Postgrad Med J 2000;76:399–404 399

Diagnosis of 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 surface damage: mothorax, as are various practical proce- Trauma—for example, 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 . 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 and the visceral pleura on the outer surface of shunt, poorly compliant , 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, , 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 , 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 .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 the presence Diagnosis of pneumothorax of ARDS,20 high peak airway pressures,21 and The diagnosis of pneumothorax in critical previous pneumothorax.22 Unfortunately, even illness is made from the history and examina- when lung protection strategies are used to tion of the patient and confirmed, where possi- reduce airway pressures there is still a signifi- ble, by radiological investigation. cant incidence of pneumothorax,23 this has lead some authors to question the importance of HISTORY high pressures or lung volumes in the develop- The factors that are important in the history ment of barotrauma.20 relate to the underlying disease process and any As previously stated a pneumothorax is often potential for iatrogenic pneumothorax (box 2). present in patients with ARDS without the Outside intensive care practice the majority lung completely collapsing. If a chest drain is of pneumothoraces are idiopathic or associated inserted into such a pneumothorax the drain Pneumothorax in critically ill adults 401

Box 3: Examination findings associated Postgrad Med J: first published as 10.1136/pmj.76.897.399 on 1 July 2000. Downloaded from with pneumothorax and tension pneumothorax x Ventilator observations: reduction in tidal volume during pressure controlled ventilation. Increase in airway pressure with volume controlled ventilation. x Chest signs: increased percussion note. Decreased breath sounds. Tracheal deviation away from the side of the pneumothorax. x General examination: hypoxia, surgical emphysema. x Examination of drainage systems: reduction or cessation of air leak through the system, blockage of a drain. Cardiovascular system x Tachycardia and hypotension. x Increased pulmonary diastolic pressure and central venous pressure. x Pulsus paradox. x Drop in cardiac output.

of 1303 central line placements, pneumothorax occurred on five occasions.28 The incidence is suYciently small after guidewire exchange of central lines for the routine ordering of chest Figure 1 (A) The chest drain appears to be placed well 29 into the chest on the frontal radiograph (arrows). A radiography to have been questioned. Simi- computed tomogram (B) shows that the drain is lying larly, although pneumothorax is a recognised posterior to the chest wall having been tunnelled in the complication of percutaneous tracheostomy,30 subcutaneous tissues. its incidence is felt to be suYciently small to may lie posteriorly behind the lung or within a question the value of a routine postprocedure lung fissure and can then be occluded by the chest radiography.31 heavy consolidated areas in the posterior The passage of air from the mediastinum http://pmj.bmj.com/ portions of the lung. The presence of a chest into the neck, retroperitonium, and peritonium drain does not therefore preclude the possi- can be reversed if appropriate pressure gradi- bility of a recurrent pneumothorax on that side. ents exist. For this reason laparoscopic proce- In a description of this problem chest tubes dures, particularly involving the oesophagus, misplaced in this way were found to be may be a cause of pneumothorax.32 Pneumo- horizontal on frontal radiographs while cor- thorax may also be caused by dental rectly placed tubes ran laterally up the side of procedures33 and even colonoscopy.34 35 The the chest wall.22 In patients with horizontal pressure of gas used to distend the colon may on October 1, 2021 by guest. Protected copyright. misplacement nine out of 20 pneumothoraces cause gas to leak into the retroperitoneal space recurred, four under tension. and hence into the mediastinum and pleural As well as malposition of a chest drain within cavity. Similarly the use of compressed air in the thoracic cavity it is also possible that drains, dental procedures may also result in pneumo- particularly those placed in suboptimal condi- thorax. A recent history of any of these proce- tions, may not even enter the thoracic cavity.24 dures as well as more obvious procedures in the Figure 1 shows an example of this, the drain thorax may therefore point to a diagnosis of appears well placed on a frontal radiograph, pneumothorax. but computed tomography shows it to have been placed in the subcutaneous tissues. As Examination well as being malpositioned chest drains may Several findings in the examination of the res- also damage the lung parenchyma and hence piratory and cardiovascular systems may help be a cause of pneumothorax, even in the establish the diagnosis of pneumothorax and contralateral lung.25 The increased use of blunt tension pneumothorax (box 3). It is important dissection and the abandonment of the use of to note that these signs are all non-specific. The trochars for drain insertion should reduce this changes in ventilator observations, for exam- complication,26 however, a drain may still dam- ple, could also be found with an obstruction to age the underlying lung particularly if the lung the endotracheal tube. The chest signs associ- is abnormal27 and may even enter the substance ated with pneumothorax are particularly diY- of the lung.25 cult to interpret, for example collapse and con- Pneumothorax is a well recognised compli- solidation on one side of the chest will cause cation of other practical procedures. In a study increased percussion note on the other side of 402 Rankine, Thomas, Fluechter

