The pathogenesis of ventilator-associated pneumonia: I. Mechanisms of bacterial transcolonization and airway inoculation

Respiratory nosocomial infections in the medical intensive care unit

Intensive care unit (ICU)-acquired lower respiratory tract infections include acute tracheobronchitis and hospital-acquired and ventilator-associated pneumonia (VAP). Nosocomial pneumonia is the second most common hospital-acquired infection and the leading cause of death in hospital-acquired infections. The mortality rate in VAP ranges from 24% to 76% in several studies. ICU ventilated patients with VAP have a 2- to 10-fold higher risk of death than patients without it. Early oropharyngeal colonization is pivotal in the etiopathogenesis of VAP. The knowledge of risk factors for VAP is important in developing effective preventive programs. Once the physician decides to treat a suspected episode of ICU-acquired pneumonia, some issues should be kept on mind: first, the adequacy of the initial empiric antibiotic therapy; second, the modification of initial inadequate therapy according to microbiological results; third, the benefit of combination therapy; and finally, the duration of the antimicrobial treatment. Additionally, a protocolized work-up to identify the causes of non-response to treatment is mandatory. All these issues are discussed in depth in this article.

Noninvasive ventilation for pediatric patients including those under 1-year-old undergoing liver transplantation

Pulmonary complications are an important cause of the mortality associated with liver transplantation. The efficacy of noninvasive ventilation (NIV) in pediatric patients following transplantation is unknown. The purpose of this retrospective study is to investigate the effects of NIV for pediatric patients undergoing liver transplantation. Of 102 pediatric patients who underwent liver transplantation, 15 patients (aged 73 months; range 2.5-179) were supported by NIV because of atelectasis, hypercapnia, hypoxemia, pneumonia, massive effusion, or postextubation ventilatory support. Of 15 patients, 5 were under the age of 1 year (range 2.5-12 months). Of the 15 patients, 7 had required multiple intubations before NIV treatment because of pulmonary complications. NIV treatment was administered to 6 patients because of hypercapnia. Partial pressure of arterial carbon dioxide (PaCO(2)) levels improved from 56.9 (95% confidence interval [CI]: 48.4-65.4) to 41.5 (95% CI: 36.8-46.2) mmHg (P = .028) within 2 days. NIV treatment was very effective for patients with atelectasis with and without other pulmonary complications. Mean inspiratory positive pressure (IPAP) was 7.2 (95% CI: 6.0-8.3) cm H(2)O and expiratory positive pressure (EPAP) was 3.5 (95% CI: 3.2-3.9) cm of H(2)O. Mean duration of NIV was 18.5 (95% CI: 8.6-28.4) days. IPAP and EPAP levels were closely and significantly correlated with height (IPAP: r = .65, P = .016; EPAP: r = .77, P = .004). A total of 13 patients recovered and 2 patients died. However, no patient died of respiratory complications. In conclusion, NIV is effective in pediatric patients undergoing liver transplantation with subsequent pulmonary complications. The IPAP and EPAP levels may be predicted by the height of the patient.

Electron microscopic analysis of biofilm on endotracheal tubes removed from intubated neonates

OBJECTIVES

To determine if the phenomenon of biofilm accumulation and associated microbial colonization occurs on the surface of endotracheal tubes in the region of the subglottis in neonates.

METHODS

Endotracheal tubes removed from 9 consecutive neonatal patients intubated for more than 12 hours were processed (range, 13 hours to 8 days). A sterile control tube was also processed. For each, the portion of the endotracheal tube that had been in contact with the subglottis was determined using a previously published nomogram. A 1-cm-long cross-sectional segment of the endotracheal tube corresponding to the level of the subglottis was divided into 2 portions for both electron microscopy and aerobic/anaerobic cultures.

RESULTS

Two of 9 (22%) luminal surface cultures grew Staphylococcus species, 1 (11%) grew normal flora, and 6 (66%) had no growth. Three of 9 (33%) outer-surface cultures grew Staphylococcus species, 1 (11%) had gram-negative rods on staining but a sterile culture, and one enterococcal contaminant was found. Electron microscopy revealed that 8 of 9 inner lumen surfaces harbored bacteria and biofilm formation. All outer lumen surfaces had biofilm formation; 6 of 9 had bacterial colonization. There was no obvious difference in the appearance of the inner and outer tube surface accretions. No time-dependent differences were noted except of the longest indwelling tube (8 days).

CONCLUSION

This study demonstrates for the first time the presence of biofilm on the outer surface of neonatal endotracheal tubes. The data suggest that the presence of bacteria and/or biofilm does not correlate with other traditional indicators of microbial colonization.

Clearing the cervical spine in unconscious polytrauma victims, balancing risks and effective screening

Cervical spine injury occurs in 5-10% of cases of blunt polytrauma. A missed or delayed diagnosis of cervical spine injury may be associated with permanent neurological sequelae. However, there is no consensus about the ideal evaluation and management of the potentially injured cervical spine and, despite the publication of numerous clinical guidelines, this issue remains controversial. In addition, many studies are limited in their application to the obtunded or unconscious trauma victim. This review will provide the clinician managing unconscious trauma victims with an assessment of the actual performance of clinical examination and imaging modalities in detecting cervical spine and isolated ligamentous injury, a review of existing guidelines in light of the available evidence, relative risk estimates and a proposed management scheme.

