Postgrad Med J 2000;76:399–404 399 Diagnosis of pneumothorax in critically ill adults Postgrad Med J: first published as 10.1136/pmj.76.897.399 on 1 July 2000. Downloaded from James J Rankine, Antony N Thomas, Dorothee Fluechter Abstract The diagnosis of pneumothorax is estab- Box 1: Mechanisms of air entry lished from the patients’ history, physical causing pneumothorax examination and, where possible, by ra- x Chest wall damage: diological investigations. Adult respira- Trauma and surgery tory distress syndrome, pneumonia, and trauma are important predictors of pneu- x Lung surface damage: mothorax, as are various practical proce- Trauma—for example, rib fractures dures including mechanical ventilation, Iatrogenic—for example, attempted central line insertion, and surgical proce- central line insertion dures in the thorax, head, and neck and Rupture of lung cysts abdomen. Examination should include an inspection of the ventilator observations x Alveolar air leak: and chest drainage systems as well as the Barotrauma patient’s cardiovascular and respiratory Blast injury systems. x Via diaphragmatic foramina from Radiological diagnosis is normally con- peritoneal and retroperitoneal structures fined to plain frontal radiographs in the critically ill patient, although lateral im- x Via the head and neck ages and computed tomography are also important. Situations are described where an abnormal lucency or an apparent lung will then recoil away from the chest wall and a edge may be confused with a pneumotho- pneumothorax will be produced.1 rax. These may arise from outside the Air can enter the pleural space in a variety of thoracic cavity or from lung abnormali- diVerent ways that are summarised in box 1. In ties or abdominal viscera inside the chest. most situations the passage of air will be limited ( 2000;76:399–404) Postgrad Med J either by the closure of the causative defect or Keywords: pneumothorax; adult respiratory distress by the equilibration of pleural and atmospheric syndrome; critical care; radiography pressures. Unfortunately the pressure within the pneumothorax may increase above atmos- pheric pressure. This occurs if the opening to In critical illness the diagnosis of pneumotho- the pleura acts like a valve allowing air to enter, http://pmj.bmj.com/ rax is often complicated by other disease proc- but not to leave. It also occurs when the patient esses and by diYculties in imaging sick and is subjected to positive pressure ventilation. unconscious patients. This article discusses the The high pressure within the chest may then pathophysiology of pneumothorax and then produce severe haemodynamic eVects and the describes the clinical and radiological diagno- pneumothorax will be described as a tension sis. Some examples of diYculties surrounding pneumothorax. the radiological diagnosis of pneumothorax are On the intensive care unit pneumothorax is then presented. The subject is important commonly caused by barotrauma associated on October 1, 2021 by guest. Protected copyright. because pneumothorax is common in venti- with the ventilation of patients with adult lated critically ill patients and failures in respiratory distress syndrome (ARDS). It is diagnosis can cause life threatening complica- therefore important to describe the mecha- tions. nisms of barotrauma associated with ARDS. ARDS is an inflammatory disease of the lung Pathophysiology caused primarily by an abnormal immune Hope Hospital, Salford, UK: The pleural space is the area between the pari- response, commonly as a result of major 2 Department of etal pleura on the inner surface of the chest wall trauma or infection. It results in pulmonary Radiology and the visceral pleura on the outer surface of shunt, poorly compliant lungs, and pulmonary J J Rankine the lung. The space normally contains only a infiltrates. ARDS tends to cause more atelecta- very small volume of fluid that allows the pari- sis and loss of lung volume in the posterior, Department of etal and visceral pleura to move smoothly over gravity dependent areas of the lung.3 Mechani- Intensive Care A N Thomas each other. The chest wall and lung are both cal ventilation is often essential in ARDS to D Fluechter elastic in nature, with the lung tending to recoil maintain adequate oxygenation and remove the inwards and the chest wall to spring outwards. considerable work of breathing from the Correspondence to: These two opposing forces produce a negative patient. Unfortunately ventilation may cause Dr James J Rankine, Department of Radiology, St (subatmospheric) pressure in the pleural space. further damage, known as barotrauma. The James’s University Hospital, The weight of the lung tends to make this pres- initial process in barotrauma is the production Beckett Street, Leeds sure