Indwelling blood compatible chemical sensors

Progress in surgery has frequently been preceded by progress in technology. Thus positive clinical results may be anticipated with the emerging use of catheter-tip chemical probes. In these devices, the sensor is based on (1) fluorometric or colorimetric sensing, coupled via a fiberoptic light guide to the external environment, or (2) the potentiometric determination of ionic species via catheter-tip ISFET devices. The stages of development for these devices range from laboratory formulations, with some in vitro testing, to limited clinical experience with production prototype models. Advantages reported for the fiberoptic-based devices include no electrical interference, no reference electrode requirement, potentially low-cost fabrication, O₂ tension analysis capability, and the possibility of multi-wavelength determinations to improve stability. Disadvantages of the fiberoptic-based probes include ambient light and temperature sensitivity, long-term instability of some reagents, halocarbon anesthetic sensitivity, slow response time, limited dynamic range, and trade-offs between amount of reagent phase, quenching of probe radiation, and stability. The semiconductor-based devices respond only to ionic species but feature the possibility of determining multiple species in a single-chip, low-cost fabrication, on-chip signal processing, clinically useful frequency response, robust design, and long shelf life. Disadvantages are a follows: long-term instability in situ, requirement for a reference electrode, ambient light and temperature sensitivity, and interference (in some cases) by competing ions, necessitating signal compensation. Both types of probes require treatment to avoid fouling of the probe surface and danger to the patient from thromboembolism. Some approaches to resolution of the outstanding problems are outlined. It appears that, given the current pace of industrial development, several of these probes will become a clinical reality in the near future.