Surgery – Diagnostic testing – Measuring anatomical characteristic or force applied to or...
Reexamination Certificate
1999-04-02
2001-07-10
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Measuring anatomical characteristic or force applied to or...
C600S504000, C600S505000
Reexamination Certificate
active
06258046
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to methods and devices for assessing perfusion failure in a patient. More particularly, the invention relates to assessment of perfusion failure in a patient by measuring blood flow in a mucosal tissue in the body of a patient.
BACKGROUND
Very low blood flow, or low “systemic perfusion,” is typically due to low aortic pressure and can be caused by a number of factors, including hemorrhage, sepsis and cardiac arrest. The body responds to such stress by reducing blood flow to the gastrointestinal tract to spare blood for other, more critical organs. Thus, when there is a reduced flow of blood from the heart, the body directs a higher portion of blood to critical organs, such as the brain, which will not survive long without a continuous supply of blood, while restricting the flow to less critical organs, whose survival is not as threatened by a temporary large reduction in blood flow. For example, blood flow to the splanchnic vasculature which supplies the stomach and intestines, and also the esophagus and oral
asal cavity, is drastically reduced when there is a reduced blood flow from the heart. For this reason, decreased blood flow to the splanchnic blood vessels is thus an indication of perfusion failure in a patient. Physicians commonly take advantage of this phenomenon by taking CO
2
and pH measurements in the stomach and intestine to assess perfusion failure.
Assessment of CO
2
concentration in the less critical organs, i.e., those organs to which blood flow is reduced during perfusion failure, has been useful in perfusion assessment. Carbon dioxide production, which is associated with metabolism, continues in tissues even during conditions of low blood flow. The concentration of CO
2
builds-up in tissues experiencing low blood flow because CO
2
is not rapidly carried away. This CO
2
build-up (an increase in partial pressure of CO
2
(PCO
2
)) in the less critical organs in turn results in a decrease in pH in nearby tissue. Therefore, perfusion failure is commonly assessed by measuring pH or PCO
2
at these sites, especially in the stomach and intestines. For examples of catheters used to assess pH or PCO
2
in the stomach or intestines, see, e.g., U.S. Pat. Nos. 3,905,889; 4,016,863; 4,632,119; 4,643,192; 4,981,470; 5,105,812; 5,117,827; 5,174,290; 5,341,803; 5,411,022; 5,423,320; 5,456,251; and 5,788,631.
The inventors have found that increases in PCO
2
may be measured throughout the body, including in accessible organs and tissues fed by splanchnic vessels, and used to assess perfusion failure. For example, the inventors have found that a useful measurement of perfusion failure can be obtained by measuring CO
2
in the upper respiratory/digestive tract. In U.S. Pat. No. 5,579,763, a method is described that can be used to accurately assess perfusion failure by measuring PCO
2
in the patient's esophagus, rather than in the less accessible stomach and/or intestine as previously practiced in the art. Tests showed that measurements of PCO
2
in the esophagus are closely correlated with aortic pressure, and, furthermore, that measurements made in the esophagus are even more closely correlated to aortic pressure than measurements of CO
2
in the stomach. More recently, in co-pending, commonly assigned U.S. Ser. No. 09/160,224, the inventors further showed that PCO
2
measurements in a patient's mucosal tissues (e.g., mouth, nasal mucosa, and throat) are also closely correlated to aortic pressure. As disclosed in U.S. Ser. No. 09/160,224, the CO
2
sensor may be placed at a site within the oral-nasal cavity (e.g, under the tongue at a site in contact with the tongue or the floor of the mouth) where it effectively measures CO
2
in the tissue. Since carbon dioxide can readily pass through mucosal surfaces, CO
2
generated by metabolic activity occurring in tissue below the mucosal surface that is not carried away by blood flow readily migrates through the mucosal surface, where its build-up provides a good measure of perfusion failure. Placement of a CO
2
sensor adjacent a mucosal surface of the upper respiratory/digestive tract thus provides a very good quantification of perfusion failure at all times, including the most critical minutes after the onset of perfusion failure when treatment is likely to be most effective. Thus, mucosal measurements of tissue perfusion can be used to assess perfusion failure in patients.
However, PCO
2
and pH are indirect measures of blood flow in tissue, being based upon the build-up of metabolites that result from poor perfusion. In addition, measurements of pH may be complicated by the presence of saliva, food, or stomach acids. CO
2
measurements may be affected by ambient CO
2
, and, since they depend on equilibration with tissue CO
2
levels, are slow. Thus, there is a need for a more direct method for measuring blood flow in a tissue, to more accurately assess perfusion failure and to monitor the effectiveness of methods taken to increase perfusion, e.g., blood infusion or the like.
SUMMARY OF THE INVENTION
Methods and devices are provided for assessing impairment of circulatory function in a patient, such as that in perfusion failure, by measurement of blood flow in the GI tract and/or upper respiratory/digestive tract of a patient. The perfusion of a tissue is a function of both the velocity of blood cells flowing through tissue, and of the number of blood cells, so that the blood flow through tissue is a more direct measurement of tissue perfusion than pH or CO
2
measurements. Previously, the belief in the art was that decreased blood flow was a localized phenomenon during perfusion failure. It has now been discovered that decreased blood flow, decreased pH and increases in tissue CO
2
occur throughout the body during perfusion failure, and in particular occur not only in the stomach, jejunum, colon and rectum, but also in the esophagus, throat, mouth and nose. Thus, new and useful methods and devices are now provided, for assessing perfusion failure and perfusion levels in a patient by measuring blood flow in tissues of the GI tract and/or of the upper respiratory/digestive tract of a patient.
In one embodiment, then, a method is provided for assessing impairment of circulatory function, such as that in perfusion failure, in a patient. The method comprises introducing a blood-flow sensor into the GI tract or into the upper respiratory/digestive tract of a patient, measuring blood flow in the tissue adjacent the sensor, and providing that measurement for assessment of perfusion failure. Specifically, a blood-flow sensor is placed adjacent a mucosal surface within a patient's body, preferably without passing the sensor down through or beyond the patient's epiglottis, most preferably within the oral or a nasal cavity of the patient. The blood-flow sensor is preferably introduced sublingually, and preferably to one side of the frenulum. The invasiveness of such a technique is minimal, being substantially no more than in the use of an oral thermometer. Preferably, the sensor is a laser-Doppler sensor. The output of the sensor can be detected by a device which electronically converts the sensor output to provide the blood flow in a form that is easily understood by persons viewing the display. The device can optionally further sense the rate of change of blood flow with time to indicate the patient's condition.
Accordingly, in another embodiment the invention features a device for assessing perfusion failure in a patient, where the device is composed of a laser-Doppler blood-flow sensor means for measuring blood flow in a tissue, the sensor means being adapted for lying adjacent a mucosal surface in a patient's body, e.g. in the upper respiratory/digestive tract of a patient, and measuring blood flow in vessels in the mucosal tissue; and an indicating means connected to the sensor means, wherein the indicating means indicates a degree of perfusion failure of the patient associated with the detected blood flow. The device may also include a posi
Bisera Jose
Kimball Victor E.
Tang Wanchun
Weil Max Harry
Institute of Critical Care Medicine
Nasser Robert L.
Reed Dianne E.
Reed & Associates
Wu Louis L.
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