Comparative and clinical types
Previously it has been
the custom to divide those empyemas which complicate pneumonia into two types :
(1) synpneumonic and (2) metapneumonic. In the synpneumonic group the effusion
usually formed rapidly and occurred very early in the course of a streptococcal
broncho-pneumonia, which was often a sequel to influenza. The patients were
already seriously ill from the effects of the pneumonia, and infection of the
pleural cavity led to a further deterioration of the general condition, marked
by distressing dyspnoea and an increase in fever and pulse rate. Aspiration
of the thin pleural fluid
containing haemolytic
streptococci had to be repeated frequently, sometimes
more than once a day, owing to its rapid re-accumulation, in order to relieve
the patient's dyspnoea. Death often occurred and was inevitable if early
drainage by rib resection was undertaken.
In the metapneumonic cases, the pleural fluid
gradually formed after an attack of lobar pneumonia had passed its crisis. The
pus, which was usually caused by pneumococci, thickened rapidly and soon became
localized to one part of the pleural space. These patients were not seriously
ill but, instead of making a progressive return to health following the febrile
crisis, they either continued to run a low grade-fever or, if the temperature
had returned to normal, again became febrile about a week after the pneumonic crisis.
Because pneumonia is now almost invariably controlled
within 72 hours by appropriate chemotherapy, it is no longer practical to
divide empyemas into synpneumonic and metapneumonic categories, but this old
classification serves to remind the surgeon never to undertake drainage by rib
resection until the empyema is localized by adhesions and the pneumonic process
completely resolved.
Symptoms
and signs
Nowadays the presence of pleural fluid following or
accompanying pneumonia is usually recognized from routine physical or
radiological examination, although severe pleural pain in the early stages of
the pneumonia, or persistence of pyrexia in spite of adequate chemotherapy, may
have already led the clinician to speculate on the likelihood of this complication.
It is important to realize that the absence of fever by no means excludes the
presence of pus, particularly if the pus is sterile as a result of intensive
systemic antibiotic therapy. In children, a staphylococcal pyopneumothorax
starts with a spontaneous pneumothorax, which arises during the course of a
staphylococcal pneumonia ; the occurrence of the pneumothorax is usually
denoted by a sudden deterioration in the general condition and by increased
dyspnoea, but some cases develop remarkably insidiously. Occasionally, when an
empyema does not receive prompt and adequate treatment, the pleural pus finds
its escape within a few weeks by perforating into a bronchus. This complication
leads to the sudden expectoration of large quantities of pus, but this
development is often preceded by a period lasting several days, during which
the patient develops an increasingly "wet" cough, due to irritation
of the bronchus into which the pus later perforates. Just before the fistula is
formed, the sputum sometimes becomes slightly blood-stained. After the initial
episode occasioned by the formation of the broncho-pleural fistula, the patient
will continue to expectorate pus and usually notices that this is exacerbated,
by a change in posture.
With regard to the physical signs, every student is
taught the classical findings of impaired movement, absent tactile fremitus,
dullness or impaired note on percussion, absent or reduced breath sounds, and
diminished voice conduction on auscultation ; but these signs are not always
present, for it is not uncommon to find bronchial breathing and bronchophony
over the. site of the fluid, especially in children. These latter findings may
be explained by the occurrence of compression collapse of the lung tissue
beneath the fluid. The position of the mediastinum is useful in distinguishing
a pleural effusion from pulmonary atelectasis, but it cannot be relied on to
differentiate between the two conditions,
for
the mediastinum may not shift towards the opposite side unless an effusion is
very large, and collapse of a whole lobe often occurs without causing the
mediastinum to move towards the side of the lesion.
