New insights into the pathogenesis of ventilator-associated pneumonia

Periodontopathogenic bacteria in subglottic samples from patients undergoing elective intubation for general anesthesia: A pilot study

BACKGROUND

Translocation of periodontal pathogens into the respiratory tract could either cause pneumonia or disrupt local defense mechanisms, predisposing the host to infection by respiratory pathogens. The objective of this pilot study was to evaluate the levels of periodontopathogenic bacteria in subglottic samples of intubated and mechanically ventilated patients and the impact of oral decontamination with chlorhexidine (CHX) on subglottic levels of these microorganisms.

METHODS

Patients scheduled to undergo elective surgical procedures requiring endotracheal intubation and mechanical ventilation for at least 3 hours were included. Following full-mouth periodontal examination, patients were randomly assigned to groups that rinsed preoperatively with 0.12% CHX or 0.9% saline (control). After 3 hours of orotracheal intubation, subglottic contents were collected. Quantification of Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans), Porphyromonas gingivalis (P. gingivalis), and Tannerella forsythia (T. forsythia) in subglottic samples was determined using quantitative real-time polymerase chain reaction. Data were analyzed by Fisher Exact Probability, unpaired Student's t and Mann-Whitney tests.

RESULTS

Of the 69 patients included, 43 completed study participation. There were no differences between control and CHX groups in subglottic detection rates and abundance levels of P. gingivalis (P = 0.59), T. forsythia (P = 0.83) and A. actinomycetemcomitans (P = 0.07). Moreover, our data indicate that periodontal health has no impact on subglottic levels of P. gingivalis, T. forsythia, and A. actinomycetemcomitans.

CONCLUSIONS

Periodontal pathogens were detected in subglottic samples of intubated and mechanically ventilated patients. Moreover, a single CHX rinse prior to endotracheal intubation may have no effect on subglottic contamination by P. gingivalis, T. forsythia, and A. actinomycetemcomitans.

Endotracheal tube biofilm and ventilator-associated pneumonia with mechanical ventilation

OBJECTIVE

To analyze biofilm on internal and external surfaces of endotracheal tubes after their use in critical care patients, and to produce evidence of association between use of the tube, presence of biofilm, and the occurrence of pneumonia.

METHODS

This was a clinical study performed at the Intensive Care Unit of an emergency hospital in the interior of São Paulo state, Brazil. Data collection involved 30 endotracheal tubes used on adult patients for a period of ≥48 h of mechanical ventilation for scanning electron microscopy.

RESULTS

Analysis of the biofilm on the 30 tubes by scanning electron microscopy showed various abiotic and biotic structures, predominantly on the internal surface, such as: fibrin network, erythrocytes, leukocytes, cocci, bacilli, and molds, among others. The intubation period of the endotracheal tube for ≥8 days represented one of the risk factors for ventilator-associated pneumonia (RR 7.41, P < 0.001).

CONCLUSIONS

The presence of the endotracheal tube permits microbial colonization, overall contributing to the development of biofilm and the occurrence of pneumonia.

Management and prevention of ventilator-associated pneumonia caused by multidrug-resistant pathogens

Ventilator-associated pneumonia (VAP) due to multidrug-resistant (MDR) pathogens is a leading healthcare-associated infection in mechanically ventilated patients. The incidence of VAP due to MDR pathogens has increased significantly in the last decade. Risk factors for VAP due to MDR organisms include advanced age, immunosuppression, broad-spectrum antibiotic exposure, increased severity of illness, previous hospitalization or residence in a chronic care facility and prolonged duration of invasive mechanical ventilation. Methicillin-resistant Staphylococcus aureus and several different species of Gram-negative bacteria can cause MDR VAP. Especially difficult Gram-negative bacteria include Pseudomonas aeruginosa, Acinetobacter baumannii, carbapenemase-producing Enterobacteraciae and extended-spectrum β-lactamase producing bacteria. Proper management includes selecting appropriate antibiotics, optimizing dosing and using timely de-escalation based on antiimicrobial sensitivity data. Evidence-based strategies to prevent VAP that incorporate multidisciplinary staff education and collaboration are essential to reduce the burden of this disease and associated healthcare costs.

Higiene bucal com clorexidina na prevenção de pneumonia associada à ventilação mecânica

A pneumonia associada à ventilação mecânica (PAVM) é uma infecção freqüente nas unidades de terapia intensiva (UTI), e anti-sépticos bucais são utilizados preventivamente. Revisamos metanálises e ensaios clínicos randomizados indexados no Medical Literature Analysis and Retrieval System e Cumulative Index to Nursing and Allied Health Literature sobre o uso tópico da clorexidina na prevenção da PAVM. Oito publicações foram avaliadas. Em sete (87,5%), a clorexidina diminuiu a colonização da orofaringe, e em quatro (50%) houve redução de PAVM. A clorexidina parece diminuir a colonização, podendo reduzir a incidência da PAVM.

