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Original Article

Diagnosis, management and prevention of ventilator-associated pneumonia in the UK

Hunter, J.*; Annadurai, S.; Rothwell, M.*

Author Information
European Journal of Anaesthesiology: November 2007 - Volume 24 - Issue 11 - p 971-977
doi: 10.1017/S0265021507001123

Abstract

Introduction

Nosocomial infections continue to be a major cause of morbidity and mortality. Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in the intensive care unit [1], and its development is associated with an attributable increase in morbidity and mortality [2,3]. Intubation of the trachea and mechanical ventilation is associated with a 7- to 21-fold increase in the incidence of pneumonia and up to 28% of patients receiving mechanical ventilation will develop this complication [4-7].

Despite extensive research into the disease, controversy still exists on the ideal methods for its diagnosis, prevention and management [8]. For instance, there is no accepted ‘gold standard’ for the diagnosis of VAP, the optimal duration of antibiotic therapy is uncertain and there is widespread variation in the employment of evidence-based techniques to prevent its occurrence [9,10]. In addition, the majority of the guidelines and consensus papers on the management of VAP originate in North America, and may not reflect British practice [11,12].

Because of the perceived wide variations in clinical practice we thought it would be useful to assess the current management of VAP in the UK by conducting a national postal questionnaire survey of UK intensivists.

Materials and methods

We identified all hospitals in the UK from the Directory of Operating Theatres and Departments of Surgery with intensive care services [13]. Hospitals concerned solely with paediatric, obstetric, ophthalmic or dental services were excluded. A postal questionnaire (Appendix) addressed to the ‘Lead Clinician, Intensive Care Unit’ was sent along with a covering letter explaining the purpose of the study to all the identified hospitals (n = 207). A second mail shot was sent if no reply had been received within 6 weeks.

Results

Fully completed questionnaires were received from 160 of the 207 hospitals surveyed (77.3% response rate). Of the responders, 63 (39.3%) were from teaching hospitals and 97 (60.7%) from non-teaching hospitals.

An invasive technique (e.g. bronchoalveolar lavage, protected specimen brushing) was used by 48 units (30%) to obtain specimens for microbiological diagnosis, while the remaining 70% of units relied on tracheal aspirates. Invasive diagnostic techniques were more commonly employed in teaching units, with 54.1% of those respondents using invasive techniques coming from teaching hospitals. In those relying on tracheal aspirates as the prime method of obtaining microbiological specimens, only 28.2% had the microbiological results reported in a quantitative manner (i.e. colony-forming units (cfu) mL−1). The invasive methods employed to obtain samples and their frequency of usage are shown in Figure 1. The principal reasons given for not employing an invasive diagnostic strategy include: no equipment available (18), laboratory unable to process specimens (21), expertize unavailable (12) and tracheal aspirates felt to be adequate (66).

Figure 1.
Figure 1.:
Invasive diagnostic strategies employed to collect microbiological specimens. Because some units use a variety of techniques, the sum of responses is >100%.

The majority of respondents (77.2%) would commence antibiotic therapy empirically if there was a clinical suspicion of VAP. Opinion was almost equally divided on whether monotherapy or combination antimicrobial therapy was the most appropriate treatment for the empirical management of suspected VAP, with 49.1% preferring monotherapy and 50.9% preferring combination therapy. There was wide variation in the involvement of a microbiologist in the choice of antimicrobial therapy, with less than a fifth of units always seeking expert microbiological advice before commencement of antibiotics (Fig. 2). Of the responding units, 48.7% had specific guidelines on the choice of antibiotic therapy, and 19.6% routinely rotated antibiotic usage. The vast majority (90.5%) received regular feedback from their microbiology departments on susceptibility patterns, resistance, etc. Antibiotics were continued for a median of 7 days (inter-quartile range 5-8.5, range 2-14 days). Factors influencing the duration of antibiotic therapy include: severity of pneumonia (53), clinical response (1 0 1), organism isolated (76) and microbiology advice (115).

Figure 2.
Figure 2.:
Percentage of respondents who consult the hospital microbiologist for advice before commencement of antibiotics.

Strategies employed by the responding units for the prevention of VAP are shown in Table 1.

Table 1
Table 1:
Utilization of strategies for the prevention of ventilator-associated pneumonia.

Discussion

This study demonstrates the widespread variations in practice throughout the UK in the diagnosis, management and prevention of VAP.

The accurate diagnosis of VAP remains challenging. While the presence of infiltrates on the chest X-ray and clinical signs of infection such as pyrexia and tachycardia should raise suspicion of VAP, clinical diagnosis alone is overly sensitive and lacks specificity [14,15]. Confirmation of the presence of pneumonia requires a lower respiratory tract culture, which can be obtained invasively or non-invasively (tracheal aspirates). Invasive samples can be obtained bronchoscopically or blindly. Bronchoalveolar lavage (BAL), protected specimen brushing (PSB) and mini-BAL are usually performed with the aid of a bronchoscope.

