Surgery – Truss – Pad
Patent
1987-02-09
1989-07-04
Richman, Barry S.
Surgery
Truss
Pad
128637, 604 4, 422 68, 436 68, A61B 505
Patent
active
048440973
DESCRIPTION:
BRIEF SUMMARY
There is a need, for example during operations involving heart-lung bypass, in prolonged respiratory support in acute respiratory failure or in kidney dialysis, to provide an accurate measurement of the concentration of certain gases and electrolytes in the blood. In essence this involves measuring the concentration of "atomic scale species", which in the present context means dissolved atoms and molecules of gases or charged ions. Conventionally such measurements are carried out by taking a sample of the blood, transferring it to a measuring cell, and effecting the measurement. An example of this in vitro technique is disclosed in WO-A-83/03006 in which a blood sample is removed, mixed with an acid reagent and placed in communication with an electrolyte in a measuring cell through a membrane permeable only to a gas derived from the species under test. This is inconvenient as the blood circuit has to be opened to take the sample, the sample taken is wasted, and there is inevitable delay in obtaining the required measurement.
Recently, coatings have been developed which are permeable to selected ions and it has been suggested that the concentration of ions in blood might be monitored continuously by exposing the gate electrode of an ion sensitive field effect transistor (ISFET), which electrode is protected with an appropriate coating permeable to a selected ion, in a blood chamber, and sensing the concentration of the ion by virtue of the corresponding conductivity of the ISFET. Although this technique would enable continuous monitoring of the concentration in the blood of the selected ion, it has the disadvantage that the ion selective coating itself quickly becomes coated with protein and other blood components, thus reducing its permeability to the selected ion. As a result the life of the apparatus is short and frequent recalibration of the ISFET is necessary. Recalibration involves purging the chamber of blood and refilling it with a calibrating liquid of which the concentration of the selected ion is known. The technique therefore requires frequent interruption of the blood flow through the chamber.
Similar problems would arise if the technique were to be used for measuring the concentration of atomic scale species in other liquids, such a milk or liquids used in biotechnological processes, e.g. cell culture and fermentation, as these liquids, like blood, contain components which would be deposited on, and foul, sensitive surfaces. Such liquids are hereinafter referred to as "thick liquids".
In accordance with the present invention, apparatus for testing the concentration of a selected atomic scale species in a thick liquid comprises a first chamber which contains, in use, the thick liquid under test, the chamber being a least partly defined by one face of a microporous membrane which is permeable to atomic scale species; and a measuring cell incorporating a second chamber which is arranged to be filled with a clean liquid and which is at least partly defined by the opposite face of the membrane whereby atomic scale species in the thick liquid under test diffuse through the membrane and are present in the clean liquid in a concentration related to that at which they exist in the thick liquid under test; the cell also incorporating a sensing device which is responsive substantially only to the selected species and which has an electrode or other sensor in communication with the clean liquid in the second chamber whereby the device provides an output related to the concentration of the selected species.
In this context the term "clean liquid" means a liquid which substantially does not inhibit the response of the sensor to the selected species with which it is, in use, in communication. In practice the clean liquid may be distilled water, preferably containing a concentration of the species similar to that which is to be expected in the thick liquid under test.
An advantage of this apparatus is that it is substantially non-invasive and may operate attached to, e.g. a blood circuit without blood loss fr
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Bellhouse Brian J.
Pugh Sydney M.
Bellhouse Technology Limited
McMahon Timothy M.
Richman Barry S.
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