This invention relates to a probe for monitoring constituents in a bodily fluid such as blood, and more particularly, the invention relates to a probe as part of an apparatus for continuously monitoring the constituents in the blood including, pH, pCO.sub.2 and pO.sub.2, blood electrolytes and blood pressure.
Over the years, considerable research and development work has been carried on in the field of monitoring gases but not necessarily restricted to blood gases. Within the last twenty years or so, attention has been given to the development of monitoring systems having the following components: a dye to react with the constituents being monitored, a structure for holding the dye, a membrane separating the monitored analyte from the dye, and a system for directing light onto the dye and monitoring the returned radiation, the intensity of the return radiation being a measure of the constituent passing through the membrane and contacting the dye.
Two primary systems have been proposed. In the first, a system for measuring O.sub.2, for example, a fluorescent dye is excited by the incoming light source to cause it to fluoresce. The wavelength of fluorescence is different from the wavelength of the incoming light source. Oxygen will tend to quench the intensity of fluorescence. The degree of quenching becomes a measure of the pressure of oxygen in the fluid being monitored.
Another known system employs an absorption based dye. The dye is irradiated by light of known intensity. The absorption capability of the dye is affected by the constituent whose presence is being monitored. The intensity of the incoming light is compared to the intensity of the light scattered back from the dye to determine the quantity of the constituent in the blood.
At the present time, there has been no production of a single probe which is small enough (less than a millimeter in dimension) to be inserted into a blood vessel for the continuous monitoring of the triad of pH, CO.sub.2 and O.sub.2. The problem appears to be that there has been no practical design for and method of manufacturing such a tiny device which satisfies all the criteria for a commercially successful device such as low cost for disposability, absence of toxicity, capability of being sterilized and the like.