VENTILATOR-ASSOCIATED PNEUMONIA

[Nosocomial pneumonia]

Nosocomial pneumonia is defined as pneumonia occurring ≥ 48 h after hospital admission in a patient without severe immunosuppression. It can occur in spontaneously breathing patients or with noninvasive ventilation (NIV) and mechanically ventilated patients. In patients with suspected ventilator-associated pneumonia (VAP) (semi)quantitative cultures of tracheobronchial aspirates or bronchoalveolar lavage fluid should be perfomed. The initial empirical antimicrobial treatment is determined by the risk for multidrug-resistant pathogens (MDRP). The advantage of combination treatment increases with the prevalence of MDRPs. The antibiotic treatment should be adapted when the microbiological results are available. After 72 h a standardized re-evaluation including the response to treatment and also checking of the suspected diagnosis of pneumonia in a structured form is mandatory. Treatment failure can occur as a primary or secondary failure and in the case of primary progression necessitates another comprehensive diagnostic work-up before any further antibiotic treatment.

Immunological blocking of spermidine-mediated host-pathogen communication provides effective control against Pseudomonas aeruginosa infection

Pseudomonas aeruginosa is known to cause life-threatening infections. The previous studies showed that the type III secretion system (T3SS) of this pathogen is a key virulence determinant, which is activated by polyamines signals spermidine (Spd) and spermine (Spm) from mammalian host. To test the potential of blocking host-pathogen communication in disease control, in this study we developed a high potency mouse monoclonal antibody (Mab 4E4, IgG1 sub-isotype) by using Spm-protein conjugate as an immunogen. Antibody specificity analysis showed that the antibody specifically recognize Spd and Spm. In vitro study showed the antibody significantly protected A549 cells against P. aeruginosa infection, and this protection was achieved by blocking polyamine uptake and downregulating T3SS expression. In vivo single injection of mouse with Mab 4E4 drastically reduced the serum polyamine level, which was maintained for more than 1 week. In a murine model of P. aeruginosa acute infection, injection of Mab 4E4 protected mice from lung injury and significantly improved the survival rate of mice.

Antibiotic management of suspected nosocomial ICU-acquired infection: does prolonged empiric therapy improve outcome?

OBJECTIVE

To characterize empiric antibiotic use in patients with suspected nosocomial ICU-acquired infections (NI), and determine the impact of prolonged therapy in the absence of infection.

DESIGN AND SETTING

Multicenter prospective cohort, with eight medical-surgical ICUs in North America and Europe.

PATIENTS

195 patients with suspected NI.

METHODS

The diagnosis of NI was adjudicated by a blinded Clinical Evaluation Committee using retrospective review of clinical, radiological, and culture data.

RESULTS

Empiric antibiotics were prescribed for 143 of 195 (73.3%) patients with suspected NI; only 39 of 195 (20.0%) were adjudicated as being infected. Infection rates were similar in patients who did (26 of 143, 18.2%), or did not (13 of 52, 25.0%) receive empiric therapy (p = 0.3). Empiric antibiotics were continued for more than 4 days in 56 of 95 (59.0%) patients without adjudicated NI. Factors associated with continued empiric therapy were increased age (p = 0.02), ongoing SIRS (p = 0.03), and hospital (p = 0.004). Patients without NI who received empiric antibiotics for longer than 4 days had increased 28-day mortality (18 of 56, 32.1%), compared with those whose antibiotics were discontinued (3 of 39, 7.7%; OR = 5.7, 95% CI 1.5-20.9, p = 0.005). When the influence of age, admission diagnosis, vasopressor use, and multiple organ dysfunction was controlled by multivariable analysis, prolonged empiric therapy was not independently associated with mortality (OR = 3.8, 95% CI 0.9-15.5, p = 0.07).

CONCLUSIONS

Empiric antibiotics were initiated four times more often than NI was confirmed, and frequently continued in the absence of infection. We found no evidence that prolonged use of empiric antibiotics improved outcome for ICU patients, but rather a suggestion that the practice may be harmful.

Ketamine inhibits lipopolysacharide (LPS) induced gastric luminal fluid accumulation

INTRODUCTION

Lipopolysacharide (LPS) causes gastrointestinal ileus and gastric luminal fluid accumulation. Ketamine, an anti-inflammatory anesthetic agent attenuates accumulation of luminal fluid. However, its effects on gastrointestinal transit induced by endotoxemia are unknown. The purpose of this study was to determine if the anti-inflammatory properties of ketamine improve impaired gastric emptying and gastrointestinal transit because of LPS.

