Preventing ventilator associated pneumonia
Authors: Christian Brun-Buisson
Journal: BMJ (2007)

Pneumonia occurring during mechanical ventilation (ventilator associated pneumonia) is the most common infection acquired by patients in intensive care. Reported rates range from 9% to 67% and 4.4 to 15.7 cases per 1000 ventilator days.1 In this week's BMJ, a systematic review by Chan and colleagues2 assesses the effect of oral decontamination with antiseptics on ventilator associated pneumonia and mortality in mechanically ventilated adults.

Ventilator associated pneumonia prolongs lengths of stay in intensive care and hospital, and it increases costs of care and possibly increases mortality.3 4 The prevention of this infection is therefore a high priority for infection control in intensive care.5

Preventive procedures deal with three broad areas: prevention of cross transmission; upper digestive tract colonisation and the risk of inhalation; and maintenance and care of the artificial and natural airways.5 6 7 Because the oropharynx and upper intestinal tract are the major sources of organisms causing pneumonia in intensive care, they would appear to be good targets for preventive measures.

Many studies have assessed prevention using antimicrobials administered via various routes, alone or combined. “Selective digestive tract decontamination,” which uses various combinations of systemic and topical (oropharyngeal and intestinal) antibiotics has generated the largest number of trials, summarised in at least eight successive systematic reviews, including one by the Cochrane group.8 In the latest update, which included 36 trials involving 6922 patients, topical and combined systemic antibiotics reduced respiratory tract infections (odds ratio 0.35, 95% confidence interval 0.29 to 0.41). Mortality was also reduced with the combination (0.78, 0.68 to 0.89), but not with topical (intestinal, with or without oropharyngeal) antibiotics alone, despite a comparable effect on rates of pneumonia.8 Selective digestive tract decontamination has not been accepted widely5 7 because of controversy about the balance of benefits and risks—particularly on overall use of antibiotics and selection of resistant microorganisms with prolonged use—and uncertainty about the respective or added value of components of the antimicrobial regimens tested, whether topical, systemic, or both.

Limiting the application of topical antibiotics to the oropharynx is one option, but too few studies have investigated this question.2 8 In addition, infection rates may be difficult to interpret because of the spill over of antibiotics from the oropharynx into the lower airways. Of even more concern is the presumably high risk of selection of resistant strains in an environment both heavily loaded with microorganisms and exposed to rapid colonisation by hospital acquired organisms. Applying antiseptics rather than antibiotics to the oropharynx might be a solution, but until recently few data were available on this intervention.5 9

The review by Chan and colleagues of seven trials involving 2144 patients found that topical antiseptics significantly reduced the rate of pneumonia (relative risk 0.56, 0.39 to 0.81; P=0.002).2 The findings are comparable to those of another recently published review (limited to topical chlorhexidine), which also included seven trials but only 1650 patients.9 The two reviews differ by the selection or exclusion of two trials each. Specifically, Chan and colleagues2 were able to include the most recently published placebo controlled trial conducted in 954 patients who had undergone cardiovascular surgery, which showed a significant reduction in the rate of pneumonia (9.3% v 15.8%; P=0.002) with 0.12% chlorhexidine applied four times daily to the nasal mucosa and oropharynx compared with a placebo similarly applied.10 However, as is the case for topical antibiotics only,8 the review by Chan and colleagues found that oropharyngeal antiseptics had no impact on mortality (0.96, 0.69 to 1.33; P=0.82) or length of stay in the intensive care unit.2

Results varied greatly across the trials included in the review (P=0.07),2 which might in part be explained by differences in design, populations studied (medical versus surgical or mixed), duration of mechanical ventilation, and type and frequency of antiseptics applied. For example, 60% of patients included in the review2 had received cardiac surgery and had a short (mean <48 h) exposure to mechanical ventilation and treatment.10 However, in subgroup analyses, the effect size was comparable with short (<48 h) or longer duration of mechanical ventilation, although it was significant only in the larger group of surgical patients.2 Further studies should deal with these problems and confirm the efficacy of antiseptics, especially in larger groups of medical patients in intensive care who receive prolonged mechanical ventilation.

Preventing ventilation associated pneumonia is difficult, because of the insertion of an indwelling device within a contaminated area. Only substituting invasive mechanical ventilation with non-invasive ventilation, when appropriate, can circumvent this problem.11 However, implementing a group of multifaceted and targeted preventive measures—including education of personnel, semirecumbent positioning of patients, care of ventilator circuit, and no-touch suctioning—can substantially reduce rates of infection.12 The data now available, while still limited, suggest that oropharyngeal care with antiseptics may be included in such preventive strategies. However, as is the case for antibiotics, the risk of a long term effect of widespread use of antiseptics on the emergence and spread of bacterial resistance to these agents needs to be considered.