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534 PART 4: Pulmonary Disorders

could have a sustained antimicrobial effect within the proximal air- The largest randomized trial comparing ranitidine to sucralfate showed
ways and block biofilm formation at its surface. 400-405 Such a device was that ranitidine was superior in preventing gastrointestinal bleeding
evaluated in a large, randomized, multicenter, single-blind trial by Kollef and did not increase the risk of VAP. Therefore, despite the potential
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et al. The authors conclude that the new device was able to lower the advantage of sucralfate (potentially less VAP with more gastrointestinal
406
VAP frequency from 7.5% for the control group to 4.8% for the group bleeding) over H -blockers (potentially more VAP with less gastroin-
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receiving the silver-coated endotracheal tube. The silver-coated tube, testinal bleeding) in preventing VAP, stress ulcer prophylaxis with H -
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however, did not reduce mortality rates, the duration of intubation, blockers appears to be safe in patients who are at high risk for bleeding
hospital length of stay, or the frequency or severity of adverse effects. as well as VAP. Although proton-pump inhibitors are now widely used
416
■ VENTILATOR CIRCUIT MANAGEMENT for gastric bleeding prophylaxis in the ICU, based on their potentially
higher efficacy, their use is associated with similar rates of nosocomial
Decreased frequency of ventilator-circuit change, replacement of heated pneumonia as H -blockers. 415,417-421
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humidifiers by heat and moisture exchangers, decreased frequency of heat ■ SELECTIVE DIGESTIVE DECONTAMINATION
and moisture exchanger change, and closed suctioning systems have been
tested for preventing VAP. 1,328,329,407 Four randomized trials of decreased Selective decontamination of the digestive tract (SDD) includes a short
frequency of ventilator circuit changes have been published. Changes course of systemic antibiotic therapy, such as cefotaxime, trimethoprim
every 2 days, 7 days, and no scheduled change did not find significant or a fluoroquinolone, and topical administration of nonabsorbable
difference in the rate of VAP as summarized in a recent meta-analysis. antibiotics (usually an aminoglycoside, polymyxin B and amphotericin)
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One meta-analysis summarized the results of five randomized, controlled to the mouth and stomach, in order to eradicate potentially patho-
422
trials which compared the effects of heated humidifiers and heat and genic bacteria and yeast that may cause infections. Since the original
423
moisture exchangers on the risk of VAP. Only one out of these five study published by Stoutenbeck et al in 1984, which demonstrated a
329
studies found a significant reduction of VAP rate with the use of heat and decrease of the overall infection rate in patients receiving the SDD regi-
moisture exchangers. Efficacy of both humidification strategies seems men, more than 40 randomized, controlled trials, and 8 meta-analyses
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comparable. Two studies, however, reported increased rates of endotra- have been published. All eight meta-analyses reported a significant
cheal tube occlusion with the use of heat and moisture exchangers; the reduction in the risk of VAP, and four reported a significant reduction
increased resistive load can cause difficulties in ventilation and weaning in in mortality. 90,424-427 Recently, three prospective, randomized, controlled
patients with severe acute respiratory distress syndrome—related to larger trials, all performed in ICUs with low rates of antibiotic resistance, have
dead space. No other adverse effects were observed. No effect on mortality been published that were large enough to show a significant survival
was reported. Finally, one study has evaluated the impact of less frequent benefit in SDD treated patients. 428-430 All three were in favor of treatment
changes (daily vs every 5 days) in heat and moisture exchangers on the with SDD, the largest and most recent one by De Smet et al demon-
development of VAP. No difference in the VAP rates was observed. strating a relative decrease in 28-day mortality rate (OR 0.83, 95% CI,
409
To avoid hypoxia, hypotension and contamination of suction catheters 0.72-0.97) and an absolute survival benefit of 3.5%. 430
entering the tracheal tube, investigators have examined closed suctioning In spite of these benefits, widespread use of SDD in ICU patients