Radiological
appearances
All types of pleural fluid—serous, purulent, bloody and chylous—produce a
similar homogeneous opacity on x-ray examination of the chest. In the earliest
stages of an empyema the fluid is free in the pleural space, and its position
is influenced to a certain degree by gravity, but to a much less extent than
would be expected (Fig. 7). With moderate-sized effusions, skiagrams taken with
the patient sitting upright show a diffuse opacity at the base, and this often
rises highest in the axilla. In films taken with the patient supine, the
opacity becomes slightly less dense at the base and extends further upwards,
but the change is usually not great. The skiagrams taken with the patient
sitting upright may show a fluid level, but only if there is gas as well
as fluid in the pleural cavity. A fluid level therefore indicates one of three
possible alternatives : (1) air has been allowed to enter the pleural cavity
from the exterior, either through a needle introduced at a previous
paracentesis or as a result of a surgical or accidental wound ; (2) a
broncho-pleural fistula has formed, permitting air to pass from the lung into
the empyema ; or (3) the suppuration is caused by gas-producing organisms (Fig.
8). With regard to the last-mentioned, the appearances after infection of a
haemothorax by gas-producing organisms, such as Clostridium welchii, may
be very striking, for the gas is prone to become trapped in many fibrinous
loculi, giving rise to multiple fluid levels.
As soon as the empyema becomes localized by adhesions,
the radiological opacity remains constant whatever the position of the patient.
Frontal and lateral skiagrams should be taken, using a penetration above that
normally employed for routine chest radiography, in order to show the exact
position and extent of the empyema. Empyemas of medium or small dimensions are
usually located in the paravertebral gutter and extend upwards from the
diaphragm ; less commonly the pus is localized to the axillary region. The
uncommon interlobar empyema gives rise in a lateral skiagram to an elliptical
shadow in the line of one of the fissures. The rare mediastinal empyema appears
in a frontal view as an opaque bulge, continuous with the opacity normally
produced by the mediastinal structures.
Diagnostic
aspiration
The diagnosis requires confirmation by the aspiration
of a sample of pleural fluid. In order to avoid unnecessary discomfort to the
patient, it is preferable that the position of the fluid should be demonstrated
radiologically before aspiration is attempted.
Paracentesis is performed under local anaesthesia,
with the patient firmly but comfortably supported in bed. If the pus is located
posteriorly, the patient may either lean forwards across a cardiac table or sit
sideways on the edge of the bed (Fig. 9a and b). If the axilla is chosen
as the site for puncture, the patient need not move in bed, except to put the
hand of the affected side behind his head so that the arm is lifted out of the
operator's way (Fig. 9c). Because the
initial aspiration is made primarily for diagnostic purposes, it is
preferable to select an intercostal space which is considered to lie well above
the lowest limit of the empyema, for attempts to enter the bottom of the cavity
may lead either to penetration of the diaphragm, which may be higher than
expected, or to obstruction of the needle by fibrin, which tends to gravitate
to the bottom of an empyema. The skin and soft tissues over the selected
site for aspiration are infiltrated with procaine solution through a fine
hypodermic needle, and the skin is punctured with the point of a scalpel. A
large-bore needle (at least size 17 B.W.G.) is then fixed to the end of a two-way
adaptor, which is connected to a 20-millilitre syringe filled with procaine
solution. This needle is introduced into the skin puncture and steadily
advanced through the chest wall, simultaneously infiltrating the tissues freely
with procaine solution in order to ensure a painless puncture. Three
test-tubes, one of which contains a small quantity of 3-8 per cent sodium
citrate solution, should be ready to receive samples of the aspirate ; the tube
containing citrate is used only if the fluid is found to be serous and therefore
likely to clot. One of the non-citrated specimens is placed in a rack in the
ward and the others are sent for pathological examination.
If pus is
obtained, it is worth while to continue the aspiration for therapeutic
purposes, using the two-way adaptor to discharge the fluid into a receiver,
thus making sure that no air is allowed to enter the empyema. If the empyema is
likely to have arisen from infection by penicillin-sensitive bacteria, it is
advisable to have 500,000 units of penicillin available, so that this may be
injected into the pleural space at the end of the aspiration.
