Pneumonia

PNEUMONIA

OUTLINE

– Definition

– Classification

– Causes

– Clinical Presentation

– Investigations

– Complications

– Treatment

DEFINITION

Pneumonia is an infection of the lungs that causes inflammation of lung tissues. It can be caused by bacteria, viruses, or fungi. If managed poorly, it can be a life-threatening condition.

CLASSIFICATION

– Community-acquired pneumonia

– Hospital-acquired pneumonia

– Aspiration pneumonia

– Pneumonia in immunocompromised individuals

COMMUNITY-ACQUIRED PNEUMONIA

Community-acquired pneumonia refers to pneumonia contracted by individuals with little contact with the healthcare system. It can be caused by various pathogens, including Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, Klebsiella pneumoniae, Mycoplasma pneumoniae, Legionella pneumophila, and Staphylococcus aureus.

HOSPITAL-ACQUIRED PNEUMONIA

Hospital-acquired pneumonia refers to pneumonia that is not present at the time of hospital admission but appears clinically 2 or more days after hospitalization. It is also known as nosocomial pneumonia and is commonly caused by pathogens such as Pseudomonas aeruginosa, Staphylococcus aureus (including methicillin-resistant strains), Klebsiella pneumoniae, and Escherichia coli.

ASPIRATION PNEUMONIA

Aspiration pneumonia occurs when gastric contents are aspirated into the lungs. This usually happens during periods of impaired consciousness and is often associated with anaerobic and gram-negative bacterial infections. The pneumonia typically affects the apical and posterior segments of the right lower lobe.

PNEUMONIA IN IMMUNOCOMPROMISED INDIVIDUALS

Immunocompromised individuals are at higher risk of developing pneumonia due to their weakened immune system. This includes people with HIV infection, certain hematological malignancies, malnutrition, and those undergoing chemotherapy. Pneumocystis jiroveci is a common cause of pneumonia in these individuals.

The pathophysiology of pneumonia involves several key processes:

  1. Microbial invasion: Pneumonia usually begins when microorganisms, such as bacteria, viruses, fungi, or atypical pathogens, gain entry into the lungs. This can occur through inhalation of airborne pathogens or by aspiration of microorganisms from the upper respiratory tract or stomach.
  2. Alveolar inflammation: The presence of pathogens triggers an immune response, leading to inflammation in the alveoli, which are the tiny air sacs in the lungs where gas exchange takes place. The inflammatory response involves the recruitment of immune cells, especially neutrophils, to the site of infection.
  3. Increased vascular permeability: Inflammatory mediators released during the immune response cause increased permeability of the blood vessels in the lungs. This leads to leakage of fluid, proteins, and immune cells from the bloodstream into the alveoli, resulting in consolidation and impaired gas exchange.
  4. Consolidation and impaired gas exchange: As the immune response progresses, the alveoli fill with inflammatory exudate, consisting of fluid, immune cells, and debris from the infection. This consolidation impairs the normal exchange of oxygen and carbon dioxide, leading to respiratory symptoms such as cough, shortness of breath, and decreased oxygen saturation.
  5. Impaired mucociliary clearance: The normal clearance mechanism of the respiratory tract, which involves the coordinated movement of cilia and mucus, is disrupted in pneumonia. The excess fluid and inflammation inhibit the ciliary function and impair the ability to clear mucus and pathogens from the airways, further contributing to lung infection.
  6. Systemic response: Severe pneumonia can trigger a systemic inflammatory response, with the release of pro-inflammatory cytokines into the bloodstream. This systemic response can lead to symptoms such as fever, increased heart rate, and changes in blood pressure.

The specific pathophysiology of pneumonia can vary depending on the causative organism, the individual’s immune response, and other factors. Understanding the underlying pathophysiological processes is crucial for appropriate diagnosis, treatment, and prevention of complications associated with pneumonia.

CLINICAL PRESENTATION

Symptoms:

– Fever

– Productive cough

– Pleuritic chest pain

– Breathlessness

– Arthralgia

Note: Symptoms may be less pronounced in elderly and immunocompromised individuals.

Signs:

– Rapid breathing (tachypnea)

– Use of accessory muscles for breathing

– Restricted movement on the affected side due to pain

– Fever

– Rapid heartbeat (tachycardia)

– Normal or reduced blood pressure

– Signs of lung consolidation

– Decreased oxygen saturation

CURB-65 CRITERIA

The CURB-65 criteria are used to assess patients with community-acquired pneumonia and guide treatment decisions:

– C – Confusion

– U – Urea > 7 mmol/L

– R – Respiratory rate > 30 breaths per minute

– B – Blood pressure (systolic \< 90 mmHg, diastolic \< 60 mmHg)

– Age > 65

Based on the score, patients are categorized as follows:

– 0-1: Treat as an outpatient

– 2: Admit to the hospital

– 3 or more: Requires ICU/HDU care

INVESTIGATIONS

-Chest X-ray for consolidation

– Full blood count for leucocytosis with differential neutrophillia

-Bio-inflammatory markers: Erythrocyte sedimentation rate(ESR), C-reactive protein(CRP)

– Sputum microscopy and culture

– Acid-fast bacilli staining using Zeihl-Neelsen stain

– Blood culture and sensitivity

– Blood urea and electrolyte levels

COMPLICATIONS

– Pleural effusion

– Lung abscess

– Empyema

– Pneumothorax

– Pericarditis and pericardial effusion

– Sepsis with multi-organ failure

– Meningitis

– Acute respiratory distress syndrome (ARDS)

TREATMENT

– Antibiotic therapy: Start empiric antibiotics based on suspected pathogens while awaiting culture results.

– Antipyretics for temperature control-Paracetamol

– Intravenous fluid therapy

Specific antibiotic regimens:

– Gram-positive organisms: Amoxiclav 1.2 g every 8 hours for 7 days

– Gram-negative organisms: Intravenous ceftriaxone 2 g once daily for 7 days

– Anaerobic organisms in aspiration pneumonia: Intravenous metronidazole 500 mg every 8 hours for 7 days

– Atypical organisms: Oral or intravenous azithromycin 500 mg once daily for 3 days

Switch to oral therapy once the intravenous course is completed and the temperature has completely settled for at least 24 hours.