systems. 407,410,411 They either found a nonsignificantly lower prevalence of remains controversial. The major concern with use of SDD is that it
VAP for patients managed with the closed system compared to the open probably needs to be used in nearly all patients in a given ICU, and this
system, without any adverse effect, or they found that its use was associ- widespread use has been shown in some studies to promote the emer-
411
ated with an increased frequency of endotracheal colonization. Closed- gence of resistant bacteria, particularly gram positives such as MRSA. 431-
410
suction systems also failed to reduce cross-transmission and acquisition 435 This is likely to be even a greater problem in ICUs with a high baseline
rates of the most relevant gram-negative bacteria in ICU patients in a rate of resistance. 328,329,436 In contrast to what was expected, however,
prospective crossover study in which 1110 patients were enrolled. 407 most studies that have evaluated this issue showed a lower incidence
of colonization with (multi)resistant bacteria in SDD treated patients
■ METHODS OF ENTERAL FEEDING than in control patients. 429,437 In a single-center observational study
Nearly all ventilated patients have a nasogastric tube inserted to man- from Germany, 5-year use of SDD was not associated with an increase
of MRSA or aminoglycoside and beta lactam resistance in gram-
age gastric and enteral secretions, prevent gastric distention, or provide negative bacteria. Putative explanations why colonization with resistant
438
nutritional support. A nasogastric tube may increase the risk for gastro- microorganisms is lower after treatment with SDD include the almost
esophageal reflux, aspiration, and VAP. Four randomized, controlled invariable sensibility of gram-negative aerobic bacteria for the com-
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trials have evaluated methods of enteral feeding aimed at preventing monly used combination of polymyxin E and tobramycin, the fact that
VAP: postpyloric or jejunal feeding (vs gastric feeding), the use of motil- treatment with polymyxin E rarely induces resistance, the very high local
ity agents (metoclopramide vs placebo), acidification of feeding (with concentrations in the bowel of the used antibiotics, and the lower rate of
addition of hydrochloric acid), and intermittent (vs continuous) feed- use of systemic antibiotics in SDD-treated patients. 439
ing 116,412,413 These studies did not find differences in incidence of VAP or
mortality rates. Potentially serious adverse affects have been observed in ■ IMPLEMENTING A STRUCTURED PREVENTION POLICY
patients receiving acidified feeding (gastrointestinal bleeding) or inter- The application of consistent evidence-based interventions to prevent
mittent enteral feeding (increased gastric volume and lower volumes of VAP has been highly variable from one ICU to another and often
feeding). Thus, to date, methods of enteral feeding aimed at reducing the suboptimal. 440,441 Moreover, no single preventive measure can succeed
incidence of VAP cannot be recommended for routine use. alone, emphasizing the need to use multifaceted and multidisciplinary
■ STRESS ULCER PROPHYLAXIS programs to prevent VAP. Such programs are frequently referred to as

“care bundles.” A care bundle is a set of readily implementable interven-
Gastric colonization by potentially pathogenic organisms has been tions that are required to be undertaken for each patient on a regular
shown to increase with decreasing gastric acidity. Thus, medications basis. The key goal is that every intervention must be implemented
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442
that decrease gastric acidity (antacids, H -blockers, proton-pump inhibi- for every patient on every day of his or her stay in the ICU. Compliance
2
tors) may increase organism counts and increase the risk of VAP. In is assessed for the bundle as a whole, so failure to complete even a single
contrast, medications that do not affect gastric acidity (sucralfate) may intervention means failure of the whole bundle at a particular assess-
not increase this risk. Several meta-analyses of more than 20 random- ment. The interventions need to be packaged in such a way that they are
ized trials have evaluated the risk for VAP associated with the methods easy to assess for compliance, which usually means that no more than
used to prevent gastrointestinal bleeding in critically ill patients. 99,100,415 five interventions are included in each care bundle. The performance

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