Airway colonisation in long-term mechanically ventilated patients

OBJECTIVE

To evaluate the impact of continuous subglottic suctioning and semi-recumbent body position on bacterial colonisation of the lower respiratory tract.

DESIGN

A randomised controlled trial.

SETTING

The ten-bed medical ICU of a French university hospital.

PATIENTS

Critically ill patients expected to require mechanical ventilation for more than 5 days.

INTERVENTIONS

Patients were randomly assigned to receive either continuous suctioning of subglottic secretions and semi-recumbent body position or to receive standard care and supine position.

MEASUREMENTS AND RESULTS

Oropharyngeal and tracheal secretions were sampled daily and quantitatively cultured. All included patients were followed up from day 1 (intubation) to day 10, extubation or death. Ninety-seven samples of oropharynx and trachea were analysed (40 for the suctioning group and 57 for the control group). The median bacterial counts in trachea were 6.6 Log10 CFU/ml (interquartile range, IQR, 4.4-8.3) in patients who received continuous suctioning and 5.1 Log10 CFU/ml (IQR 3.6-5.5) in control patients. Most of the patients were colonised in the trachea after 1 day of mechanical ventilation (75% in the suctioning group, 80% in the control group). No significant difference was found in the daily bacterial counts in the oropharynx and in the trachea between the two groups of patients.

CONCLUSION

Tracheal colonisation in long-term mechanically ventilated ICU patients was not modified by the use of continuous subglottic suctioning and semi-recumbent body position.

Hospital-acquired pneumonia: etiologic considerations

The development of pneumonia requires the pathogen to reach the alveoli and the host defenses to be overwhelmed, either by microorganism virulence or by inoculums size. The endogenous sources of microorganisms are nasal carriers, sinusitis, mouth, oropharynx, gastric, or tracheal colonization, and hematogenous spread. The exogenous sources of microorganisms are biofilm of the tracheal tube, ventilator circuits, nebulizers, and humidifiers. Health care workers may also play a role in this setting. Different microorganisms can be found depending on the onset time of pneumonia and on the local pattern variation encountered between different institutions and countries. Healthy patients may be chronically colonized. A very important, unresolved issue is the definition of early and late-onset pneumonia; it still remains uncertain from the literature whether the given threshold refers to the number of days in hospital or to the number of days following intubation. Noninvasive ventilation is demonstrating that the term "ventilator-associated pneumonia" is perhaps inaccurate and should be referred to as "intubation-associated pneumonia."

Herpes simplex virus in the respiratory tract of critical care patients: a prospective study

BACKGROUND

Herpes simplex virus (HSV) is occasionally detected in the lower respiratory tract of patients in intensive care, but its clinical importance in such situations remains unclear. We did a prospective cohort study to define the prevalence, origin, risk factors, and clinical relevance of HSV in the respiratory tract of patients undergoing critical care.

METHODS

We tested 764 patients admitted to intensive care for the presence of HSV in the respiratory tract, and assessed statistical relations between this virus and clinical variables.

FINDINGS

HSV was detected by oropharyngeal swab in the upper respiratory tract of 169 (22%) of 764 patients, within 10 days of admission for 150 (89%) of these individuals. The virus was isolated in 58 (16%) of 361 patients whose lower respiratory tract was sampled. The presence of HSV in the throat was a risk factor for development of HSV infections in the lower respiratory tract (p<0.001). HSV was isolated most frequently in patients with severe disease. HSV in the throat was associated with acute respiratory distress syndrome (p<0.001) and with increased length of stay in intensive care (p<0.001).

INTERPRETATION

Our data suggest that HSV reactivation or infection of the upper respiratory tract is frequent among patients in intensive care, and is a risk factor for development of lower respiratory tract infection with this virus, possibly by means of aspiration.

Nosocomial infections in adult intensive-care units

Nosocomial infections affect about 30% of patients in intensive-care units and are associated with substantial morbidity and mortality. Several risk factors have been identified, including the use of catheters and other invasive equipment, and certain groups of patients-eg, those with trauma or burns-are recognised as being more susceptible to nosocomial infection than others. Awareness of these factors and adherence to simple preventive measures, such as adequate hand hygiene, can limit the burden of disease. Management of nosocomial infection relies on adequate and appropriate antibiotic therapy, which should be selected after discussion with infectious-disease specialists and adapted as microbiological data become available.

Ambulant erworbene und nosokomiale Pneumonie

Mortality of pneumonia is low in the outside setting (1%) but rises up to 20% in hospital admitted patients. Early diagnosis and standardized therapy improve patient's prognosis. For community acquired pneumonia age, comorbidity and the setting of therapy (outside department, normal ward or intensive care unit) are the most important variables to choose an adequate antibiotic treatment. For nosocomial pneumonia risk stratification is according to severity of illness, length of hospital stay and antibiotic pretreatment. In the outpatient setting a 7-day monotherapy is mostly successful. In severe illness the combination of a betalactam antibiotic with a new fluorchinolon seems to be superior to an aminoglycosid therapy. Antibiotic resistance due to mistakes in antibiotic therapy is an increasing problem in the intensive care unit. Therefore, pneumonia preventive measures like influenza and pneumococcal vaccination become more important. Standardized hygienical procedures help to reduce nosocomial, mainly ventilator associated 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.

