Aspiration pneumonia primary prevention
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
Overview
Primary Prevention
In 2014, the Society for Healthcare Epidemiology of America (SHEA) and the Infectious Diseases Society of America (IDSA) issued updated practice recommendations to reduce the risk of ventilator-associated pneumonia (VAP) (table 1) [36]. Basic practices that are recommended by SHEA/IDSA for preventing VAP in all acute care hospitals include avoiding intubation when possible (eg, noninvasive ventilation), minimizing transport while ventilated (when feasible), implementation of weaning protocols, minimizing sedation, maintaining and improving physical conditioning, minimizing pooling of secretions above the endotracheal tube cuff, elevating the head of the bed, and maintaining ventilator circuits. We agree with the recommendations included in these guidelines. Although evidence supporting the use of bundles is mixed, combining a core set of prevention measures into a bundle can be a practical way to enhance care [36-43]. (See 'Prevention bundles' below.)
The following discussion will review some of the modalities that have been evaluated for preventing VAP. The approach to mechanical ventilation, noninvasive ventilation, maintenance of the ventilator circuit, and sedation are discussed separately. (See "Overview of mechanical ventilation" and "Complications of the endotracheal tube following initial placement: Prevention and management in adult intensive care unit patients", section on 'Suctioning and oral care' and "The ventilator circuit" and "Sedative-analgesic medications in critically ill adults: Selection, initiation, maintenance, and withdrawal".)
General issues related to prevention of infections in the intensive care unit (ICU) and infection control are discussed separately. (See "Infections and antimicrobial resistance in the intensive care unit: Epidemiology and prevention" and "Infection prevention: Precautions for preventing transmission of infection".)
Preventing aspiration
Aspiration is a major predisposing mechanism for both hospital-acquired pneumonia (HAP) and VAP. Appropriate patient positioning and subglottic drainage in ventilated patients are two important modalities for the prevention of aspiration. Other factors that may reduce aspiration include maintaining endotracheal tube airway cuff pressure (20 to 30 cm H2O) and application of positive end-expiratory pressure [44,45]. (See "Complications of the endotracheal tube following initial placement: Prevention and management in adult intensive care unit patients", section on 'Maintain optimal cuff pressure' and "Positive end-expiratory pressure (PEEP)".)
Patient positioning
Supine positioning appears to predispose to aspiration and the development of HAP. The head of the bed should therefore be elevated to 30 to 45° [36]. In a meta-analysis of eight randomized trials evaluating over 750 mechanically ventilated adults, semirecumbent positioning (≥30 to 60°) appeared to reduce rates of clinically suspected VAP when compared with supine positioning [46]. A single randomized trial, included within this meta-analysis, found that the reduction in VAP risk was most pronounced for patients receiving enteral feeding [47]. Although no effect of positioning on mortality has been demonstrated, it seems prudent to preferentially place intubated patients in the semirecumbent position unless contraindicated [41,47].
Subglottic drainage
Drainage of subglottic secretions may lessen the risk of aspiration and thereby decrease the incidence of VAP. Specially designed endotracheal tubes have been developed to provide continuous or intermittent aspiration of subglottic secretions (figure 1) [48-50]. However, these devices cost more than standard endotracheal tubes and are not widely available. When available, they should be used for patients expected to require >48 or 72 hours of mechanical ventilation [36]. In a 2016 meta-analysis of 17 randomized trials evaluating 3369 patients, subglottic secretion drainage reduced the risk of VAP from 21 to 13 percent (risk ratio [RR] 0.58, 95% CI 0.51-0.67) [51]. No significant differences in mortality, length of ICU stay, duration of mechanical ventilation, or antibiotic use were found.
Gastric volume monitoring
t has long been standard clinical practice to monitor the patient's gastric residual volume at regular intervals and/or prior to increasing the infusion rate of gastric tube feeding, with the hope of minimizing the risk of unrecognized gastric fluid accumulation and vomiting resulting in pneumonia. However, several studies have shown that measurement of gastric residuals correlates poorly with aspiration risk and is associated with a decrease in calorie delivery [52-54]. Furthermore, a randomized trial has shown that the rate of VAP was not higher in patients who did not undergo monitoring of gastric residuals [55]. Based on these findings, we do not routinely check gastric residual volumes in asymptomatic patients receiving tube feedings. This is discussed in greater detail separately. (See "Nutrition support in critically ill patients: Enteral nutrition", section on 'Monitoring'.)
Decontamination of the digestive tract
Decontamination of the digestive tract represents an attempt to reduce the incidence of pneumonia in critically ill patients by decreasing colonization of the upper respiratory tract. The methods used include antiseptics (eg, chlorhexidine) in the oropharynx, selective decontamination of the oropharyngeal tract (SOD) with nonabsorbable antibiotics applied in the oropharynx, and selective decontamination of the digestive tract (SDD) with nonabsorbable antibiotics applied to the oropharynx and administered orally, with or without intravenous antibiotics.
Gingival and dental plaques rapidly become colonized with aerobic pathogens in ICU patients due to poor oral hygiene and lack of mechanical elimination. Based upon the available data, we favor performing regular oral care with an antiseptic solution in patients receiving mechanical ventilation. Chlorhexidine has been best studied. Although the optimal regimen has not been established, we favor chlorhexidine 0.12% oral solution (15 mL twice daily until 24 hours after extubation). We do not use SOD or SDD due to concerns about promoting the growth of resistant bacteria.
