Patterns and routes of tracheobronchial colonization in mechanically ventilated patients. The role of nutritional status in colonization of the lower airway by Pseudomonas species

Ventilator-associated pneumonia: The central role of transcolonization

Ventilator-associated pneumonia remain frequent and serious diseases since they are associated with considerable crude mortality. Pathophysiology is centered on modifications of regional bacterial flora, especially tracheobronchial tree and oropharyngeal sphere. Bacterial migration from an anatomical area to another seems to be the main explanation of these alterations which are called "transcolonization". The association of transcolonization and lack of tightness of the endotracheal tube cuff provides a direct pathway for bacteria from the upper to the subglottic airways, eventually leading to ventilator-associated pneumonia. Although modification of bacterial flora has been largely studied, the mechanism which underlays the ability of the implantation, growing and interactions with the local microbiome that leads to the observed transcolonization remains to be more clearly deciphered. The aim of our review is to emphasize the cornerstone importance of the "transcolonization" as a nosological entity playing a central role in ventilator-associated pneumonia.

Are tracheal surveillance cultures useful in the intensive care unit?

Endotracheal aspirate (ETA) surveillance cultures have been used to predict the microorganisms responsible for ventilator associated pneumonia (VAP) in intensive care unit (ICU) patients for 3 decades. However, although more than a dozen studies have been performed, the usefulness and the safety of this strategy are still debated. Tracheobronchial bacterial colonization often precedes the occurrence of VAP, and it has been postulated that the microbes present in the tracheal secretions a few days before VAP might be the same as those retrieved in the lower respiratory tract. A large number of studies, with heterogeneous designs and variable results, have questioned the possibility of predicting, by regular ETA cultures after the 48^th hour of mechanical ventilation (MV), the microbiology of VAP and therefore of determining the adequate antibiotic therapy to limit the over-prescription of broad spectrum molecules when following guidelines. Although it has shown some promising results, the strategy has not achieved unanimity because of some discordant data. The aim of this review is to provide an updated overview of the literature available in the field and to attempt to determine the strengths and weaknesses of antibiotic stewardship based on ETA surveillance cultures in VAP, particularly in the global context of drug resistant microorganism emergence and the crucial necessity of broad spectrum molecule preservation.

Ventilator-Associated Pneumonia Patients who Do Not Reduce Bacteria from the Lungs have a Worse Prognosis

The authors determined the significance of serial semi-quantitative bronchoalveolar lavage (BAL) culture results in patients undergoing therapy for ventilator-associated pneumonia. A total of 32 patients underwent at least 2 nonbronchoscopic BAL studies. Fourteen patients had methicillin-resistant Staphylococcus aureus(MRSA). Of these, 11 had more than 100 colony-forming units (cfu) of MRSA/mL of BAL from the follow-up BAL. Eighteen patients had an organism other than MRSA, and 7 of these patients had > 100 cfu of bacteria/mL of BAL from the follow-up BAL. Of the 18 patients with > 100 cfu of bacteria/mL of BAL at follow-up, 14 (79%) died, whereas only 5 of 14 (36%) patients who cleared their bacteria at follow-up died within 28 days. The inability to reduce the bacterial burden from the lower respiratory tract within the first few days of therapy for ventilator-associated pneumonia was associated with increased mortality.

Innate Mucosal Immune System Response of BALB/c vs C57BL/6 Mice to Injury in the Setting of Enteral and Parenteral Feeding

BACKGROUND

Outbred mice exhibit increased airway and intestinal immunoglobulin A (IgA) following injury when fed normal chow, consistent with humans. Parenteral nutrition (PN) eliminates IgA increases at both sites. Inbred mice are needed for detailed immunological studies; however, specific strains have not been evaluated for this purpose. BALB/c and C57BL/6 are common inbred mouse strains but demonstrate divergent immune responses to analogous stress. This study addressed which inbred mouse strain best replicates the outbred mouse and human immune response to injury.

METHODS

Intravenously cannulated mice received chow or PN for 5 days and then underwent sacrifice at 0 or 8 hours following controlled surgical injury (BALB/c: n = 16-21/group; C57BL/6: n = 12-15/group). Bronchoalveolar lavage (BAL) was analyzed by enzyme-linked immunosorbent assay for IgA, tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6, while small intestinal wash fluid (SIWF) was analyzed for IgA.

RESULTS

No significant increase in BAL IgA occurred following injury in chow- or PN-fed BALB/c mice (chow: P = .1; PN: P = .7) despite significant increases in BAL TNF-α and SIWF IgA (chow: 264 ± 28 vs 548 ± 37, P < .0001; PN: 150 ± 12 vs 301 ± 17, P < .0001). Injury significantly increased mucosal IgA in chow-fed C57BL/6 mice (BAL: 149 ± 33 vs 342 ± 87, P = .01; SIWF: 236 ± 28 vs 335 ± 32, P = .006) and BAL cytokines. After injury, PN-fed C57BL/6 mice exhibited no difference in BAL IgA (P = .9), BAL cytokines, or SIWF IgA (P = .1).

CONCLUSIONS

C57BL/6 mice exhibit similar airway responses to injury as outbred mice and humans, providing an appropriate model for studying mucosal responses to injury. The BALB/c mucosal immune system responds differently to injury and does not replicate the human injury response.

Accuracy of alpha amylase in diagnosing microaspiration in intubated critically-ill patients

OBJECTIVES

Amylase concentration in respiratory secretions was reported to be a potentially useful marker for aspiration and pneumonia. The aim of this study was to determine accuracy of α-amylase in diagnosing microaspiration in critically ill patients.

METHODS

Retrospective analysis of prospectively collected data collected in a medical ICU. All patients requiring mechanical ventilation for at least 48 h, and included in a previous randomized controlled trial were eligible for this study, provided that at least one tracheal aspirate was available for α-amylase measurement. As part of the initial trial, pepsin was quantitatively measured in all tracheal aspirates during a 48-h period. All tracheal aspirates were frozen, allowing subsequent measurement of α-amylase for the purpose of the current study. Microaspiration was defined as the presence of at least one positive tracheal aspirate for pepsin (>200 ng.mL-1). Abundant microaspiration was defined as the presence of pepsin at significant level in >74% of tracheal aspirates.