less negative in the dependent areas of the of perivascular interstitial emphysema.4 When LS9 7TF, UK lung. If the pleural space is opened to the the pressure gradient between the alveoli and Submitted 7 July 1999 atmosphere then the subatmospheric pressure the interstitium exceeds a critical level alveoli Accepted 27 October 1999 will suck air into the pleural space. The lung rupture and air enters the interstitium. The 400 Rankine, Thomas, Fluechter pressure at which this occurs is determined by the degree of lung damage. This damage may Box 2: Disease processes and Postgrad Med J: first published as 10.1136/pmj.76.897.399 on 1 July 2000. Downloaded from be produced by the underlying disease process, iatrogenic procedures associated with the inflammation associated with ARDS or the pneumothorax use of excessive tidal volumes during Disease processes 5 ventilation. Some clinicians believe that posi- x ARDS tive end expiratory pressure may have some protective eVect in preventing this damage,6 x Pneumonia: while any eVects of hyperoxia remain Pneumocystis 7 unknown. Tuberculosis Air escaping from ruptured alveoli then Bacterial pneumonia tracks proximally along the vascular sheaths and interlobular septa centrally to the hilum, x Trauma resulting in a pneumomediastinum. Multiple x Chronic obstructive lung disease areas of rupture must occur to produce Iatrogenic procedures clinically significant emphysema, however, once the process has occurred air will continue x Positive pressure ventilation to move proximally into the mediastinum as x Attempted central line insertion long as the driving pressure gradient remains x Surgical procedures in the thorax, head, high. As well as this proximal movement, extra- or neck alveolar air may also form subpleural air cysts.8 Abdominal procedures using bowel or These are most common along the anterior, x peritoneal distension medial, and inferior surfaces of the lung. Although normally a few millimetres across, these cysts may reach several centimetres in diameter. Rupture of either pleural air cysts or with chronic obstructive lung disease.12 Idio- the mediastinal pleura will then result in a pathic pneumothoraces are associated with pneumothorax. small areas of emphysema and cystic change, The over-distension of the non-dependent normally found at the apex of the lung.13 Any areas of the lung, and the role of the mediasti- pneumonic process may also produce pneu- nal pleura explain why anterior medial and mothorax. The original descriptions of pneu- subpulmonary pneumothoraces are more com- mothorax were commonly associated with mon in ARDS.9 As well as causing a pneumo- tuberculosis.14 Pneumocystis is also frequently thorax, air in the mediastinum may also extend associated with pneumothorax15 as are more along perivascular connective tissue into the common bacterial pneumoniae. neck, retroperitoneum, peritoneum, and sub- Pneumothorax is also common after trauma. cutaneous tissues.10 Subcutaneous emphysema In a retrospective review of blunt thoracic is not directly harmful, however its detection trauma, pneumothorax was present in almost on clinical or radiological examination is 20% of patients.16 The majority of patients with important as it suggests the lung has been sub- thoracic trauma are multiply injured, hence http://pmj.bmj.com/ ject to significant barotrauma. Once a pneu- examination of these patients is diYcult and mothorax has occurred, the high pressures cases of pneumothorax or haemothorax may generated during mechanical ventilation may not be diagnosed on initial assessment.17 easily cause the pneumothorax to tension and Although pneumothorax may be caused by produce haemodynamic eVects. Even with fractured ribs, it may also be present with an these high pressures the stiV, non-compliant intact rib cage.16 In this situation pneumotho- nature of the lung and the pleural inflammation rax is most commonly caused by alveolar air associated with ARDS may stop the surround- leak occurring during deceleration at the time on October 1, 2021 by guest. Protected copyright. ing lung from collapsing. A tension pneumo- of injury. Pneumothorax may also rarely be thorax may therefore exist without total lung caused by tracheobronchial18 or oesophageal collapse or mediastinal shift.11 injury.19 The proximal movement of air from rup- tured alveoli towards the hilum is also an Iatrogenic factors important mechanism in barotrauma caused The importance of barotrauma in relation to by other disease processes, for example blast mechanical ventilation has already been de- injury, positive pressure ventilation, and rapid scribed. Although any ventilated patient will be deceleration associated with trauma. at risk, some factors in the history may point to an increased risk. These include