Empyema and complicated parapneumonic effusion

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

A parapneumonic effusion spans a biological continuum. Free-flowing sterile exudate may resolve with pneumonia treatment. Bacterial invasion, falling glucose and pH, rising LDH and fibrin deposition create a complicated parapneumonic effusion. Frank pus is empyema. Organisation can form a rigid peel that traps the lung and makes late medical drainage difficult. A patient may have modest radiographic pneumonia but a large infected pleural burden, so pleural assessment must be explicit.

Diagnosis rests on ultrasound, fluid appearance and prompt biochemistry rather than CT alone. Pleural pH is vulnerable to error: local anaesthetic contamination lowers it, air exposure or delay can distort it, and purulent fluid need not be sent for pH because it already mandates treatment as infection. If pH cannot be measured reliably, glucose, LDH, fluid volume, ultrasound septation, CT pleural enhancement and clinical progress guide the decision.

Management is a coordinated sequence: give appropriate antibiotics, drain an accessible infected collection, maintain drain function, reassess residual anatomy and escalate when sepsis persists. Small-bore drains are generally suitable and cause less pain, but image-guided position and patency matter more than nominal size. Intrapleural fibrinolytic plus DNase treatment can improve drainage in selected residual collections; bleeding risk and local governance require senior review. Video-assisted thoracoscopic surgery is considered when medical treatment fails or anatomy predicts poor success, with timing individualised to physiology, frailty and operative fitness.

Key points

Frank pleural pus establishes empyema and should prompt intercostal drainage when a safe ultrasound window exists.
For non-purulent fluid, measure pH immediately on a blood-gas analyser: pH 7.20 or below indicates high risk and usually warrants drainage.
At pH 7.21 to 7.39, LDH 900 IU/L or above plus large volume, glucose 4.0 mmol/L or below, septations or CT pleural enhancement supports drainage.
A pleural pH of 7.40 or above usually means no immediate drain, but ongoing fever or sepsis requires reassessment and sometimes repeat aspiration.
Send pleural fluid in sterile containers and inoculate aerobic and anaerobic blood-culture bottles at the bedside; obtain blood cultures as well.
Use ultrasound-guided small-bore chest drainage with regular patency checks; a drain in the wrong locule is not source control.
If drainage stalls with residual infected collection, combined intrapleural tPA and DNase may be considered; either agent alone is not the evidence-based combination.
Persisting sepsis despite antibiotics and drainage needs early thoracic-surgical discussion rather than serial ineffective procedures.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Spread from pneumonia

Bacterial infection and inflammation extend across visceral pleura into an adjacent effusion, the common route to complicated parapneumonic fluid or empyema.

Direct pleural inoculation

Thoracic surgery, trauma, drains and oesophageal rupture can introduce organisms directly into the pleural space, and several contributors may coexist in the same patient.

Haematogenous or distant spread

Bloodstream infection or subdiaphragmatic disease can seed the pleura, particularly in immunosuppressed or critically ill patients.

Impaired host and drainage factors

Frailty, aspiration, poor dentition, diabetes and delayed pneumonia treatment increase microbial burden and reduce effective clearance.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Exudative pleural inflammation
Pneumonic inflammation increases pleural permeability, first producing a free-flowing sterile exudate, which helps produce the characteristic physiological impairment.
2
Bacterial invasion
Organisms enter pleural fluid, where neutrophil metabolism lowers pH and glucose while cell injury raises lactate dehydrogenase.
3
Fibrin deposition
Inflammatory coagulation forms septations and locules, preventing uniform drainage and shielding infected pockets, contributing to the resulting loss of respiratory reserve.
4
Pleural organisation
Fibroblasts create a thick rind that traps lung, prolongs sepsis and may require surgical clearance, and the downstream physiological effect determines clinical severity.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Pleural sepsis

Pneumonia with persistent fever, pleuritic pain, tachypnoea, weight loss or failure to improve, plus a unilateral effusion. Older or immunocompromised patients may have muted fever but functional decline.

Large or loculated collectionRed flag

Reduced breath sounds and expansion, mediastinal displacement or ultrasound septations suggest substantial burden. Respiratory compromise or haemodynamic effect requires urgent respiratory and procedural review.

Established empyemaRed flag

Frank pus on aspiration is diagnostic. Do not wait for culture, pH or CT confirmation before organising antibiotics and safe drainage.

Organised or trapped lung

A rind, persistent pleural space and incomplete re-expansion despite a patent drain suggest organisation. A bronchopleural fistula may cause continuous bubbling and changes the procedural plan.

