Adherence to an established diagnostic threshold for ventilator-associated pneumonia contributes to low false-negative rates in trauma patients

From bedside to bedside: how iterative clinical research influenced the diagnosis and management of pneumonia at the Elvis Presley Trauma Center

Ventilator-associated pneumonia is a well-acknowledged complication after hospitalization for injury or surgical emergency. The contribution to the literature on this topic by Dr Timothy Fabian and the Memphis group at the Elvis Presley Trauma Center resulted in the contemporary recognition that the diagnosis and management of pneumonia is an essential component of surgical critical care. During three decades, the Memphis group, under Dr Fabian's leadership, performed numerous clinical studies that led to the publication of over 40 articles concerning the epidemiology, diagnosis, and treatment of pneumonia after injury. The purpose of this review is to survey the consecutive studies from Memphis specifically that led to the development of a clinical pathway that has stood the test of time. Examination of the research output during this period provides a case study in how bedside clinical research can inform clinical practice and is a model for applied science in the intensive care unit.

Early pneumonia diagnosis decreases ventilator-associated pneumonia rates in trauma population

BACKGROUND

Ventilator-associated pneumonia (VAP) is a source of morbidity and mortality for trauma patients. Aspiration events are also common because of traumatic brain injury, altered mental status, or facial trauma. In patients requiring mechanical ventilation, early pneumonias (EPs) may be erroneously classified as ventilator associated.

METHODS

A prospective early bronchoscopy protocol was implemented from January 2020 to January 2022. Trauma patients intubated before arrival or within 48 hours of admission underwent bronchoalveolar lavage (BAL) within 24 hours of intubation. Patients with more than 100,000 colony-forming units on BAL were considered to have EP.

RESULTS

A total of 117 patients underwent early BAL. Ninety-three (79.5%) had some growth on BAL with 36 (30.8%) meeting criteria for EP. For the total study population, 29 patients (24.8%) were diagnosed with VAP later in their hospital course, 12 of which had previously been diagnosed with EP. Of EP patients (n = 36), 21 (58.3%) were treated with antibiotics based on clinical signs of infection. Of EP patients who had a later pneumonia diagnosed by BAL (n = 12), seven (58.3%) grew the same organism from their initial BAL. When these patients were excluded from VAP calculation, the rate was reduced by 27.6%. Patients with EP had a higher rate of smoking history (41.7% vs. 19.8%, p < 0.001) compared with patients without EP. There was no difference in median hospital length of stay, intensive care unit length of stay, ventilator days, or mortality between the two cohorts.

CONCLUSION

Early pneumonia is common in trauma patients intubated within the first 48 hours of admission and screening with early BAL identifies patients with aspiration or pretraumatic indicators of pneumonia. Accounting for these patients with early BAL significantly reduces reported VAP rates.

LEVEL OF EVIDENCE

Therapeutic/Care Management; Level IV.

Evaluation of GeneXpert PA assay compared to genomic and (semi-)quantitative culture methods for direct detection of Pseudomonas aeruginosa in endotracheal aspirates

Introduction

Pseudomonas aeruginosa is a common cause of ventilator-associated pneumonia (VAP). Rapid and accurate detection of lower respiratory tract colonization and/or infection with P. aeruginosa may advise targeted preventive (antibody-based) strategies and antibiotic therapy. To investigate this, we compared semi-quantitative culture results from 80 endotracheal aspirates (ETA) collected from mechanically-ventilated patients, to two culture and two non-culture-based methods for detection of P. aeruginosa.

Methods

P. aeruginosa-positive (n = 40) and -negative (n = 40) ETAs from mechanically ventilated patients analyzed initally by (i) routine semi-quantitative culture, were further analyzed with (ii) quantitative culture on chromogenic ChromID P. aeruginosa and blood agar; (iii) enrichment in brain heart infusion broth followed by plating on blood agar and ChromID P. aeruginosa; (iv) O-antigen acetylase gene-based TaqMan qPCR; and (v) GeneXpert PA PCR assay.

