Pleural infection-current diagnosis and management
Clinical Pleural Fellow, Respiratory Dept, Sir Charles Gairdner Hospital, Perth WA 6009, Australia
Review Article
Pleural infection-current diagnosis and management
Clinical Pleural Fellow, Respiratory Dept, Sir Charles Gairdner Hospital, Perth WA 6009, Australia
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Abstract
Pleural infection is a common and increasing clinical problem in thoracic medicine, resulting in significant morbidity and mortality. In recent years there has been a marked increase in interests and publications relating to evolving interventions and management options for pleural infection and empyema. Recently published research data as well as guidelines have suggested better approaches of radiological assessment, updated management algorithms for pleural infection, intrapleural adjunct therapies and re-examined the roles of biomarkers, pleural drainage techniques, and the role of surgery. This review highlights some of the recent advances and recommendations relevant to clinical care of pleural infection.
Key words
Pleural effusion; empyema; infection; disease managementJ Thorac Dis 2012;4(2):186-193. DOI: 10.3978/j.issn.2072-1439.2012.01.12
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Introduction
Pleural infection (either complicated parapneumonic effusion or empyema) is an ancient problem, with the first recorded descriptions to be found in the medical texts of ancient Greece. Approximately four million people are affected by pneumonia each year, with close to half estimated to develop a parapneumonic effusion. Pleural infection is a common complication of pneumonia, reported to affect 65,000 patients per year in the USA and UK alone (1,2) at an estimated total healthcare cost approximating USD $320 million (3). Pleural infection significantly increase the morbidity and mortality associated with pulmonary infections, with a mortality rate in adults approaching 20% (4,5). This review summarizes recent advances in management of pleural infection including recommendations from the latest clinical guidelines. A detailed overview is outside the scope of this review and can be found elsewhere (6).
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Rising burden of pleural infection
Regions (where pleural infection is likely to be substantially more common) are lacking. The incidence of pleural infection appears to be increasing globally, across all age ranges (7). On a recent review of national hospitalisation data in the USA by Grijalva et al., a 2 fold increase (3.04 per 100,000 in 1996 to 5.98 in 2008) in hospitalisations was reported. Overall in-hospital mortality rate was 8%, reaching 16.1% in adults ≥65 years (8). In this study pneumococcal empyema rates were stable from 1996 to 2008, but pleural infection from streptococci (non-pneumococcal) and staphylococci were rising. Staphylococcal-related empyema was associated with longer hospital stays and higher in-hospital mortality. These findings are a reflection of similar studies in the last five years noting a global increase in rates of pleural infection (9,10).
A different picture of the incidence of pneumococcal empyema has been reported by Burgos et al., suggesting an increased incidence in young adults in the post pneumococcal vaccine period (11). In an observational study of all adults hospitalized with invasive pneumococcal disease presenting with empyema, the rates of empyema in patients aged 18-50 years increased from 7.6% to 14.9%, i.e. an increase from 0.5 to 1.6 cases per 100,000 patient-years, since the introduction of pneumococcal conjugate vaccine (PCV7) in Spain in 2001. These infections appeared predominantly due to an increase of cases involving serotype 1 (43.3% of cases), a serotype not covered by PCV7. These findings highlight the changing epidemiology of pneumococcal empyema in adults, and the need for awareness by the clinician of local as well as global trends in pleural infection.
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Pathophysiology
Bacteriology
Streptococcus pneumoniae, S. pyogenes and Staphylococcus aureus
are the organisms traditionally associated with pleural infection
(11). Additionally the S. anginosus group (often known as S.
milleri group) consisting of S. anginosus, S. constellatus and
S. intermedius are part of normal human flora which become
significant in the context of pleural infection, accounting for 30-
50% of adult cases of community acquired empyema (11-14). S.
aureus is more commonly seen in the older, hospitalised patient
with co-morbidities. It is associated with cavitation and abscess
formation, with empyema present in 1-25% of adult cases.
Increasing numbers of cases of empyema caused by community
acquired MRSA are being reported, and such a pathogen should
be considered in the appropriate setting of both community and
hospital acquired empyema (15). Anaerobic bacteria however
contribute significantly to pleural infection, being identified as
the sole or co-pathogen in 25-76% of pediatric cases (16).
The importance of differentiating community acquired
empyema from hospital acquired cases is being increasingly
recognized, as the latter often has a different bacteriology.