continue to fluctuate with the respiratory cycle. Hence a pulsus paradoxus may also be Postgrad Med J: first published as 10.1136/pmj.76.897.399 on 1 July 2000. Downloaded from observed on the arterial trace. Although non-specific, the association of respiratory and haemodynamic signs found with a tension pneumothorax are a medical emergency. Severe haemodynamic compro- mise will require urgent needle decompression of the pneumothorax before its diagnosis being confirmed radiologically. Fortunately this situ- ation is uncommon and there is frequently time for radiological investigations to help establish the diagnosis of a simple pneumothorax.

Radiological investigations The erect posteroanterior expiratory normally recommended for the investigation of pneumothorax is not practical Figure 2 A pneumothorax in a supine patient. The deep in critical illness. The supine anteroposterior sulcus sign (arrows). Compare with the costophrenic angle and lateral chest radiographs are frequently all on the other side. that is available on the intensive care unit. Much more accurate information may also be the chest and this may then be misinterpreted obtained from thoracic computed tomograms as a pneumothorax. As previously stated even a in those patients well enough to be tension pneumothorax may exist in ARDS transported.39 without complete collapse of the ipisilateral With a patient in the supine position, large lung and even without ARDS a haemothorax amounts of free air can collect in the anterior or pneumothorax may easily be missed. Careful inspection and repeated auscultation of the chest, particularly in both mid-axillary lines, is therefore important. In addition to examining the patient and ventilator any chest drains should also be examined together with their drainage systems. The use of drainage systems is outside the scope of this article but has been well reviewed elsewhere.36 The haemodynamic changes associated with a tension pneumothorax are also quite non- specific. The principle change in the pulmo-

nary waveform is an elevation in the pul- http://pmj.bmj.com/ monary artery diastolic pressure.37 The increase in thoracic pressure associated with the tension causes the alveolar pressure to rise above the pulmonary venous pressure. The pulmonary artery diastolic pressure is then Figure 4 A skin fold over the right side of the chest. Note determined by alveolar pressure, a situation the broad nature of the opacification. Lung markings are similar to that described for West’s zone 2 of visible beyond the edge of the opacification. This was 38 mistaken for a pneumothorax and attempted aspiration the lung. Pressure within the chest will caused a pneumothorax and surgical emphysema. on October 1, 2021 by guest. Protected copyright.

Figure 3 A right sided pneumothorax with underlying lung consolidation and pleural fluid. There are absent lung Figure 5 lying within the left side of the chest. A markings as a result of consolidation, and pleural fluid lying stab wound to the lower left chest has ruptured the posteriorly contributes to the increased opacification of the diaphragm allowing the stomach to rise into the chest. Note hemithorax. A pneumothorax lying anteriorly in the chest the absence of a normal left hemidiaphragm. At surgery it causes a sharp outline to the mediastinum and right was found that the chest drain had fortunately displaced border. rather than perforated the stomach. Pneumothorax in critically ill adults 403

