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PNEUMONIA - COMPLETE CLASS PREPARATION GUIDE

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1. DEFINITION

• Harrison's Principles of Internal Medicine 22E, p. 1066

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2. CLASSIFICATION - THE BIG PICTURE

PNEUMONIA
├── Community-Acquired (CAP)
│   └── Outpatient / Non-ICU / ICU
├── Hospital-Acquired (HAP)
│   └── Onset ≥48 hrs after admission
├── Ventilator-Associated (VAP)
│   └── Onset ≥48–72 hrs after intubation
└── Aspiration Pneumonia
    └── 5–15% of CAP cases
    (Note: "Healthcare-Associated Pneumonia" (HCAP) is now DISCONTINUED
     — it over-predicted resistant organisms & increased broad-spectrum
       antibiotic use unnecessarily)

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3. PATHOPHYSIOLOGY FLOWCHART

ENTRY OF PATHOGENS
(microaspiration / inhalation / direct mucosal spread)
         ↓
LUNG MICROBIOTA DISRUPTED
(normally kept in homeostasis by microbial entry, elimination,
 regional growth conditions — pH, O2, temperature)
         ↓
INFLAMMATORY TRIGGER
(epithelial / endothelial injury)
         ↓
CYTOKINE / CHEMOKINE RELEASE
(promotes growth of S. pneumoniae, Pseudomonas aeruginosa)
         ↓
POSITIVE FEEDBACK LOOP
(inflammation → nutrient release → more bacterial growth)
         ↓
ALVEOLAR EXUDATE + CONSOLIDATION

Stages of Lobar Pneumonia (classic — best described for pneumococcal):

Pattern: Lobar = typical bacterial CAP | Bronchopneumonia = nosocomial | Interstitial = viral (but Pneumocystis is actually alveolar despite appearance)

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4. ETIOLOGY - "WHO CAUSES IT?"

Typical vs. Atypical Organisms

CAP Organisms by Site of Care (Harrison's Table 131-1):

Special Epidemiologic Exposures to Remember:

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5. CLINICAL FEATURES FLOWCHART

PATIENT PRESENTS WITH:
Fever + Cough + Sputum + Dyspnea + Pleuritic chest pain
                ↓
ASSESS FOR PNEUMONIA
                ↓
    ┌───────────────────────────────────┐
    │ KEY DIFFERENTIATING FEATURES:    │
    │ • Abrupt onset → TYPICAL         │
    │ • Gradual onset → ATYPICAL       │
    │ • Productive cough → bacterial   │
    │ • Dry cough → viral / Mycoplasma │
    │ • "Rusty" sputum → pneumococcal  │
    │ • "Currant jelly" → Klebsiella   │
    │ • Blood-streaked + pleurisy      │
    │   → S. pyogenes / S. pneumoniae  │
    └───────────────────────────────────┘
                ↓
Also check for: GI symptoms (abdominal pain, diarrhea) → suggests LEGIONELLA
Extra-pulmonary features:
  - Rash + arthralgia → Mycoplasma
  - Relative bradycardia + hyponatremia → Legionella
  - Bullous myringitis → Mycoplasma

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6. DIAGNOSIS FLOWCHART

SUSPECTED PNEUMONIA
        ↓
CHEST X-RAY (MANDATORY)
  → Confirms infiltrate / consolidation
  → Lobar = typical bacterial
  → Patchy bilateral = atypical / viral
  → Cavitation = Klebsiella, Staph, anaerobes, TB
  → Empyema = S. pyogenes (30–40% cases)
        ↓
LABORATORY WORKUP
  ┌─────────────────────────────────────┐
  │ ALL hospitalized patients:          │
  │  • CBC with differential           │
  │  • BUN, creatinine, electrolytes   │
  │  • LFTs                            │
  │  • Blood cultures (x2 before Abx) │
  │  • ABG / O2 saturation            │
  │  • Sputum Gram stain + culture     │
  └─────────────────────────────────────┘
        ↓
  ┌────────────────────────────────────────┐
  │ SPECIAL TESTS (when indicated):        │
  │  • Urinary Ag: Legionella, S. pneumo   │
  │  • Procalcitonin (guide Abx use)       │
  │  • Multiplex PCR (mPCR) panels         │
  │  • Bronchoscopy + BAL (ICU/atypical)   │
  │  • HIV test (if at risk)               │
  │  • Pleural fluid analysis if effusion  │
  └────────────────────────────────────────┘
        ↓
ASSESS SEVERITY → CURB-65 / PSI

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7. SEVERITY SCORING

CURB-65 (Simple - Best for quick bedside use)

Score 0–1 → Outpatient treatment
Score 2   → Short hospitalization or supervised outpatient
Score 3–5 → HOSPITALIZE (score 4–5 → consider ICU)

PSI (Pneumonia Severity Index)

