Lung abscess

A lung abscess is a non-specific inflammation of the lung tissue, accompanied by its melting in the form of a limited focus and the formation of one or more purulent-necrotic cavities.

A lung abscess is a necrotizing infection characterized by a localized collection of pus. Abscesses are almost always caused by aspiration of oral secretions by patients with impaired consciousness. Symptoms of a lung abscess include persistent cough, fever, sweating, and weight loss. Diagnosis of a lung abscess is based on history, physical examination, and chest radiography. Treatment of a lung abscess is usually with clindamycin or a combination of beta-lactam antibiotics and beta-lactamase inhibitors.

In 10-15% of patients, the process may develop into a chronic abscess, which can be discussed no earlier than 2 months from the onset of the disease.

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What causes a lung abscess?

Most lung abscesses develop following aspiration of oral secretions by patients with gingivitis or poor oral hygiene who are unconscious or have decreased consciousness due to alcohol, illicit drugs, anesthesia, sedatives, or opioids. Elderly patients and patients unable to remove oral secretions, often because of nervous system damage, are at risk. Lung abscess is less commonly a complication of necrotizing pneumonia, which may result from hematogenous seeding of the lungs by septic emboli from intravenous drug use or from suppurative thromboembolism. Unlike aspiration, these conditions usually cause multiple rather than single lung abscesses.

The most common pathogens are anaerobic bacteria, but about half of all cases are caused by a mixture of anaerobic and aerobic organisms. The most common aerobic pathogens are streptococci. Immunocompromised patients with lung abscess are more likely to have an infection caused by Nocardia, mycobacteria, or fungi. People in developing countries are at risk of abscess due to Mycobacterium tuberculosis, amoebic infestation (Entamoeba histolytica), paragonimiasis, or Burkholderia pseudomallei.

The introduction of these pathogens into the lungs initially results in inflammation, which leads to tissue necrosis and then to abscess formation. Most often, abscesses rupture into a bronchus, and their contents are coughed up, leaving an air- and fluid-filled cavity. In about a third of cases, direct or indirect extension (via a bronchopleural fistula) into the pleural cavity leads to empyema. Pulmonary cavitary lesions are not always abscesses.

Causes of cystic lesions in the lungs

Anaerobic bacteria

• Gram-negative bacilli
  • Fusobacterium sp.
  • Prevotella sp.
  • Bacteroides sp.
  • Gram-positive cocci
  • Peptostreptococcus sp.
• Gram-positive bacilli
  • Clostridium sp.
  • Actinomycetes

Aerobic bacteria

• Gram-positive cocci
  • Streptococcus milleri and other streptococci
  • Staphylococcus aureus
• Gram-negative bacilli
  • Klebsiella pneumoniae
  • Pseudomonas aeruginosa
  • Burkholderia pseudomallei
• Gram-positive bacilli
  • Nocardia
  • Mycobacteria
  • Mycobacterium tuberculosis
  • Mycobacterium avium-cellulare
  • Mycobacterium kansasii
• Mushrooms
  • Histoplasmosis
  • Aspergillosis
  • Blastomycosis
  • Coccidioidomycosis
  • Cryptococcal infection
  • Mucormycosis
  • Sporotrichosis
  • Pneumocystis jiroveci (formerly P. carinii) infection
• Parasites
  • Paragonimiasis
  • Echinococcosis
  • Amebiasis
  • Bronchiectasis

Non-infectious causes

• Lung cancer
• Bulla with fluid level
• Pulmonary sequestration
• Pulmonary embolism
• Wegener's granulomatosis
• Nodular silicosis nodule with central necrosis

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Symptoms of a lung abscess

Before the pus breaks through into the bronchus, the following are typical: high body temperature, chills, profuse sweating, dry cough with chest pain on the affected side, difficulty breathing or dyspnea due to the inability to take a deep breath or early respiratory failure. Percussion of the lungs reveals intense shortening of the sound over the affected area, auscultation reveals weakened breathing with a harsh tone, sometimes bronchial. Typical symptoms of a lung abscess are detected in typical cases during examination. Pale skin, sometimes a cyanotic blush on the face, more pronounced on the affected side, are noted. The patient takes a forced position (usually on the "sick" side). The pulse is rapid, sometimes arrhythmic. Blood pressure often tends to decrease, with an extremely severe course, bacteremic shock with a sharp drop in blood pressure is possible. Heart sounds are muffled.

After a breakthrough into the bronchus: a coughing fit with the release of a large amount of sputum (100-500 ml), purulent, often foul-smelling. With good drainage of the abscess, the state of health improves, the body temperature decreases, with percussion of the lungs - the sound is shortened over the lesion, less often - a tympanic shade due to the presence of air in the cavity, auscultation - fine bubbling rales; within 6-8 weeks. the symptoms of the lung abscess disappear. With poor drainage, the body temperature remains high, chills, sweats, cough with poor separation of foul-smelling sputum, shortness of breath, symptoms of intoxication, loss of appetite, thickening of the terminal phalanges in the form of "drumsticks" and nails in the form of "watch glasses".

Course of lung abscess

In a favorable course of the disease, after a spontaneous breakthrough of the abscess into the bronchus, the infectious process is quickly stopped and recovery occurs. In an unfavorable course, there is no tendency to clear the inflammatory-necrotic focus, and various complications appear: pyopneumothorax, pleural empyema, respiratory distress syndrome (symptoms are described in the relevant chapters), bacteremic (infectious-toxic) shock, sepsis, pulmonary hemorrhage.

Bleeding is a common complication of lung abscess. It is arterial and caused by damage (erosion) of the bronchial arteries. Pulmonary hemorrhage is the release of more than 50 ml of blood per day when coughing (blood loss of up to 50 ml is considered hemoptysis). Blood loss in the amount of 50 to 100 ml per day is considered minor; from 100 to 500 ml - as average and over 500 ml - as profuse or severe.

