Open Access

Number needed to treat and cost-effectiveness in the prevention of ventilator-associated pneumonia

Critical Care201216:430

https://doi.org/10.1186/cc11346

Published: 7 June 2012

While clinicians continue to redefine ventilator-associated pneumonia (VAP), numerous innovations that claim to reduce pulmonary microaspiration and its consequences - that is, novel endotracheal cuff shapes and cuff materials, subglottic drainage, automatic cuff pressure controllers, oral anti-septics, selective digestive decontamination (SDD), and devices to combat biofilm formation within the lumen of the tracheal tube - are coming to the market [1, 2]. There are two questions that clinicians ask when deciding whether to incorporate a new product or intervention into a VAP prevention bundle. Firstly, what are its efficacy and effectiveness? In other words, what is the relative risk reduction (RRR) and therefore the number needed to treat (NNT) to prevent one additional VAP. Secondly, is this new intervention cost-effective in my local patients?

To answer the first question, one needs data from clinical trials and the knowledge of the baseline VAP rate with the likely RRR of the local case mix. We have calculated (Table 1) the NNT required to prevent one additional VAP for patients who require intubation and mechanical ventilation (MV) for more than 72 hours and an average time of MV of 10 days. The NNTs are based on an RRR ranging from 5% to 50% and a control event rate for VAP ranging from 1% to 20%, given a uniform distribution of NNTs across the range of RRRs. For example, with a VAP rate of approximately 8% and an intervention that reduces VAP by 45%, the NNT is 28 - a scenario that is realistic given a recent meta-analysis of one particular intervention [3].
Table 1

Number needed to treat in ventilator-associated pneumonia

 

Relative risk reduction

 

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

Baseline VAP rate

          

1%

2,000

1,000

667

500

400

333

286

250

222

200

2%

1,000

500

333

250

200

167

143

125

111

100

4%

500

250

167

125

100

83

71

63

56

50

6%

333

167

111

83

67

56

48

42

37

33

8%

250

125

83

63

50

42

36

31

28

25

10%

200

100

67

50

40

33

29

25

22

20

15%

133

67

44

33

27

22

19

16.7

15

13

20%

100

50

33

25

20

17

14

12.5

11

10

Number needed to treat (NNT) was calculated as: NNT [relative risk of event] = 1/(pc × RRR), where pc is the proportion of control group subjects who suffer an event and RRR is relative risk reduction. These NNTs are based on events per 10 days of mechanical ventilation, meaning that more than one event can occur in a single patient who is ventilated for more than 10 days. VAP, ventilator-associated pneumonia.

To establish whether the intervention is cost-effective, further knowledge of the cost of the intervention and the cost to treat an episode of VAP is required. A recent US study estimated the cost of VAP to be nearly $40,000 (£25,000 or €30,000) [4]. If costs are assumed to be lower in Europe, then a conservative estimate of the cost per episode of VAP would still be around £10,000, which is equivalent to an extra 7 days of intensive care unit (ICU) stay. What should we consider when assessing the cost-effectiveness of VAP prevention?

We have calculated (Table 2) the additional money (in pounds) that can be spent to prevent an episode of VAP (per 10 days of MV) to achieve cost-neutrality. If we assume a hypothetical VAP cost of £10,000, then with a VAP rate of 8% and an RRR of 45%, it is cost-effective to spend up to £360 . Furthermore, even for an ICU with a VAP rate of only 4% and an intervention that reduces VAP by just 25%, it is still cost-effective to spend up to £100 per 10 days of MV. It should be noted that some VAP prevention interventions (for example, a modified tracheal tube cuff) require just a 'one-off' initial cost whereas other interventions (for example, SDD) require an 'ongoing' daily cost.
Table 2

Cost-effectiveness of an intervention based on baseline ventilator-associated pneumonia rate and its relative risk reduction

 

Relative risk reduction

 

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

Baseline VAP rate

          

1%

£5

£10

£15

£20

£25

£30

£35

£40

£45

£50

2%

£10

£20

£30

£40

£50

£60

£70

£80

£90

£100

4%

£20

£40

£60

£80

£100

£120

£140

£160

£180

£200

6%

£30

£60

£90

£120

£150

£180

£210

£240

£270

£300

8%

£40

£80

£120

£160

£200

£240

£280

£320

£360

£400

10%

£50

£100

£150

£200

£250

£300

£350

£400

£450

£500

15%

£75

£150

£225

£300

£375

£450

£525

£600

£675

£750

20%

£100

£200

£300

£400

£500

£600

£700

£800

£900

£1,000

Values (£) refer to the average additional expense that can be spent for an intervention, per 10 days of mechanical ventilation, for it to be cost-neutral assuming a VAP cost of £10,000. VAP, ventilator-associated pneumonia.

We think that this analysis might help clinicians in making the important economic decision of whether to adopt a new VAP prevention device or procedure. Our calculations can easily be adapted to local currencies and circumstances worldwide.

Abbreviations

ICU: 

intensive care unit

MV: 

mechanical ventilation

NNT: 

number needed to treat

RRR: 

relative risk reduction

SDD: 

selective digestive decontamination

VAP: 

ventilator-associated pneumonia.

Declarations

Authors’ Affiliations

(1)
Department of Adult Critical Care, Guy's and St Thomas' NHS Foundation Trust, St Thomas' Hospital

References

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Copyright

© BioMed Central Ltd 2012

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