Please read the comments below this post for a correction.
The cuff of an endotracheal tube is hardly a robust barrier to aspiration of contaminated secretions from the oropharynx. High volume, low pressure cuffs tend to fold over on themselves, forming invaginations and crevices that yukky stuff can slip through relatively easily. Underinflation of the cuff is another common problem. (That’s the rationale for continuous subglottic suctioning, which likely revents ventilator associated pneumonias but does require some bedside attention, adding a hassle / labor cost / culture change barrier.)
Nseir et al tried out an automatically-titrating pneumatic device that kept the endotracheal tube cuff at 25 cm H2O. They randomized 122 patients in one French MICU expected to need mechanical ventilation for 48+ hours to either the fancy device or usual care.
RESULTS: The pneumatic cuff significantly reduced their primary outcome, pepsin (which comes from the stomach) measured in the trachea, as well as the rate of VAP (10% vs. 26%) and the concentrations of bacteria in the lower airways, which were secondary outcomes. There was no increased incidence of tracheal ischemic injury, which was formally scored.
A positive study! But, wait a second. Valencia et al performed a near identical study using pressure-controlled endotracheal tube cuffs, publishing the results in Crit Care Med 2007 — which were negative for any reduction in pneumonia. The main difference seemed to be the use of chlorhexidine mouth rinses in the Valencia study (which should be standard I humbly suggest) but chlorhexidine rinses were apparently not part of the protocol in this current study. If chlorhexidine were standard here, it might have reduced/eliminated the observed benefit of cuff pressure control.
As seems common in studies when VAP is the outcome, the VAP rate in the control arm was high. Reported or acknowledged VAP rates vary widely between institutions — at times, almost unbelievably so (there is a MICU in an academic system in my city that reports having one VAP over the past 2 years, for example). One expert wag even wondered in print if doctors and administrators are gaming the system by renaming many VAPs, “VATs” to avoid payer-imposed penalties for “never-events.” When trying to interpret seemingly very well conducted studies and apply them reasonably in practice, that added layer of uncertainty makes me sigh. (Of course this study was conducted in France, where things in the medical care system may make more sense — Je ne sais pas.)
What else does the literature say can you do to help prevent ventilator-associated pneumonia, you ask?
Silver-coated ET tubes also prevented VAP in the NASCENT randomized trial, but they haven’t been shown to improve clinical outcomes to my knowledge, and they cost $90 (vs $2 for ordinary ET tubes); they haven’t yet caught on.
Head of bed elevation wasn’t shown to prevent ventilator-associated pneumonia in the best-conducted multicenter RCT, but don’t tell that to nurse managers, they’ll hit you over the head.
Chlorhexidine mouth rinses do substantially reduce VAP rates, according to this meta-analysis of randomized trials of 2,300 patients.
Continuous subglottic suctioning resulted in a 45% reduction in VAP, fewer vent-days and ICU-days in a meta-analysis of 13 studies. (As mentioned above, it’s not widely used in the U.S.)
The preceding list relies heavily on the excellent editorial by Mark Bonten, linked below.
Nseir S et al. Continuous Control of Tracheal Cuff Pressure and Microaspiration of Gastric Contents in Critically Ill Patients. Am J Respir Crit Care Med 2011;184:1041-1047.
Bonten MJM. Ventilator-associated Pneumonia and the Gastropulmonary Route of Infection. Am J Respir Crit Care Med 2011;184:991-993. (EDITORIAL)
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It is clearly stated in the online supplement of our manuscript (AJRCCM 2011; 184:1041-7) that oral cavity was cleaned with chlorhexidine in all patients. The different results between our study and that of Valencia could be explained by the different devices used in these studies to control cuff pressure. As explained in discussion section of the manuscript, whilst the device used by Valencia was an electronic one with important limitation (very well-described in a in vitro study by Weiss and colleagues) related to the very rapid correction of cuff pressure variations, the device used in our study was a pneumatic one which is probably more efficient in controling cuff pressure.
Dr Nseir: Thank you for clarifying this important point regarding the use of chlorhexidine mouth hygiene in your study.
I acknowledge I didn’t read the online supplement. I would hasten to add, though, that I wasn’t the only one who missed this important fact about your study. As Dr. Marc Bonten wrote in the editorial accompanying your article in the same issue of AJRCCM:
“An important difference, though [between the Nseir study and the Valencia study], may have been the routine use of chlorhexidine oropharyngeal decontamination in all patients in the latter [Valencia] study.”
Since the editorialist missed it, I think it’s understandable that I and most readers would do the same.
I respectfully suggest that something as key as this should have been placed in the main (published) portion of the manuscript. I know space is tight and every word counts, but even a short phrase such as “All components of standard ‘ventilator bundles,’ including head-of-bed elevation and chlorhexidine oropharyngeal decontamination, were implemented and adhered with; please see the online supplement for further details,” would have prevented the confusion.
I appreciate your work and your taking the time to comment here to clarify my and Dr. Bonten’s oversight. I have added a heading to the above post to direct readers to these corrections. (I did not notify the editors at AJRCCM, but you might consider doing so.)
-Matt Hoffman