An implantable wireless sensor for continuous monitoring of intracompartmental pressures

Abstract

Acute Compartment Syndrome (ACS) is one of the most severe complications which that can arise in orthopedic medicine. At the onset of ACS, high fluid pressures occlude blood flow to tissues within an anatomical compartment which, if untreated, can lead to irreversible tissue necrosis within four to twelve hours. Once necrosis occurs, wide spread tissue excision or limb amputation is often the only treatment. As such, missed or late diagnosis of ACS leads to catastrophic patient outcomes at a high cost to the healthcare system. ACS often goes undetected because there is no adequate method to screen for an impending case of ACS. A wireless pressure sensor would allow clinicians to screen for pressure indicative of ACS;, however, wireless technology for continuous monitoring of tissue pressures in patients at risk of developing ACS does not exist at this time.

We have developed a novel, implantable, pressure sensor that is wireless, miniature, robust, and inexpensive. The sensors are comprised of a passive circuit whose resonant frequency is dependent on hydrostatic pressure. This sensor transduces pressure changes into wirelessly detectable signals without an on-board battery or discrete electrical components for telemetry. Sensor behavior is modeled using a distributed component circuit approximation, allowing for sensor designs customized across applications and pressure ranges. Sensors are fabricated using techniques common to wafer level microfabrication, allowing for precise and inexpensive production. These properties give the sensor great clinical potential.

Sensors were tested in vitro and in situ in a clinically relevant model for ACS. Pressure sensors remained functional for thirty days following immersion in saline. The performance of the sensor as a displacement-frequency transducer functioned across a variety of geometries. This gives the sensor has the potential to be adapted to a be a needle injectable pressure sensor in the future. This novel diagnostic tool has the potential to reduce complications and costs after traumatic injury through early, conclusive detection of impending ACS using pressure measurements.