Makindo Medical Notes

Related Subjects: Asthma |Acute Severe Asthma |Exacerbation of COPD |Pulmonary Embolism |Cardiogenic Pulmonary Oedema |Pneumothorax |Tension Pneumothorax |Respiratory (Chest) infections Pneumonia |Fat embolism |Hyperventilation Syndrome |ARDS |Respiratory Failure |Diabetic Ketoacidosis

Introduction

Community-acquired pneumonia (CAP) is an acute infection of the lungs leading to inflammation of the alveolar spaces. It is commonly acquired outside of hospital settings and can affect individuals of all ages.

About CAP

• Acute infection causing inflammation in the alveoli.
• Can be lobar, diffuse, or bronchopneumonia.
• Caused by bacterial, viral, or fungal pathogens.
• Other causes include aspiration, radiotherapy, or allergic reactions.

Classification

• CAP: Community-acquired pneumonia (e.g., Streptococcus pneumoniae).
• HAP: Hospital-acquired pneumonia (e.g., Gram-negative bacteria).
• VAP: Ventilator-associated pneumonia (e.g., Pseudomonas, Klebsiella, Acinetobacter).

Pathogenesis

• Colonization: Pathogens colonize the oropharynx and gain access to the lower respiratory tract through microaspiration or inhalation.
• Evasion of Host Defenses: The microorganisms overcome the innate immune defenses of the respiratory tract, such as mucociliary clearance and alveolar macrophages.
• Inflammatory Response: The immune system responds to the infection, leading to the accumulation of inflammatory cells, fluid, and exudate in the alveolar spaces.
• Impaired Gas Exchange: The filling of alveoli with exudate hampers oxygen and carbon dioxide exchange, resulting in hypoxia and other clinical symptoms.

Types of Pneumonia Based on Pathology

• Lobar Pneumonia: Involves an entire lobe of the lung. Commonly caused by Streptococcus pneumoniae. The infection spreads rapidly through alveolar pores (pores of Kohn).
• Bronchopneumonia: Characterized by patchy consolidation affecting one or more lobes. The infection originates in the bronchi and bronchioles and extends to the adjacent alveoli.
• Interstitial (Atypical) Pneumonia: Involves the alveolar septa and pulmonary interstitium rather than the alveolar spaces. Commonly caused by viruses or atypical bacteria like Mycoplasma pneumoniae.

Stages of Lobar Pneumonia

• 1. Congestion (Day 1-2)
  • The affected lobe becomes heavy and red.
  • Engorgement of the pulmonary capillaries occurs.
  • Exudation of protein-rich fluid into the alveolar spaces begins.
• 2. Red Hepatization (Day 3-4)
  • The lung resembles liver tissue (hepatization).
  • Alveolar spaces are filled with exudate containing red blood cells, neutrophils, and fibrin.
  • The lobe appears red and firm.
• 3. Gray Hepatization (Day 5-7)
  • Disintegration of red blood cells occurs, leading to a grayish appearance.
  • Fibrinopurulent exudate fills the alveoli.
  • The lung remains firm but is no longer congested.
• 4. Resolution (Day 8 onwards)
  • Enzymatic digestion of the exudate occurs.
  • Macrophages remove debris through lymphatics or expectoration.
  • The lung parenchyma returns to normal architecture.