Several meta-analyses have evaluated the efficacy of chlorhexidine for prevention of VAP [56-59]. In a 2016 meta-analysis of 18 randomized trials evaluating 2451 patients, chlorhexidine reduced the risk of VAP in critically ill patients from 25 to 19 percent when compared with placebo (RR 0.74, 95% CI 0.61-0.89) [59]. No significant differences in mortality, length of ICU stay, or duration of mechanical ventilation were detected. Similar results were observed in prior meta-analysis [56-58]. However, one 2014 meta-analysis detected a possible increase in mortality with chlorhexidine use when compared with placebo (odds ratio [OR] 1.25, 95% CI 1.05-1.50) [58]. Due to the possible increase in mortality, the combined European and Latin American guidelines chose not to issue a recommendation on chlorhexidine use for VAP prevention until further efficacy data is available [11].
Meta-analyses have shown that SDD reduces the risk of VAP and HAP [60-62]. Both SOD and SDD have shown mortality benefits in trials of ICU patients performed mainly in regions with low baseline antimicrobial resistance rates. The applicability of the studies showing benefit to other settings has been questioned since very low rates of antibiotic resistance were present at the institutions included in the key trials [63,64]. These studies are discussed separately (see "Infections and antimicrobial resistance in the intensive care unit: Epidemiology and prevention", section on 'Decontamination of the digestive tract').
Because of the potential for promoting antimicrobial resistance with widespread SDD use, the practice has not been routinely adopted in North America [2,36,64-66]; the 2017 combined European and Latin American guidelines on the management of HAP and VAP recommend against SDD [11].
Probiotics
Probiotics are defined as live microorganisms of human origin that are able to tolerate the hostile gastrointestinal environment such that they persist in the lower alimentary tract to confer a health benefit to the host [67,68]. Available results do not provide sufficient evidence to draw conclusions regarding the efficacy or safety of probiotics for the prevention of VAP. We therefore do not use probiotics for the prevention of VAP.
A 2014 meta-analysis evaluated eight randomized trials with 1083 participants that compared a probiotic (eg, Lactobacillus spp) with a control (placebo, glutamine, fermentable fiber, peptide, chlorhexidine) for the prevention of VAP [69]. The use of probiotics decreased the incidence of VAP from 29 to 21 percent (OR 0.70, 95% CI 0.52-0.95). No significant differences in mortality, length of ICU stay, or duration of mechanical ventilation were detected. Adverse effects were not estimable in this analysis. Similar findings were observed in a 2017 meta-analysis [70]; however, the quality of the evidence in each meta-analysis was low.
Silver-coated endotracheal tube
We do not use silver-coated endotracheal tubes (ETTs). Silver-coated ETTs reduce the incidence of VAP but not of other important outcomes [71,72]. This was illustrated in a randomized single-blinded trial (NASCENT) in which a silver-coated ETT was compared with an uncoated ETT in 2003 patients requiring mechanical ventilation [71]. Among patients intubated for more than 24 hours, the rate of microbiologically confirmed VAP was significantly lower with the silver-coated ETT (4.8 versus 7.5 percent). The silver-coated ETT was also associated with a significant delay in the occurrence of VAP. There were no differences between the groups in the duration of intubation, ICU stay, or hospital stay; mortality; or the frequency or severity of adverse events.
In a subsequent retrospective cohort analysis of patients enrolled in the NASCENT study, in patients with VAP, use of a silver-coated ETT was associated with reduced mortality compared with use of an uncoated ETT (14 versus 35 percent) [73]. However, additional observations that were unexplained included a higher mortality in patients who used a silver-coated ETT who did not develop pneumonia and a higher frequency of death from respiratory failure in those who used a silver-coated ETT.
Glucocorticoids
Stress-dose glucocorticoids have been proposed as a possible method for preventing HAP in critically ill patients. Hydrocortisone (200 mg/day for five days followed by 100 mg on day 6 and 50 mg on day 7) was compared with placebo in a multicenter trial that included 150 intubated patients with severe trauma requiring intensive care [74]. The treatment was stopped in patients who had an appropriate adrenal response within the first 48 hours following inclusion. In the modified intention-to-treat analysis, patients who received hydrocortisone had a lower risk of HAP at 28 days compared with patients who received placebo (hazard ratio [HR] 0.47, 95% CI 0.25-0.86). Hydrocortisone use was also associated with a shorter duration of mechanical ventilation and a reduced risk of hyponatremia, but there was no difference in mortality compared with placebo.
An accompanying editorial noted that this trial was not adequately powered to assess the effect of glucocorticoids on mortality and that earlier trials have shown an increase in mortality in patients with traumatic brain injury (TBI) or persistent acute respiratory distress syndrome (ARDS) and mixed results regarding the effect on HAP [75-77]. In patients with TBI, administration of glucocorticoids was not associated with a reduced rate of HAP [76], whereas in patients with ARDS, administration of glucocorticoids was associated with lower rates of suspected or probable HAP [77]. Further studies are necessary to more clearly define the potential benefits and safety of glucocorticoid use in these populations [75].
The use of glucocorticoids in patients with septic shock and ARDS is discussed in detail separately. (See "Glucocorticoid therapy in septic shock" and "Acute respiratory distress syndrome: Supportive care and oxygenation in adults", section on 'Glucocorticoids'.)
Prevention bundles
VAP prevention bundles involve the implementation of various measures in an attempt to reduce the incidence of VAP among patients at risk. Such measures often include educational programs, technical measures, surveillance, and feedback [78]. Developing VAP prevention bundles is a practical way to enhance care. However, there is no consensus about which care processes to include, definitions of VAP vary, baseline VAP rates differ among institutions, and there is substantial heterogeneity in different hospitals' bundles [36]. In addition, bundles have been associated with variable reductions in VAP rates, bundle adherence is generally incomplete, and the relative value of each bundle component is not certain [79].