Quick Recap
Covers severe CAP requiring ICU admission; HAP/VAP addressed as a distinct sub-section given differing empiric coverage. Nests under Acute Respiratory Failure.
1. Definition
CAP: pneumonia present on admission or presenting within 48h of hospital admission.
HAP: first positive culture >48h after hospital admission, not ventilator-associated.
VAP: first positive culture >48h after intubation/mechanical ventilation.
Severe CAP (ATS/IDSA 2019): 1 major OR >=3 minor criteria:
- Major: need for invasive mechanical ventilation; septic shock requiring vasopressors
- Minor: RR >=30; P/F <=250; multilobar infiltrates; confusion/disorientation; BUN >=20 mg/dL; WBC <4,000/mm3; platelets <100,000/mm3; core temp <36C; hypotension requiring aggressive fluid resuscitation
2. Pathophysiology
Microaspiration or inhalation of pathogens overwhelms mucociliary/immune defenses -> alveolar inflammatory exudate -> consolidation, V/Q mismatch, shunt. Severe CAP reflects an exaggerated systemic inflammatory response (often meeting sepsis criteria) superimposed on the local alveolar process. HAP/VAP arise from a hospital microbiome shifted toward resistant organisms (Pseudomonas, MRSA) due to antibiotic pressure and altered oropharyngeal flora in ventilated/hospitalized patients.
Typical CAP pathogens: S. pneumoniae (most common), H. influenzae, S. aureus, M. catarrhalis, atypicals (Mycoplasma, Legionella, Chlamydophila), respiratory viruses (influenza, RSV, SARS-CoV-2, others). Emerging community MRSA/Pseudomonas in select populations.
HAP/VAP pathogens: more resistant gram-negatives (Pseudomonas, Enterobacterales), MRSA — risk rises with recent hospitalization/antibiotic exposure.
3. Immediate Stabilization (ABCDE)
Airway: intubate for respiratory failure per major criterion; anticipate difficult secretions management.
Breathing: O2/HFNC/NIV per severity; lung-protective ventilation if ARDS develops (common complication of severe pneumonia).
Circulation: treat septic shock per Surviving Sepsis bundle if present (major criterion) — 30 mL/kg crystalloid if hypotensive/lactate >=4, vasopressors for MAP >=65 if fluid-refractory.
Disability: assess for confusion/disorientation (minor severity criterion and possible hypoxemia/sepsis-associated encephalopathy).
Exposure: temperature (hypothermia <36C is a minor severity criterion, not just fever).
Checklist:
4. Focused History
Onset and symptom timeline; sick contacts/exposures (birds -> Chlamydophila psittaci, farm animals -> Coxiella burnetii, rabbits -> tularemia); travel history; influenza/COVID exposure or vaccination status; aspiration risk (dysphagia, altered consciousness, recent vomiting); recent hospitalization/antibiotics (resistance risk); prior respiratory culture results (documented MRSA/Pseudomonas colonization); immunosuppression/HIV risk factors; smoking; comorbidities (diabetes, CKD, liver disease, heart failure — modify antibiotic choice per guidelines).
5. Examination + POCUS
Focal or multifocal crackles, bronchial breath sounds, dullness to percussion (consolidation/effusion), signs of respiratory distress. Assess for parapneumonic effusion/empyema (dullness, reduced breath sounds).
POCUS: focal consolidation with air bronchograms ("hepatization" sign), effusion characterization (simple vs complex/septated suggesting empyema) — guides need for diagnostic/therapeutic thoracentesis.
6. Syndrome Identification
Alveolar filling/consolidation syndrome, confirm severity tier (severe CAP vs HAP vs VAP) as this dictates empiric antibiotic breadth.
