The ED calls you regarding a 65-year-old man with a history of hypertension presenting with fever and cough. He is tachycardic to 125/min, with a respiratory rate of 35/min. Physical examination is notable for dullness to percussion and crackles over the right upper lung field, and his labs reveal a white blood cell count of 13,000/µL but are otherwise within normal limits. His chest radiograph demonstrates the following:
His clinical and imaging findings are consistent with pneumonia. He has not had any recent contact with the healthcare system. You discuss with the ED provider whether admission to the hospital is warranted.
Which patients diagnosed with community-acquired pneumonia (CAP) are suitable for outpatient treatment rather than hospital admission?
Patients who may be suitable for outpatient treatment can be identified using severity of illness scores and prognostic models, such as the Pneumonia Severity Index (PSI) and CURB-65.
This question was addressed in a 1997 study evaluating how treatment decisions could be standardized with a prognostic model of illness severity.1 Using a derivation cohort of 14,199 inpatients with CAP, the authors identified 20 factors independently associated with mortality, each assigned point values based on the magnitude of association. This model, known as the PSI, produced five risk classes and was then tested on two validation cohorts consisting mostly of inpatients with a small cohort of outpatients (Table 14.1). Mortality did not differ within risk classes. For example, mortality ranged from 0.1% to 0.4% (class I), 0.6% to 0.7% (class II), and 0.9% to 2.8% (class III) (P > .05 for all).
Given barriers to the use of PSI (e.g., numerous variables and need for time-intensive calculation), a 2003 cohort study sought to derive a simpler model.2 Based on British Thoracic Society (BTS) guidelines previously validated to identify patients with severe CAP, a derivation cohort of 1068 patients hospitalized with CAP was used to identify five variables independently associated with mortality. From these data, authors derived the CURB-65 model, which stratified patients into three classes according to mortality risk (Table 14.1). CURB-65 was then applied to an inpatient validation cohort and demonstrated no observed differences in mortality within risk classes between the derivation and validation cohorts. Despite the benefit of its simplicity for clinical use, the CURB-65 was derived and validated among inpatients only, potentially limiting its applicability in the outpatient setting.
While not substitutes for clinical judgment, Infectious Diseases Society of America (IDSA) guidelines support the use of these prognostic models for guiding risk stratification and identifying patients at the lowest risk of mortality who may be appropriate for outpatient treatment (strong recommendation; level I evidence).3
TABLE 14.1 PSI and CURB-65 Prognostic Models
Prognostic Model
Variables
Risk Category
Suggested Treatment Site
Pneumonia Severity Index (PSI)
Demographics:
Points:
Class I (<50)
Outpatient
Age:
Men
Age (years)
Class II (50-70)
Outpatient
Women
Age (years) -10
Nursing home resident
+10
Class III (71-90)
Outpatient vs. brief inpatient
Comorbidities:
Neoplastic disease
+30
Liver disease
+20
Class IV (91-130)
Inpatient
Congestive heart failure
+10
Cerebrovascular disease
+10
Renal disease
+10
Class V(>130)
Inpatient
Physical examination/vitals:
Altered mental status
+20
Respiratory rate ≥30/min
+20
Systolic blood pressure <90 mm Hg
+20
Temperature <35°C or ≥40°C
+15
Pulse ≥125/min
+10
Labs/imaging:
Arterial pH <7.35
+30
BUN ≥30 mg/dL
+20
Sodium <130 mmol/L
+20
Glucose ≥250 mg/dL
+10
Hct <30%
+10
PaO2 <60 mm Hg
+10
Pleural effusion
+10
CURB-65
One point given for each:
Score 0-1: Mortality low (1.5%)
Outpatient
Confusion
Urea >19 mg/dL (>7 mmol/L)
Score 2: Mortality intermediate (9.2%)
Outpatient vs. brief inpatient
Respiratory rate ≥30/min
Systolic blood pressure <90 mm Hg or Diastolic blood pressure ≤60 mm Hg
Age ≥65 years
Score 3 or more: Mortality high (22%)
Inpatient
PSI reprinted from Fine MJ, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997;336(4):243-250, with permission. CURB-65 data from Lim WS, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58(5):377-382.
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