieved by simply inserting a small needle (16G) into the pleural space even without any under water seal to relieve the tension till an ICTD can be put in place.

2. Preventing Recurrence

About 20-25% patients with primary spontaneous pneumothorax have recurrence in the first year.  Risk for second and third recurrence is even higher reaching up to 80% after the third episode.  The recurrence rates for secondary spontaneous pneumothorax are a little higher.

Pleurodesis:  Pleurodesis involves instillation of talc or other adhesive material into the pleural cavity before removal of ICTD. The resultant fusion of pleural membranes prevents recurrence of pneumothorax in future. Some people advocate instillation of sclerosing agent after the first episode of primary spontaneous pneumothorax while others believe it to be necessary only after the second episode on the same side. 

Role of Thoracoscopy: Thoracoscopy is a useful method to examine the pleural cavity from within, remove the air/fluid and produce pleurodesis. One can also look for the cause of recurrent of persistent air leaks, if any. Indications for thoracoscopy in a case of pneumothorax are:

 a) Poor expansion of lung after 5 days of ICTD.

 b) Persistent air leak after 5 days of ICTD.

 c) Failed chemical pleurodesis.

RE-EXPANSION PULMONARY EDEMA can rarely occur following drain of a massive pneumothorax in a short span of time. It occurs more frequently if the lung has remained collapsed for longer period and if negative pressure is applied.  Preventive steps include slow removal of fluid/air, avoidance of negative pressures in draining pneumothorax and careful monitoring.

 SUMMARY

• Pneumothorax is a medical emergency which needs to be recognized with a high index of suspicion and should be treated promptly.
• It can occur in previously healthy lungs or in a patient with a pre-existing lung disease.
• Symptoms will depend on the amount of air present in the pleural cavity and if under tension, it can be life threatening.
• Treatment lies in the drainage of air from the pleural space which can be achieved with the help of inter-costal tube insertion.
• Chances of recurrence are prevented by pleurodesis done through instillation of sclerosing agents within the pleural cavity.
• Thoracoscopy is important to do especially in cases of persistent and/or recurrent pneumothorax both to examine the source of air leak and to produce pleurodesis.