RESULTS

Amylase was measured in 1055 tracheal aspirates, collected from 109 patients. Using mean α-amylase level per patient, accuracy of α-amylase in diagnosing microaspiration was moderate (area under the receiver operator curve 0.72±0.05 [95%CI 0.61-0.83], for an α-amylase value of 1685 UI.L-1). However, when α-amylase levels, coming from all samples, were taken into account, area under the receiver operator curve was 0.56±0.05 [0.53-0.60]. Mean α-amylase level, and percentage of tracheal aspirates positive for α-amylase were significantly higher in patients with microaspiration, and in patients with abundant microaspiration compared with those with no microaspiration; and similar in patients with microaspiration compared with those with abundant microaspiration. α-amylase and pepsin were significantly correlated (r2 = 0.305, p = 0.001).

CONCLUSION

Accuracy of mean α-amylase in diagnosing microaspiration is moderate. Further, when all α-amylase levels were taken into account, α-amylase was inaccurate in diagnosing microaspiration, compared with pepsin.

Proinflammatory cytokine surge after injury stimulates an airway immunoglobulin a increase

BACKGROUND

: Injury stimulates an innate airway IgA response in severely injured patients, which also occurs in mice. Tumor necrosis factor (TNF)-α and interleukin (IL)-1β stimulate the production of polymeric immunoglobulin receptor, the protein required to transport immunoglobulin A (IgA) to mucosal surfaces. Blockade of TNF-α and IL-1β eliminates the airway IgA response to injury. IL-6 stimulates differentiation of B cells into IgA-secreting plasma cells at mucosal sites. We investigated the local and systemic kinetics of TNF-α, IL-1β, and IL-6 after injury in mice. We also hypothesized that injection of exogenous TNF-α, IL-1β, and IL-6 would replicate the airway IgA response to injury.

METHODS

: Experiment 1: male Institute of Cancer Research mice were randomized to uninjured controls (n = 8) or to surgical stress with laparotomy and neck incisions, with killing at 1, 2, 3, 5, or 8 hours after injury (n = 8/group). Bronchoalveolar lavage (BAL) and serum levels of TNF-α, IL-1β, and IL-6 were analyzed by enzyme-linked immunosorbent assay. Experiment 2: male Institute of Cancer Research mice were randomized to uninjured controls (n = 6), injury (surgical stress that was similar to experiment 1 except the peritoneum was left intact, n = 6), or cytokine injection with intraperitoneal injection of recombinant TNF-α, IL-1β, and IL-6. Animals were killed at 2 hours after injury, and nasal airway lavage and BAL IgA were analyzed by enzyme-linked immunosorbent assay.

RESULTS

: Experiment 1: BAL TNF-α, IL-1β, and IL-6 levels increased in bimodal pattern after injury at 3 hours and 8 hours versus controls (p < 0.05). Serum IL-6 did not increase at 3 hours, but did show a significant increase by 5 hours versus control (p < 0.05). Serum levels of TNF-α and IL-1β did not change. Experiment 2: both Injury and combination TNF-α, IL-1β, and IL-6 cytokine injection significantly increased IgA levels in airway lavage (BAL + nasal airway lavage) compared with control (p < 0.01 for both).

CONCLUSIONS

: Airway levels of TNF-α, IL-1β, and IL-6 increase in a bimodal pattern after injury with peaks at 3 hours and 8 hours, which do not correspond to serum changes. The peak at 8 hours is consistent with the known increase in airway IgA after injury. Intraperitoneal injection of a combination exogenous TNF-α, IL-1β, and IL-6 replicates the airway IgA increase after injury. This effect is not seen with individual cytokine injections.

Viral colonization in intubated patients: initial pathogen pattern and follow-up

INTRODUCTION

Colonization of the lower respiratory tract is an independent risk factor for ventilator-associated pneumonia. Little is known about the frequency of viral colonization on intubation and during mechanical ventilation.

METHODS

Overall, 65 eligible intubated patients with no initial signs of pulmonary infection were studied over a period of up to 7 days. Tracheobronchial aspirates were taken: (i) within 48 h after intubation; and (ii) when clinical signs of nosocomial tracheobronchitis were present, before extubation, or after 7 days. Presence of respiratory viruses was investigated using quantitative polymerase chain reaction.

RESULTS

Patients were 67 +/- 11 years old and had been in hospital for 5.1 +/- 8.4 days when intubated (major cause for intubation: cardio-pulmonary resuscitation 25/65, 38%). The average Acute Physiology and Chronic Evaluation II score was 27.3 +/- 4.9. Microbiology detected Candida spp. (17/65; 26%) and Staphylococcus aureus (methicillin sensitive: 11/65; 17%; methicillin resistant: 3/65; 5%) and only few respiratory viruses (4/65, 6%). Thirty-eight percent of the samples (25/65) were sterile. At the given endpoints, 27/65 (42%) patients were available for follow-up and only one aspirate became positive for respiratory syncytial virus (RSV).

CONCLUSIONS

After endotracheal intubation, fungi, but not viruses were most frequently isolated. Only one patient acquired RSV, therefore colonization with respiratory viruses does not seem to play a major role early after intubation.

Ventilator-associated pneumonia in long-term ventilator-assisted individuals

BACKGROUND

Information on the characteristics of pneumonia in long-term ventilator-assisted individuals is scarce. We evaluate the incidence, risk factors and outcome of ventilator-associated pneumonia (VAP) in a large series of chronically ventilated patients.

METHODS

All patients assisted in a chronic ventilator-dependent unit were prospectively followed up for the development of VAP. Patients with a new and persistent lung infiltrate and a purulent tracheal aspirate were suspected to have VAP. Pneumonia was considered microbiologically confirmed in the presence of (1) a positive blood culture and/or (2) ≥10⁵ CFU ml⁻¹ in quantitative bacterial culture of tracheal aspirates or ≥10³ CFU ml⁻¹ in quantitative mini-bronchoalveolar lavage cultures.