The use of prehospital continuous positive airway pressure treatment in presumed acute severe pulmonary edema

OBJECTIVE

To describe the prehospital use of a continuous positive airway pressure (CPAP) system for the treatment of presumed acute severe pulmonary edema (ASPE).

METHODS

The efficacy of prehospital CPAP treatment was analyzed in terms of changes in oxygen saturation, need for intubation or ventilatory support, and possible morbidity associated with the CPAP therapy. This was a retrospective cohort study conducted in the mobile intensive care unit of a university hospital. Participants included all consecutive patients with a clinical picture of ASPE treated by a mobile intensive care unit between January 1, 1998, and December 31, 1999.

RESULTS

121 patients were included in this study. 116 patients received prehospital CPAP therapy. Two patients (1.7%) from the CPAP-treated patients were intubated in the field. A total of six patients required endotracheal intubation before hospital, and six other patients after that. After the beginning of CPAP treatment, there was statistically significant elevation in blood oxygen saturation (mean and standard deviation [SD] before CPAP 77% +/- 11% and after CPAP 90% +/- 7%) (p < 0.0001) as well as reductions in the respiratory rate (mean and SD before CPAP 34 +/- 8 breaths/min and after CPAP 28 +/- 8 breaths/min) (p < 0.0001), systolic blood pressure (mean and SD before CPAP 173 +/- 39 mm Hg and after CPAP 166 +/- 37 mm Hg) (p = 0.0002), and heart rate (mean and SD before CPAP 108 +/- 25 beats/min and after CPAP 100 +/- 20 beats/min) (p = 0.0017). The main reason for in-hospital death (8%) was myocardial infarction. No technical problems or complications occurred during CPAP treatment.

CONCLUSIONS

Prehospital CPAP treatment in patients with ASPE improved oxygenation significantly and lowered respiratory rate, heart rate, and systolic blood pressure. Because of the retrospective nature of this study, the hemodynamic effects of nitroglycerine and morphine cannot be excluded. The mortality rate was low, which needs to be confirmed in a controlled, prospective study.

The significance of distal bronchial samples with commensals in ventilator-associated pneumonia: colonizer or pathogen?

STUDY OBJECTIVE

To investigate the role of oropharyngeal and cutaneous commensal microorganisms (OCCs) as a cause of ventilator-associated pneumonia (VAP).

DESIGN

Retrospective analysis of the medical and microbiological records.

SETTING

One medical-surgical ICU.

PATIENTS

All VAP episodes recorded during a 10-year period were reviewed. All patients with suspected VAP underwent bronchoscopy with protected-specimen brush (PSB) sampling and BAL before any change in antibiotic therapy was made. OCC-VAP was defined as VAP with significant growth in quantitative cultures (PSB yielded > or = 10(3) cfu/mL and/or BAL yielded > or = 10(4) cfu/mL) of OCCs only. Three experts reviewed the episodes. Exposed patients (ie, those with OCC-VAP) and unexposed patients (ie, patients without VAP) matched on condition severity at ICU admission and mechanical ventilation duration were compared.

RESULTS

Twenty-nine episodes in 28 patients with > or = 10(4) cfu/mL OCCs in BAL fluid and/or > or = 10(3) cfu/mL OCCs in PSB specimens were found. All patients in these episodes had new radiologic lung infiltrates, with 26 episodes involving purulent tracheal aspirates, 23 episodes involving temperatures > or = 38.5 degrees C, and 18 episodes involving > or = 11,000 leukocytes/ microL. The main OCCs found were non-beta-hemolytic Streptococcus spp (n = 12), Neisseria spp (n = 7), and coagulase-negative Staphylococcus spp (n = 6). Other possible reasons for fever and the presence of new chest infiltrates were found in 20 and 17 patients, respectively. Histologic evidence of pneumonia was found in 2 of the 10 patients who died. The three experts agreed on the diagnosis for 23 patients. In the OCC-VAP group only, the mean (+/- SD) logistic organ dysfunction (LOD) scores increased significantly (LOD score, 2 +/- 4; p = 0.008) during the 3 days before bronchoscopy, and ICU stay duration was longer than in the unexposed group. The exposed/unexposed study found no difference in mortality.

CONCLUSION

OCCs may behave like classic nosocomial pathogens in critically ill patients.

An outbreak of multidrug-resistant Pseudomonas aeruginosa associated with increased risk of patient death in an intensive care unit

OBJECTIVE

To investigate an outbreak of multidrug-resistant Pseudomonas aeruginosa in an intensive care unit (ICU).

DESIGN

Epidemiologic investigation, environmental assessment, and ambidirectional cohort study.

SETTING

A secondary-care university hospital with a 10-bed ICU.

PATIENTS

All patients admitted to the ICU receiving ventilator treatment from December 1, 1999, to September 1, 2000.

