Toward Enhancing Critical Care Monitoring: Continuous Assessment of Blood Lactate and Potassium with Fiber Optic Sensors Integrated into Intravascular Catheters

The determination of disease severity and prediction of outcomes in emergency medicine heavily rely on blood lactate (Lac) and potassium (K⁺) levels. Traditionally, these biomarkers are assessed through repeated invasive blood sampling and subsequent analysis using laboratory blood gas analyzers. However, recent studies have emphasized the dynamic nature of these biomarkers, highlighting the need for continuous monitoring. In trauma cases, elevated blood Lac levels and poor Lac clearance have been associated with higher mortality rates, demonstrating potential for effectively triaging conditions such as lung cancer, lacunar infarction, sepsis, and cardiac failure. Likewise, high K⁺ levels, known as hyperkalemia, are linked to life-threatening conditions including arrhythmias and mortality following severe trauma, kidney disease, hemolysis, and acid-base imbalances. In hemorrhaging patients, hyperkalemia can be induced by tissue ischemia, blood transfusion, and acidosis, significantly heightening the risk of death. Consequently, there is an urgent demand for continuous monitoring of blood Lac and K⁺ levels in critical care settings. This study aims to develop and evaluate the performance of specialized fiber optic sensors that enable real-time monitoring of Lac and K⁺, thereby providing healthcare providers with timely guidance in rapidly changing situations.<br/>The sensors in this study employ a measurement method known as dual lifetime/luminophore referencing (DLR), which ensures high accuracy and mitigates sensitivity to the amplitude of the optical signal. In contrast to previous fiber optic sensors that are single point sensors located at the tip of the fiber and are susceptible to intermittent contact with tissue, a phenomenon referred to as the "wall-effect," the current sensors utilize a tunable distributed sensing approach. This is accomplished by incorporating redundant "mini-sensors" along a specific section of the optical fiber. Furthermore, optimization of sensor fabrication was conducted to enhance sensitivity specifically for physiologic concentrations. The Lac sensor utilized in this research consists of multiple layers, including a luminescent transducer layer for measuring partial pressure of oxygen, a catalytic enzymatic hydrogel layer, and a diffusion barrier layer to overcome substrate-dependent inhibition. The K⁺ sensor is designed as a hydrogel that incorporates a luminescent ionophore for K⁺ detection, and a separate reference luminophore. Finally, sensor-integrated catheter prototypes were tested in an ex vivo flow circuit with fresh porcine blood. The sensor-integrated catheter prototypes showed strong pairwise correlation between the optical sensor measurements and blood gas analysis (Spearman correlation R² = 0.981 and 0.970, p-value: &lt;0.0001 and &lt;0.0001 for Lac and K⁺, respectively).<br/>In summary, our study has successfully shown that the DLR-based fiber optic sensors for continuous Lac and K⁺ monitoring, when integrated into intravascular catheters and evaluated under ex vivo circulation conditions using donor blood, offer a viable alternative to repetitive blood gas analysis. These sensors hold great promise in enhancing clinical decision-making and are now poised for further validation in translational studies focusing on trauma and critical care scenarios under in vivo conditions.