Results

Of the 80 ETA samples included, one sample that was negative for P. aeruginosa by semi-quantitative culture was found to be positive by the other four methods, and was included in an “extended” gold standard panel. Based on this extended gold standard, both semi-quantitative culture and the GeneXpert PA assay showed 97.6% sensitivity and 100% specificity. The quantitative culture, enrichment culture and O-antigen acetylase gene-based TaqMan qPCR had a sensitivity of 97.6%, 89.5%, 92.7%, and a specificity of 97.4%, 100%, and 71.1%, respectively.

Conclusion

This first evaluation of the GeneXpert PA assay with ETA samples found it to be as sensitive and specific as the routine, hospital-based semi-quantitative culture method. Additionally, the GeneXpert PA assay is easy to perform (hands-on time ≈ 5 min) and rapid (≈ 55 min assay time). The combination of the high sensitivity and high specificity together with the rapid acquisition of results makes the GeneXpert PA assay a highly recommended screening technique. Where this equipment is not available, semi-quantitative culture remains the most sensitive of the culture methods evaluated here for P. aeruginosa detection in ETA samples.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13756-021-00978-9.

Augmented Renal Clearance Following Traumatic Injury in Critically Ill Patients Requiring Nutrition Therapy

The intent of this study was to ascertain the prevalence of augmented renal clearance (ARC) in patients with traumatic injuries who require nutrition therapy and identify factors associated with ARC. Adult patients admitted to the trauma intensive care unit from January 2015 to September 2016 who received enteral or parenteral nutrition therapy and had a 24 h urine collection within 4 to 14 days after injury were retrospectively evaluated. Patients with a serum creatinine concentration > 1.5 mg/dL, required dialysis, or had an incomplete urine collection were excluded. ARC was defined as a measured creatinine clearance > 149 mL/min/1.73 m². Two hundred and three patients were evaluated. One hundred and two (50%) exhibited ARC. A greater proportion of patients with ARC were male (86% vs. 67%; p = 0.004), had traumatic brain injury (33% vs. 9%; p = 0.001), a higher injury severity score (30 ± 11 vs. 26 ± 12; p = 0.015), were younger (36 ± 15 vs. 54 ± 17 years; p = 0.001), had a lower serum creatinine concentration (0.7 ± 2 vs. 0.9 ± 0.2 mg/dL; p = 0.001) and were more catabolic (nitrogen balance of −10.8 ± 13.0 vs. −6.2 ± 9.2 g/d; p = 0.004). The multivariate analysis revealed African American race and protein intake were also associated with ARC. Half of critically ill patients with traumatic injuries experience ARC. Patients with multiple risk factors for ARC should be closely evaluated for dosing of renally-eliminated electrolytes, nutrients, and medications.

Tigecycline to treat Stenotrophomonas maltophilia ventilator-associated pneumonia in a trauma intensive care unit as a result of a drug shortage: A case series

WHAT IS KNOWN AND OBJECTIVE

Stenotrophomonas maltophilia is an intrinsically multidrug-resistant (MDR) organism which commonly presents as a respiratory tract infection. S. maltophilia is typically treated with high-dose sulfamethoxazole/trimethoprim (SMX/TMP). However, SMX/TMP and other treatment options for S. maltophilia can be limited because of resistance, allergy, adverse events or unavailability of the drug; use of novel agents may be necessary to adequately treat this MDR infection and overcome these limitations.

CASE DESCRIPTION

This small case series describes two patients who underwent treatment with tigecycline for ventilator-associated pneumonia (VAP) caused by S. maltophilia after admission to a trauma intensive care unit. At the time of admission for the two reported patients, a national drug shortage of intravenous (IV) SMX/TMP prevented its use. Tigecycline was chosen as a novel agent to treat S. maltophilia VAP based on culture and susceptibility data, and it was used successfully. Both patients showed clinical signs of improvement with eventual cure and discharge from the hospital after treatment with tigecycline, and one patient demonstrated confirmed microbiological cure with a negative repeat bronchoscopic bronchoalveolar lavage (BAL).

WHAT IS NEW AND CONCLUSION

To our knowledge, this small case series is the first documentation of utilizing tigecycline to treat S. maltophilia VAP in the United States. Although it likely should not be considered as a first-line agent, tigecycline proved to be an effective treatment option in the two cases described in the setting of a national drug shortage of the drug of choice.

