Silver-Coated Tracheal Tubes Reduce Pneumonia

Endotracheal tubes coated with silver, which has shown potent broad-spectrum antimicrobial activity in vitro, reduced the incidence of ventilator-associated pneumonia by 35% in a multicenter study, researchers reported.

“This is the first intervention demonstrated to reduce ventilator-associated pneumonia [VAP] incidence that does not require more effort or supervision from clinicians providing bedside care,” said Dr. Marin H. Kollef of Washington University, St. Louis, and associates.

However, the reduced rate of pneumonia did not translate into decreased mortality, duration of intubation, duration of ICU stay, duration of hospitalization, or frequency or severity of the adverse effects of intubation.

In an editorial comment, Dr. Jean Chastre said that physicians should “probably” consider using silver-coated endotracheal tubes for “the subset of patients at very high risk of developing early-onset VAP, such as neurologically impaired patients or trauma patients.” But the value of the device for other patients, particularly those who might need prolonged ventilation, has not yet been shown.

Dr. Kollef and associates compared the silver-coated endotracheal tube with standard tubes in a prospective trial sponsored by the device manufacturer, C.R. Bard Inc. A total of 1,509 patients requiring mechanical ventilation for 24 hours or longer were treated at 54 medical centers.

Microbiologically confirmed VAP developed in 4.8% of patients using the silver-coated tube, compared with 7.5% of those using the standard tube—a relative risk reduction of 35.9% and an absolute risk reduction of 2.7%.

The number of patients needed to be treated with the silver-coated tube to prevent one case of VAP was 37, the investigators said (JAMA 2008;300:805–13).

The device appeared to be most effective in preventing VAP during the first 10 days of intubation, “which is clinically relevant because the median duration of intubation is less than 10 days, and more than 75% of patients are extubated before 10 days,” Dr. Kollef and colleagues said.

Mortality was not significantly different between patients who used the silver-coated tube (30%) and those who used standard tubes (27%). There also were no significant differences between the two groups in duration of intubation, ICU stay, or hospital stay, or in the frequency and severity of adverse events related to endotracheal intubation.

This lack of between-group differences might have been related to the unusually low rate of VAP in the control group, which was approximately half of the expected rate of 15%, the investigators noted.

In his editorial comment, Dr. Chastre of the University of Pierre and Marie Curie, Paris, noted that more than 7,000 potential subjects were screened but not enrolled in the trial because they were unable to provide informed consent within the time frame necessary for emergency intubation or were unlikely to require intubation for 24 hours or longer. This threatens both the external validity of the trial and its clinical relevance, he said.

Moreover, the number of cases of VAP was so low that the addition of only three cases among patients using the silver-coated tube “would have sufficed to render the trial statistically inconclusive,” Dr. Chastre wrote (JAMA 2008;300:842–4).

In addition, there was a statistically significant imbalance in the proportion of patients who had preexisting chronic obstructive pulmonary disease between the two groups, which favored the group using the silver-coated tube. And the number of cases of late-onset VAP—pneumonia developing after 7 days of mechanical ventilation—was so small that it limited the study's ability to show efficacy with prolonged intubation.

“Consequently, silver-coated tubes should not be viewed as the definitive answer for VAP prevention, and, until additional data confirm the clinical effectiveness and cost benefit of these devices, their use should be restricted to high-risk patients” in ICUs with low background infection rates, Dr. Chastre noted.

All the authors of this study received grant support from Bard, and Dr. Kollef and Dr. Chastre have received fees from other companies.