Filter unit for end-tidal carbon monoxide monitor

• US 5,404,885 A
• Filed: 01/21/1994
• Issued: 04/11/1995
• Est. Priority Date: 06/16/1992
• Status: Expired due to Fees

• Current Assignee: Natus Medical Incorporated
• Original Assignee: Natus Medical Incorporated
• Inventors: Stone, Robert T., Sheehan, Neil J., Rouw, Scott R.
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): NASSER, ROBERT L
• Application Number:
  US08/184,379
• Time in Patent Office: 445 Days
• Field of Search: 128/716, 128/719, 128/204.22, 128/204.23, 128/205.22, 422/83, 422/84, 73/23.3
• US Class Current: 600/529
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: G01N 33/004 CO or CO2
• CPC Class Codes: G01N 33/497 of gaseous biological material, e.g. breath
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

A noninvasive device and methods for measuring the end-tidal carbon monoxide concentration in a patient'"'"'s breath, particularly newborn and premature infants. The patient'"'"'s breath is monitored. An average carbon monoxide concentration is determined based on an average of discrete samples in a given time period. The ratio of the end-tidal portion of the breath flow sample is separately determined, preferably based on monitoring the level of carbon dioxide in the gas sample and identifying the carbon dioxide concentration levels corresponding to the end-tidal portion of the breath sample. The sensed carbon monoxide level is converted to the end-tidal carbon monoxide level by subtracting the ambient carbon monoxide level and dividing the remainder by the ratio of end-tidal breath to breath in the breath sample. An easy to use microcontroller-based device containing a carbon dioxide detector, a carbon monoxide detect and a pump for use in a hospital, home, physician'"'"'s office or clinic by persons not requiring high skill and training is described. A replaceable filter unit made of a single tri-lumen PVC extrusion and a tube segment inter-connecting two of the lumens used to provide the consumable filtration material. The filtration material is interposed between the carbon dioxide sensor and the carbon monoxide sensor which are mounted inside the monitor housing. The filter unit also interfaces the canula for receiving the patient'"'"'s breath sample and a hydrophobic filter between the patient and the carbon dioxide monitor.

Claims

1. A method of filtering a gas sample for use with a non-invasive end-tidal gas flow monitor containing a first sensor for detecting the amount of a first gas component in a gas sample, a second sensor for detecting the amount of a second gas component in the gas sample, a first connector in communication with the first sensor, a second connector in communication with the first sensor, a third connector in communication with the second sensor, comprising:

providing a body having a first end and a second end and first, second, and third lumens extending through the body between the first and second ends;

providing a first consumable filtration medium for removing selected undesired components from the gas sample;

locating the first consumable filtration medium in one of the second and third lumens;

connecting the second and third lumens with a tube segment at one of the first and second ends, thereby providing the first lumen as a first gas flow path between the first and second ends of the body and providing the interconnected second lumen, tube segment, and third lumen as a second gas flow path through the body; and

passing said sample of gas through said first consumable filtration medium.

2. The method of claim 1 further comprising forming the body as an extruded tri-lumen body having simultaneously coextruded first, second, and third lumens.

3. The method of claim 2 wherein forming the body further comprises providing the first, second, and third lumens with walls of about the same thickness.

4. The method of claim 2 wherein forming the body further comprises co-extruding the first, second, and third lumens with respective first, second, and third longitudinal axes in a common plane.

5. The method of claim 1 wherein providing the body further comprises providing the first, second, and third lumens with different inner dimensions.

6. The method of claim 5 further comprising inserting a plug in one of the second and third lumens at the one end receiving the tube segment, and providing an interior flow passageway through the plug having an inner dimension that corresponds to the inner dimension of the other of the second and third lumens, wherein the inserting step further comprises inserting the tube segment into the plug flow passageway and the other lumen.

7. The method of claim 6 further comprising providing said first, second, and third lumens and said plug with a generally circular cross section.

8. The method of claim 7 wherein providing the body further comprises forming the body as an extruded or molded tri-lumen tube.

9. The method of claim 7 wherein inserting the tube segment further comprises bonding the tube segment to the plug flow passageway and the other of the second and third lumens.

10. The method of claim 5 further comprising providing the lumens with longitudinal axes in a common plane.

11. The method of claim 5 further comprising forming the first, second, and third lumens with dimensions for interconnecting to the first, second and third connectors to form a secure frictional engagement.

12. The method of claim 1 wherein providing the first filtration medium further comprises:

providing a first length of cellulose acetate;

providing a second length of cellulose acetate;

providing a length of activated carbon having an outer circumference; and

positioning the length of activated carbon between the first and second lengths of cellulose acetate.

13. The method of claim 12 further comprising sealingly interposing a thin cap between the outer circumference of the activated carbon and an interior wall of the second gas flow path, and providing the cap with an aperture at each end of the carbon for providing a gas flow path therethrough.

14. The method of claim 1 further comprising:

providing a fitting having a barbed end for connecting to one end of the first lumen;

providing a hydrophobic filter; and

connecting the hydrophobic filter to the fitting.

15. The method of claim 14 further comprising providing a canula having a first end and a second end, the first end having a first and second aperture for receiving said sample of gas from the patient and marking the canula with an insertion mark at a distance from the first end on the order of 1.0 centimeter, and connecting the second end to the hydrophobic filter.

16. The apparatus of claim 14 wherein the passing step further comprises passing said gas sample, in sequence, through said hydrophobic filter, said first sensor, said first consumable filtration medium, and said second sensor.