RESULTS

In total, 100 consecutive long-term ventilated individuals with spinal cord injury (mean age 49 years) were prospectively followed up. The length of mechanical ventilation before admission in the unit was 54±37 days, and the follow-up after admission was 119±127 days. There were 32 episodes of VAP in 27 patients (1.74 episodes per 1000 days of mechanical ventilation). By logistic regression analysis, hypoalbuminaemia (P=0.03), administration of antacids (P=0.002) and length of mechanical ventilation (P=0.05) were independent risk factors for VAP. The most frequently isolated organisms were Pseudomonas aeruginosa (62%), methicillin-resistant Staphylococcus aureus (25%) and Acinetobacter baumannii (15%); 9 (28%) episodes were polymicrobial. Antimicrobial treatment, including monotherapy in 66%, was successful in most patients. Only three patients (11%) died in relation to VAP.

CONCLUSIONS

Patients on long-term ventilation are at significant risk for the development of VAP, but the mortality is low.

[Association between aspiration pneumonia and malnutrition in patients from active geriatric units]

PURPOSE

To study the association between malnutrition and aspiration pneumonia (AP) in patients from active geriatric units and describe patients who developed AP.

METHODS

Cases of AP were identified from archived medical charts of two active geriatric units between 2001 and 2007 (n=2238). The prevalence of neurologic disorders, dysphagia and malnutrition was assessed in patients who developed AP and those who did not.

RESULTS

Cumulative incidence of AP was low in both units investigated (1.1%). Aspiration pneumonia was highly associated with neurologic disorders (stroke and Parkinson's disease) and dysphagia (p<0.01), and tended to be more prevalent in those who were malnourished (p<0.10). In AP cases, about 80% of patients were malnourished as assessed by the dietitians, a result supported by a high prevalence of nutritional risk indicators.

CONCLUSIONS

Results support the hypothesis that malnutrition could have contributed to AP in these two active geriatric units. Prevention and treatment of malnutrition, especially in dysphagic patients, could reduce risk of AP in hospitalized elderly.

Diversity and site-specificity of the oral microflora in the elderly

The purpose of the present study was to describe the bacterial diversity in the oral cavity of the elderly without root caries using bacterial microarrays, and to determine the site- and subject-specificity of bacterial colonization. Samples were collected from the tongue dorsum, mucosa of the buccal fold, hard palate, supragingival plaque from sound root surfaces, and subgingival plaque from the same roots. A new 16 S rRNA gene-based microarray method was used for the simultaneous detection of approximately 300 bacterial species. Overall, 175 species and clusters were detected, representing eight phyla. Species belonging to the genera Streptococcus, Veillonella, and Fusobacterium were common in all sites. The number of species per subject varied from 51 to 81. Statistical analyses revealed about 40 species or clusters with significant associations with at least one of the sites. The bacterial diversity was highest in the cheek and palate regions. Species typically associated with caries and periodontitis were detected rarely or not at all. The oral bacterial flora of the elderly appears to be diverse, and, to a large extent, site- rather than subject-specific.

Risk factors and outcome in ICU-acquired infections

BACKGROUND

Nosocomial infections are common in intensive care units (ICU). The objectives of this study were to determine risk factors of ICU-acquired infections, and potential mortality attributable to such infections.

METHODS

An observational study was performed in a 10-bed multidisciplinary ICU. For a period of 27 months, all patients admitted for >or=48 h were included. Infections were diagnosed according to Centers for Disease Control and Prevention definitions. Airway colonization was explored by molecular typing. Risk factors for infection were determined by multivariable logistic regression. Survival was analyzed with time-varying proportional hazards regression.

RESULTS

Of 278 patients, 81 (29%) were infected: urinary tract infections in 39 patients (14%), primary bloodstream infections in 25 (9%), surgical site infections in 22 (8%) and pneumonia in 21 (8%). Of the total of 147 episodes, Gram-negative bacilli were isolated in 90, Gram-positive cocci in 49 and Candida sp. in 25. Risk factors for pneumonia were mechanical ventilation [odds ratio (OR=7.9, CI 1.8-35), lack of enteral nutriment (OR=8.0, CI 1.4-45) and length of time at risk (OR=1.8, CI 1.2-2.8), while gastric acid inhibitors did not affect the risk (OR=0.99, CI 0.32-3.0). Transmission of bacteria from the stomach to the airway was not confirmed. The risk of death was increased as patients were infected with pneumonia [hazard ratio (HR)=3.6; CI: 1.6-8.1], or primary bloodstream infection (HR=2.5; CI: 1.2-5.4), independent of age and disease severity.

CONCLUSIONS

Mortality was increased by ICU-acquired pneumonia and primary bloodstream infections. Our findings did not support the gastro-pulmonary hypothesis of ICU-acquired pneumonia. The proposition that blood transfusions increase the risk of ICU-acquired nosocomial infections was not supported.

Injury stimulates an innate respiratory immunoglobulin a immune response in humans

BACKGROUND

Secretory immunoglobulin A (SIgA) is the specific immune antibacterial defense. Since pneumonia frequently complicates the course of trauma patients, we studied early airway immune responses after injury.

METHODS

Twelve severely injured, intubated (expected for >/=5 d) patients had tracheal and bilateral lung lavage (BAL) within 30 hours of injury (n = 12). Epithelial lining fluid (ELF) volume and SIgA were measured by urea dilution and enzyme-linked immunosorbent assay (ELISA), respectively. Control BAL specimens were obtained from eight healthy elective surgical patients. Anatomically based comparisons were made between groups with Welch's unpaired t test. To verify human data, 30 male mice received no injury (time 0, n = 7) or injury with abdominal and neck incisions and were killed for airway IgA at 4 (n = 7), 8 (n = 8), and 24 (n = 8) hours. Analysis of variance (ANOVA) and Fisher's protected least significant difference testing was used to analyze animal data.

