Changing heat and moisture exchangers every 48 hours does not increase the incidence of nosocomial pneumonia

Unusually High Incidences of Staphylococcus aureus Infection within Studies of Ventilator Associated Pneumonia Prevention Using Topical Antibiotics: Benchmarking the Evidence Base

Selective digestive decontamination (SDD, topical antibiotic regimens applied to the respiratory tract) appears effective for preventing ventilator associated pneumonia (VAP) in intensive care unit (ICU) patients. However, potential contextual effects of SDD on Staphylococcus aureus infections in the ICU remain unclear. The S. aureus ventilator associated pneumonia (S. aureus VAP), VAP overall and S. aureus bacteremia incidences within component (control and intervention) groups within 27 SDD studies were benchmarked against 115 observational groups. Component groups from 66 studies of various interventions other than SDD provided additional points of reference. In 27 SDD study control groups, the mean S. aureus VAP incidence is 9.6% (95% CI; 6.9–13.2) versus a benchmark derived from 115 observational groups being 4.8% (95% CI; 4.2–5.6). In nine SDD study control groups the mean S. aureus bacteremia incidence is 3.8% (95% CI; 2.1–5.7) versus a benchmark derived from 10 observational groups being 2.1% (95% CI; 1.1–4.1). The incidences of S. aureus VAP and S. aureus bacteremia within the control groups of SDD studies are each higher than literature derived benchmarks. Paradoxically, within the SDD intervention groups, the incidences of both S. aureus VAP and VAP overall are more similar to the benchmarks.

Impact of selective digestive decontamination on respiratory tract Candida among patients with suspected ventilator-associated pneumonia. A meta-analysis

The purpose here is to establish the incidence of respiratory tract colonization with Candida (RT Candida) among ICU patients receiving mechanical ventilation within studies in the literature. Also of interest is its relationship with candidemia and the relative importance of topical antibiotic (TA) use as within studies of selective digestive decontamination (SDD) versus other candidate risk factors towards it. The incidence of RT Candida was extracted from component (control and intervention) groups decanted from studies of various TA and non-TA ICU infection prevention methods with summary estimates derived using random effects. A benchmark RT Candida incidence to provide overarching calibration was derived using (observational) groups from studies without any prevention method under study. A multi-level regression model of group level data was undertaken using generalized estimating equation (GEE) methods. RT Candida data were sourced from 113 studies. The benchmark RT Candida incidence is 1.3; 0.9-1.8 % (mean and 95 % confidence intervals). Membership of a concurrent control group of a study of SDD (p = 0.02), the group-wide presence of candidemia risk factors (p < 0.001), and proportion of trauma admissions (p = 0.004), but neither the year of study publication, nor membership of any other component group, nor the mode of respiratory sampling are predictive of the RT Candida incidence. RT Candida and candidemia incidences are correlated. RT Candida incidence can serve as a basis for benchmarking. Several relationships have been identified. The increased incidence among concurrent control groups of SDD studies cannot be appreciated in any single study examined in isolation.

Guidelines for the prevention of ventilator-associated pneumonia and their implementation. The Spanish "Zero-VAP" bundle

BACKGROUND

"Zero-VAP" is a proposal for the implementation of a simultaneous multimodal intervention in Spanish intensive care units (ICU) consisting of a bundle of ventilator-associated pneumonia (VAP) prevention measures.

METHODS/DESIGN

An initiative of the Spanish Societies of Intensive Care Medicine and of Intensive Care Nurses, the project is supported by the Spanish Ministry of Health, and participation is voluntary. In addition to guidelines for VAP prevention, the "Zero-VAP" Project incorporates an integral patient safety program and continuous online validation of the application of the bundle. For the latter, VAP episodes and participation indices are entered into the web-based Spanish ICU Infection Surveillance Program "ENVIN-HELICS" database, which provides continuous information about local, regional and national VAP incidence rates. Implementation of the guidelines aims at the reduction of VAP to less than 9 episodes per 1000 days of mechanical ventilation. A total of 35 preventive measures were initially selected. A task force of experts used the Grading of Recommendations, Assessment, Development and Evaluation Working Group methodology to generate a list of 7 basic "mandatory" recommendations (education and training in airway management, strict hand hygiene for airway management, cuff pressure control, oral hygiene with chlorhexidine, semi-recumbent positioning, promoting measures that safely avoid or reduce time on ventilator, and discouraging scheduled changes of ventilator circuits, humidifiers and endotracheal tubes) and 3 additional "highly recommended" measures (selective decontamination of the digestive tract, aspiration of subglottic secretions, and a short course of iv antibiotic).

