Pleural
conditions
Normal
pleural physiology (Fig. 47.28)
There is a potential space between the parietal and visceral pleura that
contains only about S ml of pleural fluid at any one time. The amount of
pleural fluid is governed by the factors producing and absorbing it (capillary
hydrostatic pressure, capillary permeability, lymphatic drainage and colloid
osmotic pressure). The turnover of fluid in the human pleural space is about 1
litre in 24 hours. Protein-depleted
Any
disturbance of the equilibrium will lead to the development of a pleural
effusion. There are two described types depending on the protein content of the
fluid, although the distinction is not always clear.
Accumulation
of protein in the pleural space results if the lymphatic drainage is deranged.
This alters the osmotic pressure within the space and leads to the formation of
an effusion. There is usually in excess of 30 g of protein per litre and this is
termed an effusion. The underlying pathological mechanisms are:
• increased capillary permeability — capillary damage or
inflammation;
• lymphatic obstruction;
• venous obstruction.
The
most common pathologies associated with exudative effusions are:
• malignancy;
• infection;
• connective tissue disease;
• pulmonary infarction.
A
transudate has less than 30 g/litre of protein and is the result of low colloid
osmotic pressure from liver cirrhosis or high hydrostatic pressure from cardiac
failure or a combination of both.
Presentation
The clinical signs depend on the rate of effusion growth. Rapidly
developing effusions may cause severe dyspnoea, whereas slowly developing ones
may be very large but asymptomatic. On clinical examination there are reduced
breath sounds on the affected side with tracheal deviation to the opposite side.
The chest is stony dull to percussion. A pleural effusion may be the initial
presentation of a systemic malignancy in up to 30 per cent of cases.
Investigation
Radiology
A chest radiograph will determine the size of the effusion and may give
a clue as to the aetiology (coexistent tuberculosis, hilar shadow, etc.).
Further information about the lung may be obtained by CT it the lung is the
primary pathology. Pleural thickening is best distinguished from fluid by
ultrasonography.
Aspiration
Pleurocentesis (Fig. 47.29) is performed under local anaesthesia using
aseptic precautions. The needle is introduced just above a rib (to avoid the
neurovascular
Cytology
Histological examination of the aspirated fluid may be useful but the
absence of malignant cells does not rule out malignancy. The yield may be
increased by pleural biopsy (using an Abram’s needle) taken at the same time.
Thoracoscopy
This is a more invasive technique performed under general anaesthesia.
The patient is positioned and draped as for a thoracotomy. A small incision is
made over an intercostal space down to the pleura. The pleura is opened and the
effusion drained by suction. The thoracoscope is introduced and the parietal
pleural and lung are inspected thoroughly. Any suspicious nodules or plaques may
be biopsied and in the case of a recurrent malignant pleural effusion,
definitive pleurodesis may be done.
Treatment
The prognosis for malignant pleural effusion is very poor and therefore the treatment should be simple and effective if the patient is to enjoy a reasonable quality of life. Simple aspiration is a temporary solution in the symptomatic patient, because the effusion usually re accumulates and repeated aspiration merely results in loculation of the fluid. Treatment of the underlying malignancy may lead to resolution of the effusion but the distressing dyspnoea will be prolonged. A much better method of palliation is aspiration of the effusion and pleurodesis.
Three requirements must be met for successful pleurodesis:
The pleura must be aspirated to dryness, the pleural surfaces must
be kept apposed and the fluid must not be allowed to re accumulate. This can be
Tumours
of the pleura
The pleura is often secondarily involved as a result of direct or
transcoelomic spread of lung or breast malignancy resulting in a malignant
pleural effusion. However, there is one malignant tumour of the pleura that
deserves mention.
Mesothelioma
Fibrous plaques overlying the pleura are often seen at thoracotomy and
are benign in most cases. The most important malignant tumour affecting the
pleura is a mesothelioma. This is an aggressive tumour that grows in diffuse
layers, encapsulating and compressing the lung substance. It is associated with
asbestos exposure and is a notifiable condition because sufferers may be
eligible for compensation. There are several different cell types seen within
the tumour (adenomatous, squamous or sarcomatous), although there is usually a
predominance of one cell type.
Clinical
features. The patients often present with large unilateral pleural effusions and
dyspnoea and occasionally chest pain. Advanced disease is heralded by weight
loss, pyrexia and night sweats.
Investigation.
Chest radiography suggests the diagnosis but CT will show marked pleural
thickening with compression of the lung. Pleural aspiration may reveal atypical
cells but the diagnosis is more certain if thoracoscopic biopsy is performed.