A low-volume, low-pressure tracheal tube cuff reduces pulmonary aspiration*

OBJECTIVE

Leakage of fluid from the subglottic space to the lungs occurs along the longitudinal folds within the wall of an inflated high-volume, low-pressure (HVLP) cuff. The low-volume, low-pressure (LVLP) cuff does not have these folds yet allows for convenient and reliable control of tracheal wall pressure. Pulmonary aspiration during anesthesia has been linked with postoperative pneumonia and during critical illness causes ventilator-associated pneumonia.

DESIGN

Prospective, blinded, randomized controlled trial; prospective observational study; and benchtop models.

SETTING

Department of Anaesthesia and Critical Care, Queen Elizabeth Hospital.

PATIENTS

Anesthetized patients (n=38) and critically ill patients with either an LVLP or HVLP cuffed tracheostomy tube following swallow assessments (n=67).

INTERVENTIONS

The LVLP cuff was compared with HVLP cuffs for leakage of dye placed in the subglottic space to the tracheobronchial tree in a rigid tracheal model and a benchtop pig trachea model (before and after a standardized cuff movement).

MEASUREMENTS AND MAIN RESULTS

In the rigid tracheal model, the incidence of leakage was 0% in the LVLP group and 100% in the HVLP group (p<.01). Dye leakage in the pig tracheal model with HVLP cuffs was 44% before tube movement, increasing to 79% afterward. The LVLP cuff did not leak in the pig tracheal model. Dye leakage in anesthetized patients was 0% before movement and 5% after in the LVLP group and in the HVLP group 22% increasing to 67% after movement (p<.001). Forty-nine percent of swallow assessments were scored as failed in the critical care patients with HVLP tracheostomy tube cuffs, and there were no episodes of aspiration following swallow assessment in the LVLP group (p<.05).

CONCLUSIONS

The LVLP cuffed tracheal and tracheostomy tubes reduced pulmonary aspiration in the benchtop models and in anesthetized and critically ill patients. The single failure of the LVLP cuff in the anesthesia group was probably associated with accidental endobronchial intubation following tube movement.

The role of oral microbial colonization in ventilator-associated pneumonia

The present article reviews the association between microbial colonization of the oral cavity and the lungs in critically ill patients that develop ventilator-associated pneumonia (VAP) in the intensive care unit (ICU) setting. The risk factors and microorganisms associated with VAP are presented. The role of oral colonization of VAP-associated pathogens (VAP-AP) in the development of VAP is examined. We explore the potential factors involved in oral colonization of VAP-AP, which are atypical bacteria for the oral cavity. Strategies for the prevention or moderation of oral colonization of VAP-AP have had limited success. We need a deeper understanding of the pathophysiology of VAP in order to reduce the morbidity, mortality, and cost from this common complication in ICU medicine and surgery.

Endotracheal tube intraluminal volume loss among mechanically ventilated patients*

OBJECTIVE

To measure endotracheal tube intraluminal volume loss among mechanically ventilated patients.

DESIGN

Prospective observational study.

SETTING

Medical intensive care unit (19 beds) of an urban university-affiliated teaching hospital.

PATIENTS

A total of 101 patients with acute respiratory failure requiring >24 hrs of mechanical ventilation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Acoustic reflectometry was employed to measure the intraluminal volume of 13-cm endotracheal tube segments. The endotracheal tube segment volumes were statistically smaller among endotracheal tubes used in patients compared with unused endotracheal tubes (5.4 +/- 0.7 vs. 6.0 +/- 0.6 mL, p <.001). The average percentage difference in endotracheal tube segment volumes, between the unused endotracheal tubes and the endotracheal tubes used in patients, was 9.8% (range, 0-45.5%). The percentage difference in the endotracheal tube segment volumes increased significantly with increasing duration of tracheal intubation (r2 =.766, p <.001). The minimum diameter of the endotracheal tube segments was also statistically smaller among endotracheal tubes used in patients compared with the unused endotracheal tubes (7.5 +/- 0.4 vs. 6.7 +/- 1.2 mm, p <.001).

CONCLUSIONS

Endotracheal tube intraluminal volume loss is common among patients with acute respiratory failure requiring mechanical ventilation and increases with prolonged tracheal intubation.

