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Number needed to treat for subglottic secretion drainage technology as a ventilator-associated pneumonia prevention strategy


The number needed to treat can be calculated for ventilator-associated pneumonia reduction strategies such as subglottic secretion drainage technology based on previous work establishing its relative risk reduction. Assuming an incidence of 4%, employing subglottic secretion drainage in 33 patients will prevent one case of ventilator-associated pneumonia, and thus potentially 4 cases annually in an average hospital in the United States. With a previously described limit of £300 ($470 USD) additional cost per 10 days of ventilation as a threshold of investment for technologies to reduce ventilator-associated pneumonia, subglottic secretion drainage technology is both clinically and cost effective.

Wyncoll and Camporota's correspondence [1] provides a valuable tool allowing clinicians the ability to assess the number needed to treat (NNT) and cost-effectiveness of various ventilator-associated pneumonia (VAP) prevention strategies. Subglottic secretion drainage (SSD) technology is one VAP-reduction strategy for which NNT can easily be calculated based on its established relative risk reduction.

Smulders and colleagues [2] conducted a randomized clinical trial in 150 patients receiving mechanical ventilation and found that intermittent SSD reduced the risk of VAP by 75% (P = 0.014). Utilizing Wyncoll and Camporota's table, and assuming a VAP incidence of 4%, utilizing SSD in 33 patients will prevent one episode of VAP. In the United States, the average hospital has approximately 131 patients per year who require mechanical ventilation >96 hours (unpublished observations). Utilizing SSD in these average hospitals would likely prevent four cases of VAP per year. In addition, SSD is a cost-effective intervention. At the assumed VAP rate of 4%, Wyncoll and Camporota determined an upper threshold of £300 ($470 USD) additional cost per 10 days of ventilation to be a cost-effective investment in technologies that reduce VAP by up to 75%. Costs of SSD technology interventions are beneath this threshold.

Wyncoll and Camporota's framework illustrates that use of SSD is both a clinically and cost-effective strategy to reduce VAP. The NNT demonstrates that average hospitals will observe and benefit from these strategies. SSD technologies warrant further adoption and appropriate utilization.



number needed to treat


subglottic secretion drainage


ventilator-associated pneumonia.


  1. 1.

    Wyncoll D, Camporota L: Number needed to treat and cost-effectiveness in the prevention of ventilator-associated pneumonia. Crit Care. 2012, 16: 430-10.1186/cc11037.

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  2. 2.

    Smulders K, can der Hoeven H, Weers-Pothoff I, Vandenbroucke-Grauls C: A randomized clinical trial of intermittent subglottic secretion drainage in patients receiving mechanical ventilation. Chest. 2002, 121: 858-862. 10.1378/chest.121.3.858.

    Article  PubMed  Google Scholar 

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SK would like to thank Mary Erslon, RN, MSN, MBA (Covidien) for writing assistance.

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Correspondence to Scott D Kelley.

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SK is an employee of Covidien, and receives salary and equity compensation.

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Kelley, S.D. Number needed to treat for subglottic secretion drainage technology as a ventilator-associated pneumonia prevention strategy. Crit Care 16, 446 (2012).

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  • Clinical Trial
  • Pneumonia
  • Mechanical Ventilation
  • Emergency Medicine
  • Prevention Strategy