Hospital-Acquired Pneumonia: Pathophysiology, Diagnosis, and Treatment

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Hospital-acquired pneumonia (HAP) is one of the most common causes of nosocomial infection, morbidity, and mortality in hospitalized patients. Many patient- and disease-specific factors contribute to the pathophysiology of HAP, particularly in the surgical population. Risk-factor modification and inpatient prevention strategies can have a significant impact on the incidence of HAP. While the best diagnostic strategy remains a subject of some debate, prompt and appropriate antimicrobial therapy in patients suspected of having HAP has been shown to significantly decrease mortality. Because the pathogens responsible for HAP are frequently more virulent and have greater resistance to commonly used antimicrobials than other pathogens, clinicians must have knowledge of the resistance patterns at their institutions to choose appropriate therapy.

Section snippets

Incidence

HAP represents one of the most common nosocomial infections, with significant impact on patient morbidity and mortality, as well as on the cost of health care. Accounting for 15% of all hospital-acquired infections, nosocomial pneumonia is a frequent lethal complication of hospitalization.6 At a rate of 3 to 10 cases per 1000 hospital admissions, HAP may increase a patient's hospital stay by more than a week, resulting in up to $40,000 in additional costs and a threefold increase in mortality.1

Microbiology

The causative organisms for HAP differ significantly from those typically responsible for community-acquired pneumonia.1, 14, 15, 16 The clinical setting in which HAP arises is likely to influence the likely causative organisms. Not only does this change in microbiology affect the appropriate treatment, but it also has implications on morbidity and mortality. HAP arising early (<5 days) in the hospital course is associated with a better prognosis than late-onset HAP.1 Thus, HAP can be divided

Patient Risk Modification

Preoperative risk factors to help stratify and modify risk in patients have been widely applied in cardiac prediction models.27 Several substantial studies have attempted to create a similar pulmonary risk index.28, 29, 30, 31 The National Surgical Quality Improvement Program (NSQIP) and the Patient Safety in Surgery (PSS) study are national collaborative efforts that have sought to decrease complications among surgical patients. Using data from the NSQIP and PSS, Johnson developed the

Clinical Evaluation

The method of establishing the diagnosis of HAP remains controversial and no method has emerged as the gold standard. A multitude of possible explanations exist for new-onset fevers and leukocytosis. Attempting to establish the diagnosis of pneumonia on radiological studies alone is similarly unreliable. For these reasons, clinical guidelines are available to aid in decision making about who does and does not have pneumonia. The Centers for Disease Control and Prevention and the National

Bacteriologic Evaluation

The bacteriologic diagnosis of pneumonia involves sampling the lower airways to obtain quantitative cultures. Blind tracheobronchial aspiration (TBAS) is a noninvasive technique accomplished by inserting a flexible catheter into the distal trachea via the endotracheal tube. Suction samples are obtained and sent for quantitative culture. The typical threshold for diagnosis of pneumonia is growth of more than 105 colony forming units per milliliter (cfu/mL). This technique has the advantage of

Empiric Therapy

The most important factor influencing the mortality of HAP is prompt and adequate empiric treatment. Multiple studies have demonstrated that delays in appropriate antibiotic therapy are associated with increased mortality.1, 15, 96, 97 In a study looking at inadequate empiric therapy for VAP in trauma patients, Mueller97 found that mortality, ICU length of stay, and duration of mechanical ventilation all increased with the number of episodes of inadequate empiric therapy. Treatment should be

Outcomes

HAP has a significant impact both medically and economically. Specifically, ICU patients with VAP experience longer ICU and hospital lengths of stay, cost more to treat, and have higher mortality rates than other patients.4, 5, 7 In their evaluation of 127 episodes of VAP at a single institution, Warren and colleagues3 cited increased costs of almost $50,000 per episode of VAP. Perhaps more importantly, VAP in this study was associated with an overall mortality of 32%, versus 11% in patients

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