Characterisation and evaluation of novel surfactant bacterial anti-adherent coatings for endotracheal tubes designed for the prevention of ventilator-associated pneumonia

It is accepted that ventilator-associated pneumonia is a frequent cause of morbidity and mortality in intensive care patients. This study describes the physicochemical properties of novel surfactant coatings of the endotracheal tube and the resistance to microbial adherence of surfactant coated endotracheal tube polyvinylchloride (PVC). Organic solutions of surfactants containing a range of ratios of cholesterol and lecithin (0:100, 25:75, 50:50, 75:25, dissolved in dichloromethane) were prepared and coated onto endotracheal tube PVC using a multiple dip-coating process. Using modulated temperature differential scanning calorimetry it was confirmed that the binary surfactant systems existed as physical mixtures. The surface properties of both surfactant-coated and uncoated PVC, following treatment with either pooled human saliva or phosphate-buffered saline (PBS), were characterised using dynamic contact angle analysis. Following treatment with saliva, the contact angles of PVC decreased; however, those of the coated biomaterials were unaffected, indicating different rates and extents of macromolecular adsorption from saliva onto the coated and uncoated PVC. The advancing and receding contact angles of the surfactant-coated PVC were unaffected by sonication, thereby providing evidence of the durability of the coatings. The cell surface hydrophobicity and zeta potentials of isolates of Staphylococcus aureus and Pseudomonas aeruginosa, following treatment with either saliva or PBS, and their adherence to uncoated and surfactant-coated PVC (that had been pre-treated with saliva) were examined. Adherence of S. aureus and Ps. aeruginosa to surfactant-coated PVC at each successive time period (0.5, 1, 2, 4, 8 h) was significantly lower than to uncoated PVC, the extent of the reduction frequently exceeding 90%. Interestingly, the microbial anti-adherent properties of the coatings were dependent on the lecithin content. Based on the impressive microbial anti-adherence properties and durability of the surfactant coating on PVC following dip coatings, it is proposed that these systems may usefully reduce the incidence of ventilator-associated pneumonia when employed as luminal coatings of the endotracheal tube.

Silver-coated endotracheal tubes associated with reduced bacterial burden in the lungs of mechanically ventilated dogs

STUDY OBJECTIVES

To evaluate the influence of silver-coated endotracheal tubes on the lung bacterial burden of mechanically ventilated dogs.

DESIGN

Randomized, double-blinded, controlled experiment.

SETTING

Animal research facility of a regional medical university.

PATIENTS OR PARTICIPANTS

Eleven healthy adult dogs.

INTERVENTIONS

The dogs were intubated either with cuffed, noncoated endotracheal tubes or with endotracheal tubes having a novel antimicrobial silver hydrogel coating and were challenged with buccal administration of Pseudomonas aeruginosa.

MEASUREMENTS AND RESULTS

The silver coating delayed the appearance of bacteria on the inner surface of the endotracheal tubes ([mean +/- SD] duration of mechanical ventilation before appearance of bacteria, 3.2 +/- 0.8 days; mean duration of mechanical ventilation, 1.8 +/- 0.4 days; p = 0.016). The mean total aerobic bacterial burden in the lung parenchyma was statistically lower among the dogs receiving the silver-coated endotracheal tubes compared to those not receiving them (4.8 +/- 0.8 vs 5.4 +/- 9 log cfu/g lung tissue, respectively; p = 0.010). Pronounced differences were seen in the gross and histologic assessments of inflammation in the lung. Using an increasing severity scale of 0 to 12 to assess four components of histology (ie, hyperemia, edema, cellular infiltration, and bacterial presence), dogs receiving noncoated endotracheal tubes had statistically greater histology scores compared to dogs receiving silver-coated endotracheal tubes (7.1 plus minus 1.6 vs 2.8 plus minus 1.2, respectively; p < 0.001).

CONCLUSION

These results suggest that the silver coating of endotracheal tubes may delay the onset of and decrease the severity of lung colonization by aerobic bacteria. Based on these results, clinical studies are planned to determine the safety and clinical efficacy of silver-coated endotracheal tubes in patients requiring mechanical ventilation in the ICU setting.

A randomized clinical trial of intermittent subglottic secretion drainage in patients receiving mechanical ventilation

OBJECTIVE

To study the effect of subglottic secretions drainage on the incidence of ventilator-associated pneumonia (VAP) in patients receiving mechanical ventilation.

DESIGN

A randomized clinical trial.

SETTING

A 12-bed general ICU.

PATIENTS

One hundred fifty patients with an expected duration of mechanical ventilation > 72 h were enrolled in the study.

INTERVENTION

Patients were randomly assigned to receive either an endotracheal tube for intermittent subglottic secretions drainage or a standard endotracheal tube.

OUTCOME MEASUREMENTS

Incidence of VAP, duration of mechanical ventilation, length of ICU stay, length of hospital stay, and mortality.

RESULTS

Seventy-five patients were randomized to subglottic secretion drainage, and 75 patients were randomized to the control group. The two groups were similar at the time of randomization with respect to demographic characteristics and severity of illness. VAP was seen in 3 patients (4%) receiving suction secretion drainage and in 12 patients (16%) in the control group (relative risk, 0.22; 95% confidence interval, 0.06 to 0.81; p = 0.014). The other outcome measures were not significantly different between the two groups.