MATERIALS AND METHODS

Rats were given ketamine (70 mg/kg i.p.) or saline 1 h before LPS (20 mg/kg, i.p.) or saline injection. Five hours after LPS injection, rats were gavaged with 1 cc consisting of 0.1 ml of 5 mm FITC Dextran added to 0.9 ml of saline. After 30 min, rats were sacrificed, and gastric emptying, gastrointestinal transit, and gastric fluid accumulation determined. Gastric and ileal mucosa were harvested for analysis of inducible nitric oxide synthase (iNOS) (Western immunoblot). Results are reported as mean +/- SE (n > or = 5 per group; ANOVA).

RESULTS

Ketamine did not prevent LPS induced gastrointestinal ileus, nor did it improve gastric emptying. More importantly, it did not worsen gastrointestinal function or gastric emptying when compared to saline controls. However, it did decrease LPS induced gastric luminal fluid accumulation and blunted iNOS expression in both the stomach and ileum.

CONCLUSION

These data indicate that the ability of ketamine to attenuate gastric fluid accumulation is not because of improved gastric emptying or improved gastrointestinal transit. Moreover, while iNOS may play a role in LPS induced gastric luminal fluid accumulation, it does not appear to be a major mediator of the gastrointestinal ileus caused by LPS.

Ventilator-associated pulmonary infection: the germ theory of disease remains viable

Pulmonary infection complicating mechanical ventilation is a major problem in critical care. The key issues surrounding care of patients suspected of having this disease are 1) appropriate diagnostic criteria; 2) when antibiotic therapy should be started; and 3) what constitutes adequate antibiotic therapy. Current data support use of quantitative cultures obtained by either bronchoscopic or blind catheter lavage or mini-brushing. Antibiotic therapy should be guided by duration of hospitalization prior to presumed infection and local predominating nosocomial organisms and their microbial resistance patterns. The key issue with timing of therapy now centers around early termination of therapy if quantitative cultures are negative.

Clinical resolution in patients with suspicion of ventilator-associated pneumonia: A cohort study comparing patients with and without acute respiratory distress syndrome*

OBJECTIVES

To determine the pattern of resolution of classic infectious and respiratory variables in patients with ventilator-associated pneumonia (VAP) and appropriate empirical therapy, depending on the presence of acute respiratory distress syndrome (ARDS). A secondary objective was to identify clinical variables that might be useful for monitoring response to therapy.

DESIGN

Prospective, observational cohort study.

SETTING

Medical-surgical intensive care unit.

PATIENTS

Seventy-five episodes of VAP without ARDS were identified and compared with 20 episodes with ARDS at VAP onset. Six episodes were excluded due to in vitro resistance to the initial antibiotic choice and six due to death in the first 72 hrs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Resolution of fever, Pao2/Fio2 >250 mm Hg, and white blood cell count in episodes of VAP were present in 73.3%, 74.7%, and 53.3% of patients after 3 days of therapy. Indeed, >50% of episodes with the absence of ARDS presented resolution of fever and Pao2/Fio2 >250 within the first day of therapy. In contrast, resolution of radiologic opacities and clearance of secretions (median of 14 and 6 days of resolution) were late events. In patients with ARDS, resolution of fever remained the earliest variable. However, similar to Pao2/Fio2 250 and white blood cell count, fever showed a significantly worse pattern after 3 days of therapy: 45%, 15% and 25%, respectively. Radiologic resolution was an extremely poor indicator, being present in only 10% of ARDS patients after 15 days of follow-up. Failure to improve after 48 hrs of therapy was documented in 65% of ARDS patients and 14.7% of controls (p < .05).

CONCLUSIONS

Measures of oxygenation and core temperature can help physicians to individualize and shorten the duration of antibiotic therapy in VAP episodes. ARDS patients with VAP take twice as long to resolve fever, whereas hypoxemia should be ignored in defining resolution in this subset.