Organisms such as MRSA, Enterobacteriae and anaerobes are
more prevalent in nosocomial empyema and will influence
the choice of antibiotics (17). Awareness of local prevalence
and antimicrobial sensitivities is essential to guide clinical
decisions and antibiotic selection. Identification of the causative
pathogen(s) in pleural infection can be difficult, with the
microbiological diagnosis remaining elusive in 40% of cases in
one study despite standard pleural fluid culture (18).
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Diagnosis
Clinical presentation
A high index of suspicion is required for the diagnosis of pleural
infection.
Patients may present with the finding of a pleural effusion on
chest X-ray in the setting of pneumonia, with failure to clinically
improve as expected. Patients may also present with fever, chest
pain, cough, purulent sputum and dyspnoea. The absence of
pleuritic pain does not exclude pleural infection (1).
When faced with patients with a parapneumonic effusion, no
specific clinical features accurately predict the need for pleural
drainage. Sampling of an effusion is often required to assess
whether the pleural space is infected (19).
Imaging
Chest X-rays have long been the initial radiologic investigation for the assessment of pulmonary pathology including the
presence of pleural space infections. The chest X-ray will usually
show a small to moderate effusion with or without parenchymal
infiltrates. The effusions may be bilateral, the larger usually on the
side primarily affected by pneumonia. In the setting of complex
effusions, loculations and air fluid levels may be apparent
(19). Prior to the greater use of thoracic ultrasound and CT,
lateral decubitus X-rays were used in the assessment of pleural
collection, with Light demonstrating that effusions less than
1cm would resolve with antibiotic therapy alone and not require
further intervention (1). Current guidelines recommend the
sampling of parapneumonic effusions with a thickness ≥10mm
(20). However parapneumonic effusions are often loculated and
assessment of thickness on chest X-ray is therefore problematic
and is not a clinically reliable guide. A recent study of 61 patients
with pneumonia and parapneumonic effusion showed that CXR,
taken as anteroposterior, posteroanterior, or lateral, all missed
more than 10% of parapneumonic effusions. Hence alternatives,
such as ultrasound or CT, particularly in the setting of lower lobe
consolidation (22) are now considered the mainstay imaging
modalities for parapneumonic effusions.
Pleural ultrasound
The last decade has seen a significant trend worldwide to employ
pleural ultrasound at the bedside to assess for the presence of
pleural effusions, especially in the context of pleural infection.
Pleural ultrasound is fast, safe and effective in confirming the
presence of pleural fluid, and in localising the optimal site for
diagnostic and therapeutic intervention in real time (23). Use
of real-time pleural ultrasound by trained operators has been
shown to improve the safety of sampling effusions, with reported
reductions in iatrogenic pneumothoraces compared to un-guided
thoracenteses (in two studies) from 10.3% and 18% to 4.9% and
3% respectively (24,25). Its role in risk reduction has been stressed
in a recent meta-analysis and reviews of pleural procedures
(26,27). It has been incorporated into diagnostic algorithms in
major centres in recent years (28). It is sensitive in detecting small
volumes of fluid and may detect loculations not evident on CT
(19). Ultrasound of the pleural space is rapidly being considered
as an extension of the physical examination and a core skill in
those routinely assessing pleural effusions (Figure 1).
CT
Pleural effusions are commonly detected on review of CTs
organised for assessment of pneumonia. In terms of diagnosis
and planning of intervention, contrast enhanced thoracic CT
is the imaging investigation of choice, with correct timing of
contrast injection allowing better definition of the pleural
abnormalities as suggested by Raj et al. (29). Thoracic CT allows not only assessment of the pleura itself, but chest tube position,
presence and degree of loculations, parenchymal changes,
endobronchial lesions and differentiation of lung abscess from
empyema (28,30).
MRI and PET
MRI is not routinely used for the assessment of the pleural
space, though it has been shown to allow assessment of complex
loculated effusions, and demonstrate chest wall involvement.
Davies et al. also found that exudates produced higher signal
than transudates on T1 and T2 weighted images, theoretically
allowing differentiation of transudates and exudates (31). Use of
MRI minimizes radiation from contrast media and is therefore
theoretically superior to CT especially in young patients who
require repeated imaging. PET cannot differentiate infection
from malignancy in the setting of a pleural collection and has no
clinical role in pleural infection.
