Intensive care unit (ICU) admission is required for patients who Need mechanical ventilation Have hypotension (systolic blood pressure ≤ 90 mm Hg) that is unresponsive to volume resuscitation Other criteria, especially if ≥ 3 are present, that should lead to consideration of ICU admission include Hypotension requiring fluid support Respiratory rate > 30 / minute PaO2 / fraction of inspired oxygen (FIO2) < 250 Multilobar pneumonia Confusion Blood urea nitrogen (BUN) > 19.6 mg / dL (> 7 mmol / L) Leukocyte count < 4000 cells / microL (< 4 × 10 9 / L) Platelet count < 100, 000 / microL (< 100 × 10 9 / L) Temperature < 36° C The Pneumonia Severity Index (PSI) is the most studied and validated prediction rule.