RESULTS

An outbreak in an ICU with multidrug-resistant isolates of P aeruginosa belonging to one amplified fragment-length polymorphism (AFLP)-defined genetic cluster was identified, characterized, and cleared. Molecular typing of bacterial isolates with AFLP made it possible to identify the outbreak and make rational decisions during the outbreak period. The outbreak included 19 patients during the study period. Infection with bacterial isolates belonging to the AFLP cluster was associated with reduced survival (odds ratio, 5.26; 95% confidence interval, 1.14 to 24.26). Enhanced barrier and hygiene precautions, cohorting of patients, and altered antibiotic policy were not sufficient to eliminate the outbreak. At the end of the study period (in July), there was a change in the outbreak pattern from long (December to June) to short (July) incubation times before colonization and from primarily tracheal colonization (December to June) to primarily gastric or enteral July) colonization. In this period, the bacterium was also isolated from water taps.

CONCLUSION

Complete elimination of the outbreak was achieved after weekly pasteurization of the water taps of the ICU and use of sterile water as a solvent in the gastric tubes.

Physiologic factors contributing to a transition in oral immunity among mechanically ventilated adults

Ventilator-associated pneumonia (VAP), a specific type of nosocomial pneumonia, occurs in approximately 21% of patients in intensive care, and the mortality can be as high as 71%. VAP causes considerable mortality and morbidity, and it exponentially increases health care costs. The incidence of VAP is associated with oropharyngeal colonization of gram-negative bacteria. Within 48 h of hospital admission, the composition of the oropharyngeal flora of critically ill patients undergoes a change from the usual gram-positive streptococci and dental pathogens to a predominant gram-negative flora that includes more virulent organisms, which predispose patients to VAP. Identification and understanding of this oral transition from gram-positive to predominantly gram-negative flora may assist health care professionals in differentiating among oral immune markers that suggest compromised immunity. The purpose of this article is to provide a review of the literature that promotes an understanding of current knowledge about the transition of oral immunity in mechanically ventilated patients.

Oral bacteria and respiratory infection: effects on respiratory pathogen adhesion and epithelial cell proinflammatory cytokine production

Several microbiologic and epidemiologic studies have suggested an association between dental plaque, poor oral health, and respiratory diseases such as nosocomial pneumonia and chronic obstructive pulmonary disease (COPD). A number of hypotheses are suggested to help explain how oral bacteria may participate in the pathogenesis of respiratory infection. Resident bacteria in oral secretions are likely aspirated along with respiratory pathogens and may affect the adhesion of the later organisms to the respiratory epithelium. Preliminary studies performed in our laboratory suggest that oral bacteria may modulate the adhesion of respiratory pathogens to epithelial cell lines. In addition, oral bacterial products or cytokines in oral/pharyngeal aspirates may stimulate cytokine production from respiratory epithelial cells, resulting in recruitment of inflammatory cells. The resulting inflamed epithelium may be more susceptible to respiratory infection. Further preliminary data are presented that some species of oral bacteria may induce the release of proinflammatory cytokines from epithelial cell lines to an extent similar to that seen for respiratory pathogens.

Role of acid suppressants in intensive care medicine

Bleeding from stress-induced mucosal lesions continues to be a potential problem in critically ill patients, although its incidence has decreased dramatically over the past decade. Patients considered to be at risk are those with respiratory failure, coagulopathy, severe burns or tetraplegia. The most important cause of stress ulcer bleeding is tissue hypoxia. Provided that appropriate dosage regimens are administered, all agents approved for stress ulcer prophylaxis may reduce the incidence of overt as well as clinically important bleeding. However, the efficacy of stress ulcer prophylaxis does not correlate with the efficacy of gastric acid inhibition. Although numerous studies have demonstrated that an alkaline gastric juice is associated with gastric Gram-negative bacterial overgrowth, controversy remains over whether the pharmacological suppression of gastric acid in critically ill patients facilitates nosocomial pneumonia. The reasons for these divergent results are discussed, as is a possible association between gastric acid suppression and other systemic infections. Finally, several cost-effectiveness analyses performed over recent years have demonstrated that, in properly selected critically ill patients, stress ulcer prophylaxis is cost-effective.

Aspiration pneumonia: dental and oral risk factors in an older veteran population

OBJECTIVES

To investigate the importance of medical and dental factors in aspiration pneumonia in an older veteran population.

DESIGN

Prospective enrollment of subjects with retrospective analysis of data.

SETTING

Department of Veterans Affairs outpatient clinic, inpatient ward, and nursing home.

PARTICIPANTS

358 veterans age 55 and older; 50 subjects with aspiration pneumonia.

MEASUREMENTS

Demographic and medical data; functional status; health-related behaviors; dental care utilization; personal oral hygiene; comprehensive dental examination; salivary assays including IgA antibodies; and cultures of saliva, throat, and dental plaques.

RESULTS

Two logistic regression models produced estimates of significant risk factors. One model using dentate patients included: requiring help with feeding (odds ratio (OR) = 13.9), chronic obstructive pulmonary disease (COPD) (OR = 4.7), diabetes mellitus (OR = 3.5), number of decayed teeth (OR = 1.2), number of functional dental units (OR = 1.2), presence of important organisms for decay, Streptococcus sobrinus in saliva (OR = 6.2), and periodontal disease, Porphyromonous gingivalis in dental plaque (OR = 4.2), and Staphylococcus aureus presence in saliva (OR = 7.4). The second model, containing both dentate and edentulous patients included: requiring help with feeding (OR = 4.7), COPD (OR = 2.5), diabetes mellitus (OR = 1.7), and presence of S. aureus in saliva (OR = 8.3).