The optimal method of specimen collection remains highly controversial. Culture of tracheal aspirates may simply yield organisms that have colonized the tracheal tube and may not reflect invasive infection. However, quantitative culture of specimens obtained by simple tracheal aspiration may improve diagnostic accuracy. A sensitivity of 68% and a specificity of 84% have been reported when 106 cfu mL−1 was used as the threshold for diagnosis [16]. In this study, 70% of respondents used tracheal aspirates for the diagnosis of VAP. Although there is controversy surrounding the utility of using tracheal aspirates, there is increasing evidence to suggest that quantitative analysis of tracheal aspirate specimens offers a reliable and cost effective alternative to invasive techniques [17-19]. However, only 28.2% had the microbiological results reported in a quantitative manner. As non-quantitative analysis of tracheal aspirates is associated with decreased specificity and increased sensitivity [20], there may be widespread over utilization of antibiotics for suspected VAP in the UK.

Of those using invasive methods to obtain specimens, BAL and ‘blind’ mini-BAL were the predominant methods of choice. The popularity of BAL probably reflects the familiarity of this technique amongst respiratory physicians. Unsurprisingly, ‘blind’ mini-BAL is also popular. This is a simple, cheap technique for obtaining specimens from the distal airways without the aid of a bronchoscope. It has also been shown to be effective in accurately identifying the organisms responsible for VAP, demonstrating the diffuse nature of the disease [21]. A recent meta-analysis of randomized, controlled trials of invasive diagnostic strategies in suspected VAP reported that an invasive approach did not alter mortality (odds ratio 0.89, 95% CI 0.56-1.41), but did alter antibiotic utilization (odds ratio for change in antibiotic management after invasive sampling, 2.85, 95% CI 1.45-5.59) [22]. Again, the relatively low utilization of invasive diagnostic techniques within the UK may be leading to inappropriate antibiotic therapy. It would appear that the reticence to use an invasive technique is mainly because clinicians feel that accurate microbiological analysis can be obtained from tracheal aspirates, although a significant number of hospitals seem unable to process specimens in the quantitative manner required for invasively obtained specimens.

Almost a third of respondents stated that they would not empirically commence antibiotics despite a clinical suspicion of VAP. However, there is emerging evidence and opinion that appropriate antibiotics should be immediately initiated in patients suspected of developing VAP [2,12,23-26]. Inappropriate initial antibiotic therapy is strongly associated with a poor outcome [4,27].

Clinicians were almost equally divided on whether empirical antibiotic therapy should be monotherapy or combination therapy. This likely reflects the equipoise that currently exists in the literature on the benefits of mono vs. combination therapy. Traditionally, a combination of two or even three different antibiotics has been used empirically in suspected VAP to increase antibiotic spectrum and decrease the emergence of resistance. A synergistic benefit may also exist, although this is difficult to prove [28,29]. However, a recent study comparing empirical monotherapy with empirical combination therapy in patients suspected of VAP could not demonstrate any difference in length of stay, ventilator-free days or mortality [30].

Involvement of the hospital microbiologist in the choice of antimicrobial chemotherapy was highly variable with less than 20% of units invariably seeking advice before administration of antibiotics. However, most units received regular feedback from the microbiology department, suggesting that antibiotics were being used in a rational manner. Almost half of units had specific guidelines for the treatment of VAP. This approach has been shown to increase the likelihood that initial antimicrobial treatment is adequate and appropriate [31].

Antibiotic cycling may reduce the emergence of antibiotic resistance in the intensive care unit [32], although this strategy does not appear to be popular within the UK. The overall incidence of VAP may also decrease with the introduction of a scheduled antibiotic rotation regimen [33,34].

The ideal duration of antibiotic therapy in VAP is uncertain with many experts advocating a 14-21 day course [5,12]. However, the duration of antibiotic therapy in the UK appears to be much shorter that this perhaps reflecting concerns about the emergence of multi-resistant bacteria. There is also some evidence to support a shorter course of antibiotics. Chastre and colleagues [35] randomly assigned patients with proven VAP to receive either an 8-day or 15-day antibiotic regimen. Compared with patients treated for 15 days, those treated for 8 days had neither excess mortality (18.8% vs. 17.2%) nor more recurrent infections (28.9% vs. 26.0%). It appears that when clinicians are deciding the duration of antibiotic therapy, they are most influenced by advice from the microbiologist and the clinical response to the administration of the antibiotic.

Although evidence-based guidelines for the prevention of VAP exist [36,11], it has previously been reported that adherence to many of the recommendations are highly variable [9,10,37]. However, it appears from our study that adherence to the two principal preventive evidence-based measures for the prevention of VAP, namely nursing in the semi-recumbent position [38] and daily interruption of sedative regimes [39] are widely adhered to. This most likely reflects the widespread introduction of ‘ventilator bundles’ within the UK, of which these two strategies are key components.