7. Differential Diagnosis
Tier | Examples |
Must exclude/co-exist | ARDS (severe pneumonia is a top ARDS trigger), sepsis/septic shock |
Mimics | Pulmonary embolism/infarction, malignancy, hypersensitivity pneumonitis, granulomatosis with polyangiitis, pulmonary edema, eosinophilic pneumonia |
Complications suggesting failure to respond | Parapneumonic effusion/empyema, metastatic infection (meningitis, endocarditis, arthritis — ~10% of pneumococcal pneumonia) |
Special exposures | Legionella, Coxiella, psittacosis, tularemia, endemic fungi, PCP/opportunistic infection if HIV/immunosuppressed |
8. Severity Assessment
PSI (Pneumonia Severity Index) — preferred by guidelines for mortality risk stratification; hospitalize if class >=3.
CURB-65 — simpler bedside alternative; hospitalize if score >=2.
ATS/IDSA severe CAP criteria (Section 1) — determines direct ICU admission.
Note: patients admitted to a ward who later deteriorate to ICU have worse outcomes than those triaged directly to ICU — err toward direct ICU admission when criteria are met.
9. Investigations
- Bedside: ABG, POCUS (consolidation/effusion), vitals-based severity scoring
- Labs: CBC, renal (BUN for severity/PSI), electrolytes, LFTs, lactate
- Microbiology (mandatory for severe CAP): blood cultures x2 (before antibiotics), sputum/ETT aspirate Gram stain + culture, Legionella and pneumococcal urinary antigen, influenza/SARS-CoV-2 testing, multiplex respiratory PCR where available
- Imaging: CXR (mandatory); CT chest if diagnosis unclear, complicated effusion, or non-resolving pneumonia
- Do not delay antibiotics for diagnostic sampling
- Repeat: reassess clinically at 24-48h; repeat imaging if failing to improve or clinical deterioration
10. POCUS
Consolidation with air bronchograms confirms alveolar filling. Effusion assessment: anechoic/simple (likely sterile transudate/exudate, may not need drainage) vs complex/septated/loculated (suggests empyema — needs drainage, consider CT and cardiothoracic/interventional pulmonology involvement).
11. Evidence-Based Management
First hour: blood cultures before antibiotics; empiric antibiotics per risk stratification (below); septic shock bundle if major criterion met.
Empiric antibiotics — Severe CAP, standard risk (no prior MRSA/Pseudomonas isolation):
- Beta-lactam (ceftriaxone/cefotaxime/ampicillin-sulbactam) + azithromycin, OR
- Beta-lactam + respiratory fluoroquinolone (levofloxacin 750 mg or moxifloxacin), OR
- Respiratory fluoroquinolone + aztreonam if penicillin-allergic
Pseudomonas risk (prior isolation, recent hospitalization, local risk factors): add/substitute piperacillin-tazobactam 4.5g q6h, OR cefepime 2g q8h, OR ceftazidime 2g q8h, OR imipenem 500mg q6h, OR meropenem 1g q8h, OR aztreonam 2g q8h.
MRSA risk: add vancomycin 15 mg/kg q12h (trough-adjusted) OR linezolid 600mg q12h OR ceftaroline 600mg IV q12h. (Daptomycin is inactivated by pulmonary surfactant — never use for pneumonia.)
Influenza-positive with radiographic CAP: start oseltamivir (ideally <48h symptom onset) AND standard antibacterial coverage; de-escalate antibacterials based on clinical course.
First 24-48h: reassess response; if deteriorating, consider: uncovered/resistant pathogen, complication (empyema, metastatic infection), or non-infectious mimic (Section 7).
Duration: minimum 5 days for prompt responders; S. aureus pneumonia 2-4 weeks (4 weeks if bacteremic without endocarditis); switch IV->PO once clinically improving, hemodynamically stable, and tolerating oral intake.
HAP/VAP empiric therapy: broader gram-negative and MRSA coverage per local antibiogram, guided by 2016 IDSA/ATS nosocomial pneumonia guideline — see dedicated ventilator-associated pneumonia protocol under ICU bundle/complications for full regimen detail.
12. Organ Support
Oxygen/ventilatory support per severity; fluid resuscitation and vasopressors if septic shock; consider prone positioning/lung-protective ventilation if ARDS supervenes; nutrition; glycemic control; chest tube/pigtail drainage for empyema.
