Hospital-Acquired Pneumonia

["Author photo]Ventilator-associated pneumonia (VAP) is one of the most important infections and causes of death in intensive care units (ICUs) and in facilities where patients require prolonged mechanical ventilation. It has now been realized that VAP has a significant attributable mortality. This edition of Seminars in Respiratory and Critical Care Medicine is very timely and comes on the heels of a number of consensus conferences and publications related to VAP. The European Respiratory Society and the American Thoracic Society recently held a consensus conference of both societies to address the key issues in VAP. The articles in this issue reflect some of the most important advances in VAP to date. They are informative, authoritative, and very practical.

The article by Drs. Patel, Leeper, and McGowan discusses the epidemiology and microbiology of hospital-acquired pneumonia. The major risk factors for the development of VAP in the ICU are intubation and mechanical ventilation. The cumulative risk of developing VAP is ~1% per day of mechanical ventilation. The mortality from VAP is influenced by host factors, the virulence of the pathogens, and the adequacy of initial antimicrobial therapy. Etiologic agents for VAP differ according to the population studied, duration of hospital stay, time after intubation, and prior antimicrobial therapy. The impact that invasive diagnostic techniques may have on the epidemiological characteristics of VAP is controversial but may potentially reduce problems arising from misclassification of this entity.

The pathogenesis of this disease is described in my article. The most common ways to develop VAP are inhalation and aspiration of pathogenic bacteria. Endotracheal tubes are a necessary evil in managing VAP, but their presence in the trachea allows the bacteria of the oropharynx to be aspirated through the open vocal cords. Once this occurs, the process of the development of VAP begins. Early removal of the endotracheal tube or prevention of its insertion by noninvasive ventilation decreases mortality and morbidity. The article suggests prevention strategies for inhalation and aspiration VAP.

The article by Drs. Sirgo, Bodí, Díaz, and Rello concerns pneumonia in head-injured and severe trauma patients. Trauma is the leading cause of death in young people. Infection is the major cause of late death in trauma patients. Early identification of high-risk patients can reduce morbidity and costs. Methicillin-sensitive Staphylococcus aureus (MSSA) is the predominant pathogen in multiple-trauma patients in coma, and nasal colonization at time of severe injury may increase the risk. In the remaining patients, gram-negative bacilli are responsible for the majority of cases. Prolonged mechanical ventilation, continuous enteral feeding, and craniotomy are risk factors for VAP in trauma patients. Diagnosis of VAP in these patients is difficult. In coma patients, coverage with a β-lactam active against MSSA is mandatory. Variations in organisms and sensitivities across ICUs due to differences in demographic characteristics or comorbidities should be considered when making decisions regarding empirical therapy.

Drs. Wunderink and Waterer discuss the ``deadly duo'' that is the relationship of acute lung injury and VAP. There is a high incidence of VAP in acute lung injury. The diagnosis of VAP in acute lung injury is difficult, and invasive methods are preferred. Although VAP is usually late onset with resistant organisms, the mortality seems to be the same regardless of whether the patient develops VAP. However, the time on mechanical ventilation is prolonged if VAP develops.

The evolution of antimicrobial resistance and its impact on antibiotic use are discussed in the article by Drs. Guillemot, Crémieux, and Courvalin. The increase in bacterial resistance to antibiotics has led to modifications in therapeutic recommendations. Antimicrobial exposure of human populations is the most important driving force for the continuous increase in bacterial resistance. The use of antibiotics for individual treatment rather than for the collective control has been the norm. In hospitals there has been a change in attitude, but this is not so in the community. There is a need for community education to increase health care workers' role in the prevention of resistance due to antibiotic use.

Dr. Brun-Buisson discusses the guidelines for treatment in patients with VAP. The key to an effective treatment is the diagnostic strategy used, and timely administration of appropriate antibiotic therapy. Many, but not all, patients need early, appropriate empirical therapy. This decision and the selection of the initial regimen are based on local epidemiological and surveillance data, the clinical presentation, and the recent history of the individual patient. Timely diagnostic techniques effect their interpretation. Hospitals are now plagued with infection caused by multidrug-resistant organisms; this is especially the case in ICUs, where nosocomial respiratory tract infection is the primary reason for prescribing antibiotics.

Drs. Luna and Niederman discuss the natural history of resolution of nosocomial pneumonia. Very little is known about this, and it is likely that optimal duration of therapy is not used in all patients. Patients with few risk factors for a poor outcome and infection with easily treated pathogens can be treated with a shorter course than is commonly used. Patients with risk factors for a poor outcome and infection with high-risk pathogens such as Pseudomonas aeruginosa may need longer durations of therapy. The authors review the clinical and microbiological definitions of resolution, including improvement, delayed resolution, relapse, or recurrent infection. Microbiological end points for resolution including eradication, persistence, and superinfection are defined. They also summarize the clinical parameters that affect resolution of VAP, which include patient- and treatment-related as well as microbiological factors. Currently, the time course of resolution is being defined using clinical end points such as the clinical pulmonary infection score (CPIS) and microbiological end points such as quantitative cultures of respiratory secretions. The authors discuss whether the clinical response is adequate and at what time point. This allows for interventions to help the nonresponding patient or to shorten the duration of therapy in the responding patient.

The article by Dr. Bonten discusses the benefits, risks, and controversy surrounding selective digestive decontamination (SDD) or gut antibiotic prophylaxis for preventing VAP. Studies have shown some reduction in the duration of mechanical ventilation and ICU-stay; however, only meta-analyses have shown any reduction in ICU-mortality. Such benefits should be clearly demonstrated before antibiotic prophylaxis for VAP is recommended. And even when the benefits are clear, they must be weighed against the subsequent increased risks of selection of antibiotic-resistant pathogens.

Drs. Iregui, Vaughan, and Kollef have written the article on nonpharmacological prevention of hospital-acquired pneumonia. The benefits associated with the systematic prevention of VAP include fewer infections with high-risk, antibiotic-resistant bacteria, lower rates of hospital mortality, reduced medical care costs, and shorter hospital lengths of stay. They further give practical methods to prevent VAP. These include hand washing, the use of protective gowns and gloves, and the avoidance of gastric overdistention. They also agree that endotracheal tube intubation should be shortened and that attention should be paid to handling and changing the ventilator circuits. Subglottic suctioning to decrease the amount of pathogenic bacteria above the inflated endotracheal tube cuff is also discussed. Many hospitals do not have an organized approach to the prevention of VAP, and after reading this article, clinicians can design their own strategies for the prevention of VAP.

Drs. Raymond, Pelletier, and Sawyer present various strategies for preventing or limiting antibiotic resistance in the ICUs. These are based on the four basic principles of infection prevention, infection eradication, containment of resistant species, and optimization of antibiotic utilization. These principles also include accurate diagnosis and proper treatment based on appropriate cultures and sensitivity. The authors also discuss guidelines for the use of antibiotics, as well as rotation strategies based on changing antibiotic-resistance patterns.

The articles presented in this issue provide a good summary of the current state of knowledge of VAP and will enable clinicians to more effectively treat this important disease.