CONCLUSION

This study supports the significance of oral and dental factors while controlling for established medical risk factors in aspiration pneumonia incidence.

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.

Prevalence of potential respiratory pathogens in the mouths of elderly patients and effects of professional oral care

To evaluate the effectiveness of professional oral health care in reducing the risk of aspiration pneumonia, we examined the prevalence of potential respiratory pathogens in gargled samples from elderly persons. Samples were obtained from 54 elderly subjects over 65 years of age who required daily nursing care, from 21 healthy elderly subjects over 65 years old, and from 22 healthy young subjects under 30 as controls. The prevalence of possible pathogens was determined by culture and the polymerase chain reaction. The percentages detected in samples of Streptococcus pneumoniae, Staphylococcus species, methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans from elderly patients requiring daily nursing care were 63.0, 37.0, 14.8, 5.6 and 66.7, respectively. The numbers of C. albicans cells recovered in samples from elderly subjects were significantly higher than those recovered from the healthy young group (P<0.001). Elderly patients needing daily care and receiving professional oral health care had lower prevalences and cell numbers of C. albicans than did the elderly patients without such oral care. This study showed that professional oral health care in elderly requiring daily nursing care reduced the cell numbers of potential respiratory pathogens.

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.

The prevention of pulmonary aspiration with control of tracheal wall pressure using a silicone cuff

A prospective open randomized controlled study was performed to assess the ability of Euromedical ILM endotracheal tube cuff (silicone cuff) to prevent pulmonary aspiration. The inflation characteristics of this silicone cuff enables the control of tracheal wall pressure. The silicone cuffed tube was shortened and an adjustable flange was used to convert it to a cuffed tracheostomy tube. Twelve patients requiring a tracheostomy on a four-bed intensive care unit (ICU) in a district general hospital received either a silicone or a Shiley cuffed tracheostomy tube. Tracheal wall pressures of both cuffs were maintained at 30 cm H2O with a constant pressure inflation device. Blue food dye was instilled once daily into the subglottic space through a fine catheter above the cuff. There were six patients in the Shiley group and six patients in the silicone cuff group. Dye leaked to the trachea in six (100%) of the Shiley group compared with none (0%) of the silicone cuff group (P = 0.001). This study confirms the effectiveness of this silicone cuff at preventing aspiration and the high incidence of leakage with the conventional high-volume low-pressure tracheostomy tube cuff.

Continuous and bilevel positive airway pressure in the treatment of acute cardiogenic pulmonary edema

Patients with acute cardiogenic pulmonary edema (ACPE) are commonly seen in the emergency department (ED). Although the majority of patients respond to conventional medical therapy, some patients require at least temporary ventilatory support. Traditionally, this has been accomplished via endotracheal intubation and mechanical ventilation, an approach that is associated with a small but significant rate of complications. The past 2 decades have witnessed increasing interest in methods of noninvasive ventilatory support (NVS), notably continuous positive airway pressure (CPAP) and bilevel positive airway pressure (BiPAP). We review the physiological consequences, clinical efficacy, and practical limitations of CPAP and BiPAP in the management of ACPE.

Acute respiratory failure in patients with severe community-acquired pneumonia. A prospective randomized evaluation of noninvasive ventilation

In uncontrolled studies, noninvasive positive pressure ventilation (NPPV) was found useful in avoiding endotracheal intubation in patients with acute respiratory failure (ARF) caused by severe community-acquired pneumonia (CAP). We conducted a prospective, randomized study comparing standard treatment plus NPPV delivered through a face mask to standard treatment alone in patients with severe CAP and ARF. Patients fitting the American Thoracic Society criteria for severe CAP were included in presence of ARF (refractory hypoxemia and/or hypercapnia with acidosis). Exclusion criteria were: severe hemodynamic instability, requirement for emergent cardiopulmonary resuscitation, home mechanical ventilation or oxygen long-term supplementation, concomitant severe disease with a low expectation of life, inability to expectorate or contraindications to the use of the mask. Fifty-six consecutive patients (28 in each arm) were enrolled, and the two groups were similar at study entry. The use of NPPV was well tolerated, safe, and associated with a significant reduction in respiratory rate, need for endotracheal intubation (21% versus 50%; p = 0.03), and duration of intensive care unit (ICU) stay (1.8 +/- 0.7 d versus 6 +/- 1.8 d; p = 0.04). The two groups had a similar intensity of nursing care workload, time interval from study entry to endotracheal intubation, duration of hospitalization, and hospital mortality. Among patients with chronic obstructive pulmonary disease (COPD), those randomized to NPPV had a lower intensity of nursing care workload (p = 0.04) and improved 2-mo survival (88.9% versus 37.5%; p = 0.05). We conclude that in selected patients with ARF caused by severe CAP, NPPV was associated with a significant reduction in the rate of endotracheal intubation and duration of ICU stay. A 2-mo survival advantage was seen in patients with COPD.