DISCUSSION

We present the Spanish VAP prevention guidelines and describe the methodology used for the selection and implementation of the recommendations and the organizational structure of the project. Compared to conventional guideline documents, the associated safety assurance program, the online data recording and compliance control systems, as well as the existence of a pre-defined objective are the distinct features of "Zero VAP".

Paradoxical ventilator associated pneumonia incidences among selective digestive decontamination studies versus other studies of mechanically ventilated patients: benchmarking the evidence base

Introduction

Selective digestive decontamination (SDD) appears to have a more compelling evidence base than non-antimicrobial methods for the prevention of ventilator associated pneumonia (VAP). However, the striking variability in ventilator associated pneumonia-incidence proportion (VAP-IP) among the SDD studies remains unexplained and a postulated contextual effect remains untested for.

Methods

Nine reviews were used to source 45 observational (benchmark) groups and 137 component (control and intervention) groups of studies of SDD and studies of three non-antimicrobial methods of VAP prevention. The logit VAP-IP data were summarized by meta-analysis using random effects methods and the associated heterogeneity (tau²) was measured. As group level predictors of logit VAP-IP, the mode of VAP diagnosis, proportion of trauma admissions, the proportion receiving prolonged ventilation and the intervention method under study were examined in meta-regression models containing the benchmark groups together with either the control (models 1 to 3) or intervention (models 4 to 6) groups of the prevention studies.

Results

The VAP-IP benchmark derived here is 22.1% (95% confidence interval; 95% CI; 19.2 to 25.5; tau² 0.34) whereas the mean VAP-IP of control groups from studies of SDD and of non-antimicrobial methods, is 35.7 (29.7 to 41.8; tau² 0.63) versus 20.4 (17.2 to 24.0; tau² 0.41), respectively (P < 0.001). The disparity between the benchmark groups and the control groups of the SDD studies, which was most apparent for the highest quality studies, could not be explained in the meta-regression models after adjusting for various group level factors. The mean VAP-IP (95% CI) of intervention groups is 16.0 (12.6 to 20.3; tau² 0.59) and 17.1 (14.2 to 20.3; tau² 0.35) for SDD studies versus studies of non-antimicrobial methods, respectively.

Conclusions

The VAP-IP among the intervention groups within the SDD evidence base is less variable and more similar to the benchmark than among the control groups. These paradoxical observations cannot readily be explained. The interpretation of the SDD evidence base cannot proceed without further consideration of this contextual effect.

Heated humidification versus heat and moisture exchangers for ventilated adults and children

BACKGROUND

Humidification by artificial means must be provided when the upper airway is bypassed during mechanical ventilation. Heated humidification (HH) and heat and moisture exchangers (HME) are the most commonly used types of artificial humidification in this situation.

OBJECTIVES

To determine whether HHs or HMEs are more effective in preventing mortality and other complications in people who are mechanically ventilated.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library 2010, Issue 4) and MEDLINE, EMBASE and CINAHL (January, 2010) to identify relevant randomized controlled trials (RCTs).

SELECTION CRITERIA

We included RCTs comparing heat and moisture exchangers (HMEs) to heated humidifiers (HHs) in mechanically ventilated adults and children. We included randomized crossover studies.

DATA COLLECTION AND ANALYSIS

We assessed the quality of each study and extracted the relevant data. Where appropriate, results from relevant studies were meta-analysed for individual outcomes.

