Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
1998-09-24
2001-04-10
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
active
06216024
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 the localized partial pressure of carbon dioxide within the upper respiratory/digestive tract 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. 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, such as the stomach and intestines, whose survival is not as threatened by a temporary large reduction in blood flow. Physicians commonly take advantage of this phenomenon by taking 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, is useful in perfusion assessment. Carbon dioxide production, which is associated with metabolism, continues even during low blood flow. Because CO
2
is not rapidly carried away during low blood flow, the concentration of CO
2
increases, which in turn results in a decrease in pH and an increase in partial pressure of CO
2
(pCO
2
) in the less critical organs. 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 measurement of pCO
2
to determine the extent of perfusion failure has commonly been done by threading a catheter through the nasal passage, past the epiglottis, through the esophagus, past the esophageal sphincter, and into the stomach, and sometimes through the stomach and into the intestines. Alternatively, measurement has been conducted in the colon, with a catheter being threaded through the anus. These procedures are obviously quite invasive and can cause harm and discomfort to a patient. Moreover, insertion of the catheter in this manner is also complex and time-consuming.
In U.S. Pat. No. 5,579,763, applicants described the introduction of a catheter with a carbon dioxide sensor through the nasal or oral passage, past the epiglottis, and into the esophagus so that the catheter and sensor lay within the esophagus. This method can be used to accurately assess perfusion failure by measuring pCO
2
in the patient's esophagus of a patient, rather than in the stomach and/or intestine. 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. This procedure was advantageous in that the procedure's invasiveness was reduced and CO
2
generated by digestive fluids in the stomach did not affect measurements since the esophageal sphincter blocks such gas. However, the insertion of the catheter still constituted considerable invasion and thus risk of harm to the patient. Furthermore, extension of the catheter extended past the epiglottis exposed the patient to the risk of regurgitation of stomach contents including stomach acids.
There is a need for an even less invasive method to measure 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 blood circulation in a patient, such as that in perfusion failure, by measurement of pCO
2
(partial pressure of carbon dioxide) in the upper digestive and/or respiratory tract of the patient. The method comprises introducing a carbon dioxide sensor into the upper digestive and/or respiratory tract of a patient, without passing the sensor down through or beyond the patient's epiglottis. Specifically, a carbon dioxide sensor is placed adjacent a mucosal surface within the upper digestive and/or respiratory tract, preferably within the patient's mouth or inside the patient's nose. By avoiding passage through the mouth into the throat and esophagus, discomfort is substantially avoided and the potential for injury minimized. Previously, the belief in the art was that increased partial pressure of carbon dioxide was a localized phenomenon during perfusion failure; however, applicants have now discovered that increases in tissue CO
2
occur throughout the body during perfusion failure, and the method and device of the invention are premised on this discovery.
Applicants prefer to introduce the carbon dioxide sensor 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. The sensor preferably lies at the inner end of a holder that lies stably in the patient's mouth. The holder maintains the sensor in position, and also isolates the area immediately surrounding the mucosal surface contacted by the sensor from surrounding air flow that could carry away some CO
2
and result in an incorrect measurement. Preferably, the sensor is an optical CO
2
sensor. The output of the sensor can be detected by a device which electronically converts the sensor output to provide a CO
2
concentration value. The device can further sense the rate of change of CO
2
concentration with time to indicate the patient's condition.
Accordingly, in one aspect the invention features a device for assessing perfusion failure in a patient, where the device is composed of a carbon dioxide sensor means for detecting a partial pressure of carbon dioxide (pCO
2
), the sensor means being adapted for lying adjacent a mucosal surface of the upper respiratory/digestive tract of a patient and measuring carbon dioxide at the mucosal surface; 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 partial pressure of carbon dioxide. Preferably the device also includes an isolating means for inhibiting air flow around the mucosal surface in a region surrounding the sensor means.
In a preferred embodiment, the isolating means is a holder designed to fit within the mouth of the patient and hold the sensor in place adjacent the mucosal surface. The holder may be designed to contact the bottom of the tongue and the floor of the mouth of the patient, or to fit between the inside of a lip and gum of the patient. In another embodiment, the isolating means is a holder designed to fit within a nares of the patient and hold the sensor in place adjacent the mucosal surface.
In another preferred embodiment, the device includes a moisturizing means for supplying moisture to the mucosal surface adjacent the sensor.
In a second aspect the invention features a device for use with a pCO
2
sensor assembly for assessing perfusion failure of a patient. The device is composed of a sensor holder with a sublingual holder inner portion shaped to fit in the mouth of a patient under the patient's tongue, said holder forming at least one holder passage extending from said holder outer portion to said sublingual holder portion.
In another aspect the invention features a method for assessing perfusion failure of a patient, the method involving the steps of placing a carbon dioxide sensor adjacent a mucosal surface of an upper digestive/respiratory tract of a patient, and measuring a partial pressure of carbon dioxide at the mucosal surface. A partial pressure of carbon dioxide at the mucosal surface of the upper
Bisera Jose
Tang Wanchun
Weil Max Harry
Institute of Critical Care Medicine
Nasser Robert L.
Reed Dianne E.
Reed & Associates
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