Apparatus and method to determine blood parameters

• US 6,144,444 A
• Filed: 11/06/1998
• Issued: 11/07/2000
• Est. Priority Date: 11/06/1998
• Status: Expired due to Term

• Current Assignee: Medtronic Avecor Cardiovascular Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Avecor Cardiovascular Incorporated (Medtronic Plc)
• Inventors: Thompson, Mark A., Haworth, William S., Goodin, Mark S.
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): LAUCHMAN, LAYLA G
• Application Number:
  US09/186,997
• Time in Patent Office: 732 Days
• Field of Search: 356/39, 356/41, 356/40, 600/322, 600/323
• US Class Current: 356/39
• CPC Class Codes: A61B 2560/0233 Optical standards
• CPC Class Codes: A61B 5/14535 for measuring haematocrit
• CPC Class Codes: A61B 5/14557 specially adapted to extracorporeal circuits
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes

Abstract

The present invention relates to an apparatus for monitoring blood parameters during cardio-pulmonary bypass surgery or during other procedures which utilize an extracorporeal circuit. The apparatus is typically used to monitor the percentage of hemoglobin bound with oxygen (oxygen saturation), the total amount of hemoglobin in the blood, and the percent of blood which is comprised of red blood cells (hematocrit), although the apparatus can be adapted to measure other blood parameters. The apparatus (or monitor) provides real-time results to show immediate changes (trending) in the monitored parameters.

Claims

1. An apparatus for measuring blood parameters through conduit of an extracorporeal circuit, comprising:

a light source which transmits light at a plurality of wavelengths to the conduit;

a near sensor which senses light at a plurality of wavelengths connected to receive light a first distance from the light source which has been one of reflected and transmitted by the blood, wherein signals generated by the near sensor are indicative of the intensity of the sensed light at a plurality of wavelengths;

a far sensor which senses light at a plurality of wavelengths connected to receive light a second distance from the light source which has been one of reflected and transmitted by the blood, wherein signals generated by the far sensor are indicative of the intensity of light at a plurality of wavelengths; and

an arithmetic circuit connected to receive the signals from the near sensor and the far sensor and wherein the signals are used to calculate a parameter of blood and to generate an output signal indicative thereof.

2. An apparatus as in claim 1, wherein the blood parameters are at least one of oxygen saturation, hematocrit and hemoglobin concentration.

3. An apparatus as in claim 1, wherein the light source emits wavelengths between 450 nm and 1150 nm.

4. An apparatus as in claim 1, wherein the light source is a tungsten halogen bulb.

5. An apparatus as in claim 1, wherein the near sensor is a first charge coupled device and the far sensor is a second charge coupled device of a single two-channel spectrometer.

6. An apparatus as in claim 1, wherein the near sensor is a first spectrometer and the far sensor is a second spectrometer.

7. An apparatus as in claim 1, wherein the blood parameter being measured is oxygen saturation and wherein the arithmetic circuit derives the blood oxygen saturation from the ratios of reflected light at wavelengths between 660 nm and 815 nm in accordance with the formula:

oxygen saturation=A(n680nm/n815nm)³ +B(n680nm/n815nm)² +C(n680nm/n815nm)+D(n680nm/n815nm)^-1 +E(n680nm/n815nm)^-2 +F(n710nm/n740nm)³ +G(n710nm/n740nm)² +H(n710nm/n740nm)+I(n710nm/n740nm)^-1 +J(n710nm/n740nm)^-2 +L(n760nm/n815nm)³ +M(n760nm/n815nm)² +N(n760nm/n815nm)+O(n760nm/n815nm)^-1 +P(n760nm/n815nm)^-2 +T(f680nm/f815nm)³ +U(f680nm/f815nm)² +V(f680nm/f815nm)+W(f680nm/f815nm)^-1 +X(f680nm/f815nm)^-2 +Y(f710nm/f740nm)³ +Z(f710nm/f740nm)² +AA(f710nm/f740nm)+BB(f710nm/f740nm)^-1 +CC(f710nm/f740nm)^-2 +DD(f760nm/f815nm)³ +EE(f760nm/f815nm)² +FF(f760nm/f815nm)+GG(f760nm/f815nm)^-1 +HH(f760nm/f815nm)^-2 +II(n815nm/f810nm)³ +JJ(n815nm/f810nm)² +KK(n815nm/f810nm)+LL

wherein A to GG are constants, n designates the reflectance detected by the near sensor, and f designates the reflectance detected by the far sensor.

8. An apparatus as in claim 1, wherein the blood parameter being measured is one of hemoglobin concentration and hematocrit and wherein the arithmetic circuit derives one of hemoglobin concentration and hematocrit from the ratios of reflected light at a plurality of wavelengths between 760 nm and 999 nm in accordance with the formula:

hemoglobin and hematocrit=A(n815nm/f810nm)³ +B(n815nm/f810nm)² +C(n815nm/f810nm)+D(n815nm/f810nm)^-1 +E(n815nm/f810nm)^-2 +F(n850nm/f825nm)³ +G(n850nm/n825nm)² +H(n850nm/f825nm)+I(n850nm/f825nm)^-1 +J(n850nm/f825nm)^-2 +O(n880nm/f827nm)³ +P(n880nm/f827nm)² +Q(n880nm/f827nm)+R(n880nm/f827nm)^-1 +S(n880nm/f827nm)^-2 +U(n900nm/f830nm)³ +V(n900nm/f830nm)² +W(n900nm/f830nm)+X(n900nm/f830nm)^-1 +Y(n900nm/F830nm)^-2 +Z(n999nm/f935nm)³ +AA(n999nm/f935nm)² +BB(n999nm/f935nm)+CC(n999nm/f935nm)^-1 +DD(n999nm/f935nm)^-2 +EE(n760nm/n815nm)³ +FF(n760nm/n815nm)² +GG(n760nm/n815nm)+HH