MAIN RESULTS

We included 33 trials with 2833 participants, 25 studies were parallel group design (n = 2710) and eight crossover design (n = 123). Only three included studies reported data for infants or children. There was no overall effect on artificial airway occlusion, mortality, pneumonia, or respiratory complications; however, the PaCO(2) and minute ventilation were increased when HMEs were compared to HHs and body temperature was lower. The cost of HMEs was lower in all studies that reported this outcome. There was some evidence that hydrophobic HMEs may reduce the risk of pneumonia and that blockages of artificial airways may be increased with the use of HMEs in certain subgroups of patients.

AUTHORS' CONCLUSIONS

There is little evidence of an overall difference between HMEs and HHs. However, hydrophobic HMEs may reduce the risk of pneumonia and the use of an HME may increase artificial airway occlusion in certain subgroups of patients. Therefore, HMEs may not be suitable for patients with limited respiratory reserve or prone to airway blockage. Further research is needed relating to hydrophobic versus hygroscopic HMEs and the use of HMEs in the paediatric and neonatal populations. As the design of HMEs evolves, evaluation of new generation HMEs will also need to be undertaken.

Ventilator associated pneumonia and infection control

Ventilator associated pneumonia (VAP) is the leading cause of morbidity and mortality in intensive care units. The incidence of VAP varies from 7% to 70% in different studies and the mortality rates are 20-75% according to the study population. Aspiration of colonized pathogenic microorganisms on the oropharynx and gastrointestinal tract is the main route for the development of VAP. On the other hand, the major risk factor for VAP is intubation and the duration of mechanical ventilation. Diagnosis remains difficult, and studies showed the importance of early initiation of appropriate antibiotic for prognosis. VAP causes extra length of stay in hospital and intensive care units and increases hospital cost. Consequently, infection control policies are more rational and will save money.

Double-heater-wire circuits and heat-and-moisture exchangers and the risk of ventilator-associated pneumonia

OBJECTIVE

To compare the incidence of ventilator-associated pneumonia (VAP) in patients ventilated in intensive care by means of circuits humidified with a hygroscopic heat-and-moisture exchanger with a bacterial viral filter (HME) or hot-water humidification with a heater wire in both inspiratory and expiratory circuit limbs (DHW) or the inspiratory limb only (SHW).

DESIGN

A prospective, randomized trial.

SETTING

A metropolitan teaching hospital's general intensive care unit.

PATIENTS

Three hundred eighty-one patients requiring a minimum period of mechanical ventilation of 48 hrs.

INTERVENTIONS

Patients were randomized to humidification with use of an HME (n=190), SHW (n=94), or DHW (n=97).

MEASUREMENTS AND MAIN RESULTS

Study end points were VAP diagnosed on the basis of Clinical Pulmonary Infection Score (CPIS) (), HME resistance after 24 hrs of use, endotracheal tube resistance, and HME use per patient. VAP occurred with similar frequency in all groups (13%, HME; 14%, DHW; 10%, SHW; p=0.61) and was predicted only by current smoking (adjusted odds ratio [AOR], 2.1; 95% confidence interval [CI], 1.1-3.9; p=.03) and ventilation days (AOR, 1.05; 95% CI, 1.0-1.2; p=.001); VAP was less likely for patients with an admission diagnosis of pneumonia (AOR, 0.40; 95% CI, 0.4-0.2; p=.04). HME resistance after 24 hrs of use measured at a gas flow of 50 L/min was 0.9 cm H2O (0.4-2.9). Endotracheal tube resistance was similar for all three groups (16-19 cm H2O min/L; p=.2), as were suction frequency, secretion thickness, and blood on suctioning (p=.32, p=.06, and p=.34, respectively). The HME use per patient per day was 1.13.

CONCLUSIONS

Humidification technique does not influence either VAP incidence or secretion characteristics, but HMEs may have air-flow resistance higher than manufacturer specifications after 24 hrs of use.

Clinical and economic consequences of ventilator-associated pneumonia: a systematic review

BACKGROUND

Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in critically ill patients. The clinical and economic consequences of VAP are unclear, with a broad range of values reported in the literature

OBJECTIVE

To perform a systematic review to determine the incidence of VAP and its attributable mortality rate, length of stay, and costs.