Clinically, pulmonary hemorrhage is manifested by coughing up sputum mixed with foamy scarlet blood. In some cases, blood can come out of the mouth almost without coughing impulses. With significant blood loss, characteristic symptoms develop: pallor, rapid pulse of weak filling, arterial hypotension. Aspiration of blood can lead to severe respiratory failure. Severe pulmonary hemorrhage can cause death.

Diagnosis of lung abscess

Lung abscess is suspected based on the history, physical examination, and chest x-ray. In anaerobic infection due to aspiration, chest x-ray classically shows consolidation with a single cavity containing an air bubble and a fluid level in the lung compartments affected when the patient is supine (eg, posterior upper lobe or upper lower lobe). This finding helps differentiate anaerobic abscess from other causes of cavitary lung disease, such as diffuse or embolic lung disease that may cause multiple cavities or tuberculous disease in the apex of the lung. CT is not usually required but may be helpful when chest x-ray suggests a cavitating lesion or when a pulmonary mass compressing a draining segmental bronchus is suspected. Anaerobic bacteria are rarely detected in culture because uncontaminated samples are difficult to obtain and because most laboratories do not routinely test for anaerobic flora. If the sputum is putrid, the cause of the pathology is most likely an anaerobic infection. Bronchoscopy is sometimes indicated to exclude malignancy.

When anaerobic infection is less likely, aerobic, fungal, or mycobacterial infection is suspected and attempts are made to identify the causative organism using sputum, bronchoscopic aspirates, or both.

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Laboratory diagnostics of lung abscess

1. Complete blood count: leukocytosis, band shift, toxic granularity of neutrophils, significant increase in ESR. After a breakthrough into the bronchus with good drainage - gradual reduction of changes. In chronic abscess - signs of anemia, increased ESR.
2. General urine analysis: moderate albuminuria, cylindruria, microhematuria.
3. Biochemical blood test: increased content of sialic acids, seromucoid, fibrin, haptoglobin, a2- and gamma-globulins; in chronic abscess, decreased albumin levels.
4. General clinical analysis of sputum: purulent sputum with an unpleasant odor, when left standing it separates into two layers, under microscopy - a large number of leukocytes, elastic fibers, crystals of hematoidin, fatty acids.

Instrumental diagnostics of lung abscess

X-ray examination: before the abscess breaks through into the bronchus - infiltration of the lung tissue, most often in segments II, VI, X of the right lung, after the breakthrough into the bronchus - enlightenment with a horizontal fluid level.

Screening program for suspected lung abscess

1. General analysis of blood, urine, feces.
2. General clinical examination of sputum for elastic fibers, atypical cells, BK, hematoidin, fatty acids.
3. Bacterioscopy and sputum culture on elective media to obtain a culture of the pathogen.
4. Blood biochemistry: total protein, protein fractions, sialic acids, seromucoid, fibrin, haptoglobin, aminotransferases.
5. ECG.
6. Fluoroscopy and radiography of the lungs.
7. Spirometry.
8. Fiberoptic bronchoscopy.

Examples of diagnosis formulation

1. Postpneumonic abscess of the middle lobe of the right lung, moderate severity, complicated by pulmonary hemorrhage.
2. Aspiration abscess of the lower lobe of the left lung (severe course, complicated by limited pleural empyema; acute respiratory failure grade III.
3. Acute staphylococcal abscess of the right lung with damage to the lower lobe, severe course, pleural empyema.

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Treatment of lung abscess

Treatment of lung abscess is with antibiotics. Clindamycin 600 mg intravenously every 6-8 hours is the drug of choice, given its excellent antianaerobic and antistreptococcal activity. A possible alternative is a combination of beta-lactam antibiotics with beta-lactamase inhibitors (eg, ampicillin-sulbactam 1-2 g intravenously every 6 hours, ticarcillin-clavulanate 3-6 g intravenously every 6 hours, piperacillin-tazobactam 3 g intravenously every 6 hours). Metronidazole 500 mg every 8 hours can be used, but it should be combined with penicillin (ampicillin) 2 million units every 6 hours intravenously or third-generation cephalosporins intravenously (ceftriaxone 2.0 g twice daily or cefotaxime 1.0-2.0 g three times daily). In less severe cases, the patient can be given oral antibiotics such as clindamycin 300 mg every 6 hours or amoxicillin-clavulanate 875 mg/125 mg orally every 12 hours. Intravenous antibiotics can be replaced by oral ones when the patient begins to recover.

The optimal duration of treatment is unknown, but standard practice is to use the drugs for 3 to 6 weeks unless chest X-rays show complete resolution earlier. In general, the larger the lung abscess, the longer it will persist on X-ray. Large abscesses therefore usually require several weeks or months of treatment.

Most authors do not recommend chest physiotherapy and postural drainage because they may cause infection to break through to other bronchi, causing dissemination of the infection or development of acute obstruction. If the patient is weak or paralyzed or has respiratory failure, tracheostomy and suctioning of secretions may be necessary. Rarely, bronchoscopic suctioning helps achieve drainage. Concomitant empyema should be drained; the fluid is a good medium for anaerobic infection. Percutaneous or surgical drainage of lung abscesses is necessary in about 10% of patients whose disease does not respond to antibiotics. Resistance to antibiotic therapy occurs with large cavities and with infections that complicate obstructions.

When surgical treatment is necessary, lobectomy is most often performed; if the lung abscess is small, segmental resection may be sufficient. Pulmonectomy may be necessary for multiple abscesses or for drug-resistant lung gangrene.