when blood hemoglobin concentration is less than 9 or hematocrit is less than 25, and hemoglobin and hematocrit=A(n802nm^N1 /f802nm^D1)³ +B(n802nm^N1 /f802nm^D1)² +C(n802nm^N1 /f802nm^D1)+D(n802nm^N1 /f802nm^D1)^-1 +E(n802nm^N1 /f802nm^D1)^-2 +I(n803nm^N2 /f803nm^D2)³ +J(n803nm^N2 f803nm^D2)² +K(n803nm^N2 /f803nm^D2)+L(n803nm^N2 /f803nm^D2)^-1 +M(n803nm^N2 /f803nm^D2)^-2 +O(n805nm^N3 /f802nm^D2)³ +P(n805nm^N3 /f802nm^D3)² +Q(n805nm^N3 /f802nm^D3)+R(n805nm^N3 /f802nm^D3)^-1 +S(n805nm^N3 /f802nm^D3)^-2 +U(n810nm^N4 /f803nm^D4)³ +V(n810nm^N4 /f803nm^D4)² +W(n810nm^N4 /f803nm^D4)+X(n810nm^N4 f803nm^D4)^-1 +Y(n810nm^N4 /f803nm^D4)^-2 +FF(n760nm/n815nm)³ +GG(n760nm/n815nm)² +HH(n760nm/n815nm)+II

when blood hemoglobin concentration is greater than or equal to 9 or hematocrit is greater than or equal to 25 and wherein A to II are constants, n designates the reflectance sensed by the near sensor, and f designates the reflectance sensed by the far sensor.

9. An apparatus as in claim 1, further comprising a source optical fiber connected to transmit light to the conduit from the light source, the source optical fiber having a first end connected to the light source and a second terminal end connected adjacent the conduit, the near sensor receives light from a near optical fiber, the near optical fiber having a first end connected to the near sensor and a second terminal end connected adjacent the conduit, and the far sensor receives light from a far optical fiber, the far optical fiber having a first end connected to the far sensor and a second terminal end connected adjacent the conduit.

10. An apparatus as in claim 9, further comprising a clamp for mounting a terminal end of the source optical fiber, a terminal end of the near optical fiber and a terminal end of the far optical fiber such that the source fiber, the near optical fiber and the far optical fiber are in optical communication with the conduit of the extracorporeal circuit.

11. An apparatus as in claim 9, wherein a terminal end of the near optical fiber is positioned about 0.8 mm from a terminal end of the source optical fiber and a terminal end of the far optical fiber is positioned about 1.2 mm from the terminal end of source optical fiber.

12. An apparatus as in claim 9, wherein a terminal end of the near optical fiber, a terminal end of the far optical fiber and a terminal end of the source optical fiber are positioned co-axially along the flow path of blood in the conduit.

13. An apparatus as in claim 10, wherein the clamp secures the terminal ends of the optical fibers so as to bias the terminal ends of the optical fibers against the conduit.

14. An apparatus for measuring blood parameters through conduit of an extracorporeal circuit, comprising:

means for emitting light at a plurality of wavelengths into blood flowing through the conduit;

near means for receiving light reflected from the blood;

far means for receiving light reflected from the blood, wherein the far receiving means and near receiving means are connected to receive reflected light at positions which are differentially spaced from the point where light is emitted into the conduit;

means for generating signals indicative of the intensity at a plurality of wavelengths of light received at a plurality of wavelengths by the near receiving means and far receiving means; and

means for calculating receiving the signals from the signal generating means wherein, the calculating means calculates blood parameters and generates an output signal indicative thereof.

15. An apparatus as in claim 14, wherein the blood parameters are at least one of oxygen saturation, hematocrit and hemoglobin concentration.

16. A method for measuring a parameter of blood passing through conduit in an extracorporeal circuit with a blood monitor having a light source, a near sensor and a far sensor, the method comprising:

directing a plurality of wavelengths from the light source through the conduit into the blood;

directing light reflected by the blood through the conduit to the near sensor;

directing light reflected by the blood through the conduit to the far sensor;

measuring the light reflected by the blood to the near sensor and the far sensor at a plurality of wavelengths; and

calculating the blood parameter using the quantity of reflected light detected at a plurality of wavelengths by the near sensor and the far sensor.

17. A method as in claim 16, wherein the blood parameter is at least one of oxygen saturation, hemoglobin concentration and hematocrit.

18. A method for measuring blood parameters through a conduit, comprising:

providing a blood monitor including a near sensor, a far sensor and a light source which are connected by optical fibers to a clamp;

mounting the clamp on the conduit in a manner such that terminal ends of the optical fibers are held against the outer surface of the conduit;

emitting light at a plurality of wavelengths through the conduit into the blood;

receiving light at a plurality of wavelengths reflected by the blood;

quantitating the light reflected at the near sensor and the far sensor at a plurality of wavelengths; and

calculating a blood parameter from the quantity of reflected light.