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  • Pneumonia is one of the most common causes of ICU admission, usually because of impending respiratory failure or hemodynamic compromise.

  • Community-acquired pneumonia (CAP) is the leading cause of infectious death around the world and a frequent cause of ICU admission.

  • HCAP (Healthcare-associated pneumonia) is no longer an entity. Use of the HCAP designation resulted in excessive use of broad spectrum antibiotics.

  • Severe CAP (SCAP) is defined as CAP associated with mechanical ventilation and/or shock requiring vasopressors, or having three or more minor American Thoracic Society criteria.

  • Patients initially admitted to a non-ICU setting but subsequently requiring ICU transfer have high mortality that exceeds that of patients with equivalent illness at presentation who are admitted directly to the ICU. Presence of at least three of a set of minor criteria for severity identifies patients likely needing ICU care and the probability increases with an increasing number of these minor criteria.

  • The diagnostic evaluation for the etiology of pneumonia in hospitalized patients with SCAP is most commonly negative. When a pathogen is identified, it is most commonly a virus. The most common bacterial etiologies of SCAP are Streptococcus pneumoniae and Staphylococcus aureus.

  • The etiologies of SCAP are rarely multidrug resistance and in the absence of risk factors, empirical antibiotics for SCAP should be a combination of a beta-lactam plus a macrolide.


Community-acquired pneumonia (CAP) is one of the most common precipitating causes for medical or general ICU admission.1 CAP frequently causes hemodynamic compromise and septic shock (Chapter 65). Pneumonia is also one of the most common causes for the acute respiratory distress syndrome (ARDS; Chapter 52).

CAP continues to be a frequent cause of morbidity and mortality.2,3 Worldwide, CAP is the leading infectious disease cause of death and the fourth leading cause of death overall, even prior to the COVID-19 pandemic.4,5 Despite continued advances in a multitude of areas in medicine, the mortality rate from CAP has changed little in the past four decades. In addition to the deaths within the hospital, patients admitted to the hospital with pneumonia are at an increased risk of death for months to years after discharge, relative to age-matched controls.6–8



Pneumonia is the host immune response to abnormal microorganisms or abnormal numbers of microorganisms at the alveolar or respiratory bronchiole level. This contrasts with bronchitis, bronchiolitis, and even upper respiratory tract infections (URIs), all of which would not be associated with alveolar infiltrates on imaging. However, the advent of readily available chest computed tomography (CT) and increasingly sophisticated lung ultrasound have demonstrated alveolar densities in patients with normal plain chest radiographs.9–12 Therefore, a clinical diagnosis of bronchitis or URI with a normal chest radiograph may actually represent pneumonia, as was have frequently seen in the COVID-19 pandemic.


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