DATA SOURCE

Computerized PUBMED and MEDLINE search supplemented by manual searches for relevant articles, limited to articles published after 1990.

STUDY SELECTION

English-language observational studies and randomized trials that provided data on the incidence of VAP were included. Matched cohort studies were included for calculation of attributable mortality rate and length of stay.

DATA EXTRACTION

Data were extracted on patient population, diagnostic criteria for VAP, incidence, outcome, type of intensive care unit, and study design.

DATA SYNTHESIS

The cumulative incidence of VAP was calculated by combining the results of several studies using standard formulas for combining proportions, in which the weighted average and variance are calculated. Results from studies comparing intensive care unit and hospital mortality due to VAP, additional length of stay, and additional days of mechanical ventilation were pooled using a random effects model, with assessment of heterogeneity.

RESULTS

Our findings indicate a) between 10% and 20% of patients receiving >48 hrs of mechanical ventilation will develop VAP; b) critically ill patients who develop VAP appear to be twice as likely to die compared with similar patients without VAP (pooled odds ratio, 2.03; 95% confidence interval, 1.16-3.56); c) patients with VAP have significantly longer intensive care unit lengths of stay (mean = 6.10 days; 95% confidence interval, 5.32-6.87 days); and d) patients who develop VAP incur > or = USD $10,019 in additional hospital costs.

CONCLUSIONS

Ventilator-associated pneumonia occurs in a considerable proportion of patients undergoing mechanical ventilation and is associated with substantial morbidity, a two-fold mortality rate, and excess cost. Given these findings, strategies that effectively prevent VAP are urgently needed.

Bacterial Growth in Secretions and on Suctioning Equipment of Orally Intubated Patients: A Pilot Study

• Background Contamination of equipment, colonization of the oropharynx, and microaspiration of secretions are causative factors for ventilator-associated pneumonia. Suctioning and airway management practices may influence the development of ventilator-associated pneumonia.

• Objectives To identify pathogens associated with ventilator-associated pneumonia in oral and endotracheal aspirates and to evaluate bacterial growth on oral and endotracheal suctioning equipment.

• Methods Specimens were collected from 20 subjects who were orally intubated for at least 24 hours and required mechanical ventilation. At baseline, oral and sputum specimens were obtained for culturing, and suctioning equipment was changed. Specimens from the mouth, sputum, and equipment for culturing were obtained at 24 hours (n = 18) and 48 hours (n = 10).

• Results After 24 hours, all subjects had potential pathogens in the mouth, and 67% had sputum cultures positive for pathogens. Suctioning devices were colonized with many of the same pathogens that were present in the mouth. Nearly all (94%) of tonsil suction devices were colonized within 24 hours. Most potential pathogens were gram-positive bacteria. Gram-negative bacteria and antibiotic-resistant organisms were also present in several samples.

• Conclusions The presence of pathogens in oral and sputum specimens in most patients supports the notion that microaspiration of secretions occurs. Colonization is a risk factor for ventilator-associated pneumonia. The equipment used for oral and endotracheal suctioning becomes colonized with potential pathogens within 24 hours. It is not known if reusable oral suction equipment contributes to colonization; however, because many bacteria are exogenous to patients’ normal flora, equipment may be a source of cross-contamination.

Tracheostomy management in the chronically ventilated patient

Tracheotomy is a fundamentally important technique for managing patients who require long-term mechanical ventilation. Appropriate application of tracheotomy requires a skilled approach for timing the procedure, selecting the appropriate tracheostomy tube appliance, caring for the artificial airway once it is in place, and assisting patients with their specialized needs, such as articulated speech, airway humidification, and oral nutrition. Preparing patients for airway decannulation after they have weaned from mechanical ventilation requires a similar level of skill and attention to detail.