This also allows pleurodesis at the same time.
Pneumothorax
Pneumothorax is the presence of air in the thoracic space, outside the
lung, that is, between the visceral and parietal
Classification
of pneumothorax
Spontaneous — primary. The only abnormality is superficial blebs at
the apex of one or more lobes, typically the upper lobes, which either leak
spontaneously or are triggered by an otherwise unremarkable event such as
exertion. It is more common in males, occurs predominantly in the ‘teens or
twenties, may be bilateral and may be familial.
Spontaneous
— secondary. Any lung disease that breaches the pleura may cause a
pneumothorax so probably every possible lung disease will, at one time or
another, cause a pneumothorax. The most common causes are obstructive airways
disease in any form and bullous emphysema.
Traumatic.
See Thoracic trauma section.
Iatrogenic.
This is commonly seen in general hospital practice as a result of insertion of
central lines for central venous pressure monitoring, intravenous feeding or
cardiac pacing.
Open.
The air may come from a penetrating injury (stabbing or shooting) and passes in
and our of the chest wall with each breath, but no effective ventilation occurs
(see Thoracic trauma section).
Closed. Rib fracture — see Thoracic trauma section.
When air in the pleura is under pressure the situation is called
‘tension pneumothorax’ and is a medical emergency. This depends on the non
return valve-like mechanism, which is inherent in the structure of the lung.
Positive pressure, generated within the airways with coughing or groaning in
pain, forces air out which then cannot return through the collapsible peripheral
alveoli (Fig. 47.30).
Diagnosis
The first thing is to suspect a pneumothorax and look for it
deliberately in patients at risk:
• following needling of central veins;
• sudden deterioration in a ventilated patient;
• any trauma case;
• patients with obstructive airways disease.
On
examination the affected side is more resonant and the breath sounds, listened
for laterally in the axilla, are markedly different and reduced on the affected
side. Shifts of the cardiac apex and trachea require severe distortion and are
unreliable signs.
Chest
radiography should be diagnostic but beware the supine film. Standard films are
taken in inspiration. A small pneumothorax is exaggerated by expiration because
the pneumothorax occupies proportionally more of the chest cavity.
Management
Tension pneumothorax is relieved by insertion of a large-bore
intravenous cannula in a convenient intercostal space (with the usual precaution
— see Chest drains) and then the situation can be managed as for a simple
pneumothorax.
Spontaneous
pneumothorax in a fit individual may cause little in the way of symptoms but in
someone with poor respiratory reserve (chronic obstructive airway disease) it
may be life threatening.
The
natural elastic recoil of the lung is balanced by the negative pressure within
the pleural space. Disruption of this equilibrium by air in the pleural space
results in collapse of the lung to some extent. If the chest wall remains intact
but the lung is punctured by a fractured rib the situation is termed a ‘closed
pneumothorax’. The danger is that, if this injury is part of a multiple
injury, then positive pressure ventilation may lead to the development of a
tension pneumothorax. If the chest wall is breached then this is termed an
‘open pneumothorax’, with the result that air moves in and out of the chest
through the wound with each breath and there is no gas exchange across the
alveolar surface.
Spontaneous
pneumothorax may occur in any individual but is more common in young, slim men.
The condition is often associated with apical blebs and there is a 30 per cent
chance of recurrence.
Iatrogenic
pneumothorax occurs when the lung pamenchyma is breached by a medical
procedure such as thoracocentesis, lung biopsy, liver biopsy or central venous
cannulation.
Treatment
The initial treatment depends on the nature and severity of the
pneumothorax; small pneumothoraces causing little disability may be observed
with serial radiographs or may be aspirated. Large symptomatic or traumatic
pneumothoraces require the insertion of a chest drain. Repeated spontaneous
Pleurectomy.
Pleurectomy is the definitive treatment for recurrent pneumothorax. A small
posterolateral thoracotomy is performed and as much of the parietal pleura as
possible is stripped off the chest wall, particularly at the apex of the
hemithorax. There are often apical bullas that may require stapling or over
sewing. The parietal surface is abraded with a swab to induce an
inflammatory reaction. Large calibre suction drains are inserted to drain the
apex and diaphragmatic surfaces of the lung. It is essential that suction is
maintained long enough for the lung surface to become firmly adherent to the
chest wall (usually 2—3 days). The thoracoscopic method of pleurodesis is
becoming commonplace, with comparable results to open pleurodesis.