The Systemic Response to Lung Infection

The host response to microbial invasion in the lung must be sufficiently vigorous to allow for microbial eradication but appropriately controlled to prevent spillover of the response into the systemic circulation. Although inflammatory responses in pneumonia are generally compartmentalized, microbial and host factors can promote disordered systemic responses to lung infection. Assessment of the magnitude of the systemic inflammatory response in pneumonia is of limited clinical value, and attempts to suppress this response have failed to improve clinical outcomes. The systemic inflammatory response that occurs in sepsis and other critical illnesses can substantially impair lung innate and acquired immunity. Mechanisms of critical illness-induced immunoparalysis have been incompletely characterized and are the focus of ongoing clinical and basic investigations.

Nonresolving Pneumonia

Uncertainty over the expected clinical course of a community-acquired or nosocomial pneumonia is a common reason for pulmonary consultation. Determining which patients with prolonged pneumonia and at what point during therapy they should undergo further evaluation can be challenging. This article reviews "normal" resolution times for the most common pneumonias, risk factors for delayed resolution, and infectious and noninfectious conditions that can cause nonresolving pneumonia. An approach to the evaluation of the patient with this common problem is described.

Causes and predictors of nonresponse to treatment of intensive care unit–acquired pneumonia*

OBJECTIVE

To prospectively evaluate the predictive factors for the nonresponse to empirical antibiotic treatment and mortality in patients with intensive care unit-acquired pneumonia.

DESIGN

A 1-yr prospective cohort of patients with suspicion of intensive care unit-acquired pneumonia.

SETTING

Five medical and surgical intensive care units of Hospital Clinic in Barcelona.

PATIENTS

A total of 71 patients with intensive care unit-acquired pneumonia were studied. The definition of nonresponse included at least one of the following: failure to improve the Pao2/Fio2 ratio or need of intubation because of pneumonia, persistence of fever or hypothermia and purulent respiratory secretions, worsening of pulmonary infiltrates, or occurrence of septic shock or multiple organ dysfunction not present at onset of pneumonia.

INTERVENTIONS

Clinical assessment, including severity scores, blood and quantitative cultures of respiratory secretions, and cytokine measurements in serum and bronchoalveolar lavage at onset of pneumonia and 72 hrs after antimicrobial treatment.

MEASUREMENTS AND RESULTS

A total of 44 patients (62%) fulfilled criteria of nonresponse, and at least one cause of nonresponse could be determined in 28 cases (64%): inappropriate treatment in ten (23%), superinfection in six (14%), concomitant foci of infection in 12 (27%), and noninfectious causes in seven cases (16%). The remaining 16 patients with no definite cause of nonresponse presented with septic shock, multiple organ dysfunction, or acute respiratory distress syndrome. Increased levels of interleukin-6 at onset of pneumonia (odds ratio, 9.7; p =.014) was an independent predictor of nonresponse to treatment. Likewise, increased level of interleukin-6 at follow-up (odds ratio, 27; p =.001) was the only independent predictor for hospital mortality.

CONCLUSION

Increased systemic inflammatory response was the main predictor of nonresponse to treatment and mortality.

Treatment failures in patients with ventilator-associated pneumonia

Treatment failures in patients with VAP are a complex issue and form a major challenge for clinicians. The following key elements inherent to a rational approach to treatment failures have been elucidated: (1) the presence of treatment failure must be thoroughly defined and assessed; (2) the many causes behind treatment failures must be realized, particularly the possibility of pneumonia-related and extrapulmonary reasons; (3) the recognition of different patterns of treatment failures as a useful framework for decisions about modalities and intensity of diagnostic reassessment; and (4) the establishment of a protocol for the search of pulmonary and extrapulmonary sites of infection and noninfectious causes of nonresponse. Only such a rational approach precludes the adverse effects of blind empiricism, which always implies a dangerous and costly overtreatment. Many issues related to treatment failures remain unsettled, and efforts will have to be made in the future to improve current clinical attitudes to treatment failures in VAP.

Community-acquired pneumonia: causes of treatment failure in patients enrolled in clinical trials

In order to determine the causes of treatment failure in community-acquired pneumonia (CAP) clinical trials, a MEDLINE search for all CAP studies published between 1990 and 1997 was performed. Prospective, randomized studies comparing the efficacy of two or more antibiotics in CAP were selected. Treatment failure was defined as persistent fever, deterioration of patient's condition, or a change in the prescribed antibiotic regimen. In 16% of the cases included in the clinical trials, the treatment of CAP is unsuccessful. A significant number of identified failure cases were owing to antibiotic side-effects. Resistant pathogens are an unusual cause of failure whatever the antibiotic used.

