Page 850 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 65: Pneumonia 581

CAP, clear-cut cases of pneumonia have occurred in the absence of all
TABLE 65-3 Microbial Etiology of Community-Acquired Pneumonia Admitted
to the ICU of them, including radiographic infiltrates. The differential diagnosis of
CAP is listed in Table 65-4.
Common Uncommon Rare The elderly are notorious for not mounting a fever in response to
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S pneumoniae Haemophilus influenzae Burkholderia pseudomallei pneumonia and use of antipyretics may mask fever in other patients.
Other biomarkers such as C-reactive protein and procalcitonin have
S aureus Enterobacteriaceae Francisella tularensis a
been used for patients with elevated leukocyte counts. “Normal” chest
Legionella sp a P. aeruginosa Coronavirus (SARS) radiographs on presentation may represent hypovolemia and infiltrates
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Other streptococci Chlamydophila pneumoniae Parainfluenza virus will blossom on subsequent radiographs or subtle abnormalities can be
documented on chest computed tomography (CT).
Influenza Mycoplasma pneumoniae Adenovirus
Respiratory syncytial virus b Acinetobacter spp a Hantavirus a Etiologic Diagnosis: Although the clinical diagnosis of the presence
of CAP is relatively straightforward, determining the etiology is
Human metapneumovirus Mucormycoses
extremely difficult. In usual clinical practice, an etiology is deter-
Aspergillus sp Endemic fungi a mined in <15% of cases of CAP with standard blood cultures and
M. tuberculosis occasional sputum culture. The situation is significantly better in
patients admitted to the ICU. The reasons for this are threefold:
a Regional or localize risks.
(1) a higher incidence of bacteremia in patients who are critically ill,
b Particularly in children.
(2) a higher incidence of pathogens that are not eradicated by a single
dose of antibiotic, and (3) better access to a valid lower respiratory
tract sample in patients who are endotracheally intubated. Because
Recently there has been increasing concern over CA-MRSA as a the yield is significantly higher in patients admitted to the ICU, blood
cause of SCAP. 18,21 Mortality rates from this pathogen may be quite high, cultures should be drawn on all patients. 55,56 In addition, a tracheal
particularly when associated with the virulence factor Panton-Valentine aspirate specimen should be obtained as soon as possible after intuba-
leukocidin. Although the current prevalence of MRSA is too low to tion. Despite this more aggressive diagnostic testing, S pneumoniae is
influence general CAP antibiotic guidelines, this may well change in the still the pathogen most likely to be documented and it is unclear that
near future. routine aggressive diagnostic testing leads to significant changes in
Use of molecular diagnostic techniques demonstrate that streptococci antibiotic therapy. 57,58
other than S pneumoniae, including S pyogenes, S mitis, S agalactia, or The availability of urinary antigen tests for both pneumococcus and
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S milleri, may also be important pathogens for CAP. In the past, many Legionella has also increased the frequency that these pathogens are
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of these have been dismissed as oral flora when cultured from sputum documented in SCAP cases. Urinary antigen testing is complementary
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and they only rarely caused bacteremia. Some of these species are more to both blood cultures and tracheal aspirate cultures for pneumococcus
resistant to penicillin than S pneumoniae and may explain some penicil- since cultures can be negative in cases with a positive urinary antigen
lin treatment failures in culture negative patients. test and vice versa. Urinary antigen testing is more sensitive than spu-
Viral pneumonia in adults was generally underappreciated until the
SARS epidemic and the novel 2009 H1N1 influenza A pandemic. Even tum or tracheal aspirate cultures for L pneumophila but will not detect
other Legionella sp.
in CAP patients admitted to the ICU, viral pneumonia probably plays Polymerase chain reaction (PCR) is now the standard for diagnosis of
a significant role. This is even more likely in immunocompromised respiratory viruses. This should be routine during influenza season and
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patients. The spectrum of respiratory viruses has also increased with a broad-spectrum PCR should be obtained in immunocompromised
recent recognition of human metapneumovirus, Bocavirus, and the patients. The standard is nasopharyngeal sampling but the same assays
SARS-like coronaviruses with increased use of molecular diagnostic can be run on lower respiratory tract samples including tracheal aspi-
techniques. One mechanism by which viral infections can precipitate rates and BAL. Occasionally, these lower respiratory tract samples are
ICU admission is the common association with increased broncho- positive despite negative nasopharyngeal results.
spasm in patients with obstructive lung disease. The pneumonia itself
may be minimal but the associated bronchospasm will require either
frequent aerosols or ventilatory support.
Patients with endemic fungal pneumonia, such as histoplasmosis, blasto- TABLE 65-4 Differential Diagnosis for Community-Acquired Pneumonia
mycosis, or coccidiomycosis, and tuberculosis can also present to the ICU Acute exacerbation of chronic obstructive lung disease (COPD)
with CAP-like symptoms. While uncommon, failure to recognize these
pathogens not only leads to poor patient outcome but also exposes critical Central airway obstruction with atelectasis
care staff to possible infection. Opportunistic fungi, such as Aspergillus and • Bronchogenic carcinoma
Mucor, would be more common in patients with HCAP or HAP. • Foreign body
■ DIAGNOSIS • Benign adenoma
Atypical pulmonary edema
Clinical Criteria: Pneumonia is generally diagnosed by presence Pulmonary embolism/infarction
of abnormalities in three groups of clinical criteria: (1) evidence of
infection—including fever, subjective chills or rigors, or hypother- Hypersensitivity pneumonitis
mia; leukocytosis, leukopenia, or immature white blood cells; and • Allergic alveolitis
other biomarkers, (2) evidence that the infection is localized to the • Drug induced
lung—including increased sputum production, change to purulence or Acute exacerbation of pulmonary fibrosis
hemoptysis, dyspnea, chest discomfort, rales or signs of consolidation Acute eosinophilic pneumonia
on physical examination, and (3) an abnormal chest radiograph. In
certain circumstances, variations in clinical findings are also compatible Vasculitis
with pneumonia such as confusion in the elderly as evidence of infec- Bronchoalveolar carcinoma
tion or wheezing in a child as evidence that an infection is localized in Bronchiectasis
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the lung, such as viral pneumonia. While absence of any one of these
three criteria should call into question the accuracy of the diagnosis of Bronchogenic cyst

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