Pulmonary · Topic 18 of 28

Parapneumonic Effusion & Empyema

Pulmonary · pleural infection

Parapneumonic Effusion & Empyema

Pneumonia with pleural fluid: tap it, and drain it when the pH is below 7.20, the fluid is pus, infected or loculated.

Key numbers

Drain when pleural pH < 7.20pH < 7.20

Intrapleural tPA plus DNasetPA 10 mg + DNase 5 mg

Sample pneumonia effusions 10 mm or deeper≥ 10 mm

Small-bore chest tube, flushed regularly≤ 14 Fr

01 · Defined byDrain when pleural pH < 7.20

A parapneumonic effusion needs complete drainage when pleural fluid pH is below 7.20 — the most accurate single marker; glucose below 60 mg/dL is the surrogate when pH is unavailable.

02 · Defined byDrain pus, positive culture, or loculations

Also drain completely for frank pus (empyema), a positive Gram stain or culture, or loculations. Pus at the diagnostic tap means placing a chest tube at once, without waiting for chemistry.

03 · GiveIntrapleural tPA plus DNase

If drainage stalls with a residual infected collection, give intrapleural tPA 10 mg plus DNase 5 mg twice daily for 3 days (MIST2 regimen); either drug alone is ineffective.

What it is

Core idea

Free fluid → septations → pleural peelUntreated pleural infection progresses from free-flowing fluid to fibrin deposition with septations and loculations, then an organized pleural rind that can trap the lung — delay makes drainage harder.

Causes & risk factors

Why it happens

Community: streptococci; hospital: S. aureus, enterococciStreptococci dominate community-acquired pleural infection; hospital-acquired infection is mostly Staphylococcus aureus (about a quarter MRSA) and enterococci, and carries higher mortality.

Do right now

In this order

First moves

Sample pneumonia effusions 10 mm or deeper≥ 10 mm

→

Broad antibiotics that cover anaerobes

→

Drain when pleural pH < 7.20pH < 7.20

→

Intrapleural tPA plus DNasetPA 10 mg + DNase 5 mg

→

Tube and lytics fail: refer for VATS

Why each step

Sample pneumonia effusions 10 mm or deeperSample any effusion with pneumonia that is 10 mm or deeper, under ultrasound guidance; a 'simple' pneumonia that fails to improve on antibiotics should prompt a search for one.

Broad antibiotics that cover anaerobesStart broad-spectrum antibiotics that include anaerobic coverage in nearly every case, because pleural infection is usually polymicrobial; widen to Gram-negatives and MRSA for hospital-acquired infection.

Drain when pleural pH < 7.20A parapneumonic effusion needs complete drainage when pleural fluid pH is below 7.20 — the most accurate single marker; glucose below 60 mg/dL is the surrogate when pH is unavailable.

Intrapleural tPA plus DNaseIf drainage stalls with a residual infected collection, give intrapleural tPA 10 mg plus DNase 5 mg twice daily for 3 days (MIST2 regimen); either drug alone is ineffective.

Tube and lytics fail: refer for VATSIf chest tube drainage plus intrapleural therapy fails to clear the infection, refer for thoracic surgery — video-assisted thoracoscopic surgery (VATS) first, thoracotomy with decortication if needed.

Management

Orders

Small sterile free-flowing effusion: antibiotics aloneSmall free-flowing effusions with normal pH and negative Gram stain and culture are low risk and resolve with antibiotics; drainage is for moderate- or high-risk effusions (ACCP categories 3 and 4).

Small-bore chest tube, flushed regularlyA small-bore drain (14 Fr or smaller) is first line — size does not change mortality, repeat intervention or length of stay — and needs regular saline flushes (e.g., 20 mL every 6 hours).

Antibiotics usually 2–6 weeksAntibiotic courses for pleural infection usually run 2–6 weeks, set by clinical and biochemical response; duration rests mainly on expert opinion.

Red flags & don'ts

Avoid harm

Hold anticoagulation before intrapleural lytics avoidIntrapleural tPA/DNase carries a small bleeding risk (about 4%): withhold therapeutic anticoagulation if possible, or halve the tPA dose to 5 mg when anticoagulation cannot be stopped.

Uncomplicated or complicated?

Commonly confused

Pleural pH	7.20 or higher
Pleural glucose	60 mg/dL or higher
Gram stain / culture	Negative
Appearance	Small, free-flowing, not pus
Treatment	Antibiotics alone

Commonly confused

Tell apart

Low pH also in rheumatoid and malignant effusionsLow pH and glucose with high LDH also occur in rheumatoid pleuritis and malignant effusions — interpret pleural pH in clinical context.

More detail

Reference

Show 5 reference facts

Infected parapneumonic fluid typically has very high LDH (e.g., > 900 U/L), but LDH alone predicts poorly; it adds weight when pH or glucose is borderline.

The RAPID score (renal function/urea, age, non-purulent fluid, hospital-acquired source, low albumin) predicts mortality in pleural infection; it does not yet direct treatment.

In MIST2, tPA plus DNase cut surgical referral at 3 months (4% vs 16% with placebo) and hospital stay by about 7 days; DNase alone increased surgical referral.

Standard Gram stain and culture identify an organism in only about 58% of pleural infections, and far fewer after antibiotics have started.

Empyema can also follow thoracotomy, lung, liver or subdiaphragmatic abscess, or penetrating trauma; empyema necessitans is extension through the chest wall with external drainage.

Pearl

Pus in the syringe means a tube in the chest — no need to wait for the chemistry.

Sources · Merck Manual Professional — Pleural Effusion (Rahman NM, rev. Jul 2025) · Pearce C, Crapnell A, Bedawi EO, Rahman NM, Corcoran JP. Pleural Infection: Diagnosis, Management, and Future Directions. J Clin Med 2025;14:1685 (PMC11899816) · Rahman NM et al. Intrapleural use of tissue plasminogen activator and DNase in pleural infection (MIST2). N Engl J Med 2011;365:518–526 · Colice GL et al. Medical and surgical treatment of parapneumonic effusions: an evidence-based guideline (ACCP). Chest 2000;118:1158–1171 · Merck Manual Professional — Lung Abscess (anaerobic pleuropulmonary regimens) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).