Thoracentesis
Thoracentesis remains a key tool in the diagnosis and tailoring
of management in pleural infection. Current guidelines advise
sampling of effusions >10 mm in depth associated with
pneumonia, chest trauma or thoracic surgery with features
of sepsis (20). This has been questioned by Skouras et al. in a
retrospective review of patients with pneumonia diagnosed with
a pleural effusion on CT, with a low complication rate in patients
with a pleural fluid thickness of <20 mm. These results however are preliminary and retrospective, in a small subset of patients
with pneumonia, and further prospective trials are required
before altering the above recommendation.
Image guidance has been shown to decrease the risk of
complication including organ perforation in pleural fluid
sampling. Pleural ultrasound improves accuracy of sample site
selection. Simple marking of a site for pleural sampling away
from the location of the actual procedure is no better than ‘blind’
aspiration. Patient movement in transit and lack of replication
of body position from imaging to time of procedure mean that
there may be significant disparity between surface site marked
and the actual fluid collection. The ability of the clinician to use
pleural ultrasound themselves allows visualisation of pleural
anatomy and identification of barriers to thoracentesis such as
ribs, vasculature or consolidated lung (27,33-35). The role of
pleural ultrasound, together with simulation and supervision,
has been reviewed elsewhere (36).
Pleural fluid biomarkers of infection
Pleural fluid pH should be assessed if pleural infection is
suspected, except in the case of frank pus where chest tube
drainage is indicated (20). A blood gas analyser should be
used, as litmus paper is unreliable in the assessment of pleural
pH (37,38). The method of sample collection is important, as
confounders such as local anaesthetic or air in the chamber of the
sampling syringe, or prolonged time between sample collection
and processing, has been shown to artificially alter sample pH
(39). These recommendations have been incorporated into
recent guidelines (20). Clinicians should be aware that pleural
fluid pH can occasionally vary among different locules (40).
Fluid protein, glucose and lactate dehydrogenase (LDH) can also
aid characterisation of pleural fluid and determine management,
and together with microbiological culture, should be requested
on initial samples. While protein concentration can contribute
to confirming an effusion as an exudate, it does not have value
in determining the need for tube drainage of an effusion versus
less invasive management (41). Cytology and assessment for
acid fast bacilli should be performed as clinically indicated. A
predominance of polymorphonuclear cells is expected in pleural
infection. Alternative etiologies should be entertained if the
effusion is not neutrophil-dominant (42).
Newer biomarkers have been assessed to examine their
efficacy in diagnosing pleural effusions secondary to infection,
and to prognosticate on the likelihood of these effusions
becoming complicated. Porcel et al. has recently examined a
range of pleural fluid biomarkers in pleural infection, including
tumor necrosis factor-alpha, myeloperoxidase, C-reactive protein
and procalcitonin (43). None of these markers is superior to the
classically accepted markers of pleural fluid pH <7.20, or pleural
fluid glucose <60 mg/dL (44).
A promising advance in microbiological diagnosis was
recently reported by Menzies et al. utilising a readily available
bacterial culture system (the BACTEC blood culture bottle
system) (45). In this prospective trial blood culture bottles were
inoculated with pleural fluid in addition to standard pleural
fluid culture, with an absolute increase in microbiological
diagnostic yield by 21%, and a proportional increase close to
50%. In 4% of cases even where standard culture was positive,
the results of culture of pleural fluid transported in blood culture
bottles yielded additional organisms that led to an alteration in
management.
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Management
Multiple approaches exist for treating parapneumonic effusions
and pleural infection, ranging from antibiotics alone to radical
surgical intervention. The optimal management is determined
by the answers to several core questions-should the pleural space
be drained, how it should be drained, and should intrapleural
adjunct therapy be used (19). The initial imaging and results of
the pleural fluid sampling including the smell, appearance and
pH provide the earliest information determining the need for
formal chest tube insertion and drainage. Frank pus, regardless of
other determinants, warrants immediate evacuation of any pleural
collection. Further features include positive gram stain, positive
culture and pleural fluid pH <7.20 [or glucose <3.4 mmol/L
(60 mg/dL)] (20).
Observation
The American College of Chest Physicians guidelines outline
four categories of pleural fluid collection in the setting of
infection (45). These range from <1 cm effusions through to
empyema, as determined by radiological features, pH, gram
stain, culture and presence of pus. Only category 1 effusions (very
low risk), described as minimal and free flowing and <1 cm, are
considered safe for observation without diagnostic sampling.
