Method and apparatus for continuous measurement of cardiac output
First Claim
1. A method of continuous monitoring of the cardiac output of a patient comprising the steps of:
- determining a value of a cardiac output constant for the patient by measuring at least one parameter of the patient and calculating the cardiac output constant as a function of the measured parameter, wherein the cardiac output constant is calculated without employing any assumed ratio between oxygen intake and carbon dioxide production by the patient;
continuously monitoring carbon dioxide production and mixed venous oxygen saturation of the patient to obtain current values thereof; and
monitoring cardiac output of the patient over time by calculating a value of cardiac output as a function of the current values of carbon dioxide production and mixed venous oxygen saturation and the previously calculated value of the cardiac output constant.
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Abstract
A method of continuously monitoring cardiac output of a patient includes the step of determining a value of a cardiac output constant which is assumed to remain stable over the period of interest and is determined as a function of values of various measured parameters of the patient. These values may include thermodilution cardiac output, carbon dioxide production, arterial and mixed venous oxygen saturation and hemoglobin. Thereafter, cardiac output is continuously determined employing the calculated cardiac output constant and monitored values of carbon dioxide production and arterial and mixed venous oxygen saturation. Oxygen transport may also be monitored on a continuous basis.
58 Citations
33 Claims
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1. A method of continuous monitoring of the cardiac output of a patient comprising the steps of:
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determining a value of a cardiac output constant for the patient by measuring at least one parameter of the patient and calculating the cardiac output constant as a function of the measured parameter, wherein the cardiac output constant is calculated without employing any assumed ratio between oxygen intake and carbon dioxide production by the patient; continuously monitoring carbon dioxide production and mixed venous oxygen saturation of the patient to obtain current values thereof; and monitoring cardiac output of the patient over time by calculating a value of cardiac output as a function of the current values of carbon dioxide production and mixed venous oxygen saturation and the previously calculated value of the cardiac output constant. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of continuous monitoring of the cardiac output of a patient comprising the steps of:
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determining a value of a cardiac output constant for the patient by measuring at least one parameter of the patient and calculating the cardiac output constant as a function of the measured parameter wherein the step of determining the value of the cardiac output constant includes the step of making an initial measurement of cardiac output of the patient by means of a first technique and calculating the constant as a function of the initial value of cardiac output; continuously monitoring carbon dioxide production and mixed venous oxygen saturation of the patient to obtain current values thereof; and monitoring cardiac output of the patient over time by calculating a value of cardiac output as a function of the current values of carbon dioxide production and mixed venous oxygen saturation and the previously calculated value of the cardiac output constant. - View Dependent Claims (13, 14, 15, 16)
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17. A method of continuously monitoring cardiac output of a patient comprising the steps of:
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determining an initial value of cardiac output (Q) in volume per unit time of the patient by employing a first technique; determining initial values of carbon dioxide production (VCO2) in volume per unit time, percentage of arterial oxygen saturation (Sa O2) and percentage of mixed venous oxygen saturation (Sv O2) of the patient; calculating a value for a constant k employing the initial values of Q, VCO2, Sa O2 and Sv O2, where k=VCO2 /(Q(Sa O2 -Sv O2)); thereafter continuously determining current values of VCO2, Sa O2 and Sv O2 ; and calculating a current value of Q employing the calculated value of k and the current values of VCO2, Sa O2 and Sv O2, where Q=VCO2 /(k(Sa O2 -Sv O2)). - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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25. Apparatus for continuously determining cardiac output in volume per unit time of a patient comprising:
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first means for monitoring the volume of carbon dioxide expired by the patient per unit time and generating a first signal representing the current value thereof; second means for monitoring the arterial oxygen saturation of the patient and generating a second signal representative of the current value thereof; third means for monitoring the mixed venous oxygen saturation of the patient and providing a third signal representative of the current value thereof; and processing means for receiving the first, second and third values and (a) initially calculating a cardiac output constant as a function of at least one measured parameter of the patient without employing any assumed ratio between oxygen intake and carbon dioxide production for the patient and (b) thereafter calculating a current value of cardiac output of the patient as a function of the cardiac output constant and the current values of the first, second and third signals. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32)
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33. Apparatus for continuously determining cardiac output in volume per unit time of a patient comprising:
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first means for monitoring the volume of carbon dioxide expired by the patient per unit time and generating a first signal representing the current value thereof; second means for monitoring the arterial oxygen saturation of the patient and generating a second signal representative of the current value thereof; third means for monitoring the mixed venous oxygen saturation of the patient and providing a third signal representative of the current value thereof; and processing means for receiving the first, second and third values and (a) initially calculating a cardiac output constant as a function of at least one measured parameter of the patient, wherein the processing means calculates the cardiac output constant as a function of an initial measurement of cardiac output of the patient and initial values of the first, second and third signals and (b) thereafter calculating a current value of cardiac output of the patient as a function of the cardiac output constant and the current values of the first, second and third signals.
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Specification