Indicator device

Claim 1

A rapid response device for the detection of carbon dioxide in a gas mixture characterized in that it comprises an enclosure 1 defined by walls and having a transparent window 8 in a wall, an inlet 3, an outlet 5 and sealing means 14, said enclosure having mounted therein an indicator component 9 adapted to be viewed through said transparent window, said component comprising a carrier having fixedly attached thereto an indicating element formed from (i) an aqueous solution of a colorless compound which provides an alkaline solution; (ii) a hygroscopic, high boiling, transparent, colorless, water-miscible liquid; and (iii) a chromogenic pH-­sensitive indicator which changes color relative to a change in pH of the solution and which has a pK which is lower by 1.0 - 1.5 pH units then the pH of the solution, wherein the nature and concentration of the colorless compound in (i) is correlated to the nature and concentration of indicator (iii) so that no color change occurs for at least 15 minutes when the indicating element is exposed to an atmosphere having a concentration of 0.03% carbon dioxide, but a color change is produced within 5 to 20 seconds when said indicating element is exposed to an atmosphere containing at least 2% carbon dixodie, said sealing means being adapted to be opened immediately prior to use of the device.

Claim 6

A device according to any one of claims 1 to 4, characterized in that said pH-sensitive indicator is metacresol purple, thymol blue, cresol red, phenol red, xylenol blue, a 3:1 mixture of cresol red and thymol blue, bromthymol blue, neutral red, phenolphthalein, rosolic acid, α-naphtholphthalein or orange I.

Claim 7

A device according to any one of the preceding claims, characterized in that said sealing means is provided by enveloping the enclosure in a gas-impermeable metallic foil.

Claim 8

A device according to any one of the preceding claims, characterized in that said hygroscopic, water-miscible liquid is glycerol, propylene glycol or a mixture thereof.

Claim 9

A device according to any one of claims 4 to 7, characterized in that said indicator component comprises a sheet of filter paper impregnated with an indicating element formed from (i) an aqueous solution of sodium carbonate or calcium hydroxide; (ii) glycerol or a mixture of glycerol and propylene glycol; and (iii) metacresol purple sodium salt.

Claim 10

A device according to any one of the preceding claims, characterized in that said enclosure 1 is a cylinder of transparent plastic, the inlet 3 and outlet 5 thereof have narrower diameters than the main cylindrical body of the enclosure and the shape of the inlet 3 is that of a cylindrical connector which will fit on the end of a standard endotracheal catheter.