Association of periodontal infections with atherosclerotic and pulmonary diseases

Chronic infections may influence the severity and/or course of a number of systemic diseases. Periodontal diseases are localized chronic inflammatory conditions of the gingiva and underlying bone and connective tissues induced by bacteria and bacterial products of dental plaque. This paper will discuss the evidence for the role of periodontal disease in the pathogenesis of 2 important systemic diseases, atherosclerosis and pulmonary infections. Both epidemiological and laboratory studies are reviewed to assess the biological basis for the association of periodontal infections and these important diseases. Several potential mechanisms by which periodontal diseases may influence these conditions are also discussed.

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.

Role of oral bacteria in respiratory infection

An association between oral conditions such as periodontal disease and several respiratory conditions has been noted. For example, recent evidence has suggested a central role for the oral cavity in the process of respiratory infection. Oral periodontopathic bacteria can be aspirated into the lung to cause aspiration pneumonia. The teeth may also serve as a reservoir for respiratory pathogen colonization and subsequent nosocomial pneumonia. Typical respiratory pathogens have been shown to colonize the dental plaque of hospitalized intensive care and nursing home patients. Once established in the mouth, these pathogens may be aspirated into the lung to cause infection. Other epidemiologic studies have noted a relationship between poor oral hygiene or periodontal bone loss and chronic obstructive pulmonary disease. Several mechanisms are proposed to explain the potential role of oral bacteria in the pathogenesis of respiratory infection: 1. aspiration of oral pathogens (such as Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, etc.) into the lung to cause infection; 2. periodontal disease-associated enzymes in saliva may modify mucosal surfaces to promote adhesion and colonization by respiratory pathogens, which are then aspirated into the lung; 3. periodontal disease-associated enzymes may destroy salivary pellicles on pathogenic bacteria to hinder their clearance from the mucosal surface; and 4. cytokines originating from periodontal tissues may alter respiratory epithelium to promote infection by respiratory pathogens.

Are most ICU infections really nosocomial? A prospective observational cohort study in mechanically ventilated patients

A prospective cohort study was undertaken with two end points: (i) to compare the 48 h time cut-off with the carrier state criterion for classifying infections, and (ii) to determine a time cut-off more in line with the carrier state concept. All patients admitted to the intensive care unit and expected to require mechanical ventilation for a period > or = 3 days were enrolled. Surveillance cultures of throat and rectum were obtained on admission and thereafter twice weekly to distinguish micro-organisms that were imported into the intensive care unit from those acquired during the stay in the unit. A total of 117 patients with median age of 61 years and median Simplified Acute Physiology Score II of 42, were included in the study. Of these patients, 48 (41%) developed a total of 74 infection episodes. Using the 48 h cut-off point, 80% of all infections were classified as ICU-acquired. According to the carrier state criterion, 44 infections (60%) were of primary endogenous development caused by micro-organisms imported into the intensive care unit. Seventeen secondary endogenous (23%) and 13 exogenous (17%) infections were caused by bacteria acquired in the unit. The carrier state classification allowed the transfer of 49% of infections from the ICU-acquired group into the import group. A time cut-off of nine days was found to identify ICU-acquired infections better than two days. These data suggest that monitoring of carriage of micro-organisms may be a more realistic approach to classify infections developing in the intensive care unit.

Prevention of tracheal aspiration using the pressure-limited tracheal tube cuff

A new design of tracheal tube cuff, the pressure-limited cuff, used with a constant-pressure inflation system, was compared with a high-volume low-pressure cuffed tracheal tube for leakage of dye placed in the subglottic space into the trachea. Patients requiring ventilation on the intensive care unit were randomly allocated into two groups, one for each type of cuff, and blue food dye was instilled daily via a fine catheter above the cuff into the subglottic space. There were eight patients in the high-volume low-pressure group and seven in the pressure-limited cuff group. Dye leaked into the trachea in seven (87%) of the high-volume low-pressure group compared with none (0%) of the pressure-limited cuff group (p < 0.01). This study demonstrates that the pressure-limited cuffed tracheal tube, in combination with a constant-pressure inflation device, prevents leakage of fluid into the lungs that occurs with high-volume low-pressure cuffs in the critically ill, intubated patient.

Compliance characteristics of the Portex Soft Seal Cuff improves seal against leakage of fluid in a pig trachea model

BACKGROUND

The Portex Soft Seal high-volume, low-pressure cuffed tracheal tube was compared with the Mallinckrodt HiLo, Sheridan Preformed and Portex Profile tracheal tubes for leakage of dye placed in the subglottic space of a pig's trachea which was used in a benchtop mechanical ventilation model and in six isolated pig tracheas.

RESULTS

There was no leakage, either in the ventilation model or in the isolated tracheas in the Portex Soft Seal group. There was rapid leakage in the ventilation model and in all the isolated tracheas for the Mallinckrodt HiLo, and five out of six isolated tracheas for the Sheridan Preformed and the Portex Profile group.

CONCLUSIONS

This benchtop study suggests that the improved compliance characteristics of the Portex Soft Seal cuff are beneficial in preventing leakage of fluid in these models.

