We are using photoacoustic imaging to build a wearable sensor to monitor heparin anticoagulation therapy. We describe this device as being analogous to the pulse oximeter, but for heparin (500 million doses/year). Heparin is an anticoagulant or “blood thinner” given to people in intensive care, undergoing surgery, and with clotting disorders. Heparin is used in ~15% of inpatients. However, heparin has a very narrow concentration window in which it is both safe and effective. This is especially true in children who have a developing hemostasis system. An overdose results in hemorrhage and bleeding while underdose results in clotting. In addition to these inherent dangers, medication errors with heparin are also very common. In fact, heparin dosage is one of the three most common medication errors. Heparin is currently monitored with repeated blood testing, but this approach has a long turnaround time, requires relatively large blood volumes, and involves the laboratory and pharmacy, which limits tests to large research hospitals.
To solve this, we are building a family of smart catheters that not only deliver heparin, but also monitor its activity. These catheters have a small molecule dye that produce photoacoustic signal as a function of heparin concentration. We are currently validating these in small animals models and human samples. The rationale is that in vivo imaging is superior to in vitro testing because imaging: a) is non-invasive, b) can be done repeatedly over time without disturbing the patient, and c) is more accurate because it reflects the patient’s dynamic conditions rather than static blood sampling.