Ventilator-associated events, not ventilator-associated pneumonia, is associated with higher mortality in trauma patients

BACKGROUND

Ventilator-associated events (VAE), using objective diagnostic criteria, are the preferred quality indicator for patients requiring mechanical ventilation (MV) for greater than 48 hours. We aim to identify the occurrence of VAE in our trauma population, the impact on survival, and length of stay, as compared to the traditional definition of ventilator-associated pneumonia (VAP).

METHODS

This retrospective review included adult trauma patients, who were Washington residents, admitted between 2012 and 2017, and required at least 3 days of MV. Exclusions included patients with Abbreviated Injury Scale head score greater than 4 and burn related mechanisms of injury. We matched trauma registry data with our institutional, physician-adjudicated, and culture-confirmed ventilator event database. We compared the clinical outcomes of ventilator-free days, intensive care unit length of stay, hospital length of stay, and likelihood of death between VAE and VAP.

RESULTS

One thousand five hundred thirty-three trauma patients met criteria; 124 (8.1%) patients developed VAE, 114 (7.4%) patients developed VAP, and 63 (4.1%) patients met criteria for both VAE and VAP. After adjusted analyses, patients with VAE were more likely to die (hazard ratio [HR], 2.86; 95% confidence interval [CI], 1.44-5.68), than those with VAP, as well those patients with neither diagnosis (HR, 2.83; 95% CI, 1.83-4.38). Patients with VAP were no more likely to die (HR, 1.55; 95% CI, 0.91-2.68) than those with neither diagnosis. Patients with VAE had fewer ventilator-free days than those with VAP (HR, -2.71; 95% CI, -4.74 to -0.68).

CONCLUSION

Critically injured trauma patients who develop VAE are three times more likely to die and utilize almost 3 days more MV than those that develop VAP. The objective criteria of VAE make it a promising indicator on which quality indicator efforts should be focused. Future studies should be aimed at identification of modifiable risk factors for VAE and their impact on outcome, as these patients are at high risk for death.

LEVEL OF EVIDENCE

Retrospective cohort study, level III.

The Effect of Lung Lavage Volume Return on the Diagnosis of Ventilator-Associated Pneumonia

BACKGROUND

Bronchoalveolar lavage (BAL) is a commonly used tool in the diagnosis of ventilator-associated pneumonia (VAP). Previous protocols recommend 30% lavage return, though no studies have investigated this relationship. This study aims to assess the influence of BAL volume return on VAP diagnosis.

MATERIALS AND METHODS

A retrospective review was performed of a prospectively maintained database for BAL performed from January 2015 to January 2016 in the trauma and surgical ICU at a level 1 trauma center. In total, 147 ventilated patients with clinical suspicion for pneumonia underwent 264 BALs. A protocol was used with five aliquots of 20 cc of saline instilled. Quantitative cultures were performed with 10ˆ5 colony-forming organisms as the threshold for VAP diagnosis. BAL was repeated at 6-8 d on 50 patients. Univariate and multivariate regression analyses were performed to investigate the predictors of VAP diagnosis.

RESULTS

Patients with >40% lavage return had increased rates of VAP diagnosis (odds ratio [OR] 2.86, P = 0.002). Increasing volume return also trended toward a lower false-negative rate. Temperature, leukocytosis, and X-ray infiltrate were not associated with increased VAP diagnosis. Concurrent antibiotic therapy at the time of BAL predicted decreased VAP diagnosis (OR 0.58, P = 0.04). On multivariable analysis, only >40% return remained associated with increased rate of VAP diagnosis (OR 4.00, P = 0.004).

CONCLUSIONS

This study found that >40% lavage volume return was associated with increased VAP diagnosis. Clinicians should consider the reliability of a negative BAL if clinical suspicion of VAP is high and lavage return is <40%. Additional investigation is needed to further elucidate this association.

Treatment of Achromobacter Ventilator-Associated Pneumonia in Critically Ill Trauma Patients

BACKGROUND

Achromobacter sp are nonfermenting Gram-negative bacilli (NFGNB) that rarely cause severe infections, including ventilator-associated pneumonia (VAP). Data on the treatment of Achromobacter pneumonia are very limited, and the organism has been associated with a high mortality rate. Thus, more data are needed on treating this organism.