RESULTS

Initial trauma patient SIgA concentration (SIgA/mL ELF) increased compared with control in the lungs bilaterally (p < 0.05 both right and left). ELF volume was significantly higher in the right lung (p = 0.02) and just missed statistical significance (p = 0.07) on the left. Mouse IgA increased 8 hours after stress (p < 0.05 versus 0, 4, and 24 hours) and returned to normal by 24 hours.

CONCLUSION

A previously unrecognized innate human airway mucosal immune response with increased airway SIgA and ELF occurs after severe injury and is reproducible experimentally. This accessible, quantifiable human response allows study of clinical strategies to reduce infections via mucosal immune therapies.

Bacterial Infections

In Osier’s time, bacterial pneumonia was a dreaded event, so important that he borrowed John Bunyan’s characterization of tuberculosis and anointed the pneumococcus, as the prime pathogen, “Captain of the men of death.”1 One hundred years later much has changed, but much remains the same. Pneumonia is now the sixth most common cause of death and the most common lethal infection in the United States. Hospital-acquired pneumonia is now the second most common nosocomial infection.2 It was documented as a complication in 0.6% of patients in a national surveillance study,3 and has been reported in as many as 20% of patients in critical care units.4 Furthermore, it is the leading cause of death among nosocomial infections.5 Leu and colleagues6 were able to associate one third of the mortality in patients with nosocomial pneumonia to the infection itself. The increase in hospital stay, which averaged 7 days, was statistically significant. It has been estimated that nosocomial pneumonia produces costs in excess of $500 million each year in the United States, largely related to the increased length of hospital stay.

Prevention measures for ventilator-associated pneumonia: a new focus on the endotracheal tube

PURPOSE OF REVIEW

The aim of this article is to analyze the aspects related to the endotracheal tube which may influence the development of ventilator-associated pneumonia and to review the possible measures of prevention.

RECENT FINDINGS

The endotracheal tube participates in the pathogenesis of ventilator-associated pneumonia by the elimination of natural defense mechanisms, thereby allowing the entry of bacteria by the aspiration of subglottic secretions or the formation of biofilm on the endotracheal tube. The preventive measures of ventilator-associated pneumonia related to the endotracheal tube include these two mechanisms. It has been suggested that substitution of the endotracheal tube by early tracheostomy may reduce the risk of ventilator-associated pneumonia.

SUMMARY

Aspiration of the subglottic secretions seems to be an effective measure with little risk; decontamination or exhaustive control of the sealing of the cuff has not demonstrated a positive risk/benefit balance. The causal relationship between biofilm and ventilator-associated pneumonia has not been clearly established. Treatment of the biofilm with antibiotics, changes in the composition of the endotracheal tube or mechanical cleansing have achieved a reduction or elimination of the biofilm but their effect on the incidence of ventilator-associated pneumonia has not been studied. The benefit of early tracheostomy in reducing ventilator-associated pneumonia is still controversial.

Tracheobronchitis in the Intensive Care Unit

Tracheobronchitis can be broadly defined as inflammation of the airways between the larynx and the bronchioles. Clinically, this syndrome is recognized by an increase in the volume and purulence of the lower respiratory tract secretions and is frequently associated with signs of variable airflow obstruction. In the intensive care unit (ICU), tracheobronchitis is a relatively common problem with an incidence as high as 10.6% [1]. Although tracheobronchitis is associated with a significantly longer length of ICU stay and a prolonged need for mechanical ventilation, it has not been shown to increase mortality. These outcomes can be improved through the use of antimicrobial agents [1].

[Management of ventilator acquired pneumonia]

Ventilator-associated pneumonia occurs in the evolution of 8 to 70% of patients in the Intensive Care Unit. It is the main site of nosocomial infection for mechanically ventilated patients. Nosocomial pneumonia represents an important cause of morbidity and mortality, despite progresses in antibiotic prescription, use of intensive care and prevention. This review is based on the ATS guidelines, and reviews epidemiology, diagnosis and treatment of ventilator-acquired pneumonia, in non-immunocompromised adults.

Neumonía por Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the leading causes of Gram-negative nosocomial pneumonia. It is the most common cause of ventilator-associated pneumonia and carries the highest mortality among hospital-acquired infections. P. aeruginosa produces a large number of toxins and surface components that make it especially virulent compared with other microorganisms. These include pili, flagella, membrane bound lipopolysaccharide, and secreted products such as exotoxins A, S and U, elastase, alkaline protease, cytotoxins and phospholipases. The most common mechanism of infection in mechanically ventilated patients is through aspiration of upper respiratory tract secretions previously colonized in the process of routine nursing care or via contaminated hands of hospital personnel. Intravenous therapy with an antipseudomonal regimen should be started immediately when P. aeruginosa pneumonia is suspected or confirmed. Empiric therapy with drugs active against P. aeruginosa should be started, especially in patients who have received previous antibiotics or present late-onset pneumonia.

Adherence to simple and effective measures reduces the incidence of ventilator-associated pneumonia

PURPOSE

Several modalities have been shown to be individually effective in reducing the incidence (and hence associated morbidity, mortality, and costs) of ventilator-associated pneumonia, but their implementation into clinical practice is inconsistent. We introduced an intensive care unit protocol and measured its effect on ventilator-associated pneumonia.

METHODS

A multidisciplinary team constructed a multifaceted protocol incorporating low risk and low cost strategies, many of which had independent advantages of their own. Some components were already in use, and their importance was emphasized to improve compliance. New strategies included elevation of the head of the bed, transpyloric enteral feeding, and antiseptic mouthwash. The approach to implementation and maintenance included education, monitoring, audits and feedback to encourage compliance with the protocol.

RESULTS

The implementation of this prevention protocol reduced the incidence of ventilator-associated pneumonia from a baseline of 94 cases per year or 26.7 per 1,000 ventilator days to 51.3 per year or 12.5 per 1,000 ventilator days, i.e., about 50% of the pre-protocol rate (P < 0.0001).

CONCLUSION

Adherence to simple and effective measures can reduce the incidence of ventilator-associated pneumonia. The protocol described was inexpensive and effective, and estimated savings are large. Implementation and maintenance of gains require a multidisciplinary approach, with buy-in from all team members, and ongoing monitoring, education, and feedback to the participants.

