Wearable Bio-Sensor Holds Promise of Safer Anesthesia for All
Doctors at the University of Miami Miller School of Medicine are developing a unique device designed to make safe anesthesia available to doctors and patients throughout the developing world, where conventional general anesthesia is both expensive, risky, and often impractical. The device, which has no name as of yet, could also be a lifesaver in combat zones, disaster scenes, and remote areas where the equipment required for monitoring patients under anesthesia can’t be transported.
Ernesto A. Pretto, Jr., M.D., M.P.H. professor of clinical anesthesiology and former chief of abdominal transplant anesthesiology, Miami Transplant Institute, UHealth/Jackson Health System, Robert Fiala, M.D., assistant professor of clinical anesthesiology and chief of anesthesiology at UHealth Tower and Sylvester Comprehensive Cancer Center, and Carla Roscio Cordova, M.D., assistant professor of clinical anesthesia, have teamed up with two engineers from Florida International University (FIU) to create a wearable biosensor that detects the blood concentration of volatile anesthetic vapors transcutaneously, or through the patient’s skin.
“Two-thirds of the world lacks access to safe, state-of-the-art anesthesia, and mortality from general anesthesia is significantly higher in the developing world,” Dr. Pretto said. “There are several issues that limit access—availability, cost, and portability of the necessary equipment.”
With general anesthesia, isoflurane is the most commonly used inhalation agent worldwide, and making sure the patient gets just the right amount is critical. In the U.S. and many other countries, infrared spectroscopy (IRS) is used to detect exhaled anesthetic gas concentrations to ensure patient safety during anesthesia. But that equipment is costly, bulky, and not easily deployed to rural areas, a war zone, or the scene of a natural disaster. Without the ability to accurately measure the concentration or dose of isoflurane in a patient, conventional anesthesia simply isn’t as safe as it should be.
“When you don’t know exactly what percent of volatile anesthetic you’re giving a patient – or what percent they’re breathing out – you’re really flying blind,” Dr. Fiala said. “Too much can cause serious, long-lasting complications. But at the same time, you want to make sure they’re anesthetized enough that they’re not going to jump off the table the moment you start surgery.”
That’s why Dr. Pretto and his colleagues have been working for the past four years on a wearable sensor that can safely measure the inhalation amount of isoflurane during surgery. Like alcohol, isoflurane escapes through the pores, so its levels can be monitored by sensing the vapors in a patient’s perspiration.
“Our device is not designed as a substitute for IRS, but for certain situations where IRS is unavailable or impractical,” Dr. Pretto said.
The technology behind the device – a fuel cell – is quite simple and has been used for more than 80 years to generate power. But only in recent years has fuel cell technology been adapted for use as a sensing device, and it wasn’t until Dr. Pretto teamed up with FIU’s Shekhar Bhansali, Ph.D., and Yogeswaran Umasankar, Ph.D., that the promise of detecting anesthetic vapors transdermally in real time took hold.
Dr. Bhansali, professor and chair of FIU’s Department of Electrical and Computer Engineering, is an electrical engineer by training and holds 36 U.S. patents; his colleague, Dr. Umasankar, is a research assistant professor in FIU’s Biomedical Science Institute whose expertise lies in electrochemical bio-sensing, electrochemical energy generation, and energy storage devices. Together, they had been working on miniaturizing fuel cells and using them as sensors—in their case to detect blood alcohol levels.
When Dr. Pretto approached them about adapting their technology for use in general anesthesia, they were intrigued. The team developed and tested a prototype before eventually coming up with a wearable device that was reliable and whose results could be validated. The device can be designed to detect any of the volatile anesthetics as well as other volatile organic compounds, at a much lower cost than IRS monitors, and with even greater accuracy. Affixed to the skin with a FitBit™-type strap, it can detect isoflurane vapors from a patient’s perspiration in concentrations from as low as 40 parts per million (ppm) to 1,000 ppm—well within the range of what is delivered to a patient during general anesthesia, according to Dr. Pretto.
To date, they have performed clinical trials on 10 volunteers undergoing general anesthesia with isoflurane at UHealth Tower. They plan to conduct up to 50 more trials before approaching businesses in the biotechnology sector about licensing their technology and taking it to market.
“There is a lot of interest from the biotech industry in non-invasive devices such as this, but we’re probably six to 12 months away from the point that we’d be ready to talk about commercialization,” Dr. Pretto said. “We need to do more trials with patients under different conditions and circumstances, and fine-tune the device so we can see where it can be worn to deliver the best possible signal.”
One of the challenges faced by Dr. Pretto and his team was converting sensor data from parts per million to a percentage, the unit anesthesiologists use for monitoring isoflurane and other anesthetic agents. This problem was solved mathematically by Drs. Bhansali and Umasankar from FIU, so that the signal being relayed from the device is automatically converted to a percentage when displayed on the smartphone that’s been paired with the device.
In addition to monitoring levels of anesthetic agents in patients, the device may also make it possible for patients to receive “automated anesthesia,” in which the anesthesiologist could create a computerized program for target-controlled delivery of volatile anesthetic to the patient during surgery.
“We’ve never had the ability to safely deliver anesthesia based on a target, or endpoint, because we can’t measure the amount of any anesthetic agent in the patient’s blood,” Dr. Pretto said. “We have to go by the patient’s body weight, or in the case of inhalational anesthesia, the exhaled percentages, not on specific real-time plasma concentrations. With this device, however, we could create a closed feedback loop that would deliver the precise amount of anesthesia required.”
There may also be applications for veterinary medicine where, according to Dr. Pretto, the mortality rate for animals receiving general anesthesia is 10 times higher than it is for humans.
But the sole focus right now is on perfecting the technology so that the device can be licensed to an interested biotechnology firm and approved by the Food and Drug Administration (FDA). Should the device prove successful, any profits would be split equally between the University of Miami and FIU.
In the meantime, Dr. Pretto’s abstract submission, Transcutaneous measurement of volatile anesthetic gas: A Preliminary Study, has been accepted for a poster presentation at the May 2019 annual meeting of the International Anesthesia Research Society.