OBJECTIVE

To evaluate the treatment of Achromobacter VAP in critically ill trauma patients.

METHODS

This retrospective, observational study evaluated critically ill trauma patients who developed Achromobacter VAP. A previously published pathway for the diagnosis and management of VAP was used according to routine patient care. This included the use of quantitative bronchoscopic bronchoalveolar lavage cultures to definitively diagnose VAP.

RESULTS

A total of 37 episodes of Achromobacter VAP occurred in 34 trauma intensive care unit patients over a 15-year period. The most commonly used definitive antibiotics were imipenem/cilastatin, cefepime, or trimethoprim/sulfamethoxazole. The primary outcome of clinical success was achieved in 32 of 37 episodes (87%). This is similar to previous studies of other NFGNB VAP (eg, Pseudomonas, Acinetobacter) from the study center. Microbiological success was seen in 21 of 28 episodes (75%), and VAP-related mortality was 9% (3 of 34 patients).

CONCLUSIONS

Achromobacter is a rare but potentially serious cause of VAP in critically ill patients. In this study, there was an acceptable success rate compared with other causes of NFGNB VAP in this patient population.

Early bronchoalveolar lavage for intubated trauma patients with TBI or chest trauma

PURPOSE

To evaluate the efficacy of an early bronchoalveolar lavage (E-BAL) protocol. BAL was performed within 48 h for intubated patients with traumatic brain injury or chest trauma. We hypothesized that E-BAL would decrease antibiotic use and improve outcomes compared to late BAL (L-BAL) triggered by clinical signs of pneumonia.

METHODS

Retrospective cohort analysis of 132 patients with quantitative BAL and ≥1 risk factor: head Abbreviated Injury Score ≥2, ≥3 rib fractures, or radiographic signs of aspiration or pulmonary contusion. E-BAL (n=71) was compared to L-BAL (n=61). Pneumonia was defined as ≥10⁴ organisms on BAL or Clinical Pulmonary Infection Score >6.

RESULTS

There were no significant differences in age, injury severity, initial Pao₂:Fio₂, or smoking status between E-BAL and L-BAL groups. 52% and 61% of the E-BAL and L-BAL cultures were positive, respectively. E-BAL patients had fewer antibiotic days (7.3 vs 9.2, P=.034), ventilator days (11 vs 15, P=.002), tracheostomies (49% vs 75%, P=.002), and shorter intensive care unit and hospital length of stay (13 vs 17 days (P=.007), 18 vs 22 days (P=.041)).

CONCLUSIONS

More than half of all E-BAL patients had pneumonia present early after admission. E-BAL was associated with fewer days on antibiotics and better outcomes than L-BAL.

Intubated Trauma Patients Receiving Prolonged Antibiotics for Pneumonia despite Negative Cultures: Predictors and Outcomes

BACKGROUND

Despite the excellent negative predictive value of sterile respiratory cultures, antibiotics often are continued after negative endotracheal aspirate (ETA) or bronchoalveolar lavage (BAL) for critically ill trauma patients. We hypothesized that persistent elevation of the Clinical Pulmonary Infection Score (CPIS) would predict continued antibiotic therapy after a negative respiratory culture for intubated trauma patients, and that prolonged antibiotics would provide no benefit.

METHODS

We performed a four-year retrospective cohort analysis (May 1, 2011-September 30, 2015), including patients from our trauma database with ETA or BAL, excluding patients with any infection other than pneumonia or bacteremia. Cultures with <2⁺ organisms on gram stain and <2⁺ or 10⁴ organisms on culture were considered negative. The CPIS was assessed at the time of culture and five days later, when all cultures were final. Multiple logistic regression was used to identify predictors of long-term antibiotic therapy.

RESULTS

A series of 106 patients with negative cultures were included, of whom 61 had ≤5 d of antibiotics and 45 had >5 d of antibiotics. There were no differences in injury severity, head or chest trauma, initial CPIS, or subsequent culture results between the groups. Long-term antibiotic therapy did not affect intensive care unit (ICU) length of stay (LOS), ventilator days, hospital LOS, or death. Factors predicting long-term antibiotic therapy included development of a localized chest radiograph infiltrate (odds ratio [OR] 6.8; 95% confidence interval [CI] 1.7-28), CPIS >5 five days after culture (OR 6.1; 95% CI 1.2-32), and a colonized culture (OR 3.3; 95% CI 1.3-8.3).

