Pulmonary Factors
Elderly adults with decreased lung function have diminished pulmonary reserve, and
decompensation of pulmonary function may occur with superimposed CAP. In patients with
advanced lung disease/borderline pulmonary function, even relatively avirulent organisms
causing CAP may present as severe CAP since lung function is a key determinant of CAP
severity (1,2,10–21).
Cardiac Factors
Cardiac decompensation is common in patients with CAP with borderline cardiac function.
The fever from CAP increases the heart rate and alone may be sufficient to precipitate
congestive heart failure (CHF) or acute myocardial infarction (MI). The heart rate increases
10 beats per minute for each degree (Fahrenheit) of temperature elevation above normal. Fever
often precipitates CHF, increasing the clinical presentation of severe CAP. Cardiac
decompensation also results in diminished oxygenation secondary to decreased ejection
fraction in patients with CAP, which may exacerbate CHF/precipitate an acute MI (2,10,22–25).
Cardiopulmonary Factors
The heart and lung are physiologically interrelated and decompensation of one will adversely
affect the other. Elderly patients often have advanced lung and heart disease. Elderly patients
with CAP, with limited cardiopulmonary reserve, often present clinically as severe CAP
(1,2,5,9,10,26).
Table 1 Determinants of Severe CAP
Microbial/host factors Host defense factors
Microbial factors Impaired B-lymphocyte function/HI
.Bacterial virulence .Disorders associated with;HI
Legionella SLE
S. pneumoniae Multiple myeloma
.Encapsulated organisms Cirrhosis
S. pneumoniae Hyposplenia
K. pneumoniae Asplenia
.Viral virulence
Influenza A Impaired T-lymphocyte function CMI
Avian influenza (H5N1) .Disorders associated with;CMI
Swine influenza (H1N1) T-cell lymphomas
SARS High-dose/chronic steroid therapy
HPS Immunosuppressive therapy
Pulmonary factors TNF-aantagonists
.Decreased functional lung capacity HIV
Emphysema
.Advanced lung disease Impaired combined B-/T-lymphocyte function (HI/CMI)
Chronic bronchitis .Disorders associated with;HI and;CMI
Chronic bronchiectasis CLL
Interstitial fibrosis SLE with flare
SLE with flare/immunosuppressive therapy
Cardiac factors Advanced age
.CHF
.Severe valvular disease
.Severe cardiomyopathy
.CAD
Systemic factors
.Advanced age (CNS/esophageal dysfunction)
.Hepatic insufficiency
.Renal insufficiency
Abbreviations: SLE, systemic lupus erythematosus; CLL, chronic lymphocytic leukemia; CAP, community-
acquired pneumonia; CHF, congestive heart failure; HI, humoral immunity, CAD, coronary artery disease; CNS,
central nervous system; CMI; cell-mediated immunity.
Severe Community-Acquired Pneumonia in Critical Care 165