Applying the latest CAP guidelines, part 1: Patient assessment

Given the dramatic advances in antimicrobials since penicillin was introduced, why has the mortality rate associated with community-acquired pneumonia (CAP) remained essentially unchanged? Inadequate application of practice guidelines may be the chief reason, according to a committee from the Infectious Diseases Society of America (IDSA) and the American Thoracic Society (ATS).¹

The committee bases its assertion on a broad body of evidence showing that sensible application of guidelines for the diagnosis and management of CAP can reduce the incidence and duration of CAP-related hospitalization and mortality.^2-5 Slavish adherence to practice guidelines is not the goal. Rather, the committee strongly recommends that communities adapt the guidelines--newly revised jointly by the IDSA and the ATS--to reflect local circumstances.¹

A common feature of the studies analyzed by the IDSA/ATS committee was a comprehensive process of care encompassing several elements, such as objective criteria for hospital admission decisions, assessment of oxygenation, diagnostic testing, initiation of treatment with antibiotics, and follow-up evaluation. Local application of guidelines need not include all elements listed in the IDSA/ATS document, but it should be appropriately comprehensive for a given community. Local guidelines should aim to improve specific, clinically relevant outcomes, and outcome parameters should be tracked over time to determine effectiveness.

DETERMINING THE SEVERITY OF ILLNESS

As the diagnosis of CAP is being confirmed, assess the patient's condition to determine the best site of care.

Use objective measures

The use of objective admission criteria helps identify patients who require hospitalization and reduce the number of inappropriate admissions. The committee favors either of 2 scoring systems: CURB-65⁶ or Pneumonia Severity Index (PSI).⁷ One system has not been proved more accurate than the other.

•CURB-65 uses the following criteria to assess the patient's severity of illness: confusion; uremia with blood urea nitrogen (BUN) level of 20 mg/dL or higher; respiration rate of 30 or more breaths per minute; systolic blood pressure lower than 90 mm Hg or diastolic blood pressure 60 mm Hg or lower; and age 65 or older.⁶ A person who meets only 1 (or none) of these criteria can be treated as an out- patient. The presence of 2 factors supports a decision for hospitalization, and 3 or more could warrant admission to the ICU. (If assessment occurs in the office setting, the BUN measurement may be omitted.⁸)

•The PSI predicts the risk of death and is calculated with values obtained from several physical examination findings and laboratory measurements.⁷ Five levels of risk are possible. Patients at level I or II may be treated as outpatients; those at level III require closer observation, perhaps with brief hospitalization; and those at levels IV and V require inpatient treatment.

Temper scoring results with clinical judgment

The committee warns that "sole reliance on a score for the hospital admission decision is unsafe."¹ Factors disregarded in objective assessments may nevertheless influence a decision on how and where to treat a patient. For instance, even if an objective score is low, a decision to admit the patient might be made because of pneumonia complications, exacerbation of underlying disease, inadequate out- patient support, a patient's inability to take oral medication, or a concern that several of the measured risk factors are hovering at the threshold.

If your perception of a patient's condition differs from what is suggested by results of the CURB-65 or PSI, consider repeating the measures over several hours to yield a dynamic and more accurate objective assessment.

ICU admission

Either of 2 major criteria dictates ICU admission: septic shock requiring vasopressors and acute respiratory failure requiring intubation and mechanical ventilation. However, patients who do not exhibit septic shock or respiratory failure may still qualify for ICU admission. Three or more minor criteria appearing together indicate severe CAP. The last 3 items in the following list were newly added by the IDSA/ATS committee:

•Respiration rate of 30 or more breaths per minute.

•PaO₂ to fraction of inspired oxygen ratio of 250 or less.

•Multilobar infiltrates.

•Confusion/disorientation.

•Uremia (BUN level of 20 mg/dL or higher).

•Hypotension requiring aggressive fluid resuscitation.

•Leukopenia (white blood cell count less than 4000/µL).

•Thrombocytopenia (platelet count less than 100,000/µL).

•Hypothermia (core temperature less than 36°C [96.8°F]).

DIAGNOSTIC TESTING

Typical features of CAP are cough, fever, sputum production, and pleuritic chest pain. However, this constellation of features may be altered or even absent, particularly in the elderly. The diagnosis of CAP is confirmed by the finding of a pulmonary infiltrate on chest radiography or other imaging modality. Pulse oximetry can also support the diagnosis of pneumonia in the absence of other clear signs; it may detect hypoxemia in confirmed cases of pneumonia.

Microbiological tests to pinpoint the causative agent are warranted when clinical signs or epidemiological clues suggest that empiric therapy may not be effective. Consider such testing for patients who are ill enough to be hospitalized, since their condition may be caused by unusual pathogens or treatment- resistant strains of more common ones. Blood and sputum collections are best done before initiating treatment. Sputum collection is valuable only if a good-quality specimen is obtained and proper transport and processing can be guaranteed.

Such testing is optional for outpatients. The Table lists adverse clinical features that may prompt further assessment and the tests most likely to yield answers to aid treatment decisions.

Blood culture: use selectively

Blood cultures are valuable in patients with severe CAP because of the possibility of uncommon pathogens. In less dire circumstances, testing is optional because Streptococcus pneumoniae is the most likely causative organism and is adequately covered by empiric treatment. One risk in obtaining a blood culture in an optional setting is the possibility that a false-positive result may unnecessarily alter treatment and prolong the patient's hospitalization.

Sputum culture and Gram stain

Severe CAP warrants obtaining a sputum culture, and it is preferable to collect a specimen before antibiotics are given. Keep in mind that 40% or more of patients cannot produce sputum or cannot do so effectively for testing. With intubated patients, a culture of endotracheal aspirates is highly recommended.

The result of a sputum culture depends heavily on the quality of the process--collection, transport, laboratory procedure, appropriate cytological criteria, and interpretation. Any deficiency in the process will jeopardize the outcome. If a high-quality process is adhered to, a negative culture result is helpful. (For example, the absence of Staphylococcus aureus or Gram-negative bacilli supports ruling out these pathogens as causative agents.) Gram stain also aids diagnosis in 2 ways: it can prompt rethinking of empiric coverage to include less common pathogens, and it can validate later culture results.

Culture methods for special situations

Thoracentesis is indicated for patients with pleural effusions larger than 5 cm on a lateral chest radiograph. Yield generally is low, but a positive result could have a substantial effect on treatment.

Bronchoscopic bronchoalveolar lavage, specimen brushing, or transthoracic lung aspiration are best reserved for patients who are immunocompromised or for whom therapy has failed.

Urinary antigen testing

This test may help in evaluating patients with severe CAP, particularly when culture samples are difficult to obtain or when antibiotic therapy has been initiated and may confound culture results. The sensitivity of tests approved for S pneumoniae is 50% to 80%, and the specificity is greater than 90%. Tests for Legionella pneumophila have a specificity approaching 99%.

Two caveats with antigen testing are the cost and the uncertainty of its contribution to treatment decisions, since empiric antibiotic therapy covers both S pneumoniae and L pneumophila.

Additional tests

Acute-phase serological testing is reserved for cases in which atypical pathogens are most likely involved. Poor reproducibility is an issue with this testing.

Polymerase chain reaction testing is also available for identifying atypical pathogens. However, according to the CDC, only 4 of the 18 commercial reagents have proved to yield valid results.

[Editor's note: Part 2 of this Clinical Update will focus on the treatment of CAP and will appear in a coming issue of The Journal of Respiratory Diseases.]

References:

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