• 20 variables, 5 risk classes
• Class I–II: Outpatient
• Class III: Brief observation
• Class IV–V: Hospitalize (Class V → consider ICU)

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8. MANAGEMENT FLOWCHART (CAP)

DIAGNOSED CAP
      ↓
DETERMINE SITE OF CARE (CURB-65 / PSI)
      ↓
 ┌────────────────────────────────────────────────────────────┐
 │ OUTPATIENT (mild CAP, no comorbidities):                   │
 │   1st line: Amoxicillin OR Doxycycline OR Macrolide        │
 │   (Azithromycin 500mg day 1, then 250mg × 4 days)         │
 └────────────────────────────────────────────────────────────┘
      ↓
 ┌────────────────────────────────────────────────────────────┐
 │ OUTPATIENT (with comorbidities: COPD, DM, renal/liver      │
 │ disease, malignancy, asplenia, immunosuppression):         │
 │   Respiratory FQ (levofloxacin / moxifloxacin)            │
 │   OR β-lactam + macrolide combination                      │
 └────────────────────────────────────────────────────────────┘
      ↓
 ┌────────────────────────────────────────────────────────────┐
 │ HOSPITALIZED NON-ICU:                                      │
 │   β-lactam (ampicillin-sulbactam / ceftriaxone)           │
 │   + Macrolide (azithromycin)                              │
 │   OR Respiratory Fluoroquinolone MONOTHERAPY               │
 └────────────────────────────────────────────────────────────┘
      ↓
 ┌────────────────────────────────────────────────────────────┐
 │ ICU (severe CAP):                                          │
 │   β-lactam + azithromycin                                 │
 │   OR β-lactam + respiratory FQ                            │
 │   + COVER for MRSA if suspected:                          │
 │     → Add Vancomycin or Linezolid                         │
 │   + COVER for Pseudomonas if risk factors:                │
 │     → Piperacillin-tazobactam or cefepime                 │
 └────────────────────────────────────────────────────────────┘
      ↓
HAP / VAP Treatment:
   → Broad-spectrum: Piperacillin-tazobactam / Cefepime / Carbapenem
   → Add Vancomycin / Linezolid if MRSA risk
   → De-escalate based on culture results

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9. SPECIAL ORGANISMS - QUICK REVISION

Streptococcus pneumoniae (Most common CAP)

• Rusty/blood-tinged sputum, lobar consolidation
• Drug of choice: Penicillin (IV: MIC ≤2 μg/mL = susceptible)
• Macrolide resistance increasing (~40% in USA)
• Fluoroquinolone resistance: <2%
• Risk factors for penicillin resistance: age <2 or >65, recent antibiotics, HIV, daycare

Legionella pneumophila

• Relative bradycardia, hyponatremia, diarrhea, confusion
• Diagnosis: Urinary antigen test (gold standard)
• Treatment: Fluoroquinolone or Azithromycin (not beta-lactam!)

Mycoplasma pneumoniae

• Walking pneumonia, young adults
• Dry cough, patchy infiltrate, extrapulmonary features (hemolytic anemia, rash, bullous myringitis)
• Treatment: Macrolide or Doxycycline

Klebsiella pneumoniae

• Alcoholics, currant jelly sputum, upper lobe cavitation
• Treatment: 3rd gen cephalosporin or carbapenem

Staphylococcus aureus

• Post-influenza, IV drug users, nursing home
• Causes cavitation and empyema
• Treatment: Vancomycin (if MRSA), Nafcillin (if MSSA)

Aspergillus

• Neutropenic patients, halo sign on CT
• Treatment: Voriconazole

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10. COMPLICATIONS FLOWCHART

PNEUMONIA → NOT IMPROVING?
         ↓
  ┌──────────────────────────────────┐
  │ ASK:                             │
  │ 1. Right organism? (cultures)   │
  │ 2. Right antibiotic?            │
  │ 3. Right dose / route?          │
  │ 4. Complication developed?      │
  └──────────────────────────────────┘
         ↓
POSSIBLE COMPLICATIONS:
  • Parapneumonic effusion → if large → tap it
  • Empyema → chest drain / decortication
  • Lung abscess → prolonged antibiotics, percutaneous drain
  • Bacteremia / Sepsis → blood cultures + ICU care
  • ARDS → mechanical ventilation
  • Respiratory failure
  • Organizing pneumonia (COP) — post-infectious

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11. HAP vs. VAP

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12. ASPIRATION PNEUMONIA vs. PNEUMONITIS

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13. PREVENTION

• Pneumococcal vaccine (PCV20 or PCV15 + PPSV23) - all adults ≥65 and at-risk younger patients
• Influenza vaccine - annual, all ages ≥6 months
• Early mobilization + head-of-bed elevation (VAP prevention)
• Oral chlorhexidine rinse in ventilated patients

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14. KEY EXAM Q&A

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15. ONE-LINE MEMORY TRICKS

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