Developing a device to prevent the formation of pocket hematoma
I attended the Engineering Innovation in Health course and subsequently joined the Human Photonics Lab (HPL) at UW in fall 2018. During the course I was introduced to understanding the requirement of a medical device and to choose our market. We were taught how to understand the various needs of the different stakeholders involved and how to formulate the primary goals of the device.
My project was to design and develop a medical device that would prevent the formation of Pocket Hematoma in CIED implant patients. During the course, I worked together with my faculty and the Department of Cardiology at UW Medicine to develop our ideas into a design and finally as a prototype which was tested successfully.
Project duration
September 2018 - June 2019.
Role
Research Student, Design lead and pitch delivery
Relevant skills
PTC Creo, Pressure mapping systems, basic electronics
Team members.
Dr Arun Sridhar, Eric Seibel, Paritosh Raghuand
Understanding the problem
A pocket hematoma is a surgical complication due to a Cardiovascular Implantable Electronic Device (CIED). Blood could collect under the skin at the surgical site which would cause pain and patients may require to undergo a corrective procedure as well. The proposed device would provide a way to prevent this accumulation of blood so as to prevent a secondary evacuation surgery and reduce the additional risk of infections and minimize the pain.
Solution
There aren’t many solutions out there addressing this problem. Most of the current solutions involve using some form of hemostatic solution or draining the fluids out through a drain. The most effective way has been to apply pressure through bandages and tapes. I found a way to apply this pressure on the target site using a microcontroller controlled air bladder which would not only apply pressure depending on the patient’s body structure, but also notify the patient during loss of pressure.
2.1%
Ratio of all CIED implant patients that exhibit this condition.
12,600
Number of patients annually that undergo a corrective procedure for pocket hematoma condition
$182 million
With an average cost of $14,491 for the corrective surgery and the hospitalization costs per patient, this is the amount being spent on this condition annually.
The Approach
I began by first scoping the main stakeholders and understanding their gains and losses. Using this, I was soon able to understand the core functions for this device.
After determining the core functions of the device, I came up with a basic idea and sketch of the proposed device. It would be worn over the shoulder in the form of a vest and would contain a fixed housing within which lies the air bladder. The air bladder would then be pumped through a one way valve. A pressure sensor would be placed between the patient and the vest to monitor the pressure being applied and within the pressure range. After consulting with UW cardiology department, we determined the pressure required to prevent the bleed to be between 0.77-1.54 psi.
Based on the construction of the device, I classified the same as a Class 2 device which are more complicated than simple bandages and tapes but, are not intrusive. I also began to look into the regulatory pathway to be taken for this device. As my proposed device shows similar intend of purpose to other compressive vests. The most apt pathway for this device would be the 510K regulations
Cad Design
I designed a couple of simple designs for the housing containing the air bladder. The designs were made on PTC Creo using the design guidelines for plastics.
The designs were evaluated based on the the overall weight of the device and the comfort of wearing the device for extended periods of times. The second design was the more comfortable one and had a smaller design and was chosen to be prototyped.
The device was 3D printed using a FDM system and was subsequently used under the vest as the housing for the air bladder.
Prototyping
I constructed the prototype by using a compression vest from Shapewear. This vest helps keep the other parts of the device in place and prevents the bladder from slipping out of its target location. The vest is constructed from a blend of Spandex and Cotton(90:10). To apply the compressive pressure on the site of the implant, I used a spherical air bladder that had a diameter of 6 inches. The air bladder is made of Neoprene and expands to three times the original size. The pressure being applied by the bladder onto the patient is collected by a sensor which would then relate the pressure being applied to the customer through a series of Light emitting diodes (LEDs). These LEDs indicate the range of the applied pressure.
A simple analogue circuit was built to acquire the difference in the current passing through the sensor and compare this current with predefined values set according to the pressure ranges required. The circuit utilized two comparators, three potentiometers, resistors and LEDs according to the circuit diagram.
Circuit to receive data from the force sensitive resistor
A pocket was created by sewing cotton on the inside of the vest to hold the air bladder in the position over the target site. The sensor is designed to slip in between the bladder and the skin of the patient. The sensor used is a 40mm X 40mm Force sensitive sensor from Sensor Products Inc. The range of the sensor is between 0 and 50 psi. The sensor and the circuit was calibrated by using different weights to simulate the pressure being applied.
The sensor was calibrated to sense between the range of 1.7 psi and 3.5 psi of pressure. This pressure corresponds to 40mm and 80mm mercury. The LEDs were calibrated such that the red LED lights up for all pressures above 3.5psi, the amber LED lights up while the pressure is less than 1.7 psi and the green LED would illuminate for pressures between 1.7 psi and 3.5 psi.