Gross pathology

• Bronchopneumonia Pathology
  • Multiple, small areas of consolidation are scattered throughout one or several lobes, often bilateral and basal.
  • The lesions are usually elevated, dry, and granular with a gray-red to yellow coloration.
  • Histologically, there is suppurative inflammation in the airways and alveoli.
• Interstitial Pneumonia Pathology
  • Inflammation is confined to the alveolar septa and pulmonary interstitium.
  • Infiltration by lymphocytes, macrophages, and plasma cells.
  • Alveolar spaces are generally free of exudate.
  • Commonly caused by viruses and atypical organisms.
• Complications of Pneumonia
  • Abscess Formation: Necrosis of lung tissue leading to cavity formation filled with pus.
  • Pleural Effusion: Accumulation of fluid in the pleural space; may become infected (empyema).
  • Bacteremia: Spread of bacteria into the bloodstream, potentially leading to sepsis.
  • Fibrosis: Scarring of lung tissue due to unresolved inflammation.
  • Organization: Exudate may organize into fibrous tissue, causing permanent lung damage.
• Host Factors Influencing Pathology
  • Age: Extremes of age have reduced immune defenses.
  • Immunosuppression: Conditions like HIV/AIDS, chemotherapy, or chronic diseases impair immune response.
  • Chronic Lung Diseases: COPD, bronchiectasis, and cystic fibrosis alter normal lung architecture and defenses.
  • Smoking: Damages mucociliary clearance and immune function.
• Microscopic Features
  • Alveolar Exudate: Contains neutrophils, fibrin, red blood cells, and bacteria.
  • Alveolar Walls: May be thickened due to edema and inflammatory infiltrate.
  • Bronchioles and Bronchi: Show signs of inflammation with mucus and cellular debris.
• Pathological Diagnosis
  • Histopathology: Examination of lung tissue samples can confirm the type and stage of pneumonia.
  • Cytology: Analysis of sputum or bronchoalveolar lavage fluid for cellular content and microorganisms.
  • Microbiological Cultures: Identify the causative organism to guide appropriate antimicrobial therapy.
• Conclusion
  • The pathology of pneumonia involves a complex interplay between the infecting organism and the host's immune response. The resultant inflammation leads to consolidation of lung tissue and impairment of gas exchange.
  • Understanding these pathological changes is essential for diagnosis, management, and prevention of complications associated with pneumonia.

  Microbiological Causes

  Organism	Details	Investigations	Treatment
  SARS-CoV-2. COVID-19	Highly infectious coronavirus. Continuous Cough, loss of taste/smell, fever and fatigue. High risk co-morbidity, the elderly, the immunosuppressed and the obese. In the UK, black, Asian and ethnic minority (BAME)	COVID test, CXR shows bilateral changes, CT shows bilateral ground glass opacities.	High flow oxygen, VTE prophylaxis. Dexamethasone and Anti-virals, e.g. remdesivir. Some need ITU and ventilation and proning.
  Streptococcus pneumoniae	Commonest. 70%. Middle aged. Cough with green/rusty sputum, fever, pleurisy. Associated HSV cold sores. Main cause of lobar pneumonia. Cavities with serotype 3	Sputum, blood and urine - pneumococcal antigen	Penicillin (if allergic, Erythromycin) e.g., Treat with Benzyl Penicillin 1-2 g 6 hrly
  Mycoplasma pneumoniae	Children and young adults. Autumnal and 3–4-year epidemic cycle atypical pneumonia - cough and sputum absent in 1/3 cases. Preceding flu-like symptoms usually, e.g. headache, myalgia, GI upset before onset of respiratory symptoms Myocarditis, pericarditis, erythema multiforme, haemolytic anaemia, myalgia, arthralgia, meningo-encephalitis, cold agglutinins	Serology for IgM and IgG antibodies (acute and convalescent titres), cold agglutinins (in 50%).	Erythromycin, Azithromycin, Clarithromycin or doxycycline
  Haemophilus influenzae	Especially seen in the elderly, heavy smokers and COPD patients	No specific features; may be broncho- or lobar pneumonia	Cefuroxime or Co-Amoxiclav
  Moraxella catarrhalis	Common cause of bronchopneumonia especially in the elderly and COPD patients	No specific features; may be broncho- or lobar pneumonia	Cefuroxime or Co-Amoxiclav
  Staphylococcus aureus	More common following influenza pneumonia, IV drug, central line Severe pneumonia, post-influenza maybe rapidly fatal. Abscess formation, pneumothorax, empyema relatively common. Septicaemia: infective emboli causing abscesses in other organs.	Nodular consolidation and cavitation on CXR.	Flucloxacillin
  Chlamydia psittaci 'Psittacosis'	Acquired from avian excreta seen in those exposed to birds. Malaise, high fever, dry cough, hepatosplenomegaly and rose spots on the abdomen. Hepatitis, encephalitis, renal failure. Hepatosplenomegaly.	Serology for Chlamydia antibodies - complement-fixing antibodies (immunofluorescent tests to distinguish types).	Erythromycin, Azithromycin, Clarithromycin or Doxycycline
  Chlamydophila pneumoniae	Causes 5-10% of community-acquired Often mild flu-like illness or acute bronchitis recovering spontaneously. Pneumonia also usually mild	CXR:Segmental Infiltrates, Acute and convalescent sera	Erythromycin, Azithromycin, Clarithromycin or doxycycline
  Coxiella burnetii (Q fever)	Only 1% of cases overall Influenza-like illness which causes pneumonia if it persists, often with multiple CXR lesions Endocarditis. If untreated chronic infection is fatal	Serology - complement fixing antibody. CXR: Multiple segmental shadows	Erythromycin, Azithromycin, Clarithromycin or doxycycline Hypoalbuminaemia and abnormal LFTs (raised transaminases) are common. Acute renal failure.
  Legionella pneumophilia	Infection from water system. Sporadic cases source unknown. Middle-aged and older, Recent travel, Autumn time. Outbreaks in immunocompromised individuals. x 2 in Males. Usually, 2-10 day prodromal of dry cough, confusion, headache, myalgia or diarrhoea, low WCC, Low Na, abnormal LFTs. CR shadows.	Urine for specific antigen. Immunofluorescent tests on sputum or bronchial lavage.	Erythromycin, Azithromycin, Clarithromycin or Ciprofloxacin +/? rifampicin Despite these mortality ?20%
  Klebsiella	Elderly with a history of heart or lung disease, diabetes, alcohol excess or malignancy Sudden onset, severe systemic upset, purulent, mucoid sputum (Classically redcurrant jelly). Lobar pneumonia	CXR: cavitating lesions - lung abscesses Extensive lobar consolidation with cavitation. Widespread consolidation (upper lobes)	Cefuroxime and Gentamicin
  Pseudomonas aeruginosa	Nosocomial, cystic fibrosis and neutropenic patients.	Sputum and blood culture	but it does colonise the upper airway as a commensal Ciprofloxacin or ceftazidime Anaerobes - Bacteroides Aspiration, e.g. due to stroke. Diabetics Metronidazole
  Pneumocystis jiroveci (PCP) (Previously Pneumocystis carinii)	The most common opportunistic infection in AIDS (CD4 count <200/mm3) and immunosuppressed patients High fever, dry cough, shortness of breath, tachycardia. Marked hypoxia, particularly following exertion. Fine crackles or nothing to find on auscultation. Mortality now 10%	Typical CXR - perihilar 'butterfly' ground glass shadowing. but may be normal in early disease. CT shows ground-glass shadowing, bronchial lavage or induced sputum for diagnosis by silver staining or by immunofluorescence	Long-term prophylaxis is required, e.g. with co-trimoxazole Hi-dose i.v. cotrimoxazole or i.v. pentamidine
  Viral Pneumonia	Influenza, Parainfluenza, Measles, RSV in infants, Varicella can cause severe pneumonia with multiple miliary nodular shadows which may calcify	Relevant serology	Consider Neuraminidase inhibitors if Influenza