Diagnosis of ventilator-associated pneumonia

The diagnosis of ventilator pneumonia remains a controversial area. Use of standard clinical criteria has been found to be inadequate. Use of a clinical pulmonary infection score (CPIS) has improved the diagnostic utility of clinical criteria. For the intubated patient, there is ready access to the lower respiratory tract. Samples include endotracheal aspirates, bronchoalveolar lavage and protected brush specimen. The latter two can be obtained blindly or via a bronchoscope. The culture results are more meaningful if reported in a semi-quantitative model. There is increasing evidence that culture results predict mortality and can be used to direct duration and type of therapy.

Nosocomial pneumonia in the intensive care unit: controversies and dilemmas

Nosocomial pneumonia (NP), and its most serious form, ventilator-associated pneumonia (VAP), is a major cause of morbidity and mortality in the ICU. Numerous controversies exist, from diagnostic criteria to prevention and treatment, including the issues of attributable mortality of VAP, differences in the approach to early and late VAP, and the best diagnostic methods. Initial, accurate therapy is one of the most important factors determining outcome in VAP. Antibiotic monotherapy versus combination therapy is not clearly defined, as clinicians struggle with the dual risk of inadequate therapy negatively affecting outcome and overtreatment promoting antibiotic resistance. The role of airway and gastrointestinal colonization and innovative preventive strategies such as noninvasive ventilation, antibiotic rotation, and aerosolized antibiotics are discussed. No uniform standards exist for the approach to VAP. The authors highlight the major controversies and dilemmas in the clinical approach to VAP, with recommendations for the bedside management of these patients.

Bacterial infections in patients requiring admission for an acute exacerbation of COPD; a 1-year prospective study

STUDY OBJECTIVE

To investigate the frequency of respiratory bacterial infections in hospitalized patients, admitted with an acute exacerbation of chronic obstructive pulmonary disease (COPD), to identify the responsible pathogens by sputum culture and to assess patient characteristics in relation to sputum culture results.

METHODS

We prospectively evaluated clinical data and sputum culture results of 171 patients, admitted to the pulmonology department of the University Hospital Maastricht with an acute exacerbation of COPD from 1st January 1999 until 31st December 1999.

RESULTS

Eighty-five patients (50%) had positive sputum cultures, indicating the presence of bacterial infection. Pathogens most frequently isolated were: Haemophilus influenzae (45%), Streptococcus pneumoniae (27%), and Pseudomonas aeruginosa (15%). Patients with more severely compromised lung function had a higher incidence of bacterial infections (P = 0.026). There were no significant differences in age, lung function parameters, blood gas results and length of hospital stay between patients with and without bacterial infection. There were no correlations between the type of bacteria isolated and clinical characteristics.

CONCLUSION

Incidence of bacterial infection during acute exacerbations of COPD is about 50%. Patients with and without bacterial infection are not different in clinical characteristics or in outcome parameters. Patients with lower FEV1 have a higher incidence of bacterial infections, but there is no difference in the type of bacterial infection. In the future, the pathogenic role of bacterial infection in exacerbations of COPD should be further investigated, especially the role of bacterial infection in relation to local and systemic inflammation.

Colonization of lower respiratory tract with anaerobic bacteria in mechanically ventilated patients

OBJECTIVE

To study lower respiratory tract colonization by anaerobic bacteria in ICU patients on prolonged mechanical ventilation using two types of protected tracheal sampling methods.

DESIGN AND SETTING

Prospective clinical investigation in the intensive care unit of a university hospital.

PATIENTS

Twenty-six consecutive patients mechanically ventilated within 24 h after their admission in ICU and with expected duration of mechanical ventilation longer than 7 days.

MEASUREMENTS AND RESULTS

Two types of protected tracheal sampling methods were obtained without the use of bronchoscopic guidance on the day following intubation and twice a week until extubation: protected tracheal aspiration and protected tracheal specimen brush. Specific methods for anaerobic isolation were used. Early colonization was defined if colonization occurred within the first 5 days after intubation. Of the 26 patients studied 22 were colonized by at least one bacterial strain. Twenty-one patients were colonized by aerobic and 15 by anaerobic bacteria. Twenty-eight anaerobic strains were identified, with bacterial counts higher than 10(3) cfu/ml in 11 cases. Of the 15 patients colonized by anaerobes 14 were also colonized by aerobic bacteria. The use of protected specimens ruled out oropharyngeal contamination. Early onset colonization occurred in 16 of 22 patients colonized by aerobes and in 8 of 15 patients colonized by anaerobes. Five patients developed ventilatory-acquired pneumonia following colonization (by anaerobic bacteria in two cases). In eight patients colonization by anaerobic bacteria occurred despite antimicrobial therapy.

CONCLUSIONS

These results show that anaerobic bacteria frequently colonize the lower respiratory tract of mechanically ventilated patients and underline the potential importance of the anaerobic bacteria in ventilatory acquired pneumonia.

The nasogastric feeding tube as a risk factor for aspiration and aspiration pneumonia

PURPOSE OF REVIEW

Aspiration is one of the most common complications in enterally fed patients. The source of aspiration is due to the accumulation of secretions in the pharynx of reflux gastric contents from the stomach into the pharynx. The true prevalence of aspiration is difficult to determine because of vague definitions, poor assessment methods, and varying levels of clinical recognition.

RECENT FINDINGS

There is evidence in the literature showing that the presence of a nasogastric feeding tube is associated with colonization and aspiration of pharyngeal secretions and gastric contents leading to a high incidence of Gram-negative pneumonia in patients on enteral nutrition. However, other aspects may be equally important and should also be considered when evaluating a patient suspected of having aspiration and aspiration pneumonia. The mechanisms responsible for aspiration in patients bearing a nasogastric feeding tube are (1). loss of anatomical integrity of the upper and lower esophageal sphincters, (2). increase in the frequency of transient lower esophageal sphincter relaxations, and (3). desensitization of the pharyngoglottal adduction reflex.

