DEVELOPMENT OF A PORTABLE BLOOD POTASSIUM MONITORING DEVICE FOR DIALYSIS PATIENTS

Abstract

Approximately 500,000 dialysis patients in America are at a high risk of hyperkalemia, a condition where blood potassium becomes elevated above normal levels. Hyperkalemia is extremely dangerous, as it can result in severe cardiac complications if untreated. Hyperkalemia may be silent or present vague symptoms until those complications develop, at which point patients require emergency medical care. However, if patients have the ability to measure their potassium levels at home, they could detect hyperkalemia before it reaches a dangerous stage, and seek preventative medical care to avoid severe complications. Therefore, we have designed a novel device allowing patients to measure their blood potassium levels at home. The workflow of our solution is as follows: (1) patients obtain a blood sample from a finger prick, (2) potassium concentration is measured with an ion specific electrode (ISE), and (3) the device displays their potassium levels and a recommended course of action based on their hyperkalemic risk. We validate our solution with three major tests. First, our portable ISE technology must accurately measure potassium concentration in blood samples. Second, appropriate lancet parameters (gauge and depth) to minimize hemolysis in capillary blood samples must be found to minimize falsely elevated readings. Third, device portability and ease of use must be evaluated using patient input, as these factors will affect patient compliance. We have validated the use of portable ISE technology to feasibly measure potassium, and we continue to collect data for our second and third tests.

Figure 1.

The current workflow of dialysis patients with undetected hyperkalemia. As a result, dialysis patients need a way to measure their blood potassium levels in an out of clinic setting in order to quantify their risk of hyperkalemia related complications.

Figure 2:

A) Filament of copper/graphite wire. B) Electrode is coated in Poly(vinyl-ferrocene) electrolyte, cured. C) Electrode is double dipped in potassium specific membrane (Valinomycin in PVC), cured again. D) Electrode is inserted into glass microcapillary tube, and secured with epoxy. E) Final result: an electrode double dipped in a potassium specific membrane and an electrolyte.

Figure 2.

Construction of the ISE using a graphite core and valiuomycin as the ion-selective membrane. 4) Filament of copper/granite wire. B) Electrode is coated in Poly(vinyl-ferrocene) electrolyte, cured. C) Electrode is double dipped in potassium specific membrane (Valinomycin in PVC) and cured again. D) Electrode is inserted into glass micro capillary tube and secured with epoiy. E) Final result: an electrode double dipped in a potassium specific membrane and an electrolyte.

Figure 3.

Schematic of the general components of our device. A) Sample blood potassium level is measured by in house ion selective electrode. B) Signal from the ion selective electrode goes to the voltage gain which amplifies the signal. C) Signal is read by a voltmeter which converts the signal into a voltage. D) Voltage is converted into a blood potassium level as there is a linear model between voltage generated and blood potassium level.

Figure 4.

Planned circuit board for portable potassium monitor for dialysis patients.

Figure 5.

Schematic of the general workflow of our device. A) The patient will prick their finger with a disposable lancet and have the blood sample be uptaken into the test cartridge via capillary action. B) Test cartridge is inserted into the device. C) Blood potassium levels are displayed to the patient with clear color coordinated levels. D) Suggested actions are then presented to the patient depending on their blood potassium levels green = no treatment needed, orange = at risk/treatment recommended, red = seek immediate treatment

Figure 6.

Results of an ISE technology verification. A) A HORIBA potassium soil monitor is used as the ISE with 200uL of whole blood used as the sample. Each blood sample was measured by the HORIBA potassium soil monitor and was also sent to the Johns Hopkins Medical Institute Blood Laboratory. The results were graphed, resulting in a linear relationship. It was found that ISEs are indeed effective at clinically relevant levels. B) Qualitative analysis of blood samples 1–10, left to right (the darker and redder the sample is, the more hemolysis is within the sample). C) Qualitative analysis of blood samples 11–20, left to right. D) Qualitative analysis of blood samples 21–30, left to right.

Figure 7.

A) Isometric view of the final prototype - acrylic box with Arduino UNO LED screen; up, down, and select buttons; battery' clips; and a BNC connector for an ion selective electrode (ISE). B) Side view of the final prototype in A. This prototype was handed to volunteer testers who were asked to evaluate the weight, ergonomics, and dimensions.

Figure 8.

A sample UI preferences sheet that would be presented to a volunteer tester. The left-most panel of each choice would be presented in green to signify normal levels. The middle panel of each choice would be represented in orange to signify that while they do not need immediate treatment, they would be wary. The right most panel of each device would be presented in red to signify that they need immediate treatment. Different UI options varied by font size and text placement.