There appears to be very little enthusiasm for selective decontamination of the digestive tract (SDD) in the UK. This is perhaps surprising as meta-analyses have shown that the use of SDD reduces the occurrence of VAP [40,41]. Nevertheless, a recent Spanish study also highlighted the unpopularity of this technique for the prevention of VAP [9]. It may be that fear of the emergence of antimicrobial resistance is limiting its use.

Almost one-third of units perform a tracheostomy within 4 days of admission if rapid weaning is not thought possible. This practice may reduce the incidence of VAP. In a recent American study of 120 patients expected to require mechanical ventilation for longer than 14 days, those that were randomized to receive percutaneous dilatational tracheostomy within 48 h of admission had a significantly lower incidence of VAP than those who received a tracheostomy after 14-16 days (5% vs. 25%, P < 0.005) [42]. Results from a similar British Study (TracMan) are awaited.

Oral rinsing with chlorhexidine has previously been shown to decrease the incidence of VAP [43], although it is not commonplace in the UK. It may be that fear of overuse and colonization with chlorhexidine-resistant pathogens is restricting its use.

The use of prophylactic parenteral broad-spectrum antibiotic prophylaxis is not widespread, probably because of concerns regarding increasing frequency of antibiotic resistance. There is some evidence, however, that administration of such therapy may useful in the prevention of VAP, especially those with a significantly obtunded conscious level [44].

As the incidence of VAP is less when non-invasive ventilation is employed [45], it is gratifying to see that well over half of respondents would use non-invasive ventilation if clinically indicated.

Although continuous aspiration of sub-glottic secretions has been shown to be effective in the prevention of VAP [46], the need for specialized tracheal and tracheostomy tubes probably limits its widespread application.

Although it seems reasonable to ensure that the cuff of the tracheal tube is adequately inflated, studies show that aspiration of infected secretions occur even when the cuff is inflated >20 mmHg [47,48]

In conclusion, VAP is a highly complex disease and interpretation of the data from the multitude of studies published on its management can be problematic. Many important questions remain unanswered, and there remains disagreement amongst experts on many aspects of the management of this disease. It is therefore not surprising that wide variations in clinical practice exist.

References

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Appendix

Surveyed opinion of the diagnosis, management and prevention of ventilator-associated pneumonia in the intensive care unit

How many level 3 beds do you have?————

Are you a teaching or non-teaching hospital?——

Regarding the diagnosis of VAP

1. Do you routinely use invasive methods (e.g. BAL, PSB) to obtain bacteriological specimens from the lungs? If so please go to question 4.

Yes (please proceed to question 4)

No

2. If culture of tracheal aspirates is you prime method of obtaining microbiological specimens, are the results reported in a quantitative manner (i.e. >105 cfu's mL−1)

Yes

No

3. Invasive diagnostic methods are not employed because (please tick all applicable)

1. Equipment not available

2. Laboratory unable to process specimens

3. Expertise unavailable

4. I think results obtained from tracheal aspirates are adequate to guide diagnosis and treatment

4. Which invasive method(s) do you routinely employ to obtain bacteriological specimens from the lungs?

1. Bronchoalveolar lavage

2. Protected specimen brushing

3. Mini-BAL

4. ‘Blind’ mini-BAL

Regarding the treatment of VAP

1. Do you commence antibiotic therapy empirically, i.e. before culture results are available, when VAP is suspected clinically? If not please go to question 3

Yes

No (please proceed to question 3)

2. If starting empiric therapy, do you routinely use monotherapy or combination therapy?

Monotherapy

Combination therapy

3. Before administration of antibiotics do you consult the hospital microbiologist for advice?

1. Always

2. 0-25% of times

3. 25-50% of times

4. 50-75% of times

5. 75-100% of times

6. Never

6. Do you have specific guidelines for anti-microbial therapy of VAP?

Yes

No

7. Do you routinely rotate antibiotic usage?

Yes

No

8. Do you receive regular feedback from your microbiology department on susceptibility patterns, resistance, etc.?

Yes

No

9. How long do you routinely continue antibiotics for?______days

10. Please indicate the factor(s) that most influence antibiotic duration

1. Severity of pneumonia

2. Clinical response to antibiotics

3. Organism isolated

4. Microbiological advice

Regarding the prevention of VAP

1. Which of the following methods of preventing VAP do you routinely employ?

  • Nursing patient in semi-recumbent position
  • Daily interruption of sedative regimes
  • Early tracheostomy (within 4 days of admission)
  • Selective decontamination of digestive tract (SDD)
  • Chlorhexidine mouth wash daily
  • Prophylactic parenteral antibiotics
  • Non-invasive ventilation whenever possible
  • Continuous aspiration of subglottic secretions
  • Maintenance of tracheal cuff pressure >20 mmHg
Keywords:

PNEUMONIA; VENTILATOR ASSOCIATED; CRITICAL CARE; PREVENTION AND CONTROL; DIAGNOSIS; QUESTIONNAIRE

© 2007 European Society of Anaesthesiology