Continuous ex vivo and in vivo monitoring with chemical sensors.

The chemical species of principal clinical interest for continuous monitoring include oxygen, carbon dioxide, pH, potassium, and glucose. Although sensors exist for all of these analytes, relatively few continuous monitors are used for blood chemistries. Reviewing the available electrochemical and optical approaches along with the expected system performance requirements provides some insight into the reasons for this. In particular, the performance of sensor systems is significantly dependent on the environment in which they are used: transcutaneous, intravascular, intramuscular, etc. The future success and acceptance of "real-time" continuous monitoring of the critically ill patient probably does not require the development of new sensors for additional species. Rather, improvements in the stability of existing devices and protection of the sensor's chemistry from the environment are needed. Eventually, the development of new sensing technologies, e.g., near infrared spectroscopy, may lead to a completely noninvasive system capable of monitoring a broad spectrum of analytes.