Transvascular Phrenic Nerve Stimulation for Diaphragm Pacing

graduate student: Bao Tran
graduate student: Sheena Frisch
website: Transvascular Phrenic Nerve Stimulation for Diaphragm Pacing

Critically ill patients in Intensive Care Units (ICU) are frequently kept alive with mechanical ventilation (MV). Unfortunately, MV contributes to respiratory infections, longer hospital stays, poor prognosis for recovery and high cost of care. MV patients have difficulty breathing again, because during mechanical ventilation, the diaphragm muscle undergoes very rapid disuse atrophy. Our aim is to develop a simple, minimally invasive, reversible method for electrical activation of the diaphragm in ICU patients who need mechanical ventilation, so that they may breathe diaphragmatically again.

We are developing and testing a new, minimally invasive method to assist people who now need to be hooked up to a mechanical ventilator in order to breathe. Hospital inpatient care is responsible for approximately one third of all health care costs in the US, and roughly similar ratios in Canada and in British Columbia. One of the largest cost drivers in the hospital setting is the Intensive Care Unit (ICU), which despite accounting for only 5 to 10% of hospital beds, accounts for nearly 1/3 of total inpatient costs. Daily ICU care costs 3 to 5 times more than care provided on general medical/surgical floors. Much of this increased cost is due to interventions such as mechanical ventilation (MV). Patients who require MV represent approximately 36% of all patients admitted to the ICU. Patients who require more than 3 weeks of Mechanical Ventilation account for more than 50% of all ICU costs. Mechanical ventilation can be lifesaving but has a number of significant problems, since a patient on ventilation is tied to a machine. Mechanical ventilation: • tends to provide insufficient venting of the lungs. This can lead to accumulation of fluid in the lungs and susceptibility to infection. • requires insertion of a tube in the trachea and therefore interferes with eating, drinking and speaking. • requires apparatus that is not readily portable. This can lead to disuse atrophy of muscles and an overall decline in well being. • adversely affects venous return because the lungs are pressurized. An alternative to mechanical ventilation is diaphragm pacing by means of electrical stimulation of the phrenic nerve or the diaphragm. Current methods require complex, risky surgery in the neck or thorax to expose the small, delicate phrenic nerves and place electrodes directly on them, or abdominal surgery to map the diaphragm surface and insert intramuscular electrodes near phrenic nerve branches. These procedures are intended for people with paralyzed diaphragms due to spinal cord or brain injuries and require full anesthesia for lengthy periods, not suitable for fragile patients in the ICU. At the SFU we are evaluating an alternative, lower risk, minimally invasive surgical approach for diaphragm pacing, whereby special transvascular stimulation electrodes designed in the Neurokinesiology Laboratory are introduced intravenously in the neck or upper chest and deployed in close proximity to the left and right phrenic nerves. This approach requires only local anesthesia and removes the need for any surgical exposure of either the phrenic nerves or the diaphragm. Our objective is to provide a simple, disposable electrode that can be placed intravenously and used for indefinite periods of time to pace the diaphragm and maintain diaphragmatic breathing, thus removing the need for mechanical ventilation in many ICU patients. In a study of over 50,000 patients who were admitted to ICUs in 253 US hospitals in 2002, the mean ICU cost and length of stay were $31,574 and 14.4 days for patients requiring mechanical ventilation and $12,931 and 8.5 days for those not requiring mechanical ventilation. We estimate that if patients who initially need mechanical ventilation are converted to transvascular pacing of the diaphragm within the first 3 days of ICU admission, their risk of catching ventilator-born infections and their length of stay will be reduced, they will be able to speak and eat by mouth without obstruction by tracheal tubes, their health will improve faster, and the hospitalization cost savings will be very significant. This project is funded by an NSERC Idea-to-Innovation grant. References: Daily cost of an intensive care unit day: The contribution of mechanical ventilation. Dasta, Joseph F.; McLaughlin, Trent P.; Mody, Samir H.; Piech, Catherine Tak. Critical Care Medicine. 33(6):1266-1271, June 2005. Transvascular Nerve Stimulation Apparatus and Methods. Hoffer, Joaquin Andres. P.C.T. patent application No. WO2008/092246, published August 7, 2008.

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