Cytokines as targets of immunotherapy in bacterial pneumonia

The generation of a vigorous inflammatory response is essential for the rapid clearance of microbes from the alveolar space. The magnitude of the inflammatory response is tightly controlled by host-derived cytokines, which mediate lung inflammation by serving as leukocyte chemoattractants, leukocyte activating factors, or afferent signals in the induction or regulation of other effector molecules. In this article the role of specific cytokines in lung innate immunity will be reviewed. Future directions regarding the use of specific forms of immunotherapy, including compartmentalized cytokine delivery with gene therapy as adjuvant therapy in the treatment of pneumonia, will be explored.

Fiberoptic bronchoscopy in coronary care unit patients: indications, safety, and clinical implications

STUDY OBJECTIVES

To evaluate the indications, safety, therapeutic impact, and outcome of fiberoptic bronchoscopy (FOB) in coronary care unit (CCU) patients.

DESIGN

Retrospective review of all CCU patients undergoing FOB during a 6-year period.

SETTING

Tertiary care university hospital.

RESULTS

Among 8,330 patients admitted to the CCU; 40 (0.5%) patients underwent FOB to evaluate pulmonary abnormalities, most often (78%) to appraise clinically suspected pneumonia. Thirty-five (88%) patients were intubated and 21 (53%) had acute myocardial infarction (MI) before FOB. There were two major complications (bleeding, intubation) occurring within 24 h of FOB, one of which appeared due to the procedure. No episodes of chest pain or ischemic events were recorded and no significant increase in major complications was noted in MI patients (3% vs 5%). Patients having FOB within 10 days of MI had higher survival (79%) than those undergoing FOB later (29%) (p = 0.05). Seven different bacterial pathogens were isolated in 6 (15%) patients, probably reflecting prior empiric antibiotics in 32 (80%) patients. Therapy was changed in 64% of patients in whom a potential pathogen was identified. Despite alterations in treatment, patients with clinically suspected pneumonia and any organisms isolated by FOB had greater mortality (79% vs 31%, p = 0.003) than those with sterile FOB cultures.

CONCLUSION

FOB may be diagnostically useful in the evaluation of pulmonary abnormalities in selected patients with acute cardiac disease, can be performed safely, and may influence management decisions. Positive bronchoscopy cultures often influence therapy but are associated with higher mortality, suggesting a lethal effect of nosocomial pneumonia in this subset of CCU patients. The risks of FOB must be weighed with the impact of FOB results on patient outcome, and its role requires further investigation.

In vitro cellular toxicity predicts Pseudomonas aeruginosa virulence in lung infections

The role of quorum sensing by Pseudomonas aeruginosa in producing cytotoxicity has not been fully investigated. Strains of P. aeruginosa have been characterized as having an invasive or a cytotoxic phenotype (S. M. J. Fleiszig et al., Infect. Immun. 65:579-586, 1997). We noted that the application of a large inoculum of the invasive strain 6294 caused cytotoxicity of cultured epithelial cells. To investigate this dose-related cytotoxicity, we compared the behavior of 6294 to that of another invasive strain, PAO1, and determined whether the cytotoxicity could be related to quorum sensing. Both invasive strains, 6294 and PAO1, appear to have quorum-sensing systems that were operative when large doses of bacteria were applied to cultured lung epithelial cells or instilled into the lungs of animals. Nonetheless, only 6294 was cytotoxic. Cytotoxicity induced by 6294 correlated with increased elastase production. These experiments suggest that there are multiple mechanisms for the induction of cytotoxicity, pathology, and mortality in vivo. However, in vivo cytotoxicity and mortality, but not pathology, could be predicted by quantitative in vitro cellular damage experiments utilizing a range of bacteria-to-cell ratios. It appears that quorum sensing may inversely correlate with virulence in that strains that produced PAI [N-(3-oxododecanoyl) homoserine lactone] also appeared to attract more polymorphonuclear leukocytes in vivo and were possibly eliminated more quickly. In addition, exoproduct production in bacteriological medium in vitro may differ significantly from exoproduct expression from infections in vivo or during cocultivation of bacteria with tissue culture cells.