A pneumothorax is a collection of air between the visceral and parietal pleura causing a real rather than potential pleural space. Recognition and early drainage can be lifesaving. Predisposing and precipitating factors include necrotizing lung pathology, chest trauma, ventilator-associated lung injury and cardiothoracic surgery.
Primary spontaneous pneumothorax (PSP)
This is caused by rupture of small apical subpleural air cysts ('blebs') but rarely causes significan physiological disturbance. Tall young (20-40 years old) men (male/female 5:1) with no underlying lung disease are usually affected. It is the most common type of pneumothorax (prevalence 8/105 per year, rising to 200/105 per year in subjects >1.9 m in height). Following a second primary spontaneous pneumothorax (PSP), recurrence is likely (>60%). Pleurodesis to fuse the visceral and parietal pleura using medical (e.g. pleural insertion of bleomycin or talc) or surgical (e.g. abrasion of the pleural lining) means is recommended.
This is associated with respiratory diseases that damage lung architecture, most commonly obstructive (e.g. chronic obstructive pulmonary disease (COPD) and asthma), fibroti or infective (e.g. pneumonia), and occasionally rare or inherited disorders (e.g. Marfan's and cystic fibrosis) The incidence of secondary pneumothorax (SP) increases with age and the severity of the underlying lung disease. These patients usually require hospital admission as even a small SP in a patient with reduced respiratory reserve may have more serious implications than a large PSP. ICU patients with lung disease are at particular risk of SP due to the high pressures ('barotrauma') and alveolar overdistention ('volutrauma') associated with mechanical ventilation. 'Protective' ventilation strategies using low-pressure, limited volume ventilation reduce this risk.
Traumatic (iatrogenic) pneumothorax
This follows blunt (e.g. road traffi accidents) or penetrating (e.g. fractured ribs and stab wounds) chest trauma. Therapeutic procedures (e.g. line insertion and thoracic surgery) are common causes of iatrogenic pneumothorax.
A tension pneumothorax may complicate PSP or SP but is most common during mechanical ventilation and following traumatic pneumothorax. It occurs when air accumulates in the pleural cavity faster than it can be removed. Increased intrathoracic pressure causes mediastinal shift, compression of functioning lung, inhibition of venous return and shock due to reduced cardiac output. It is a medical emergency and fatal if not rapidly relieved by drainage. Detection is a clinical diagnosis; awaiting chest X-ray (CXR) confirmatio may be life-threatening. Immediate drainage with a 14G needle in the second intercostal space in the midclavicular line is essential. A characteristic 'hiss' of escaping gas confirm the diagnosis. A chest drain is then inserted.
Pneumothorax is graded and treated according to Fig. 35a and Table b. Sudden breathlessness and/or sharp pleuritic pain suggests a pneumothorax. Most PSPs are small (<30%) and cause few symptoms other than pain. Clinical signs can be surprisingly difficul to detect, but in larger pneumothoraxes reduced air entry and hyperresonant percussion over one hemithorax are characteristic and may be associated with tachypnoea and cyanosis. Cardiorespiratory compromise may develop remarkably quickly in a tension pneumothorax and requires immediate drainage. Occasionally, other pulmonary air leaks may occur (see below). Monitoring reveals tachycardia, hypotension and desaturation. Blood gases may demonstrate respiratory failure. CXR confirm the diagnosis (Fig. 35a). Computed tomography (CT) scan may detect localized pneumothoraxes.
Immediate supportive therapy includes supplemental oxygen and analgesia. Treatment is dependent on the cause, size and symptoms.
A tension pneumothorax must be drained immediately. A small PSP (<30%) is simply observed and spontaneous reabsorption is confirme on serial outpatient CXR. A PSP >30% may be aspirated through a 16G needle in the second intercostal space in the midclavicular line, using a 50 mL syringe connected to a three-way tap and underwater seal (Fig. 35c). Following overnight observation, successful aspiration is confirme by lung re-expansion on repeat CXR. Occasionally, intercostal tube drainage is required for a large PSP with respiratory failure or if aspiration is unsuccessful.
In general, SP and traumatic pneumothoraxes always require hospital admission and intercostal chest drain insertion (Fig. 35d). Multiple intercostal drains may be needed to ensure adequate lung rexpansion in some patients with multiple loculated pneumothoraxes. In mechanically ventilated patients, high airway pressures or large tidal volumes encourage persistent leaks and must be avoided.
Small chest drains (16 G) are nearly always adequate. Large chest drains are painful and have no significan benefits
A persistent drain leak suggests development of a bronchopleural ﬁstula (BPF). High f ow, wall suction with pressures of 5-50 cmH2O, may oppose visceral and parietal pleura, allowing spontaneous pleurodesis. Physiotherapy and bronchial toilette are required to maintain airway patency. Early advice on surgical BPF management is essential. Video-assisted thoracoscopy is as effective as thoracotomy at correcting BPF but causes less respiratory dysfunction.
Chest drains are removed when CXR confirm lung expansion and there has been no air leakage through the drain for more than 24 hours. Drains should not be clamped before removal. Following adequate analgesia, the drain is pulled out when the patient is in inspiration. Purse string sutures around the drainage site are then tightly secured.
Pneumomediastinum describes air in the mediastinal-pleural reflection, outlining the heart and great vessels on CXR. Air may also dissect along perivascular sheaths into the neck, causing subcutaneous emphysema (SE) or around the heart with pneumopericardium, which may cause tamponade. Air leaks follow traumatic damage to the trachea, bronchus and oesophagus or ventilator-induced barotrauma. SE may cause localized cervical or grotesque facial and body swelling. It has a characteristic crackling sensation on palpation. The voice may have a nasal quality, and auscultation over the precordium may reveal a 'crunch' with each heart beat (Homan's sign). Management includes good drainage of pneumothorax and 'protective' ventilation strategies (Chapter 42). Failure of spontaneous resolution should prompt investigation, including bronchoscopy, for problems that decrease chest drain efficiency or undetected air leaks.