Category 2 (low risk) effusions (≥10 mm but <1/2 hemithorax,
pH >7.2 and negative gram stain and culture) may be observed
without formal drainage. Category 3 (moderate risk) effusions
(large but free flowing effusions, loculated effusions, or effusions
with thickened parietal pleura; or pH <7.2; or positive gram stain
or culture) and 4 (empyema) should be drained urgently due to
the associated risk of poor outcome. It is important to note that
these recommendations can serve as a useful guide, but are based
mainly on expert opinion and supported by limited quality data.
Antibiotics
All patients with suspected pleural infection should receive
appropriate antibiotic cover from the time of first review. Initial antibiotic choice should be determined by local
prescribing guidelines and resistance patterns, and where
possible refined by available microbiological samples and
culture. In cases of community acquired pleural infection with
confirmed bacteriology, 50% of cases are reported to be due
to penicillin-sensitive streptococci, with the remainder due to
organisms that are penicillin resistant, such as staphylococci
and Enterobacteriaceae. Roughly 25% of community acquired
pleural infections include anaerobic bacteria. Approximately
40% of cases will be culture negative (13). As such empiric
antibiotic choice should cover common community-acquired
bacterial pathogens and anaerobic bacteria (21). Penicillins,
penicillins with beta-lactamase inhibitors, cephalosporins, and
fluoroquinolones all have good penetration of the pleural space
(21,45-50). Metronidazole and clindamycin also penetrate
well and cover anaerobic bacteria. Aminoglycosides have poor
penetration, and may be less effective in the acidic environment
of the pleural space during infection (51). The low prevalence
of legionella and mycoplasma as causative agents of significant
pleural infections means that specific antibiotic cover is not
routinely indicated (17,21). In the setting of hospital-acquired
pleural infection antibiotic selection should also cover MRSA
and anaerobic bacteria (17). More extensive review of antibiotic
choice for pleural infection is available elsewhere (17,21).
Duration of antibiotic therapy is based on a combination of
clinical response, bacteriology where available and inflammatory
marker (e.g., CRP, procalcitonin) response. Radiological changes
can persist after clinical improvement and should not be the
sole criteria for continuation of therapy, nor would that be an
indication of treatment failure. The exact timing of change from
intravenous to oral antibiotic therapy is not rigorously defined,
with expert opinion suggesting at least 1 week of intravenous
therapy followed by 1-2 weeks of oral therapy as appropriate
based on clinical response (6).
Thoracentesis
The risk of complications in pleural infections is decreased by
minimising the number of interventions. Initial thoracentesis
should be therapeutic as well as diagnostic if possible (52). The
reasoning behind this is that if fluid is drained and does not recur
and it may not require further invasive treatment. Alternatives
include insertion of a small bore catheter or a therapeutic
thoracentesis. These three approaches have not been directly
compared in prospective studies. Further management will
depend on initial fluid findings and clinical progress.
Chest tube drainage
A large volume of recent literature has emphasized the need to
be aware of complications of pleural procedures (21,26,27,36). Guidelines exist for insertion of chest tubes, as do safety
protocols and web based simulations (53). Whenever possible,
imaging guidance should be used, and adequate supervision is
paramount (54).
Historically large bore tubes (>20 Fr) have been used for
drainage of pleural infection with minimal evidence based
support of superiority. Recent evidence from a large prospective
series indicates that small bore chest tubes (≤14 Fr) are as
effective, and better tolerated due to less pain (55). Failure of
successful drainage with a small bore tube often results from
loculations. Rather than insertion of a larger tube, consideration
should be given to repeated imaging of the pleural space and
insertion of additional small bore tubes to remaining sizeable
locules.
Intrapleural therapy
Multiple observational studies and small randomised trials have
examined the role of administration of intrapleural fibrinolytics
in improving drainage of loculated pleural effusions. These
studies were promising, though most were uncontrolled or
had significant limitations. A large randomised control study,
assessing 454 patients, examined the efficacy of streptokinase
compared to saline. This study did not show a difference in
length of hospitalisation or need for surgery between the
groups, and sub-group analyses did not show any benefits from
the intrapleural streptokinase (13). A meta-analysis in 2008
reviewing all available randomised controlled data, totalling
seven studies and 761 patients, found no mortality benefit with
intrapleural fibrinolytics alone (55).