SUMMARY

Sometimes it is possible to differentiate whether the aspirate is gastric or pharyngeal. The kind of bacterial contamination is, however, more difficult to establish. Oral or dental disease, antibiotic therapy, systemic illness or malnutrition and reduction of salivary flow are responsible for colonization of Gram-negative bacteria in oral and pharyngeal flora in nasogastric-tube-fed patients. The use of a nasogastric feeding tube and the administration of food increase gastric pH and lead to colonization of gastric secretions. It has also been suggested that gastric bacteria could migrate upward along the tube and colonize the pharynx.

Staple-assisted laryngectomy for intractable aspiration

Staple-assisted laryngectomy is a unique method previously reported by Lukyanchenko to prevent wound contamination by using a stapling device for suturing pharyngeal defects in total laryngectomy. We have modified his method and applied it to prevent a postoperative pharyngocutaneous fistula in the treatment of intractable aspiration. In contrast to laryngeal cancer patients, a combined use of an intraluminal light to guide the dissection and laryngofissure to pull the epiglottis can be used to facilitate the use of the stapling device. For most patients with intractable aspiration who have significant malnutrition and drug-resistant bacterial colonization of the pharynx, this method offers certain advantages. This report describes our successful experience with this method in the management of patients with intractable aspiration.

Prolonged mechanical ventilation and tracheostomy in the elderly

Mechanical ventilation is a life-sustaining technology used with increasing frequency in the elderly population. Prolonged mechanical ventilation is associated with high morbidity, mortality, and poor functional status. Care of these complex patients requires a coordinated multidisciplinary approach to optimize outcome. To minimize mortality and morbidity and contain health care costs, it is essential to identify patients at high risk for prolonged ventilation and to implement early interventions to curtail functional decline. In this article, the incidence and outcome of prolonged mechanical ventilation is reviewed, along with interventions to promote recovery. In particular, the role of tracheostomy timing and placement is discussed.

Impact of oral diseases on systemic health in the elderly: diabetes mellitus and aspiration pneumonia

Evidence is increasing that oral health has important impacts on systemic health. This paper presents data from the third National Health and Nutrition Examination Survey (NHANES III) describing the prevalence of dental caries and periodontal diseases in the older adult population. It then evaluates published reports and presents data from clinical and epidemiologic studies on relationships among oral health status, chronic oral infections (of which caries and periodontitis predominate), and certain systemic diseases, specifically focusing on type 2 diabetes and aspiration pneumonia. Both of these diseases increase in occurrence and impact in older age groups. The NHANES III data demonstrate that dental caries and periodontal diseases occur with substantial frequency and represent a burden of unmet treatment need in older adults. Our review found clinical and epidemiologic evidence to support considering periodontal infection a risk factor for poor glycemic control in type 2 diabetes; however, there is limited representation of older adults in reports of this relationship. For aspiration pneumonia, several lines of evidence support oral health status as an important etiologic factor. Additional clinical studies designed specifically to evaluate the effects of treating periodontal infection on glycemic control and improving oral health status in reducing the risk of aspiration pneumonia are warranted. Although further establishing causal relationships among a set of increasingly more frequently demonstrated associations is indicated, there is evidence to support recommending oral care regimens in protocols for managing type 2 diabetes and preventing aspiration pneumonia.

Respiratory infection in the chronically critically ill patient. Ventilator-associated pneumonia and tracheobronchitis

The long-term ventilated patient is at high risk for developing nosocomial pneumonia or tracheobronchitis. In general, the frequency of infection increases with the duration of mechanical ventilation, but the risk appears to be greatest in the first week of intubation. Although these types of infection are common and may have morbidity and mortality impact, the daily risk is less in the long-term ventilated patient than in the acutely ill intubated patient. This reduced daily risk may reflect a "survivor effect," with less healthy patients dying early in the hospital stay and not surviving long enough to undergo tracheostomy and long-term ventilation. A number of factors predispose these patients to infection, including host defense impairment and exposure to large numbers of bacteria. This exposure can occur through the airway, and proper care of respiratory therapy devices is essential to minimize the risk for infection. Most infections of the lower respiratory tract are preceded by airway colonization with EGN bacteria and, with improvement in host defenses and nutrition, infection in the face of colonization is less likely. In some patients, colonization can be eliminated. When the long-term ventilated patient does develop infection, it generally involves highly resistant gram-negative or gram-positive organisms and therapy should be prompt and appropriate. Not all such patients respond to systemic antibiotics, and the use of adjunctive aerosol therapy may have benefit for those with either tracheobronchitis or pneumonia, especially if highly resistant pathogens are present.

The effect of acidified enteral feeds on gastric colonization in critically ill patients: results of a multicenter randomized trial. Canadian Critical Care Trials Group

OBJECTIVE

To evaluate the effect of acidified enteral feeds on gastric colonization in critically ill patients compared with a standard feeding formula.

DESIGN

Randomized, double-blind, multicenter trial.

SETTING

Eight mixed intensive care units at tertiary care hospitals.

PATIENTS

We recruited mechanically ventilated critically ill patients expected to remain ventilated for >48 hrs. We excluded patients with gastrointestinal bleeding, acidemia, and renal failure requiring dialysis. We enrolled 120 patients; 38% were female, age (mean +/- SD) was 57.6+/-19.3 yrs, and Acute Physiology and Chronic Health Evaluation II score (mean +/- SD) was 21.6+/-7.6.

INTERVENTIONS

Vital High Nitrogen (Abbott Laboratories, Ross Products Division, Columbus, OH) was used as the standard feeding formula for the control group (pH = 6.5). Hydrochloric acid was added to Vital High Nitrogen to achieve a pH of 3.5 in the experimental group.

MEASUREMENTS AND MAIN RESULTS

The main outcome measure was gastric colonization. Secondary outcomes included gastric pH, pneumonia, and mortality. The mean gastric pH in patients receiving acid feeds was lower (pH = 3.3) compared with controls (pH = 4.6; p<.05). One patient (2%) on acid feeds was colonized in the stomach with pathogenic bacteria, compared with 20 patients (43%) in the control group (p<.001). There was no difference in the incidence of pneumonia (6.1% in the acid feeds group vs. 15% in the control group; p = .19). Overall, there were 15 deaths in the acid feeds group and seven in the control group (p = .10); four patients in the acid feeds group and three in the control group died during the study period (p not significant).

