SAN ANTONIO (Aug. 21, 2008)—“Every cloud has a silver lining,” the proverb goes, and a study released this week suggests silver actually can help severely ill respiratory patients.
Intensive care patients breathing through a silver-coated endotracheal tube while on mechanical ventilation were 36 percent less likely to develop ventilator-associated pneumonia (VAP) than patients breathing through a regular tube, according to the multi-center study that included The University of Texas Health Science Center at San Antonio and the South Texas Veterans Health Care System, Audie L. Murphy Division.
The silver-coated tube was most protective against VAP during the first 10 days of mechanical ventilation, the period when most patients are weaned from breathing machines.
Co-authors including Antonio Anzueto, M.D., and Marcos I. Restrepo, M.D., M.Sc., of the UT Health Science Center and the Audie L. Murphy Division, reported the results on behalf of the North American Silver-Coated Endotracheal Tube (NASCENT) Study Investigation Group. The Journal of the American Medical Association (JAMA) published the findings online Tuesday (Aug. 19).
“Ventilator-associated pneumonia is a leading cause of death in these patients,” Dr. Anzueto said. “This is the first time an intervention has been shown to significantly reduce the incidence of this important complication.”
The incidence of VAP in patients on mechanical ventilators is estimated to be as high as 30 percent. One-third to one-half of deaths among these patients may be VAP-related. According to the NASCENT article, VAP patients remain longer on ventilation (14 days versus four), longer in intensive care (11.7 days versus 5.6), and longer in hospitals (25.5 days versus 14). The cost to institutions and individuals is more than $40,000 per inpatient.
The San Antonio collaborators enrolled patients at the Audie L. Murphy Division and University Hospital. Drs. Anzueto and Restrepo helped design the research protocol and interpret the results. The study randomly assigned equal numbers of patients needing ventilation for 24 hours or longer to undergo intubation with either the silver-coated endotracheal tube or the regular tube.
Fifty-four centers in North America screened patients 18 or older. The final research study cohort consisted of 1,509 subjects assigned in a 1:1 ratio to the treatment groups.
In the group breathing through the silver-coated tube, 4.8 percent of patients (37 of 766) developed VAP as confirmed by rigorous microbiological analysis. In the other group, 7.5 percent (56 of 743) developed VAP. This difference was statistically significant.
Other endpoints, such as mortality and hospital stay, were not statistically significant between the groups and the study was limited in its ability to measure those outcomes, Dr. Anzueto said.
The experimental endotracheal tube, which is coated with silver ions dispersed in a proprietary polymer, is manufactured by C.R. Bard Inc., a New Jersey-based company that funded the research study. All study sites received grant support from C.R. Bard to conduct this trial.
Silver, which is considered nontoxic, demonstrates “broad-spectrum antimicrobial activity” in cell cultures, the article stated. It also blocks bacterial ability to stick to surfaces and, in animal models, prevented biofilm formation. The researchers noted that the NASCENT study relative risk reduction of 36 percent replicated an earlier finding of VAP risk reduction in an animal model.
An accompanying editorial in JAMA stated: “Important uncertainties exist regarding the exact benefit of silver-coated endotracheal tubes.” The author noted several study limitations voiced by the researchers themselves, but Dr. Anzueto again stressed: “Regardless of these limitations, this in the first time that an intervention has been able to decrease this deadly complication.”
Dr. Restrepo, an investigator with the Veterans Evidence-Based Research Dissemination & Implementation Center (VERDICT), said the silver-coated tube is a “passive” preventive measure for VAP. “In other words, with so many things our nurses, therapists and physicians have to do in the Intensive Care Unit, it is helpful to have a tube that is working all the time just lying in the trachea,” he said.
The U.S. Centers for Medicare & Medicaid Services will not reimburse hospitals if patients develop VAP. Although a silver-coated endotracheal tube costs more than a regular tube or a special suction tube, this higher cost is a small fraction of the tens of thousands of dollars required to treat a single case of VAP. The number of patients needed to treat with the silver-coated tube to prevent one case of VAP is 37, the NASCENT investigators said.
As mentioned in the editorial, the silver-coated tube is not a “magic bullet” to prevent VAP, and other interventions also should be done, such as elevating the head of the bed, interrupting sedation periodically and weaning the patient from the ventilator.
The University of Texas Health Science Center at San Antonio is the leading research institution in South Texas and one of the major health sciences universities in the world. With an operating budget of $576 million, the Health Science Center is the chief catalyst for the $15.3 billion biosciences and health care sector in San Antonio’s economy. The Health Science Center has had an estimated $35 billion impact on the region since inception and has expanded to six campuses in San Antonio, Laredo, Harlingen and Edinburg. More than 23,000 graduates (physicians, dentists, nurses, scientists and allied health professionals) serve in their fields, including many in Texas. Health Science Center faculty are international leaders in cancer, cardiovascular disease, diabetes, aging, stroke prevention, kidney disease, orthopaedics, research imaging, transplant surgery, psychiatry and clinical neurosciences, pain management, genetics, nursing, allied health, dentistry and many other fields. For more information, visit www.uthscsa.edu.