CONCLUSIONS

Long-term antibiotic therapy for intubated trauma patients with negative respiratory cultures provided no benefit and was predicted by development of a localized chest radiograph infiltrate, persistently elevated CPIS, and a contaminated/colonized culture. Although long-term antibiotic use did not worsen outcomes, better strategies are needed to diagnose pneumonia accurately and ensure timely discontinuation of antibiotics when appropriate.

Short-course versus prolonged-course antibiotic therapy for hospital-acquired pneumonia in critically ill adults

BACKGROUND

Pneumonia is the most common hospital-acquired infection affecting patients in the intensive care unit (ICU). However, current national guidelines for the treatment of hospital-acquired pneumonia (HAP) are several years old and the diagnosis of pneumonia in mechanically ventilated patients (VAP) has been subject to considerable recent attention. The optimal duration of antibiotic therapy for HAP in the critically ill is uncertain.

OBJECTIVES

To assess the effectiveness of short versus prolonged-course antibiotics for HAP in critically ill adults, including patients with VAP.

SEARCH METHODS

We searched CENTRAL (2015, Issue 5), MEDLINE (1946 to June 2015), MEDLINE in-process and other non-indexed citations (5 June 2015), EMBASE (2010 to June 2015), LILACS (1982 to June 2015) and Web of Science (1955 to June 2015).

SELECTION CRITERIA

We considered all randomised controlled trials (RCTs) comparing a fixed 'short' duration of antibiotic therapy with a 'prolonged' course for HAP (including patients with VAP) in critically ill adults.

DATA COLLECTION AND ANALYSIS

Two review authors conducted data extraction and assessment of risk of bias. We contacted trial authors for additional information.

MAIN RESULTS

We identified six relevant studies involving 1088 participants. This included two new studies published after the date of our previous review (2011). There was substantial variation in participants, in the diagnostic criteria used to define an episode of pneumonia, in the interventions and in the reported outcomes. We found no evidence relating to patients with a high probability of HAP who were not mechanically ventilated. For patients with VAP, overall a short seven- or eight-day course of antibiotics compared with a prolonged 10- to 15-day course increased 28-day antibiotic-free days (two studies; N = 431; mean difference (MD) 4.02 days; 95% confidence interval (CI) 2.26 to 5.78) and reduced recurrence of VAP due to multi-resistant organisms (one study; N = 110; odds ratio (OR) 0.44; 95% CI 0.21 to 0.95), without adversely affecting mortality and other recurrence outcomes. However, for cases of VAP specifically due to non-fermenting Gram-negative bacilli (NF-GNB), recurrence was greater after short-course therapy (two studies, N = 176; OR 2.18; 95% CI 1.14 to 4.16), though mortality outcomes were not significantly different. One study found that a three-day course of antibiotic therapy for patients with suspected HAP but a low Clinical Pulmonary Infection Score (CPIS) was associated with a significantly lower risk of superinfection or emergence of antimicrobial resistance, compared with standard (prolonged) course therapy.

AUTHORS' CONCLUSIONS

On the basis of a small number of studies and appreciating the lack of uniform definition of pneumonia, we conclude that for patients with VAP not due to NF-GNB a short, fixed course (seven or eight days) of antibiotic therapy appears not to increase the risk of adverse clinical outcomes, and may reduce the emergence of resistant organisms, compared with a prolonged course (10 to 15 days). However, for patients with VAP due to NF-GNB, there appears to be a higher risk of recurrence following short-course therapy. These findings do not differ from those of our previous review and are broadly consistent with current guidelines. There are few data from RCTs comparing durations of therapy in non-ventilated patients with HAP, but on the basis of a single study, short-course (three-day) therapy for HAP appears not to be associated with worse clinical outcome, and may reduce the risk of subsequent infection or the emergence of resistant organisms when there is low probability of pneumonia according to the CPIS.