Mimics

Malignant, rheumatoid, tuberculous and oesophageal-rupture effusions may be acidic or loculated. Very low glucose, unusual history, food material, recurrent unilateral fluid or failure to respond should prompt a broader work-up.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Thoracic ultrasoundFirst step
Why
Confirm fluid, estimate depth and volume, identify septations and mark a safe aspiration or drain site in real time.
Interpretation and limitations
Echogenic swirling or septation supports complexity but does not replace chemistry. Procedures should not be performed from a remote mark after patient position changes.
02
Pleural fluid appearance and immediate pH
Why
Inspect for pus; if non-purulent, collect anaerobically and measure pH promptly on a calibrated blood-gas analyser without local anaesthetic contamination.
Interpretation and limitations
Pus means empyema. pH 7.20 or below is high risk; 7.21 to 7.39 is intermediate; 7.40 or above is very low risk for immediate drainage, subject to clinical progress.
03
Pleural protein, LDH and glucose
Why
Classify exudate and refine an intermediate-pH decision; send paired serum protein and LDH when useful.
Interpretation and limitations
At pH 7.21 to 7.39, LDH 900 IU/L or above and glucose 4.0 mmol/L or below strengthen the case for drainage, especially with large or septated fluid.
04
Pleural and blood microbiology
Why
Send pleural fluid for Gram stain and culture, including bedside inoculation into aerobic and anaerobic blood-culture bottles, and take blood cultures before antibiotics where safe.
Interpretation and limitations
Yield is imperfect after antibiotics. A negative culture does not exclude pleural infection; growth of skin flora needs context, whereas a plausible anaerobe or pathogen can focus treatment.
05
Contrast-enhanced CT chest
Why
Map locules, pleural enhancement, parenchymal necrosis, tumour, oesophageal disease or an alternative source when anatomy or progress is unclear.
Interpretation and limitations
CT helps plan drainage and surgery but should not delay drainage of obvious pus or a clinically urgent accessible collection.
06
Serial chest imaging and drain assessment
Why
Use radiography and bedside ultrasound to verify drain position, residual fluid and lung expansion after intervention.
Interpretation and limitations
No output may mean successful emptying, viscous fluid, kinking, blockage or a drain outside the target locule; inspect the system before concluding treatment has failed.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Uncomplicated parapneumonic effusion

Small free-flowing fluid without purulence, microbial evidence or adverse pleural biochemistry may resolve with pneumonia treatment alone.

Malignant pleural effusion

Recurrent unilateral fluid, pleural nodularity and malignant cytology support cancer, although malignancy and infection can coexist.

Tuberculous pleuritis

Subacute constitutional symptoms, epidemiological risk and lymphocyte-predominant exudate prompt mycobacterial tissue and culture assessment, while the contrasting pattern directs the next diagnostic test.

Haemothorax

Trauma, procedure or anticoagulation with a high pleural-fluid haematocrit indicates blood rather than purulent infection, so the complete clinical pattern must be compared before attributing symptoms.

Lung abscess

An intraparenchymal cavity with an air-fluid level can mimic loculated pleural infection; CT defines its relationship to pleura.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01DrainInitial pleural-infection decisionFirst stepPneumonia with an accessible pleural effusion requiring diagnostic sampling.

1Perform ultrasound-guided aspiration, identify frank pus and send appropriate microbiology; for non-purulent fluid obtain immediate uncontaminated pH.
2Insert an image-guided intercostal drain for pus or pH 7.20 or below, assuming a safe accessible volume; at pH 7.21 to 7.39 integrate LDH, glucose, size, septations, CT enhancement and clinical course.
3For pH 7.40 or above without other high-risk features, treat pneumonia and monitor closely rather than draining automatically.
4Record the reasoning and a review time because biochemical thresholds do not replace reassessment of a deteriorating patient.

02OptimiseAntibiotics and functioning drainageComplicated parapneumonic effusion or empyema is being treated.

1Start antibiotics covering likely community or hospital organisms and anaerobes according to acquisition, allergy, prior cultures and local policy; narrow when reliable results arrive.
2Use a small-bore ultrasound-guided drain in most patients, connect and secure it correctly, prescribe flushing if local protocol supports it, and provide analgesia.
3Review observations, inflammatory markers, drain output and ultrasound daily; correct kinks or blockage and ensure the catheter enters the dominant locule.
4Individualise intravenous-to-oral switch and total duration to clinical, biochemical and radiological response with microbiology input.

03EscalateResidual collection or persistent sepsisEscalationInfected fluid remains despite an appropriately placed and patent drain, or systemic illness is not resolving.

1AlternativeRepeat ultrasound or CT to define residual locules, blocked drainage, a fistula, necrotising lung or an alternative diagnosis.
2Discuss combined intrapleural tPA and DNase with the pleural team when drainage has ceased and a residual collection persists; assess active bleeding, anticoagulation, recent surgery and consent.
3Seek early thoracic-surgical review for ongoing sepsis, organised disease, unsuitable anatomy or failure of medical management; do not wait for profound deconditioning.
4Choose further catheter placement, intrapleural treatment or VATS through a multidisciplinary, patient-centred decision rather than a fixed sequence.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

Common community-acquired empirical cover including many streptococci and anaerobes, followed by culture-directed narrowing.

