Following a diagnosis of pneumonia, the clinician needs to decide the appropriate location for care (outpatient care, hospital, or the intensive care unit [ICU]) and the appropriate antibiotic treatment. Patients at low risk of complications are candidates for outpatient care, which reduces inappropriate hospitalization and consequent inherent morbidity and costs.[81]

The use of severity assessment tools such as the Pneumonia Severity Index (PSI),[79] CURB-65,[80] severe CAP (SCAP),[82] and SMART-COP[83] can facilitate decision-making and guide the antibiotic choice. The PSI score classifies patients in 5 risk classes associated with the risk of mortality while the CURB-65 score uses 5 variables to calculate severity. However, the decision to admit a patient depends not only on the severity of CAP, but also on the patient’s comorbidities and on social factors. A delay in determining the severity of the illness and where best to treat the patient can have an impact on clinical outcome and costs.[84] PSI is preferred over CURB-65 in the US, as PSI identifies larger proportions of patients as low risk and has a higher discriminative power in predicting mortality.[17]

Management of severe CAP in accordance with guidelines has been associated with decreased mortality.[85][86] Increasing numbers of risk factors consistently increases the probability of ICU transfer and the need for vasopressors and mechanical ventilation. Probably the best use of these severity scores is to identify at-risk patients who need additional evaluation and monitoring, even if they are not initially admitted to the ICU.

Pneumonia Severity Index (PSI)[79]

Recommended by the American Thoracic Society (ATS)/Infectious Diseases Society of America (IDSA), PSI is a scoring system derived from a retrospective analysis of a cohort of 14,199 patients with CAP and prospectively validated in a separate cohort of 38,039 patients.[79] The PSI score predicts the risk of 30-day mortality; patients with a high risk are managed in the hospital, and those with the highest risk are managed in the ICU. The PSI stratifies patients into 5 categories based on patient age, comorbidities, physical exam, and results of laboratory testing. The principal limitation is the high score accorded to variables such as age and comorbidities.

  • Risk class I: 0-50 points: outpatients; 0.1% mortality

  • Risk class II: 51-70 points: outpatients; 0.6% mortality

  • Risk class III: 71-90 points: short hospital stay for observation; 2.8% mortality

  • Risk class IV: 91-130 points: hospital admission; 8.2% mortality

  • Risk class V: >130 points: hospital admission; 29.2% mortality.

Scoring of the PSI for CAP

  • Demographics

    • Male: points = age in years

    • Female: points = age in years -10 points

    • Nursing home resident: +10 points

    • Liver disease: +20 points

    • Neoplastic disease: +30 points

    • Congestive heart failure: +10 points

    • Cerebrovascular disease: +10 points

    • Renal failure: +10 points

  • Physical exam findings

    • Altered mental status: +20 points

    • Respiratory rate ≥30 breaths/minute: +20 points

    • Systolic blood pressure <90 mmHg: +20 points

    • Temperature <95°F (<35°C) or ≥104°F (≥40°C): +15 points

    • Pulse rate ≥125 beats/minute: +10 points

  • Laboratory and radiographic findings

    • Arterial pH <7.35: +30 points

    • Blood urea nitrogen (BUN) ≥30 mg/dL (≥10.7 mmol/L): +20 points

    • Sodium <130 mEq/L (<130 mmol/L): +20 points

    • Glucose ≥250 mg/dL (≥13.9 mmol/L): +10 points

    • Hematocrit <30%: +10 points

    • PaO₂ <60 mmHg (<90% O₂ saturation): +10 points

    • Pleural effusion: +10 points

[ Community-acquired pneumonia severity index (PSI) for adults ]

CURB-65 score[80]

Recommended by the British Thoracic Society, CURB-65 stratifies patients on the basis of the presence of confusion, BUN levels >19.6 mg/dL (>7 mmol/L), respiratory rate ≥30 breaths/minute, blood pressure <90/60 mmHg, and age ≥65 years. Mortality at 30 days increases with the number of criteria that are met. The limitation of this score is the low number of variables used.[87] This tool may help physicians in emergency departments to risk-stratify patients, as it has been found to have good accuracy for predicting 30-day mortality among patients who have been discharged.[88]

Scoring of the CURB-65 for CAP

  • Prognostic factors

    • Confusion: 1 point

    • BUN >19.6 mg/dL (>7 mmol/L): 1 point

    • Respiratory rate ≥30 breaths/minute: 1 point

    • Blood pressure <90 mmHg systolic or <60 mmHg diastolic: 1 point

    • Age ≥65 years: 1 point

  • Score

    • Score 0-1: low risk; recommendation is for outpatient care; 30-day mortality <3%

    • Score 2: moderate risk; recommendation is for hospitalization; 30-day mortality 9%

    • Score 3-5: high risk; recommendation is for ICU admission; 30-day mortality 15% to 40%

[ CURB-65 pneumonia severity score ]

Infectious Diseases Society of America/American Thoracic Society criteria for defining severe community-acquired pneumonia[17]

The 2007 IDSA/ATS CAP guidelines recommended a set of two major and nine minor criteria to define severe pneumonia requiring ICU admission. These criteria were revalidated in the 2019 update of this guideline. The presence of either of the major criteria or three or more minor criteria is considered to indicate severe CAP, and ICU admission is recommended.[17]

Major criteria:

  • Respiratory failure requiring mechanical ventilation

  • Septic shock with need for vasopressors.

Minor criteria:

  • Respiratory rate ≥30 breaths/minute

  • Arterial oxygen pressure/fraction of inspired oxygen (PaO₂/FiO₂) ratio ≤250

  • Multilobar infiltrates

  • Confusion/disorientation

  • Uremia (BUN ≥20 mg/dL [≥7.14 mmol/L])

  • Leukopenia due to infection alone (WBC <4000 cells/mm³ [<4.0 x 10⁹ cells/L])

  • Thrombocytopenia (platelet count <100,000 cells/mm³ [<10 x 10⁹ cells/L])

  • Hypothermia (core temperature <96.8°F [<36°C])

  • Hypotension requiring aggressive fluid resuscitation.


SMART-COP or SCAP severity criteria can also be used to predict the need for ICU admission. SMART-COP is the easiest severity assessment tool to use. It shares some of the most common risk factors included in CURB-65 and PSI (systolic blood pressure, multilobar infiltrates, albumin, respiratory rate, tachycardia, confusion, oxygen, and pH). A score >3 identifies 92% of patients who need vasopressor support. It provides a sensitivity of 58% to 85% and specificity of 46% to 75%.[83]

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