CONCLUSION

Intermittent subglottic secretion drainage reduces the incidence of VAP in patients receiving mechanical ventilation.

The concomitant development of poly(vinyl chloride)-related biofilm and antimicrobial resistance in relation to ventilator-associated pneumonia

Ventilator-associated pneumonia is a major cause of death in intensive care patients and the endotracheal tube, commonly fabricated from poly(vinyl chloride) (PVC), is acknowledged as a significant factor in this. Bacteria colonise the biomaterial, thereby adopting a sessile mode of growth that progresses to the establishment of an antibiotic-resistant biofilm by the accretion of a protective glycocalyx. This study examined the sequential steps involved in the formation of biofilm on PVC by atomic force microscopy and the concomitant development of resistance to an antibiotic (ceftazidime) and to a non-antibiotic antimicrobial agent (hexetidine). Staphylococcus aureus and Pseudomonas aeruginosa isolated from ET tube biofilm were employed. The surface microrugosity of bacteria growing in sessile mode on PVC decreased significantly (p < 0.05) over the period 4, 24, 48 h and 5 d. The progressive accretion of bacterial glycocalyx was readily visualised in micrographs leading to a smoother surface topography with time. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) for ceftazidime and hexetidine against planktonic (suspension) S. aureus were lower than for Ps. aeruginosa. Furthermore, sessile populations of S. aureus and Ps. aeruginosa on PVC exhibited greater resistance to both ceftazidime and hexetidine when compared to planktonic bacterial growth. The efficacy of the agents, determined by kill kinetics, against sessile bacteria was dependent on age, with established biofilms (> or = 24 h) significantly more resistant (p < 0.05) than early sessile populations (< or = 4 h). Importantly, for practice, even newly colonised bacteria (1 h) were significantly more resistant to antibiotic than planktonic bacteria. Hexetidine was significantly more active (p < 0.05) than ceftazidime on biofilms of both isolates, irrespective of age, with total kill within 24 h treatment. Hexetidine may offer promise in the resolution of infection associated with PVC endotracheal tubes.

Epidemiology and risk factors for nosocomial pneumonia. Emphasis on prevention

VAP is a complex nosocomial infection, the disease expression and resulting patient outcome of which is dependent on host factors, the causative organism, the timing and adequacy of treatment, and the presence of intrinsic or inducible antibiotic resistance. Significant improvements have been achieved in our ability to reduce the occurrence of VAP in the hospital setting. Clinicians caring for mechanically ventilated patients should strive to develop focused programs for the prevention of VAP, other nosocomial infections, and the occurrence of antibiotic-resistant infections at their institutions. The benefits of such programs are well demonstrated. The components of a PDSA (Plan-Do-STUDY-Act) model that can be simply employed to develop a VAP prevention program are as follows: Stages Plan: 1. Identify potentially modifiable risk factors for VAP at the institutional level. 2. Develop a strategy to modify or prevent the occurrence of these risk factors. [figure: see text] Do: 1. Carry out the planned intervention strategy. 2. Identify problems in the implementation of the designed intervention. 3. Update the intervention with solutions for the identified problems. 4. Collect basic data (e.g., VAP rates, severity of illness).

STUDY

1. Analyze data. 2. Summarize the results. Act: 1. Determine the overall success or failure of the intervention. 2. Identify potential modifications to improve the intervention strategy. 3. Prepare for next PDSA cycle. Inherent in the development and application of such programs is the concept that they are continuous processes striving to improve clinical performance over time (Fig. 3). At any given institution, the most likely approach to the prevention of NP and VAP will be a multifaceted one, employing interventions aimed at reducing the occurrence of aerodigestive tract colonization with pathogenic bacteria and aspiration. To be successful, such quality improvement programs must be embraced at the institutional level. Only in this way can hospitals hope to successfully reduce their rates of VAP and sustain or improve upon those efforts over time.

Contribution of endotracheal tubes to the pathogenesis of ventilator-associated pneumonia

The contribution of ventilatory equipment to the pathogenesis of ventilator-associated pneumonia (VAP) is well-established but the design of endotracheal tubes has been improved only to reduce tracheal traumatization. However many factors, including the surface properties of the endotracheal tube, humidity of the ventilatory gases, ventilatory mode and nursing management result in the formation of an infective, highly viscous and adhesive layer inside of the endotracheal tube. Endotracheal tubes may contribute to the pathogenesis of VAP when infective particles of this adhesive layer are dislodged into the lower airways by shear forces imparted by the respiratory gasflow. The current state of research is reviewed and potential solutions to this problem are discussed.