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Interact CardioVasc Thorac Surg 2005;4:110-115. doi:10.1510/icvts.2004.100149 © 2005 European Association of Cardio-Thoracic Surgery
Continuous subglottic suction is effective for prevention of ventilator associated pneumoniaDepartment of Cardiothoracic Surgery, Freeman Hospital, Newcastle upon-Tyne NE7 7DN, UK Received 5 October 2004; accepted 21 December 2004
*Corresponding author. Tel/fax: +44 7801548122.
A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether subglottic suction is an effective preventative measure for ventilator associated pneumonia (VAP) after cardiac surgery. Altogether 457 papers were found using the reported search, of which 13 presented the best evidence to answer the clinical question. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results, and study weaknesses of these papers are tabulated. We conclude Subglottic suction significantly reduces the incidence of VAP in high risk patients (NNT of 8 if ventilated over 3 days), although the benefit is lower in elective cardiac patients. Subglottic suction is currently not commonly used, but even with marginal benefits, its use is likely to be highly cost effective.
Key Words: Evidence-based medicine; Subglottic suction; Ventilator-associated pneumonia; Review
A best evidence topic was constructed according to a structured protocol. This protocol is fully described in the ICVTS [1]. 1.1. Clinical scenario You performed a difficult Aortic Valve replacement and triple-coronary arterial-bypass-graft on a 77-year-old man, with a 30-year history of smoking. The operation proceeded uneventfully, but in the Intensive care it was not possible to extubate him on the first night due to basal collapse, and over the next few days he develops a ventilator-associated-pneumonia (VAP).You search the internet for manoeuvres that may avoid this frustrating complication and find that continuous subglottic suction would avoid pooling of secretions around the endotracheal tube and thus perhaps reduce VAP. Thus you resolve to search for evidence for this simple intervention. 1.2. Three-part question In patients undergoing [mechanical ventilation] does [subglottic suction] reduce the incidence of [Ventilator associated pneumonia]?1.3. Search strategy Medline 1966–Sept 2004 using the Ovid interface.[glottic.mp OR subglottic.mp OR sub-glottic.mp] AND [exp pneumonia/OR pneumonia.mp OR secreti$.mp OR ventilat$. mp OR aspirat$.mp] Limit to human studies. 1.4. Search outcome Four hundred and fifty seven papers were found from the reported search and cross-checking reference lists, of which 13 were deemed to be relevant. This included 7 RCTs, one cohort study and several reviews, from which 3 were selected [2–14]. The papers are presented in Table 1.
Valles et al. in 1995 [2] performed a large randomized study in 190 patients who were likely to be ventilated for more than 3 days. They found a relative reduction of 43% in ventilator-associated-pneumonia (VAP) and continuous suction delayed the time to the onset of VAP from a mean of 5 days to 12 days (NNT of 5). The same authors [3] then performed a cohort study in 83 patients intubated in their general ICU or emergency department, where all patients received continuous subglottic suction. They found that 43% of patients who developed pneumonia suffered failure of the suction compared to 30% of those who did not. In addition low cuff pressure was also significantly associated with pneumonia. Smulders et al. in 2002 [5] performed a large PRCT in 150 general ICU patients with predicted ventilation of over 3 days. They used subglottic suction, but in order to avoid possible tracheal wall damage they instituted intermittent suction with 8 seconds of suction every 20 seconds. They found a significantly reduced incidence of pneumonia in the suction group, reducing the incidence of VAP from 16% to 4%. This is a number needed to treat of 8. Pneumatikos et al. [6] performed a slightly different study where they randomised 61 patients to use of the Hi-Low Evac subglottic suction tubing or controls. However, instead of simple suction they used a continuous infusion of antibiotics down the tube with intermittent suction. They found a marked reduction of VAP from 53% down to 16%. Mahul [7] performed a randomized trial in 145 patients with a predicted intubation time of over 3 days. A significant reduction in nosocomial pneumonia was found with hourly subglottic suction. 29% of controls suffered pneumonia compared to only 13% in the suction group. Kollef et al. [9] performed the only study in patients post cardiac surgery. They randomized 343 patients using their birth years to either continuous subglottic suction or normal ET-tube. They found a non-significant reduction of VAP from 8.2% in controls to 5% in the subglottic suction group, P=0.238. They did, however, find a significant delay in the onset of VAP, with a mean time of 2.9 days in the control group compared to 5.6 days in the subglottic suction group (P=0.006). They concluded that 1006 patients would have been required to achieve significance for the difference that they found, but that if their findings were significant, the number needed to treat to prevent one pneumonia in all cardiac surgical patients would be 32. Marin Kollef [10] also performed a systematic review for the New England Journal of Medicine in the same year and concluded that there was grade A evidence to support the use of continuous subglottic suction routinely. Among the many reviews in the literature Collard [11] performed one of the most recent and well performed. They stated that the evidence was in fact quite mixed, grading it at IIa and stated that continuous suction has not convincingly been shown to reduce VAP in all patients but should perhaps be considered in all patients who may require more than 3 days of ventilation. In addition a recent systematic review performed by Dodek et al. in 2004 [14] for the Canadian Critical Care trials Group recommended that clinicians consider the use of subglottic secretion drainage in all their patients. A survey of practise was performed in 2002 in France and Canada [12] into protocols used to reduce VAP in university affiliated ICUs. They found that less than 5% of units used subglottic suction. The primary reason cited was lack of evidence for benefit, with cost and lack of availability also cited. In contrast an interesting cost analysis was performed in 2003 [13]. The cost of subglottic suction is $15 per tube compared to $1 per conventional ET tube, and the cost of one episode of VAP was estimated to be $5,365. With a 30% reduction assumed for the suction strategy they estimated the cost benefit to be $4,992 per case of VAP saved. They also reported that the cost of VAP would have to be as low as $330 for the strategy to be non-cost effective. Thus, in summary, clinical benefits have been shown for subglottic suction in the highest-risk patients. Only 8 patients being ventilated for more than 3–5 days need to be treated to prevent one episode of pneumonia. The benefits markedly reduce when you consider lower risk patients such as patients post cardiac surgery where 32-patients must be treated to prevent one pneumonia. Subglottic suction has also been shown to delay the onset of VAP but no benefits in terms of ventilation time, hospital stay or mortality benefit have ever been shown. However, it has been shown that even if the benefits of subglottic suction are marginal, the cost benefit of this cheap intervention is likely to substantial. 2.1. Clinical bottom line Subglottic suction significantly reduces the incidence of VAP in high-risk patients (NNT of 8 if ventilated over 3 days), although the benefit is lower in elective cardiac patients. Subglottic suction is currently not commonly used, but even with marginal benefits, its use is likely to be highly cost effective.
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Abstract
1. Introduction