Key Clinical Questions
What are common mimickers of hospital-acquired pneumonia (HAP)?
Is an invasive sampling procedure necessary for accurate diagnosis?
Which pathogens typically cause HAP?
Which antibiotics are indicated for treatment?
For how long should patients be treated?
What can be done to prevent HAP?
More than 100 years ago, Sir William Osler noted the frequent mismatch between clinical and postmortem diagnoses of pneumonia. The disparity ran both ways: clinicians both overdiagnosed and underdiagnosed the disease. Despite profound advances in the tools available to clinicians, including computed tomography (CT) scans, bronchoscopy, and advanced microbiological diagnostics, the diagnosis of hospital-acquired pneumonia (HAP), or pneumonia acquired more than 48 hours after hospital admission, continues to be elusive, partly because it has many mimickers, and partly because the population at risk tends to be very complex.
Misdiagnosis has three serious consequences: failure to treat truly infected patients is associated with increased mortality; inappropriate use of antibiotics in uninfected patients promotes antibiotic resistance and Clostridium difficile colitis; and premature closure may result in alternative diagnoses being missed.
The selection of appropriate antibiotic regimens for patients with hospital-acquired pneumonia is hampered by limitations in both diagnostic tools and the evidence base. Guidelines published in 2005 recommended rapid, empiric broad-spectrum coverage for all patients with HAP and health care associated pneumonia (HCAP), given observational data suggesting that delayed treatment is associated with increased mortality, inappropriate treatment is associated with increased mortality, and that HAP and HCAP can be caused by pathogens resistant to the typical agents used to treat community-acquired pneumonia. While this strategy may be appropriate for some patients, overtreatment may result, leading to C. difficile colitis, adverse drug reactions, and excess costs. The HCAP concept in particular has come under scrutiny, because more recent case series suggest that only a fraction of HCAPs are due to resistant pathogens. A consensus has yet to emerge on how to best stratify patients into those who require early and aggressive broad-spectrum regimens versus those in whom it is safe to observe, treat using narrower spectrum agents, or await the results of further diagnostic testing.
This chapter will focus primarily on ventilator-associated pneumonia (VAP), since mechanically ventilated patients are at greater risk and better studied than other populations. However, many of the treatment principles for VAP can inform the approach to other kinds of HAP.
VAP rates have dropped dramatically over the past 20 years. Older literature suggested incidence rates of 10% to 15% of ventilated patients, but more recent series report VAP in 5% or fewer of ventilated patients. The risk of VAP is primarily related to the duration of mechanical ventilation. Consequently, the risk of VAP tends to be higher in burn and trauma units, and lower in medical and cardiac units. On meta-analysis, an episode of VAP appears to extend intensive care length of stay by about ...