A comparison of noninvasive positive-pressure ventilation and conventional mechanical ventilation in patients with acute respiratory failure

BACKGROUND AND METHODS

The role of noninvasive positive-pressure ventilation delivered through a face mask in patients with acute respiratory failure is uncertain. We conducted a prospective, randomized trial of noninvasive positive-pressure ventilation as compared with endotracheal intubation with conventional mechanical ventilation in 64 patients with hypoxemic acute respiratory failure who required mechanical ventilation.

RESULTS

Within the first hour of ventilation, 20 of 32 patients (62 percent) in the noninvasive-ventilation group and 15 of 32 (47 percent) in the conventional-ventilation group had an improved ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2:FiO2) (P=0.21). Ten patients in the noninvasive-ventilation group subsequently required endotracheal intubation. Seventeen patients in the conventional-ventilation group (53 percent) and 23 in the noninvasive-ventilation group (72 percent) survived their stay in the intensive care unit (odds ratio, 0.4; 95 percent confidence interval, 0.1 to 1.4; P=0.19); 16 patients in the conventional-ventilation group and 22 patients in the noninvasive-ventilation group were discharged from the hospital. More patients in the conventional-ventilation group had serious complications (66 percent vs. 38 percent, P=0.02) and had pneumonia or sinusitis related to the endotracheal tube (31 percent vs. 3 percent, P=0.003). Among the survivors, patients in the noninvasive-ventilation group had shorter periods of ventilation (P=0.006) and shorter stays in the intensive care unit (P=0.002).

CONCLUSIONS

In patients with acute respiratory failure, noninvasive ventilation was as effective as conventional ventilation in improving gas exchange and was associated with fewer serious complications and shorter stays in the intensive care unit.

Rapid and specific molecular identification of methicillin-resistant Staphylococcus aureus in endotracheal aspirates from mechanically ventilated patients

Multiplex amplification of femA and mecA genetic determinants allowed an early and rapid identification of methicillin-resistant Staphylococcus aureus (MRSA) in endotracheal aspirates of mechanically ventilated patients. femA and/or mecA amplification and bacteriological results were concordant in 57 of 60 samples. In all three discrepant cases, complementary bacteriological tests confirmed the presence of MRSA first identified by molecular analysis. These results underline the value and rapidity of this molecular diagnosis for MRSA infection and control surveillance in intensive care units. Rapid MRSA detection is expected to have a significant clinical impact not only on patient outcome but also on the costs for isolation and treatment.

Associations between oral conditions and respiratory disease in a national sample survey population

Respiratory infectious diseases such as bacterial pneumonia and bronchitis are common and costly, especially in institutionalized and elderly inpatients. Respiratory infection is thought to rely in part on the aspiration of oropharyngeal flora into the lower respiratory tract and failure of host defense mechanisms to eliminate the contaminating bacteria, which then multiply to cause infection. It has been suggested that dental plaque may act as a reservoir of respiratory pathogens, especially in patients with periodontal disease. However, the impact of poor oral health on oral respiratory pathogen colonization and lung infection is uncertain, especially in ambulatory, non-institutionalized populations. To begin to assess potential associations between respiratory diseases and oral health, data from the National Health and Nutrition Examination Survey I (NHANES I) were analyzed. This database contains information on the general health status of 23,808 individual Of these, 386 individuals reported a suspected respiratory condition that was further assessed by a physician. These subjects were categorized as having a confirmed chronic respiratory disease (chronic bronchitis or emphysema) or an acute respiratory disease (influenza, pneumonia, acute bronchitis). They were compared to those not having a respiratory disease. Initial non-parametric analysis noted that individuals with a confirmed chronic respiratory disease (n = 41) had significantly greater oral hygiene index scores than subjects without respiratory disease (n = 193; P = 0.0441). Logistic regression analysis of data from these subjects, which considered age, race, gender, smoking status, and simplified oral hygiene index (OHI), suggested that subjects having the median OHI value were 1.3 times more likely to have a chronic respiratory disease relative to those with and OHI of O. Similarly, subjects with the maximum OHI value were 4.5 times more likely to have a chronic respiratory disease than those with an OHI of O. No evidence was found to support an association between the periodontal index and any respiratory disease. These results suggest OHI to have a residual effect on chronic respiratory disease of both practical and statistical significance.

Implications of oral infections on systemic diseases in the institutionalized elderly with a special focus on pneumonia

Systemic infection in the elderly patient living in a chronic care setting presents a significant burden to the health care system. The extent to which oral organisms cause systemic infections through hematogenous dissemination in the institutionalized elderly is still unknown. A more likely and common route of systemic infection by oral microorganisms is through aspiration of oropharyngeal fluids containing oral pathogenic microorganisms, which colonize the lower respiratory tract and cause pneumonia. Respiratory pathogens emerge in the dental plaque of elderly patients with very poor oral hygiene and severe periodontal disease. In the chronic care setting, aspiration of oropharyngeal fluids contaminated with these bacteria occurs in patients with diminished host defenses, resulting in bacterial pneumonia. This is also a problem in intensive care units in the hospital setting. In one study, pre-rinsing with a 0.12% chlorhexidine gluconate mouthwash significantly lowered the mortality rate from postsurgical pneumonia in patients undergoing open heart surgery. Selective digestive decontamination, a technique involving the topical application of antimicrobials to reduce the risk of colonization of the respiratory tract, has been used to reduce the incidence of nosocomial pneumonia in the acute care setting of hospitals. This technique has not been employed in the nursing home setting. Whether improving oral hygiene would also lower the risk in either of these settings has not been studied. A number of obstacles must be overcome in designing studies to investigate the relationship between oral infections and lung infections in the institutionalized elderly. Ethical issues must be addressed, and full collaboration of the medical team is required. Future studies should establish whether reducing the risk for pneumonia in the institutionalized elderly is possible through improved oral health.

