What is lobar pneumonia and how is it treated?

What is Lobar Pneumonia?

Lobar pneumonia is a distinct bacterial infection characterized by homogeneous consolidation of one or more complete lung lobes, caused primarily by Streptococcus pneumoniae, with filling of alveolar spaces by inflammatory exudate containing edema fluid and neutrophils. 1, 2

Pathophysiology and Clinical Presentation

• Lobar pneumonia creates a uniform, dense consolidation pattern affecting entire anatomic lobes, distinguishing it from bronchopneumonia which shows patchy, peribronchiolar inflammation 1
• The classic histological patterns include congestion (serous exudation with bacteria), red hepatization (fibrin and red blood cells), and gray hepatization (fibrin and neutrophils), though these patterns typically occur simultaneously rather than sequentially 2
• Patients present with acute onset (3-5 days) of fever, chills, rigors, pleuritic chest pain, productive cough with purulent sputum, and dyspnea 3
• Physical examination reveals focal consolidation findings (dullness to percussion, bronchial breath sounds, egophony) and may show tachypnea, tachycardia, or hypotension indicating systemic inflammatory response 3
• Chest radiograph demonstrates unilateral lobar or segmental consolidation, though multilobar involvement occurs in approximately 25% of cases and significantly increases mortality risk (OR 2.57) 3, 4

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Treatment of Lobar Pneumonia

Immediate Severity Assessment

Before initiating treatment, immediately assess for ICU-level care using major and minor criteria, as this determines antibiotic route and respiratory support intensity. 5

Major Criteria (any one requires ICU admission):

• Mechanical ventilation with endotracheal intubation 5
• Septic shock requiring vasopressors 5

Minor Criteria (≥3 requires ICU admission):

• Respiratory rate ≥30/min 5
• PaO₂/FiO₂ ratio ≤250 5
• Multilobar infiltrates 3, 5
• Confusion, uremia, leukopenia, thrombocytopenia, hypothermia 5
• Hypotension requiring aggressive fluid resuscitation 5
• Systolic blood pressure <90 mmHg 3

Diagnostic Workup Before Antibiotics

Obtain blood cultures (at least 2 sets) and respiratory specimens (sputum or endotracheal aspirate) before initiating antibiotics, as blood cultures are positive in 25% of pneumococcal cases and guide definitive therapy. 5, 6

• Arterial blood gas or pulse oximetry to assess oxygenation and need for supplemental oxygen 3
• Complete blood count (typically elevated WBC with left shift), basic metabolic panel, liver function tests 3
• Chest radiograph (posteroanterior and lateral preferred) to confirm consolidation and assess for complications (effusions, cavitation, multilobar involvement) 3
• Consider thoracentesis if large pleural effusion present to rule out empyema 3

Empiric Antibiotic Therapy

Initiate empiric antibiotics immediately after obtaining cultures if clinical criteria for pneumonia are met (fever, leukocytosis, purulent secretions, respiratory distress). 5

For Hospitalized Patients (Non-ICU):

• Beta-lactam (amoxicillin-clavulanate 875-125 mg PO q12h or ceftriaxone 1-2g IV q24h) PLUS macrolide (azithromycin 500mg PO/IV daily) 3, 5, 6
• This combination targets S. pneumoniae (most common), H. influenzae, and atypical organisms (Mycoplasma, Legionella, Chlamydophila) 3

For ICU Patients:

• Beta-lactam (ceftriaxone 2g IV q24h or cefotaxime) PLUS azithromycin 500mg IV daily 5
• If Staphylococcus aureus suspected (post-influenza, cavitary lesions, severe sepsis): add vancomycin 15-20 mg/kg IV q8-12h or linezolid 600mg IV q12h for MRSA coverage 5
• If Pseudomonas risk factors present (structural lung disease, recent hospitalization, prior antibiotics): use antipseudomonal beta-lactam (piperacillin-tazobactam 4.5g IV q6h) 3

Special Considerations:

• Penicillin G remains drug of choice for penicillin-susceptible S. pneumoniae (MIC ≤0.06 mcg/mL) 3
• Drug-resistant S. pneumoniae is increasing and associated with higher mortality; higher-dose beta-lactams overcome most resistance 3
• For true penicillin allergy: respiratory fluoroquinolone (levofloxacin 750mg daily or moxifloxacin 400mg daily) 3

Monitoring and Treatment Adjustment

Reassess clinical response at 48-72 hours: if cultures are sterile and no clinical improvement occurs, strongly consider stopping antibiotics and investigating alternative diagnoses (tuberculosis, atelectasis, non-infectious causes). 5, 6

Clinical Response Indicators:

• Defervescence (temperature <37.8°C) 7
• Improved oxygenation and decreased respiratory rate 5
• Decreased purulent sputum production 3
• Improved appetite and functional status 5

If Clinical Improvement Occurs:

• Continue treatment for 5-7 days total for uncomplicated pneumonia 3, 5, 1
• Short-course therapy (mean 2.4 days after fever resolution) is effective for moderately severe cases 7
• Switch from IV to oral antibiotics when hemodynamically stable, improving clinically, and able to tolerate oral intake 3

If No Improvement by 72 Hours:

• Repeat chest radiograph to assess for complications (effusion, empyema, abscess, progression) 3
• Consider CT chest for better characterization, especially if tuberculosis suspected 6
• Obtain additional cultures (blood, pleural fluid if effusion present) 3
• Broaden antibiotic coverage for resistant organisms or consider non-bacterial etiologies 5
• Evaluate for extrapulmonary complications (meningitis occurs in 11-24% of fatal cases, acute heart failure in 26%) 2

Critical Pitfalls to Avoid

• Do not delay antibiotics waiting for culture results in severely ill patients—mortality increases with delayed treatment 5
• Do not assume negative blood cultures rule out bacterial pneumonia—only 25% of pneumococcal pneumonia cases have positive blood cultures 3, 5
• A sterile respiratory culture at 48-72 hours (without recent antibiotic changes) virtually rules out bacterial pneumonia—stop antibiotics and reconsider diagnosis 3, 5
• Multilobar involvement significantly increases mortality risk (OR 2.57)—these patients require closer monitoring and consideration for ICU admission 4
• Always consider tuberculosis in upper lobe consolidation—obtain acid-fast bacilli smears and mycobacterial cultures, especially if no improvement on standard antibiotics 6
• HIV-infected patients have 100-fold higher risk of pneumococcal bacteremia—lower threshold for blood cultures and hospitalization 3