  Clinical Features

  • Cough, possibly with purulent sputum or hemoptysis.
  • Pleuritic chest pain.
  • Shortness of breath.
  • Fever and chills.
  • Confusion, especially in elderly patients.
  • Tachypnea (increased respiratory rate).
  • Tachycardia.
  • Hypoxia (low SpO₂).
  • Dullness to percussion over affected areas.
  • Bronchial breath sounds and crackles on auscultation.

  Types of Pneumonia

  • Community-acquired: Most common type.
  • Hospital-acquired: Occurs after recent hospital discharge or inpatient stay.
  • Aspiration pneumonia: Due to inhalation of oropharyngeal contents; risk factors include stroke, decreased consciousness, esophageal pathology, neurological disorders.
  • Ventilator-associated pneumonia: Occurs in patients on mechanical ventilation.

  Severity Assessment: CURB-65 Score

  The CURB-65 score helps determine the severity of pneumonia and guides management decisions.

  CURB-65 Scoring Criteria
  Confusion (new disorientation in person, place, or time)	+1
  Urea >7 mmol/L	+1
  Respiratory rate ≥30 breaths per minute	+1
  Blood pressure (systolic <90 mmHg or diastolic ≤60 mmHg)	+1
  Age ≥65 years	+1
  Interpretation of CURB-65 Score
  0–1 Points: Low risk; consider outpatient treatment.
  2 Points: Moderate risk; consider short inpatient stay or supervised outpatient treatment.
  ≥3 Points: High risk; requires hospital admission; assess for ICU care if score is 4 or 5.