CONCLUSIONS

Acidified enteral feeds preserve gastric acidity and substantially reduce gastric colonization in critically ill patients. Larger studies are needed to examine its effect on ventilator-associated pneumonia and mortality.

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.

Pulmonary host defenses. Implications for therapy

Pulmonary host defenses comprise a redundant system of protective mechanisms against invasion of the lungs by pathogenic microbes. The upper and lower airways are uniquely suited to contain and remove organisms that gain access to the respiratory mucosa. If the balance between host and organism is disputed, however, microbial clearance may be ineffective, and infection established. Pulmonary host defense mechanisms, which provide the basis for several current therapeutic strategies, are reviewed.

Therapy for ventilator-associated pneumonia

Pneumonia is a serious complication of mechanical ventilation. Pneumonia occurs despite the best efforts at prevention. Multiple methods available to prevent ventilator-associated pneumonia are reviewed, and ventilation-associated pneumonia (VAP) is divided into early versus late onset. The authors discuss the organisms associated with each of these situations, the empiric antibiotic choices, and specific issues related to antibiotic therapy such as resistance, pharmcodynamics, tissue penetration, and types of modifications necessary in empiric choice when the cause of VAP is identified.

Role of different routes of tracheal colonization in the development of pneumonia in patients receiving mechanical ventilation

STUDY OBJECTIVE

To evaluate the importance of the different pathogenic pathways involved in the development of ventilator-associated pneumonia (VAP).

DESIGN

Prospective study.

SETTING

An 18-bed medical and surgical ICU.

PATIENTS

One hundred twenty-three patients receiving mechanical ventilation (MV).

INTERVENTIONS

Tracheal, pharyngeal, and gastric samples were obtained simultaneously every 24 h. In cases where VAP was suspected clinically, bronchoscopy with protected specimen brush and BAL were performed. Semiquantitative cultures of pharyngeal samples and quantitative cultures for the remaining samples were obtained.

RESULTS

Tracheal colonization at some time during MV was observed in 110 patients (89%). Eighty patients had initial colonization, 34 patients had primary colonization, and 50 patients had secondary colonization. Nineteen patients had VAP, and 25 organisms were isolated. For none of these organisms was the stomach the initial site of colonization. Gram-positive organisms colonized mainly in the trachea during the first 24 h of MV (p<0.001). On the contrary, enteric Gram-negative bacilli (p<0.001) and yeasts (p<0.002) colonized the trachea secondarily. Previous endotracheal intubation (p<0.005) and acute renal failure before admission to the ICU (p<0.001) were associated with colonization by Pseudomonas aeruginosa; prior antibiotics were associated with colonization by Acinetobacter baumanii (p<0.05) and yeasts (p<0.006); and cranial trauma was associated with Staphylococcus aureus colonization (p<0.035).

CONCLUSIONS

Although the stomach can be a source of organisms that colonize the tracheobronchial tree, it is a much less common source of the bacteria that cause VAP. The pattern of colonization and risk factors may be different according to the type of organisms involved.

Bacterial colonization patterns in mechanically ventilated patients with traumatic and medical head injury. Incidence, risk factors, and association with ventilator-associated pneumonia

We prospectively evaluated the relation of upper airway, lower airway, and gastric colonization patterns with the development of pneumonia and its etiology in 48 patients with surgical (n = 25) and medical (n = 23) head injury. Initial colonization was assessed by cultures of nasal and pharyngeal swabs, tracheobronchial aspirates, gastric juice, and bronchoscopically retrieved protected specimen brush. Follow-up colonization was determined until the end points extubation, suspected ventilator-associated pneumonia (VAP), or death. The initial colonization rate at any site at ICU admission was 39/47 (83%). It mainly accounted for Group I pathogens (Streptococcus pneumoniae, Staphylococcus aureus, Hemophilus influenzae) of the upper and lower airways. At follow-up, colonization rates with Group II pathogens (Gram-negative enteric bacilli and Pseudomonas spp.) increased significantly. The high initial bacterial load with Group I pathogens of the upper airways and trachea decreased during Days 2 to 4, whereas that of Group II pathogens increased. Upper airway colonization was an independent predictor of follow-up tracheobronchial colonization (odds ratio [OR], 9.9; 95% confidence interval [CI], 1.8 to 56.3 for initial colonization with Group I pathogens; OR, 23.9; 95% CI, 3.8 to 153.3 for follow-up colonization with Group II pathogens). Previous (short-term) antibiotics had a protective effect against colonization with Group I pathogens of the lower respiratory tract (OR, 0.2; 95% CI, 0.05 to 0.86), but they were a risk factor for colonization with Group II pathogens (OR, 6.1; 95% CI, 1.3 to 29). Initial tracheobronchial colonization with Group I pathogens was associated with a higher probability of early onset pneumonia (OR, 4. 1; 95% CI, 0.7 to 23.3), whereas prolonged antibiotic treatment (> 24 h) independently predicted late-onset pneumonia (OR, 9.2; 95% CI, 1.7 to 51.3). We conclude that patients with head injury are colonized in the airways mainly by Group I pathogens early in the evolution of illness. The upper airways represent the main reservoir for subsequent lower airway colonization with Group I pathogens. Previous (short-term) antibiotic treatment is protective against initial tracheobronchial colonization with Group I pathogens, but it represents a risk factor for subsequent lower airway colonization by Group II pathogens.

Hospital-acquired pneumonia: epidemiology, etiology, and treatment

Despite improvements in diagnosis, treatment, and prevention, hospital-acquired pneumonia (HAP) remains the number one cause of nosocomial mortality. This article reviews the current knowledge regarding the incidence, epidemiology, and causes of HAP, with the appreciation that the available information is incomplete and that controversies are common, and thus the authors provide a rational approach to the initial management of HAP in immunocompetent adults. A discussion of therapy and what to do with patients who do not respond to the empiric therapy are included. The American Thoracic Society (ATS) statement on HAP has served as a foundation for this review but has been supplemented by newer literature that was not available when the ATS statement was developed.

