Mechanical ventilation provides life-saving support for patients with respiratory failure or those unable to sustain the physical work needed to breathe. Eventually, most patients will be able to breathe on their own, but 10 to 15 percent of patients will have trouble recovering breathing ability.
A University of Florida study reports that a training program that strengthens the muscles involved in inspiration can help patients who have been unable to get off a ventilator — a condition known as failure to wean — breathe independently. In the UF study 71 percent of patients with failure to wean who received the new treatment were able to wean from the ventilator. The study is the first published controlled trial of a rehabilitation program for patients with failure to wean. The findings appeared this spring in the journal Critical Care.
“Mechanical ventilation has a significant incidence of complications, including respiratory infections and damage to the vocal folds and lungs, and the cost of sustaining a patient on mechanical ventilation is substantial,” said lead researcher A. Daniel Martin, Ph.D., P.T., a professor in the College of Public Health and Health Professions’ department of physical therapy.
Experts believe that failure to wean could be a result of diaphragm atrophy. Previous studies have demonstrated that diaphragm weakness can occur within several hours or days of being put on mechanical ventilation.
For the study, UF researchers used an inspiratory muscle strength training program, or IMST, to help patients regain strength in the muscles used in inspiration. The program draws upon the same concept of other strength training programs in that increasing loads, or pressure, progressively strengthen muscles. The program has previously been shown to reduce the risk of post-surgery respiratory complications for patients undergoing heart or major abdominal surgery.
The UF study involved 69 participants hospitalized in intensive care units — 35 were randomly assigned to the inspiratory strength training and 34 to a sham treatment. A small, calibrated device was attached to the participants’ tracheostomy tube. Patients were told to inhale and exhale as forcefully as possible during the training breaths. For patients in the IMST group, the device was set at the highest pressure load the patient could tolerate and was increased daily, while the device used in the sham treatment group was set at a constant low pressure load. The training was conducted five days a week over a 28-day period with four sets of six to 10 training breaths a session.
By the end of the study, 71 percent of the participants who received the IMST therapy were able to wean from mechanical ventilation, compared to 47 percent of patients in the sham group, a rate comparable to usual care.
The researchers were surprised at how rapidly participants in the IMST group improved their inspiratory muscle strength, Martin said.
“The patients in the study had received mechanical ventilation for approximately six weeks prior to intervention, but after an average of 10 IMST sessions, patients were able to improve their inspiratory strength by about 30 percent,” Martin said. “Recent animal and human research has shown that the diaphragm atrophies approximately seven to eight times as rapidly as limb muscles, but it appears that the diaphragm also responds to strength training much more rapidly than do limb muscles.”
Martin and his research team are currently conducting a study examining the effect of starting inspiratory muscle strength training after only three days of mechanical ventilation. The study is being done in conjunction with colleagues from the division of critical care medicine in the UF College of Medicine department of anesthesiology.
Other researchers in the current published study include fellow department of physical therapy members Barbara Smith, Ph.D., P.T., Harsha Deoghare, Ph.D., P.T., and Tseng-Tien Huang, Ph.D., P.T.; Paul Davenport, Ph.D., from the UF College of Veterinary Medicine department of physiological sciences; Eloise Harman, M.D., Ricardo Gonzalez-Rothi, M.D., and Maher Baz, M.D., of the College of Medicine division of pulmonary, critical care and sleep medicine; and Joseph Layon, M.D., Michael Banner, M.D., Lawrence Caruso, M.D., and Andrea Gabrielli, M.D., of the College of Medicine department of anesthesiology, division of critical care medicine.
The University of Florida and Martin, Gabrielli and Banner have applied for a patent to modify clinical mechanical ventilators to provide threshold inspiratory muscle training.