Pneumonia Severity Index - The PSI Algorithm

The PSI Algorithm

The PSI Algorithm is detailed below. An online, automated PSI calculator is available on the US AHRQ website.

Step 1: Stratify to Risk Class I vs. Risk Classes II-V
Presence of:
Over 50 years of age Yes/No
Altered mental status Yes/No
Pulse ≥125/minute Yes/No
Respiratory rate >30/minute Yes/No
Systolic blood pressure <90 mm Hg Yes/No
Temperature <35°C or ≥40°C Yes/No
History of:
Neoplastic disease Yes/No
Congestive heart failure Yes/No
Cerebrovascular disease Yes/No
Renal disease Yes/No
Liver disease Yes/No
If any "Yes", then proceed to Step 2
If all "No" then assign to Risk Class I
Step 2: Stratify to Risk Class II vs III vs IV vs V
Demographics Points Assigned
If Male +Age (yr)
If Female +Age (yr) - 10
Nursing home resident +10
Comorbidity
Neoplastic disease +30
Liver disease +20
Congestive heart failure +10
Cerebrovascular disease +10
Renal disease +10
Physical Exam Findings
Altered mental status +20
Pulse ≥125/minute +20
Respiratory rate >30/minute +20
Systolic blood pressure <90 mm Hg +15
Temperature <35°C or ≥40°C +10
Lab and Radiographic Findings
Arterial pH <7.35 +30
Blood urea nitrogen ≥30 mg/dl (9 mmol/liter) +20
Sodium <130 mmol/liter +20
Glucose ≥250 mg/dl (14 mmol/liter) +10
Hematocrit <30% +10
Partial pressure of arterial O2 <60mmHg +10
Pleural effusion +10
∑ <70 = Risk Class II
∑ 71-90 = Risk Class III
∑ 91-130 = Risk Class IV
∑ >130 = Risk Class V

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