Testing and CELA

We looked into using testing facilities available at Vanderbilt Medical School’s Center for Experiential Learning and Assessment (CELA). CELA uses state of the art mannequins to train students on medical procedures. We hoped to use this facility to test our device using an endoscopy training program and mannequin. However, CELA’s endoscopy simulation is virtual reality and therefore not useful for testing our device and sensors. Additionally, the center is for the use of medical students and professors. We will be consulting our sponsor to see if he may have access to additional resources and testing programs at CELA.

Testing the pH sensor in physiologically relevant environments will not present a problem. A standard pH calibration set consists of three buffers with pH 4, 7, and 10. These sets are inexpensive and easily accessible through major vendors. One example set produced by Innovating Science would cost approximately $15. One possible alternative to test the pressure sensor would be to use a pressure chamber with variable pressure. However, this system would not apply circumferential pressure expected in the gastrointestinal system. It may be useful for initial testing and building the prototype while we arrange for more appropriate and relevant testing environments.

We did find an ideal system to test our entire device, the TIM-AGC produced by TNO Triskelion. This device is a gastrointestinal phantom that models human gastric motility, pressure forces, digestive enzymes, and liquid/solid emptying in an advanced gastric compartment. This system would perfectly determine if our device is functional. Many studies in the literature cite using this device to test novel sensors. However, the group producing this device is located in The Netherlands. We plan on researching if this device has been sold to or created by any companies or research groups near Nashville. If this search comes back with nothing, we plan on looking into alternate ways to use this device to test our nasoduodenal feeding tube.

Future Devices

Because we were unable to receive the parts for our initial prototype this week, we began to look into future technologies that we could use when miniaturizing our design. One technology that seems as if it would be particularly useful is micro-scale sensors that incorporate fiber optic signal transmission. The advantages of such a system are numerous. First, sensors using this technology are an appropriate size – while our tubing will most likely have a diameter of 1-2 mm, these sensors have diameters of around 150-300 µm. This size of this sensor will easily fit within the tubing, as well as be able to be withdrawn following placement of the device. In addition, the fiber optic tubing that will be located within the nasoduodenal feeding tube is very flexible, able to turn tight corners without breaking or interfering with signal transmission. Again, this is critical in our design, as there are often very sharp turns and kinks located within the human gastrointestinal system that our device will have to navigate. Another advantage of a fiber optic system is that the signal is transmitted extremely quickly (at the speed of light), and due to the nature of the system, does not deteriorate noticeably with distance (especially one as small as two meters). This is in contrast to the I2C signal transmission system that we are using for our initial prototype, which fails to function after relatively small distances. Finally, there are a multitude of fiber optic sensors designed for physiological applications currently in production. Because of the large availability of these products, we will be able to select one that is appropriate in all technical specifications, as well as price.

The most promising fiber optic pH sensor that has been found so far is the pH microsensor produced by PreSens. This device has a diameter of 150 µm, with a resolution of 0.01 pH units, response time of 30 seconds, and temperature range of 41° F to 122° F. One drawback to this device is that the measurement range is only 5.5 – 8.5; however, this may not be a large problem, as this is the appropriate range for the critical placement area in the intestine, which is at a pH between 6.0 and 8.0, depending on the exact placement region. In addition, this sensor does not require a reference electrode, has been shown to be biologically compatible, and is optimized for physiological solutions.

The most promising fiber optic pressure sensor is the OPP-M sensor produced by Opsens Solutions. This device has a diameter of 250 µm, a pressure range of -50 mmHg to 300 mmHg (appropriate for our application), a resolution of 0.2 mmHg, and a temperature range of 50° F to 122° F. In addition, this device has been proven to be biologically compatible and is recommended for physiologic conditions.

While these are the most promising commercial sensors, there are a large number of fiber optic pH and pressure microsensors in the literature with appropriate technical specifications, so it is possible that we could work in conjunction with a lab producing these devices.

Device Use Protocol

I. Patient Preparation

• Fast for eight hours before procedure

• Stop using blood thinners, anti-inflammatory medications, or GI medications one week before the procedure

II. Tube Placement

• Use the trainee booklet of Cortrak EAS as a reference
• Consult nurses about the actual process

III. Patient Safety

• Cough, vomit, or difficult to breathe during the procedure
• Tube obstruction, tube leakage, inadvertent removal after the procedure (7-10% incidence)
• Special concerns from using sensors

Tubing Material

Most nasoduodenal (ND) or nasojejunal (NJ) procedures use one of two types of tubing: silicon based material or polyurethane. The more common of the two materials is the polyurethane. It is used in both fluoroscopic and Cortrak tubing. This makes the material abundant and relatively easy to order from a wide selection of vendors. There are a few common traits almost all of the tubes shared. The first is centimeter-long markings that give the healthcare provider an indication as to the length of tube extending into the patient. Next is a wide range of tube diameter and aperture diameter. Both of these are often related to the size of the patient involved and how much food must be delivered. Some tube have weights added to their tips. This addition allow providers to more easily navigate the tubes as they traverse the GI tract. Lastly, literature suggests there is a slight propensity for food to congeal under certain circumstances, clogging the tube. This usually occurs when 90 degree turns in the tube occur.

Because most purchasable tubes come ready-made to deliver food on their own, we should not have to perform extensive modifications to these tubes to maintain their efficacy in our model. Our first consideration will most likely be a point of connection between the sensors and a controller. Because we do not want multiple patients using the same probes that indicate placement, creating a point in the tubing such that a controller can be disconnected from sensors at the tip of the tube and be reused in another patient will be important to fulfill the design need for versatility throughout a healthcare facility. In addition, we will also need to consider how we can get sensors connected to the tube. Because the sensors will remain in the intestines after placement, they will need to be attached such that they do not inhibit food delivery or digestion.