Parapneumonic Effusion

A pleural effusion that accompanies bacterial pneumonia, lung abscess or bronchiectasis. It develops in about 20 to 57% of patients hospitalised with pneumonia, and about 10% of these need drainage.

• Mechanism: inflammation of the lung increases capillary permeability and fluid crosses into the pleura. Stages: exudative (days 1 to 3, sterile free flowing fluid), fibrinopurulent (days 3 to 7, bacterial invasion, fibrin deposition and loculation) and organising (after 2 to 3 weeks, fibroblast ingrowth and thick pleural peel).
• Uncomplicated (simple) effusion: free flowing, pH greater than 7.2, glucose greater than 2.2 mmol/L, LDH less than 1000 U/L, Gram stain and culture negative. It resolves with antibiotics alone in most patients.
• Presence of an effusion increases mortality about 2 to 3 times (and risk of drainage and surgery), mainly because of progression to complicated effusion.
• Common organisms: Streptococcus pneumoniae, Streptococcus milleri group, Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, anaerobes, and Haemophilus influenzae. In tuberculosis endemic settings and HIV, tuberculous pleurisy must be excluded.

• Persistent fever beyond 48 to 72 hours of antibiotics, pleuritic chest pain, productive cough, breathlessness and malaise.
• Signs: dullness to percussion, reduced breath sounds and vocal resonance over the effusion, bronchial breathing at its upper margin, pleural rub; tracheal deviation with large effusions.
• Differential diagnosis: tuberculous pleural effusion, malignant effusion (post-obstructive pneumonia), empyema, heart failure, pulmonary embolism with infarction, hepatic hydrothorax, subphrenic abscess, post-cardiac injury syndrome, drug induced effusion and oesophageal rupture.
• Complications: progression to complicated effusion and empyema (about 10 to 30% if untreated), pleural thickening and trapped lung, lung abscess, sepsis, bronchopleural fistula, and reduced lung volumes.

• Chest X-ray: blunting of the costophrenic angle or an opacity with a meniscus; lateral decubitus film shows free fluid layering (greater than 10 mm).
• Thoracic ultrasound (to guide sampling, show septations and echogenic fluid); CT chest with contrast when loculation or abscess is suspected or the effusion is unexplained.
• Diagnostic thoracentesis under ultrasound for any effusion thicker than 10 mm (small effusions less than 10 mm are observed): measure pH (in a blood gas syringe), glucose, LDH, protein, cell count, Gram stain, aerobic and anaerobic culture in blood culture bottles, acid fast smear, Xpert MTB/RIF, adenosine deaminase (greater than 40 U/L with lymphocyte predominance suggests tuberculosis), and cytology.
• Pleural fluid is an exudate if protein is greater than 30 g/L, or fluid to serum protein ratio is greater than 0.5, or fluid LDH is greater than two thirds of the upper serum limit, or fluid to serum LDH ratio is greater than 0.6.
• Blood tests: full blood count, CRP, procalcitonin, creatinine, glucose, albumin, blood cultures, HIV test.

• Treat the pneumonia with IV antibiotics at once (adjust to culture):
  • Community onset: co-amoxiclav 1.2 g IV every 8 hours, or ceftriaxone 2 g IV daily plus metronidazole 500 mg IV every 8 hours.
  • Add flucloxacillin 2 g IV every 6 hours (or vancomycin 15 to 20 mg/kg IV every 8 to 12 hours, trough 15 to 20 mg/L, for methicillin resistant Staphylococcus aureus) when Staphylococcus aureus is likely.
  • Hospital onset or risk of resistance: piperacillin tazobactam 4.5 g IV every 6 to 8 hours, or meropenem 1 g IV every 8 hours.
  • Penicillin allergy: levofloxacin 750 mg daily plus metronidazole 500 mg every 8 hours, or clindamycin 600 mg IV every 8 hours.
  • Switch to oral co-amoxiclav 625 mg three times daily when afebrile and stable. Duration 2 to 4 weeks (until fever, CRP and the effusion resolve); avoid aminoglycosides (poor penetration).
• Drainage decisions:
  • Small effusion (less than 10 mm on ultrasound or decubitus film): antibiotics alone, with review at 48 hours.
  • Small to moderate free flowing effusion with pH greater than 7.2, glucose greater than 2.2 mmol/L and negative Gram stain: antibiotics alone, with repeat ultrasound at 24 to 48 hours; repeat aspiration if the patient remains febrile or the effusion enlarges.
  • Therapeutic drainage (the effusion is complicated) when pus is present, pH is less than 7.2, glucose is less than 2.2 mmol/L, Gram stain or culture is positive, the effusion is loculated, or it occupies more than half the hemithorax: place an ultrasound guided chest drain (10 to 14 French small bore with saline flushes 20 to 30 mL every 6 to 8 hours, or 24 to 28 French for thick pus) connected to an underwater seal with suction at 10 to 20 cmH2O.
  • Intrapleural alteplase 10 mg plus dornase alfa 5 mg (each in 30 to 50 mL saline, clamped for 1 hour) twice daily for 3 days for loculated or poorly draining effusions.
  • Surgical referral (video assisted thoracoscopic debridement or decortication) for failure to improve within 5 to 7 days of drainage.
• Tuberculous effusion: rifampicin 10 mg/kg (maximum 600 mg), isoniazid 5 mg/kg (maximum 300 mg), pyrazinamide 25 mg/kg (maximum 2 g) and ethambutol 15 mg/kg (maximum 1.2 g) daily for 2 months, then rifampicin and isoniazid for 4 months, with pyridoxine 25 to 50 mg daily; in HIV start antiretroviral therapy within 2 to 8 weeks (dolutegravir 50 mg twice daily with rifampicin).
• Supportive care: oxygen, IV fluids, analgesia (paracetamol 1 g four times daily, ibuprofen 400 mg three times daily with food when the kidneys allow; morphine 2.5 to 5 mg for severe pain), enoxaparin 40 mg SC daily, physiotherapy, and nutrition.
• Special groups:
  • Children: ceftriaxone 50 to 100 mg/kg/day (maximum 4 g) or ampicillin 50 mg/kg every 6 hours, plus flucloxacillin or clindamycin for suspected Staphylococcus aureus; drain for respiratory distress, mediastinal shift or a large effusion; intrapleural urokinase 40,000 units in 40 mL saline (10,000 units in 10 mL for infants under 1 year) twice daily for 3 days has been used (evidence is limited).
  • Pregnancy: ceftriaxone, ampicillin sulbactam or piperacillin tazobactam; avoid fluoroquinolones and tetracyclines.
  • HIV: test for tuberculosis and Pneumocystis pneumonia, and use broader antibiotic cover.
  • Renal impairment: adjust doses of vancomycin, piperacillin tazobactam and levofloxacin.
• Red flags: persistent fever at 72 hours, rising CRP, enlarging or loculated effusion, pH falling, sepsis, haemoptysis.
• Follow up: review at 48 to 72 hours, chest X-ray at discharge and 6 weeks (CT if an opacity or thickening persists), and tuberculosis and cancer workup for non-resolving effusions.