Nosocomial pneumonia. Diagnostic and therapeutic considerations

Many patients with presumed nosocomial pneumonia probably have infiltrates on the chest radiograph, fever, and leukocytosis resulting from noninfectious causes. Because of the high mortality and morbidity associated with nosocomial pneumonias, however, most clinicians treat such patients with a 2-week empiric trial of antibiotics. Before therapy is initiated, the clinician should rule out other causes of pulmonary infiltrates, fever, and leukocytosis that mimic a nosocomial pneumonia (e.g., pre-existing interstitial lung disease, primary or metastatic lung carcinomas, pulmonary emboli, pulmonary drug reactions, pulmonary hemorrhage, collagen vascular disease affecting the lungs, or congestive heart failure). If these disorders can be eliminated from diagnostic consideration, a 2-week trial of empiric monotherapy is indicated. The clinician should treat cases of presumed nosocomial pneumonia as if P. aeruginosa were the pathogen. Although P. aeruginosa is not the most common cause of nosocomial pneumonia, it is the most virulent pulmonary pathogen associated with nosocomial pneumonia. Coverage directed against P. aeruginosa is effective against all other aerobic gram-negative bacillary pathogens causing hospital-acquired pneumonia. The clinician should select an antibiotic for empiric monotherapy that is highly effective against P. aeruginosa, has a good side-effect profile, has a low resistance potential, and is relatively inexpensive in terms of its cost to the institution. The preferred agents for empiric monotherapy for nosocomial pneumonia are cefepime, meropenem, and piperacillin. Single organisms are responsible for nosocomial pneumonia, not multiple pathogens. S. aureus rarely, if ever, causes nosocomial pneumonia but is mentioned frequently in studies based on cultures of respiratory tract secretions. S. aureus, unless accompanied by a necrotizing pneumonia with rapid cavitation within 72 hours, in the sputum indicates colonization rather than infection and should not be addressed therapeutically. Antibiotics associated with a high resistance potential should not be used as monotherapy or included in combination therapy regimens (i.e., ceftazidime, ciprofloxacin, imipenem, or gentamicin). Combination therapy is more expensive than monotherapy and is indicated only when P. aeruginosa is extremely likely, based on its characteristic clinical presentation, or is proved by tissue biopsy. Therapy should not be based on respiratory secretion cultures regardless of technique. Optimal combination regimens include cefepime or meropenem plus levofloxacin or piperacillin or aztreonam or amikacin. Nosocomial pneumonias usually are treated for 14 days. Lack of radiographic or clinical response to appropriate empiric nosocomial pneumonia monotherapy after 14 days suggests an alternate diagnosis. In these patients, a tissue biopsy specimen should be obtained to determine the cause of the persistence of pulmonary infiltrates unresponsive to appropriate antimicrobial therapy.

Association between implementation of CDC recommendations and ventilator-associated pneumonia at selected US hospitals

BACKGROUND

To assess whether selected recommendations in the Centers for Disease Control and Prevention "Guideline for Prevention of Nosocomial Pneumonia" were being implemented and having an impact on the occurrence of ventilator-associated pneumonia (VAP) at US hospitals, we surveyed hospitals participating in the National Nosocomial Infections Surveillance (NNIS) system.

METHODS

We mailed a questionnaire to the infection control practitioner of each NNIS hospital in 1995 and used data from the NNIS system to calculate annual rates of VAP.

RESULTS

Of the 188 hospitals surveyed, 179 (95%) returned completed questionnaires. Of these, 175 (98%) had implemented the recommended change of mechanical-ventilator breathing circuits at 48-hour or greater intervals. Of 110 hospitals using the hygroscopic condenser-humidifiers or heat-moisture exchangers with ventilators, 102 (93%) changed the hygroscopic condenser-humidifiers or heat-moisture exchangers routinely, and of 98 hospitals using bubbling humidifiers, 96 (98%) used sterile water to fill these humidifiers. Other practices for which the guideline provides no recommendation and their frequency of use by NNIS hospitals include use of hygroscopic condenser-humidifiers or heat-moisture exchangers (110/179 [61%]) and use of bacterial filters in anesthesia machines (128/171 [61%]). There was a significant decrease in the VAP rate from 1987 to 1998.

CONCLUSION

Most NNIS hospitals had implemented selected recommendations in the Centers for Disease Control and Prevention "Guideline for Prevention of Nosocomial Pneumonia" before the final publication of the revised guideline. Further studies are needed to assess the impact of these recommendations on the occurrence of VAP.