Prevention of Intensive Care Unit-acquired Pneumonia

Michael Klompas, MD, MPH

Disclosures

Semin Respir Crit Care Med. 2019;40(4):548-557. 

In This Article

Endotracheal Tube Cuff Design and Pressure Monitoring

Investigators have proposed several innovations in endotracheal tube cuff materials, shape, and design to prevent VAP.[56,57] Conventional polyvinyl chloride cylindrical endotracheal tube cuffs conform imperfectly to the shape of the trachea; they develop vertical microfolds that create passageways that can allow microbe-laden secretions above the cuff to flow across the cuff and into the lungs. Innovators have tried to block this pathway to aspiration by switching to ultrathin cuff materials such as polyurethane, changing the shape of the cuff from a cylinder to a cone, and by monitoring and adjusting cuff pressures more frequently and/or consistently using either manual or automated methods. Ultrathin polyurethane better conforms to the shape of the trachea and thus decreases the number and size of channels along the tracheal wall.[58] Tapered cuffs are thought to approximate the tracheal wall more evenly and consistently at the point of maximum cuff diameter compared with conventional cylindrical cuffs. And more consistent cuff pressure monitoring is intended to protect against unappreciated drops in cuff pressure that could facilitate increased passage of secretions around the cuff.

Unfortunately, none of these innovations have thus far been proven to prevent VAP or improve objective patient outcomes. Philippart and colleagues randomized 621 patients expected to require >2 days of mechanical ventilation to four groups: cylindrical polyvinyl chloride cuffs, cylindrical polyurethane cuffs, conical polyvinyl chloride cuffs, and conical polyurethane cuffs.[59] They found no difference between any of the four groups in tracheal colonization or VAP rates. Similarly, Jaillette and colleagues randomized 326 patients to endotracheal tubes with conical versus cylindrical cuffs.[55] They documented microaspiration rates of over 50% in both groups regardless of cuff shape by assaying tracheal aspirates for pepsin and α-amylase (proxies for gastric and oropharyngeal secretions, respectively). They found no difference between groups in VAP, ventilator-associated events, mechanical ventilation-free days, antibiotic-free days, ICU length of stay, or ICU mortality. Maertens and colleagues further evaluated tapered versus conventional cuffs by combining these two trials with four others (total 1,324 patients).[60] On meta-analysis, they found no difference between cuff shapes in the frequency of hospital-acquired pneumonia nor any signals in the individual studies suggesting differences in duration of mechanical ventilation (three trials), ICU length of stay (four trials), or mortality (three trials). There is a paucity of additional studies on polyurethane cuffs that include data on clinical outcomes, but for the present at least there is no clear signal of clinical benefit.[58]

Recent studies on endotracheal tube cuff pressure monitoring frequency and method have also failed to suggest clear benefits. Letvin and colleagues quasi-randomized 305 patients to frequent manual cuff pressure checks (and inflation adjustment if needed) versus infrequent checks.[61] Both groups of patients had their cuff pressures checked immediately following intubation. Patients allocated to frequent checks subsequently had their cuff pressures re-evaluated every 8 hours. Patients allocated to infrequent checks were evaluated for cuff pressure loss only if the tube migrated or if the patient developed a clinically apparent cuff leak. The investigators found no difference in ventilator-associated event rates, hospital length of stay, or 30-day mortality.

Nseir and colleagues, by contrast, conducted a patient level meta-analysis of three nonblinded randomized studies comparing automated cuff pressure monitoring systems versus usual care amongst 543 patients.[62] Automated cuff pressure monitoring was associated with a 53% decrease in the hazard ratio for VAP, but there was no difference between groups in duration of mechanical ventilation, ICU length of stay, duration of antibiotics, or mortality. The discrepancy between the marked decrease in VAP rates in this analysis versus the lack of difference in antibiotic prescribing, duration of mechanical ventilation, or death may simply have been due to limited power, but the mismatch does underscore the risk of drawing misleading conclusions about the effectiveness of VAP prevention strategies when looking at VAP rates alone as the sole measure of success.

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