ICU · Respiratory
Severe community-acquired pneumonia (CAP)
Also known as Community-acquired pneumonia (CAP) · Severe CAP · CURB-65 · IDSA/ATS criteria · Pneumonia severity index (PSI)
Severe CAP is ICU-level community-acquired pneumonia. IDSA/ATS: one major criterion (invasive ventilation or vasopressor septic shock) or three or more minor criteria. CURB-65 (Lim) stratifies 30-day mortality (0.7/3.2/3/17/41.5/57% at scores 0–5) but detects only 39% of patients who need intensive respiratory or vasopressor support. Empiric therapy per ATS/IDSA 2019: beta-lactam (ceftriaxone 1–2 g daily) plus macrolide (azithromycin 500 mg daily) OR beta-lactam plus a respiratory fluoroquinolone — not fluoroquinolone monotherapy. Add MRSA or Pseudomonas cover only for locally validated risk factors. CAPE COD: hydrocortisone 200 mg daily, 28-day death 6.2 vs 11.9%. Hour-1 antimicrobials in septic shock: 79.9% survival; 7.6% average survival lost per hour (Kumar).
Checked against its sources on 5 Sept 2026
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Red flags
- Antibiotics within 1 hour of septic shock — first-hour survival 79.9%; each further hour costs an average 7.6% survival (Kumar)
- Septic shock or need for mechanical ventilation = IDSA/ATS major criteria = ICU admission
- Consider Legionella in severe CAP (hyponatraemia, diarrhoea, confusion, high fever) — urinary antigen
- Consider MRSA and Pseudomonas if risk factors (recent hospitalisation, broad-spectrum antibiotics, structural lung disease)
Meet the patient
A 67-year-old arrives confused, febrile, and hypotensive with a respiratory rate of 34, bilateral multilobar infiltrates, PaO2 to FiO2 ratio of 160, and rising lactate. His CURB-65 is high, but the reason he needs ICU is more immediate: oxygenation and circulation are failing together.[1][2][3]
The first-hour questions are does he need organ support, what must empiric therapy cover, and which samples can be taken without delaying treatment? Scores refine judgement; they do not replace it. In septic shock, first-hour antimicrobials carried 79.9% survival and each further hour cost an average 7.6%.[1][15]
References16ShowHide
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- [2]Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study Thorax, 2003.PMID 12728155
- [3]Salih W, Schembri S, Chalmers JD Simplification of the IDSA/ATS criteria for severe CAP using meta-analysis and observational data Eur Respir J, 2014.PMID 24114960
- [4]Soumare A, Kapfer T, Botrel T, et al. Systemic Corticosteroids, Mortality, and Infections in Pneumonia and Acute Respiratory Distress Syndrome : A Systematic Review and Meta-analysis Ann Intern Med, 2026.PMID 41325621
- [5]Metlay JP, Waterer GW, Long AC, et al. Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America Am J Respir Crit Care Med, 2019.PMID 31573350
- [6]Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults Clin Infect Dis, 2007.PMID 17278083
- [7]Chalmers JD, Taylor JK, Mandal P, et al. Validation of the Infectious Diseases Society of America/American Thoracic Society minor criteria for intensive care unit admission in community-acquired pneumonia patients without major criteria or contraindications to intensive care unit care Clin Infect Dis, 2011.PMID 21865188
- [8]Charles PG, Wolfe R, Whitby M, et al. SMART-COP: a tool for predicting the need for intensive respiratory or vasopressor support in community-acquired pneumonia Clin Infect Dis, 2008.PMID 18558884
- [9]Fine MJ, Auble TE, Yealy DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia N Engl J Med, 1997.PMID 8995086
- [10]Dequin PF, Meziani F, Quenot JP, et al. Hydrocortisone in Severe Community-Acquired Pneumonia N Engl J Med, 2023.PMID 36942789
- [11]Siemieniuk RA, Meade MO, Alonso-Coello P, et al. Corticosteroid Therapy for Patients Hospitalized With Community-acquired Pneumonia: A Systematic Review and Meta-analysis Ann Intern Med, 2015.PMID 26258555
- [12]Brower RG, Matthay MA, Morris A, et al. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome N Engl J Med, 2000.PMID 10793162
- [13]Guérin C, Reignier J, Richard JC, et al. Prone positioning in severe acute respiratory distress syndrome N Engl J Med, 2013.PMID 23688302
- [14]Wiedemann HP, Wheeler AP, Bernard GR, et al. Comparison of two fluid-management strategies in acute lung injury N Engl J Med, 2006.PMID 16714767
- [15]Kumar A, Roberts D, Wood KE, et al. Duration of hypotension before initiation of effective antimicrobial therapy is the critical determinant of survival in human septic shock Crit Care Med, 2006.PMID 16625125
- [16]Porcel JM [Parapneumonic pleural effusions and empyema in adults:current practice]. Rev Clin Esp, 2009.PMID 19889319