Response to Society for Healthcare Epidemiology (SHEA) recommendations for ventilator-associated pneumonia (VAP)

To the Editor—The Society for Healthcare Epidemiology (SHEA) published new recommendations to assist hospitals in prioritizing and implementing strategies to prevent ventilator-associated pneumonia (VAP) and ventilator-associated events (VAE) in adults, children, and neonates. ¹ These new recommendations update their published 2014 preventions strategies, ² and several recommendations have been added, removed, or changed.

According to the new guidelines, although subglottic secretion drainage (SSD) has been shown to lower VAP rates, there is insufficient evidence about its impact on the duration of mechanical ventilation, length of stay (LOS), mortality, and costs. ¹ However, 2 recent meta-analyses have demonstrated that use of endotracheal tubes (ETTs) with SSD reduced VAP rates by 44% ^3–50%. ⁴ Further, routine use of SSD may reduce the risk of postoperative VAP in patients undergoing cardiac surgery, with those undergoing intraoperative continuous and postoperative intermittent SSD reporting a 70% reduction in the rate of postoperative VAP. ⁵

Although these findings are very promising, they were not considered when reclassifying SSD recommendations in the new guidelines. Studies that have evaluated reductions in the duration of mechanical ventilation with SSD are limited to patients expected to require >48–72 hours of mechanical ventilation. ¹ However, it is difficult to determine, at the time of intubation, which patients will remain on mechanical ventilation >48 hours. ⁶ Even so, a recent meta-analysis reported that SSD delayed time to VAP by 2.66–4.04 days. ⁴

In regard to cuff material, the new guidelines contend that ultrathin polyurethane cuffs are inconsistently associated with lower VAP rates and have no, or negative, impact on duration of mechanical ventilation, LOS, or mortality. ¹ The main reference used to make this determination was a study that reported that polyurethane cuffs did not reduce bacterial colonization or VAP compared with cylindrical PVC cuffs. ⁷ However, tracheal colonization was already present at the time of intubation in several patients, and determining whether the cuff influenced tracheal colonization in these patients was difficult.

Regarding ETT cuff shape, the guidelines suggest that tapered ETTs are inconsistently associated with lower VAP rates and have no, or negative, impact on duration of mechanical ventilation, LOS, or mortality. ¹ The only referenced study for tapered cuffs is a meta-analysis that reported no difference in VAP rates or outcomes when tapered cuffs were used. ⁸ However, additional factors, including cuff underinflation, may influence risk of microaspiration over time. None of the included studies accounted for cuff-pressure management in the prevention of VAP. Underinflation, even when episodic, can lead to microaspiration of secretions regardless of cuff shape. ⁸ In previous research examining intraoperative aspiration and its association with postoperative pneumonia using dye above the cuff at time of intubation, the use of tapered-shaped cuffs had a protective role against aspiration (ie, no dye leaked into the trachea). ⁹ This publication was not cited in the new guidelines.

We understand that demonstrating that any of the mentioned ETT characteristics reduces mortality, LOS or days on ventilation, a sample size of thousands would be necessary for a single randomized controlled trial. The prevention of VAP and VAE is achieved through a bundled approach, with a variety of measures and interventions instituted at the same time to reduce the incidence of VAP and VAE. An evaluation of different strategies to reduce VAP and VAE reported that very high compliance rates, >90%, were significantly associated with reduction in VAP rates, with long-term compliance contributing to VAP rates close to zero. ¹⁰ No single characteristic of the ETT will result in significant reduction of VAP and VAE; however, neglecting the published information does not justify recommendations to not use the devices.