Infectious Diseases in Critical Care Medicine

CLINICAL APPROACH TO SEVERE CAP
Normal Hosts
Normal hosts presenting with severe CAP are those with impaired cardiac/pulmonary
function. The most common cardiopulmonary disorders likely to present as severe CAP are
CHF, cardiomyopathies, or severe valvular disease. The most common pulmonary causes
associated with a severe CAP presentation are COPD, chronic bronchiectasis, interstitial
pulmonary disease/pulmonary fibrosis. These conditions are readily diagnosed by history/
physical examination. The CXR appearance/distribution of infiltrates complements the history
and physical examination in determining the nature/severity of impaired lung/cardiac
function. In patients with good cardiopulmonary function and severe CAP, the clinician
should consider immune defects or pathogen virulence to explain CAP severity (1,2,8,10)
(Tables 2 to 7).

Disorders with Associated Immune Defects Determines Probable CAP Pathogens
Compromised hosts, like normal patients, are most often due to the usual CAP pathogens.
However, clinical severity may be increased due to compromised host defenses. Compromised
hosts have specific immune defects that predispose to a relative few, not many potential

Table 3 Severe CAP Presenting with Hypotension/Shock Disorders
Associated with Functional/Anatomic Hyposplenia

Splenic disorders Extra-splenic disorders

.Splenectomy .Sickle cell anemia

.Congenital asplenia .Hemoglobin SC disease

.Splenic atrophy .Graft-versus-host disease

.Impaired splenic blood flow .Rheumatoid arthritis

.Amyloidosis .SLE

.Infiltrative disorders of the spleen .Cirrhosis

Abbreviation: SLE, systemic lupus erythematosus.

Table 2 Diagnostic Approach to Severe CAP with Hypotension/Shock

Infectious causes Noninfectious with infectious causes

.CAP (with hyposplenia)a .Acute MI (with CAP)

.CAP (with asplenia)b .Acute gastrointestinal bleed (with CAP)

.Zoonotic CAP (tularemia, plague, Q fever) .Acute pancreatitis (with CAP)

.Human influenza A .Advanced lung disease (with CAP)

.Avian influenza (H5N1) .Severe CAD, severe cardiomyopathy, or

.Swine influenza (H1N1) severe valvular disease (with CAP)

.Severe influenza A (withS. aureusCAP)

.SARS

.HPS

.Adenovirus

.CMVc

.PCP

Infectious mimics of CAP Noninfectious mimics of CAP

.TV ABE with septic pulmonary emboli .ARDS

.Anthrax hemorrhagic mediastinitis Due to pegylated interferon-a

Due to TNF-aantagonists

Due to acute pancreatitis

aHowell–Jolly bodies on peripheral blood smear. Look for disorders associated with hyposplenism (see Table 3).
bSurgically removed or congenitally absent.
cIn normal hosts.

Abbreviations: CAD, coronary artery disease; MI, myocardial infarction; SARS, severe acute respiratory
syndrome; CMV, cytomegalovirus; ARDS, acute respiratory distress syndrome; TV, triscuspid valve; ABE,
acute bacterial endocarditis; TNF, tumor necrosis factor; HPS, hantavirus pulmonary virus.

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