The recent result from the Multicenter Intrapleural Sepsis
Trial-2 was noteworthy. In this double-blind, multicenter trial,
210 patients with pleural infection were randomized to one of the four arms: intrapleural tissue plasminogen activator
(tPA) alone, intrapleural DNase alone, placebo or intrapleural
tPA and DNase. The primary end-point was radiographic
improvement as measured by the percentage of the hemithorax
occupied by pleural fluid on chest X-ray. The combination of
tPA and DNase (but not the individual agents alone) resulted
in improved radiological appearance (mean decrease in pleural
opacity 7.9% over that from placebo), decreased surgical
referral at three months [2/48 patients (4%) vs. 8/51 patients
(16%)], and reduction in hospital stay of 6.7 days compared to
placebo, without excessive adverse events (56). This therapy
is increasingly employed by centers worldwide. Future studies
need to define if the therapy is best to be administered to every
pleural infection patients or be reserved for those who have
failed standard medical management (Figure 2).
Surgery
Surgery remains an option when medical therapy is inadequate.
Current guidelines suggest surgery should only be recommended
in patients with a residual pleural collection and persistent
sepsis despite adequate antibiotic therapy and drainage (21).
While empyema has previously been regarded as a ‘surgical’
disease, the role for surgical intervention may be declining (57).
Previous studies have been flawed by selection bias, with surgical
patients with empyema being younger by almost 10 years and
having less co-morbidity (9). In considering the role for surgery,
it needs to be remembered that the majority of patients with
pleural infection can be managed with antibiotics and chest tube
drainage. Only 18% of patients in the MIST1 trial (14) failed this
approach and only 11% in MIST2 (3). Using tPA and DNase,
96% of patients were successfully treated without surgery.
Two randomized clinical trials in adults comparing first line video-assisted thoracoscopic surgery (VATS) with medical
treatment (chest tube drainage with/without fibrinolytics and
antibiotics) have not shown a survival advantage from early
surgical intervention (58,59). These trials did suggest a modest
reduction in length of hospital stay (8.7 vs. 12.8 and 8.3 vs. 12.8
respectively). Both trials were small (n=19 and 70 respectively),
and lacked a clear clinical criteria for surgery and decortication.
As a result the Cochrane review examining this topic indicated
further research to establish best practice (60). Currently
no trials have compared VATS against the combination of
tPA and DNAse in the treatment of pleural infection. The
intermediate term complications of surgery must also be taken
into consideration. Intercostal neuralgia is not uncommon,
with Furrer et al. (61) reporting 44% of patients had pain at 6
months post thoracotomy, and Dajczman (62) reporting a series
of patients (n=56) of which 9% required nerve blocks, daily
analgesia and/or ongoing pain clinic review.
Figure 2. A: This patient presented with a pneumococcal pneumonia which was complicated by pleural infection. A small bore tube was inserted but
drainage was limited by extensive septations within the effusion. The patient remained febrile with elevated inflammatory markers; B: Intrapleural tPA
and DNase was administered twice daily for three days with dramatic clearance of the loculated effusion. Her fever and inflammatory markers settled
and was discharged on antibiotics; C: CXR at 3 months after discharge, with marked improvement of pleural opacities.
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Conclusion
Pleural infections are increasing worldwide despite modern
day medical care and antimicrobial therapies. A high index of
suspicion for and early identification of pleural space infection
is required for good clinical outcomes. Chest X-ray is the
mainstay of identification of pleural effusions in the setting
of infection, but pleural ultrasound plays a critical role in the
assessment of and guidance of drainage in pleural infection.
Emerging biomarkers together with currently available markers
of inflammation may aid recognition of effusions associated
with infection. However, the well established criteria utilising
pleural fluid pH, LDH and glucose remain a cornerstone in the
decision making process regarding drainage of the pleural space.
Appropriate antibiotic therapy remains a key initial therapeutic
intervention. The optimal size of chest tube for drainage of the
pleural space remains controversial, and small-bore tubes should
be considered as first line. In patients where standard medical
therapy has failed the use of combination intrapleural tPA and
DNase should be considered. The exact role of surgery remains
controversial, especially in face of new and highly effective
intrapleural therapies.
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References
Cite this article as: Rosenstenge A, Lee YCG. Pleural infection-current
diagnosis and management. J Thorac Dis 2012;4(2):186-193. doi: 10.3978/
j.issn.2072-1439.2012.01.12
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