A B Postgrad Med J: first published as 10.1136/pmj.76.897.399 on 1 July 2000. Downloaded from

Diaphragm

Faeces

Liver

Figure 6 (A) Large bowel obstruction has caused a dilated loop of bowel to become interposed between the right hemidiaphragm and the . The position of the diaphragm (arrows) was not appreciated and a chest drain was inserted directly into large bowel; (B) line drawing of (A).

part of the chest without the characteristic lung Learning points edge being visible (fig 2). The deep sulcus sign x Don’t wait for a radiograph if there are describes a costophrenic angle that extends clinical signs of a tension pneumothorax. more inferiorly than usual as a result of air lying 40 x A chest drain apparently well positioned in the costophrenic angle. If the patient does on the radiograph may be lying in the not have a bilateral pneumothorax it can be soft tissues. helpful to compare this with the normal side. On a normal chest radiograph the area of the x The appearances of a pneumothorax on liver is relatively opaque as the exposure is set a supine radiograph are diVerent from to maximally visualise the low density lungs. the classic appearances on an erect When air collects in the costophrenic angle radiograph. anteriorly over the liver, the liver will appear x Treat the patient not the radiograph. more radiolucent than usual. On the left, air Don’t act on a radiographic appearance will outline the medial aspect of the hemidia- if it does not fit the clinical picture. Get phragm under the heart. an expert opinion on the radiograph A pneumothorax commonly causes a radio- first. lucent hemithorax with absent lung markings, however a pneumothorax can be present in a

hemithorax that appears more radiopaque projected over the periphery of the lung that http://pmj.bmj.com/ when there is underlying lung consolidation must not be mistaken for a lung edge. and pleural fluid (fig 3).

If there is doubt about the presence of a VISCERAL GAS WITHIN THE CHEST pneumothorax on a frontal supine radiograph, Diaphragmatic hernia and diaphragmatic rup- a film with the patient in a lateral decubitus tures allow abdominal visceral contents into position, with the aVected side uppermost, can 41 the chest. Air filled stomach and bowel entering be helpful in demonstrating a lung edge. the chest through these openings must there- fore be distinguished from a pneumothorax. on October 1, 2021 by guest. Protected copyright. Radiographs which may be confused with Normal bowel mucosal folds and an inability to pneumothorax define a normal contour to the diaphragm are There are a number of situations where abnor- clues (fig 5). mal lucency or an apparent lung edge may be Dilated viscera and pneumoperitoneum may caused by abnormalities other than a pneumot- also displace an intact diaphragm high into the horax. Abnormalities outside the thoracic cav- chest, and it is important to define the position ity, abdominal contents within the chest, or of the diaphragm (fig 6). abnormalities of the lung may cause this itself.

EMPHYSEMATOUS BULLAE SKIN FOLDS The bullae of emphysema can be very large and When a portable chest radiograph is per- when situated in the periphery of the lung can formed, the x ray cassette is positioned behind mimic a loculated pneumothorax. A chest the patient and a fold of skin between the chest drain inserted into a bullous in the mistaken wall and the cassette can lead to a density on belief that it is a pneumothorax is not uncom- the radiograph, which can be mistaken for a mon. This is not surprising as emphysema is a pneumothorax.42 A pneumothorax gives rise to known predisposing factor for a pneumothorax a thin pleural edge whereas a skin fold causes a and patients with an exacerbation of their broad opaque band, with lung markings still emphysema can present with a fairly sudden visible beyond the edge (fig 4). The fold may worsening of their breathlessness. The lack of a extend beyond the confines of the chest wall, lung edge, the round nature of the bullous, and which is conclusive proof of its nature. Tubes the presence of multiple bullae elsewhere in the lying outside the patient can cause a line lung are all clues to the diagnosis. In diYcult 404 Rankine, Thomas, Fluechter

cases computed tomography can be helpful in 33 Shackleford D, Casani J. DiVuse subcutaneous emphysema,

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