  Other Severity Markers

  • Chest X-ray showing involvement of more than one lobe.
  • PaO₂ <8 kPa on arterial blood gas.
  • Low albumin levels (<35 g/L).
  • White blood cell count <4 or >20 × 10⁹/L.
  • Positive blood cultures.

  Investigations

  • Blood Tests: FBC, U&E, CRP, LFTs, blood cultures (if CURB-65 ≥2).
  • Sputum Cultures: Especially if CURB-65 ≥3 or not responding to antibiotics.
  • Urinary Antigen Tests: For pneumococcal and legionella antigens in severe cases.
  • Arterial Blood Gas (ABG): To assess oxygenation and ventilation status.
  • Chest X-Ray: To identify areas of consolidation, effusions, or cavitations.

  Management

  • ABCDE assessment: Ensure airway patency, breathing adequacy, circulation stability, disability assessment, and exposure/environmental control.
  • Oxygen Therapy:
    • Administer supplemental oxygen to maintain target saturations (94–98% for most patients; 88–92% in COPD patients).
  • Hydration: Provide intravenous fluids if the patient is dehydrated.
  • Symptomatic Relief: Antipyretics for fever; analgesics for pain.
  • Positioning: Encourage the patient to sit up to improve ventilation.
  • Chest Physiotherapy: May assist in clearing secretions.
  • Antibiotics: Administer appropriate antibiotics as soon as possible, ideally within one hour of diagnosis.
  • Consider CPAP or NIV: If hypoxia persists or if there is hypercapnia.
  • Liaise with ITU: If hypoxia/hypercapnia or acidosis continues despite treatment.

  Antibiotic Therapy

  Severity	Antibiotics
  Low Severity (CURB-65 0–1)	Amoxicillin 500 mg orally TDS for 5-7 days. Penicillin allergy: Doxycycline 200 mg on day 1, then 100 mg once daily.
  Moderate Severity (CURB-65 2)	Amoxicillin 500 mg–1 g TDS plus Clarithromycin 500 mg BD. Penicillin allergy: Levofloxacin 500 mg once or twice daily.
  High Severity (CURB-65 ≥3)	Co-amoxiclav 1.2 g IV TDS plus Clarithromycin 500 mg IV BD. Penicillin allergy: Levofloxacin 500 mg IV BD.
  Hospital-Acquired Pneumonia (HAP)	Mild HAP: Amoxicillin 500 mg TDS PO plus Metronidazole 400 mg TDS PO. Severe HAP: Co-amoxiclav 1.2 g IV TDS; if penicillin allergy, use Levofloxacin 500 mg IV/PO BD.
  Aspiration Pneumonia	Amoxicillin 500 mg TDS IV plus Metronidazole 500 mg TDS IV. Penicillin allergy: Clarithromycin 500 mg BD IV plus Metronidazole 500 mg TDS IV.

  Criteria for ITU Admission

  • PaO₂ <8 kPa on 60% oxygen.
  • PaCO₂ >6.4 kPa.
  • Patient is exhausted, drowsy, or unconscious.
  • Shock or hemodynamic instability.

  Complications

  • Respiratory failure.
  • Sepsis and septic shock.
  • Pleural effusion and empyema.
  • Lung abscess formation.
  • Acute Respiratory Distress Syndrome (ARDS).

  Prevention

  • Vaccinations:
    • Pneumococcal vaccine for at-risk populations.
    • Annual influenza vaccination.
  • Lifestyle Modifications:
    • Smoking cessation.
    • Alcohol moderation.
  • Infection Control:
    • Hand hygiene practices.
    • Avoiding close contact with individuals with respiratory infections.

  Conclusion

  Early recognition and appropriate management of community-acquired pneumonia are crucial to reduce morbidity and mortality. Severity assessment tools like the CURB-65 score aid in determining the appropriate level of care. Prompt initiation of empirical antibiotic therapy, supportive measures, and monitoring for complications are key components of effective treatment.

  References

  • National Institute for Health and Care Excellence (NICE) Guidelines on Pneumonia.
  • British Thoracic Society (BTS) Guidelines for the Management of Community-Acquired Pneumonia.
  • World Health Organization (WHO) Recommendations.