Co-amoxiclav

Use the locally approved intravenous or oral adult regimen, adjusted for renal function and severity; verify current BNF and pleural-infection policy.

Penicillin allergy, hepatic injury, renal adjustment and C. difficile. It does not cover every resistant Gram-negative or MRSA risk.

Option for severe hospital-acquired pleural infection or resistant Gram-negative risk, often pending cultures.

Piperacillin with tazobactam

Local intravenous regimen with renal adjustment and any approved extended-infusion approach; confirm current BNF.

Broad ecological effect, beta-lactam allergy, renal injury, sodium load and cytopenia with prolonged use. Add MRSA cover only when risk or microbiology supports it.

Improves drainage of selected residual infected collections when a functioning drain alone is insufficient.

Intrapleural alteplase plus dornase alfa

A commonly used BTS-referenced regimen is alteplase 10 mg plus dornase alfa 5 mg intrapleurally twice daily for 3 days; lower-dose regimens may be used locally. Prescribe only through the pleural protocol.

Assess bleeding risk, anticoagulants, recent surgery and bronchopleural fistula. Obtain informed consent because this use is off-label; stop and escalate for bleeding or severe pain.

Enables breathing, coughing, mobilisation and toleration of a pleural drain.

Analgesia

Regular paracetamol with an individualised opioid or NSAID strategy when appropriate; verify renal, gastrointestinal, respiratory and frailty risks.

Avoid NSAIDs in relevant renal, bleeding or gastrointestinal risk and titrate opioids cautiously in respiratory failure or older adults.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Sepsis and shock

An undrained infected collection sustains bacteraemia and systemic inflammation, causing haemodynamic and multi-organ dysfunction, particularly when baseline cardiopulmonary reserve is limited.

Trapped lung

An organised visceral pleural rind prevents re-expansion, leaving restriction, chronic space and ongoing breathlessness, particularly when baseline cardiopulmonary reserve is limited.

Bronchopleural fistula

Necrotic lung or intervention may create a persistent airway-pleural connection, causing air leak and difficult source control.

Chest-wall extension

Chronic infection can rarely track through parietal pleura into soft tissues, forming empyema necessitans, with severity determined by its extent and the patient's underlying reserve.

Procedure-related harm

Drain placement and intrapleural treatment can cause bleeding, organ injury or ineffective drainage if locules and anatomy are not adequately assessed.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Observe temperature, respiratory rate, oxygen need, pulse, blood pressure, mental state and urine output, escalating promptly for shock or respiratory failure.
Review drain swing, bubbling, output, tubing and insertion site each shift; document flushes and never clamp an actively bubbling drain without specialist instruction.
Trend FBC, CRP, renal and liver function; use the trajectory to support, not replace, bedside assessment.
Use bedside ultrasound to check residual fluid and drain position when output stops or progress plateaus; obtain CT for complex anatomy or surgical planning.
Monitor haemoglobin, pleural drainage colour, pain and haemodynamics during intrapleural therapy and follow the local anticoagulant plan.
Plan post-discharge review for symptom recovery and interval imaging, with investigation for malignancy or TB if resolution is incomplete or atypical.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Pus outranks pH

Do not send thick pus through a blood-gas analyser or await a number. Its appearance already defines empyema and the need for source-control planning.

pH technique changes decisions

Residual local anaesthetic can falsely lower pH, and air or processing delay can alter it. A dedicated heparinised blood-gas syringe and immediate analysis improve reliability.

A small drain can still fail

Failure often reflects position, viscosity, loculation or organisation rather than diameter. Inspect anatomy and catheter function before upsizing reflexively.

Negative culture is common

Previous antibiotics and anaerobes reduce yield. The biochemical and clinical syndrome still warrants treatment, while bedside blood-culture bottle inoculation can increase detection.

Surgery is not a punishment

Early discussion preserves options. Frailty and operative risk matter, but repeated ineffective drainage can itself cause harm and deconditioning.

11Common pitfallsFrequent interpretation and management errors.

01
Delaying drainage of frank pus while awaiting a pH or CT report.
02
Using pleural pH that was contaminated with local anaesthetic or analysed late.
03
Assuming no drain output means no residual collection without inspecting tubing and ultrasound.
04
Giving alteplase alone or DNase alone as though it were the validated combination.
05
Continuing broad antibiotics while ignoring a blocked drain or organised pleural peel.
06
Forgetting malignant, tuberculous, rheumatoid or oesophageal causes when progress is atypical.