ICU · Respiratory
Acute severe community-acquired pneumonia: severity prediction and outcome
Also known as CAP severity prediction · PSI vs CURB-65 · SMART-COP score · CRB-65 score · IDSA/ATS severity criteria · Pneumonia outcomes · Pneumonia Severity Index · PORT score
Severity prediction scores guide admission decisions (ward vs ICU) and predict mortality in CAP. PSI (Pneumonia Severity Index — 20 variables, most accurate): classes I-V. CURB-65 (5 variables, simpler): 0-1 (outpatient), 2 (inpatient), 3+ (ICU). CRB-65 (simplified CURB-65 without urea — for pre-hospital/primary care use). SMART-COP (8 variables — predicts need for ICU respiratory/vasopressor support). IDSA/ATS 2007 minor/major criteria (predict need for ICU). All scores have limitations: none are perfect — clinical judgement must always accompany scoring. Key outcome predictors: PaO2/FiO2 ratio, lactate, age, comorbidities, early appropriate antibiotics.
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Target exams
Red flags
- No single score is perfect — always use clinical judgement alongside scoring
- CURB-65 score 3+ = severe pneumonia, consider ICU admission
- IDSA/ATS: 1 major criterion (septic shock or mechanical ventilation) = ICU mandatory
- Delay in appropriate antibiotics is the strongest modifiable predictor of poor outcome
- PSI underestimates severity in young patients without comorbidities — do not discharge a hypoxic young patient
- CURB-65 and CRB-65 do NOT include oxygenation — check SpO2/PaO2 regardless of score
- CRB-65 score >=1 warrants hospital assessment; >=2 suggests severe CAP
- PSI class V is the highest-risk class — never manage as outpatient
- Scores do not capture social factors (frailty, unable to take oral meds, no support) — admit if these are absent
Meet the patient
It is 2 am in the ED. A 72-year-old man with COPD and heart failure arrives feverish, sweaty, and confused, with three days of productive cough. RR 32, SpO2 88% on air, BP 86/54 after a litre of fluid, WBC 3.2, urea 7.9, pH 7.32. The junior reaches for CURB-65, the reg reaches for PSI, the consultant reaches for the ABG and the SpO2. They are all asking the same question in different tongues: ward or ICU?[2]
Three questions drive the answer. Where does the patient go — home, ward, or ICU? What is the risk of dying? Will they need intensive respiratory or vasopressor support? Each score answers one question; no score answers all three. Choose the score to fit the question.[2]
PSI / PORT
What is the risk of death?
- Best for identifying LOW-risk patients safe for outpatient care
- Most validated; highest sensitivity for low-risk classification
- Class I-II = low risk; Class IV-V = high mortality
CURB-65
What is the risk of death? (simple)
- Bedside 5-variable score; easy to remember and calculate
- Predicts 30-day mortality
- Good for triage at the front door of the hospital
IDSA/ATS 2007
Does this patient need ICU?
- The ONLY score designed specifically to answer the ICU question
- Major criteria: mechanical ventilation or septic shock
- Minor criteria: 9 parameters, 3+ = ICU
SMART-COP
Will this patient need ICU support?
- Predicts need for intensive respiratory or vasopressor support (IRVS)
- Specifically calibrated for ICU resource need, not just mortality
References12ShowHide
- [1]Niederman MS, Torres A Severe community-acquired pneumonia Eur Respir Rev, 2022.PMID 36517046
- [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]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
- [4]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
- [5]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
- [6]Phua J, See KC, Chan YH, et al. Validation and clinical implications of the IDSA/ATS minor criteria for severe community-acquired pneumonia Thorax, 2009.PMID 19386583
- [7]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
- [8]Chalmers JD, Singanayagam A, Akram AR, et al. Severity assessment tools for predicting mortality in hospitalised patients with community-acquired pneumonia. Systematic review and meta-analysis Thorax, 2010.PMID 20729231
- [9]Man SY, Lee N, Ip M, et al. Prospective comparison of three predictive rules for assessing severity of community-acquired pneumonia in Hong Kong Thorax, 2007.PMID 17121867
- [10]Bauer TT, Ewig S, Marre R, et al. CRB-65 predicts death from community-acquired pneumonia J Intern Med, 2006.PMID 16789984
- [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]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