13. Disease-Specific Therapy
See Section 11 for antibiotic regimens. Oseltamivir/zanamivir for influenza. Consider adjunctive corticosteroids only per local protocol/evidence for specific pathogens (evidence for routine steroids in severe CAP remains debated — see Controversies).
14. Consultation Matrix
Consultation | Trigger | Timing |
Infectious Disease | Severe CAP, resistant organism, unusual exposure history | 24h |
Interventional Pulmonology/CT surgery | Complex effusion/empyema | Urgent once identified |
Critical Care | ICU-level severity criteria met | Immediate |
15. Monitoring Framework
Clinical response at 24-48h (fever curve, oxygenation, WBC trend); repeat cultures if not improving; daily CXR only if deteriorating; watch for effusion progression; de-escalate antibiotics per culture/sensitivity results and clinical response.
16. ICU Bundle Checklist (Daily)
17. Complications
Parapneumonic effusion/empyema, lung abscess, ARDS, sepsis/septic shock, metastatic infection (meningitis, endocarditis, septic arthritis — esp. pneumococcal), respiratory failure. Prevention: timely antibiotics, source control (drainage) for empyema. Rescue: chest tube/VATS decortication for empyema, ICU organ support for ARDS/shock.
18. Escalation & De-escalation
Escalate to ICU if severity criteria newly met on the ward. Broaden antibiotics if failing to respond and resistant/uncovered pathogen suspected. De-escalate to narrowest effective regimen once culture results available and patient improving; switch IV to PO per criteria above.
19. ICU Discharge Criteria
Hemodynamically stable off vasopressors, improving oxygenation off/near baseline support, afebrile trend, tolerating oral intake or stable on enteral nutrition, antibiotics de-escalated/on definitive course, no ongoing organ dysfunction requiring ICU monitoring.
20. Documentation & Medicolegal Checklist
21. Key Guidelines
ATS/IDSA 2019 CAP guideline (Metlay et al.); 2016 IDSA/ATS HAP/VAP guideline; Surviving Sepsis Campaign (if septic shock present).
22. Landmark Trials / Key Studies
- Jain S et al. Community-acquired pneumonia requiring hospitalization among U.S. adults. N Engl J Med. 2015;373:415-427 — population incidence/etiology data underpinning current guidelines.
- CAPiTA trial — PCV13 vaccine efficacy in adults, informing prevention strategy.
- Evidence on blood cultures within 24h reducing mortality via earlier resistant-pathogen identification.
23. Controversies
Role of adjunctive corticosteroids in severe CAP — evidence mixed, not routinely recommended by ATS/IDSA. Optimal duration of therapy for gram-negative/resistant pathogen pneumonia remains individualized rather than protocolized. Utility of routine multiplex PCR panels vs traditional culture-based diagnosis in guiding de-escalation is evolving. Threshold for empiric MRSA/Pseudomonas coverage varies by local antibiogram — overuse risks resistance, underuse risks treatment failure.
24. References
- Sattler L, Reynolds D. Community-Acquired Pneumonia. Washington Manual of Critical Care, 4th ed, 2025.
- Van Besien RF, Kollef MH. Nosocomial Pneumonia. Washington Manual of Critical Care, 4th ed, 2025.
- Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia: ATS/IDSA clinical practice guideline. Am J Respir Crit Care Med. 2019;200(7):e45-e67.
- Kalil AC, Metersky ML, Klompas M, et al. Management of adults with hospital-acquired and ventilator-associated pneumonia: 2016 IDSA/ATS clinical practice guideline. Clin Infect Dis. 2016;63(5):e61-e111.
- Jain S, Self WH, Wunderink RG, et al. Community-acquired pneumonia requiring hospitalization among U.S. adults. N Engl J Med. 2015;373:415-427.
- Chawla R, Todi S, eds. ICU Protocols: A Step-wise Approach. 2nd ed. Springer; 2020.