Risks and routes for ventilator-associated pneumonia with Pseudomonas aeruginosa

In a prospective study, we screened specimens from 190 mechanically ventilated patients hospitalized in a surgical intensive care unit, and from the environment to assess risks and routes of colonization/infection. Specimens from various sites were collected on admission and once a week throughout each patient's stay. All P. aeruginosa isolates were typed by determination of DNA patterns. Data were collected from patients to identify risk factors. In vitro production of exoenzymes of different strains were compared. Forty-four patients were colonized with P. aeruginosa on the bronchopulmonary tract and 13 suffered from pneumonia. The 7-d and 14-d Kaplan-Meier rates of colonization were 2.21 and 7.03%. Twenty-one patterns of bronchopulmonary tract isolates were isolated from single patients and 10 from several patients. The lower airway was often the first site of colonization. The contribution of environment to patient colonization appeared to be small. The length of hospitalization, the previous use of third-generation cephalosporins less effective against P. aeruginosa, and chronic obstructive pulmonary disease were the most significant predictors of colonization/infection. The in vitro exoprotein production was not correlated with the presence of pneumonia. Our study may be useful in identifying which patients in the mechanically ventilated population are at greater risk of P. aeruginosa pneumonia.

Recurrent Pseudomonas aeruginosa pneumonia in ventilated patients: relapse or reinfection?

A prospective observational study was performed to determine whether recurrent episodes of pneumonia caused by Pseudomonas aeruginosa in ventilated patients were due to a relapse of the previous clone or to reinfection with a new one. Diagnosis was based on quantitative cultures of secretions obtained by bronchoscopy. Comparison of strains was made by chromosomal fingerprinting based on pulsed field gel electrophoresis (PFGE). Thirty-three (89.1%) of 37 patients survived the initial week after pneumonia diagnosis; six survivors (18.1%) had multiple episodes caused by the same species. Presence of adult respiratory distress syndrome (83.3% versus 22.2%, p = 0.02) was the only factor significantly associated with clinical recurrences. The 16 isolates from five patients (nine recurrences) were analyzed by PFGE. All new isolates from recurrent episodes, excepting one, were considered as relapses. These data suggest that most recurrent episodes of P. aeruginosa pneumonia in ventilated patients occur due to persistence of strains present in a prior infection.

Total enteral nutrition versus total parenteral nutrition during pediatric extracorporeal membrane oxygenation

OBJECTIVE

To evaluate the adequacy, tolerance, and complications of enteral nutrition, compared with parenteral nutrition, in pediatric patients requiring extracorporeal membrane oxygenation (ECMO).

DESIGN

A retrospective chart review of all patients placed on extracorporeal life support from January 1991 through December 1995.

SETTING

Medical/surgical pediatric intensive care unit at Egleston Children's Hospital, a tertiary care pediatric center.

PATIENTS

Twenty-nine consecutive pediatric patients who required ECMO and were provided nutritional support, either enterally or parenterally. Group A consisted of 14 patients who were provided nutritional support using total parenteral nutrition. Group B consisted of 15 patients. Two patients were excluded from group B because their ECMO run was <36 hrs, leaving insufficient data for analysis. The remaining 13 patients were provided total enteral nutrition during ECMO.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Both groups were similar in age, weight, pre-ECMO oxygenation index, alveolar-arterial oxygen difference, type, and duration of ECMO (p = NS). Comparison of percent ideal body weight on admission did not show a statistical difference between groups A and B (p = .883). There was no difference between the two groups in the time needed to achieve caloric goal (p = .536) from the initiation of ECMO. No complications were associated with the utilization of enteral feedings. Savings for the nutritional supplement was estimated to be $170 per day for the enterally fed group. The percentage of patients surviving was higher in the enterally fed patients compared with the parenterally fed group (79% vs. 100%), although this difference was not statistically significant (p = .47).

CONCLUSIONS

Enteral nutrition in patients receiving either venoarterial or venovenous ECMO is well tolerated, provides adequate nutrition, is cost effective, and is without complications, as compared with parenteral nutrition. These data suggest that total enteral nutrition can be safely administered for nutritional support in pediatric patients undergoing either venoarterial or venovenous ECMO.

Oropharyngeal or gastric colonization and nosocomial pneumonia in adult intensive care unit patients. A prospective study based on genomic DNA analysis

Colonization of the digestive tract has been supposed to be the source of many hospital-acquired infections, especially nosocomial pneumonia. To assess the relationship between oropharyngeal and gastric colonization and subsequent occurrence of nosocomial pneumonia, we prospectively studied 86 ventilated, intensive care unit (ICU) patients. Oropharyngeal or gastric colonizations were detected and quantified on admission and twice weekly during ICU stay. When nosocomial pneumonia was suspected on clinical grounds (new chest X-ray infiltrate and purulent tracheal secretions), diagnosis was assessed on fiberoptic bronchoscopy with quantitative cultures of a protected specimen brush sampling and/or a plugged telescoping catheter sampling yielding > or = 10(3) cfu/ml of at least one microorganism. Bacterial strains responsible for colonization and infection (Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacteriaceae, and Staphylococcus aureus) were compared using pulsed-field electrophoresis. A total of 31 cases (36%) of pneumonia were diagnosed. Oropharyngeal colonization, detected either on admission or from subsequent samples, was a predominant factor of nosocomial pneumonia as compared with gastric colonization. For instance, oropharyngeal colonization with A. baumannii yielded a 7.45-fold estimated increased risk of pneumonia as compared with patients not yet or not identically colonized (p = 0.0004). DNA genomic analysis demonstrated that an identical strain was isolated from oropharyngeal or gastric samples and bronchial samples in all but three cases of pneumonia, due to S. aureus. These findings provide better knowledge of the pathophysiology of nosocomial pneumonia in mechanically ventilated patients.