Risk factors and outcome of nosocomial infections: results of a matched case-control study of ICU patients

Intensive-care-unit (ICU) patients are at risk for both acquiring nosocomial infection and dying, and require a high level of therapy whether infection occurs or not. The objective of the present study was to precisely define the interrelationships between underlying disease, severity of illness, therapeutic activity, and nosocomial infections in ICU patients, and their respective influences on these patients' outcome. In a 10-bed medical ICU, we conducted a case-control study with matching for initial severity of illness, with daily monitoring of severity of illness and therapeutic activity scores, and with analysis of the contribution of nosocomial infections to patients' outcomes. Forty-one cases of patients who developed nosocomial infections during a 1-yr period were paired with 41 controls without nosocomial infection according to three criteria: age (+/- 5 yr), Acute Physiology and Chronic Health Evaluation II (APACHE II) score (+/- 5 points), and duration of exposure to risk. Successful matching was achieved for 118 of 123 (96%) variables. Neurologic failure on the third day after ICU admission was the sole independent risk factor for nosocomial infection (adjusted odds ratio [OR]: 1.34; 95% confidence interval [CI]: 1.09 to 1.64; p = 0.007). Unlike control patients, case patients showed no clinical improvement and required a high level of therapeutic activity between ICU admission and the day of infection. Mortality attributable to nosocomial infection was 44%. Excess length of stay and duration of antibiotic treatment attributable to nosocomial infection were 14 d and 10 d, respectively. Attributable therapeutic activity as measured with the Therapeutic Intervention Scoring System (TISS) and Omega score was 368 and 233 points, respectively. Such consequences were observed in patients who developed multiple infections. These findings suggest that a persistent high level of therapeutic activity and persistent impaired consciousness are risk factors for nosocomial infections in ICU patients. These infections are responsible for excess mortality, prolongation of stay, and excess therapeutic activity resulting in important cost overruns for health-care systems.

How to use an article on therapy or prevention: pneumonia prevention using subglottic secretion drainage

Evidence based critical care medicine involves integrating clinical experience, expertise, and patient preferences with explicit, systematic, and judicious use of current best evidence in making medical decisions. Published evidence has many sources: research from the basic sciences of medicine, and from patient-centered clinical research on the accuracy of diagnostic tests, the power of prognostic markers, and the effectiveness and safety of preventive, therapeutic, rehabilitative, and palliative interventions. When critically appraising a clinical article for potential use in intensive care unit (ICU) practice, the first question we ask ourselves is: Is this study valid? If examination of the study methods reveals that the design is rigorous, we can turn to the two other key questions: What are the results? and, Will the results help me care for my patients? This approach may aid in the interpretation of an article on therapy or prevention; in it we discuss a strategy designed to prevent ventilator associated pneumonia in critically ill patients.

Oral health and history of respiratory tract infection in frail institutionalised elders

OBJECTIVES

The purpose of this study was to look for a relationship between history of respiratory tract infection (RTI) and oral health in very old subjects.

SETTING AND SUBJECTS

302 frail elders (mean age: 85 years) living in a medical care facility were examined by one dentist.

OUTCOME MEASURES

The incidence of RTI over 1 year had been recorded along with markers of nutritional status and degree of dependency. The oral examination comprised an evaluation of hygiene, quality of prostheses and the prevalence of caries, periodontal disease and mucosal disorders.

RESULTS

One third (33%) of the subjects had experienced at least one episode of RTI, and a fifth (19%) had visited the dentist in emergency. The incidence of RTI had been greater among dentate subjects and those who came to the dentist in emergency. The dentate subjects with a history of RTI had higher plaque score (P = 0.02). Half (49%) of the subjects had oral disorders that could develop in a dental emergency and these subjects had had a higher risk of RTI (relative risk: 1.9, 95% confidence interval: 1.1-3.9). The presence of selected oral disorders associated with low serum albumin increased the relative risk of having had RTI to 3.2 (1.5-6.7). The association between presence of actual oral health problems and previous experience of RTI was more noticeable in those who had poor general health or were more debilitated.

CONCLUSIONS

The present study suggests that poor oral hygiene and the presence of potential emergency could be major risk factors for RTI among the frail elderly.

Noninvasive positive-pressure ventilation in patients with acute respiratory failure

This article provides a systematic review of the literature on the application of noninvasive ventilation in various forms of hypercapnic and hypoxemic respiratory failures. A description of the underlying pathophysiology is followed by a review of physiologic data explaining the mechanisms of action of noninvasive ventilation. A critical review of clinical studies is presented with specific suggestions. The methodology of correctly implementing and monitoring noninvasive ventilation in patients with acute respiratory failure, critical to success, is detailed.