Patient monitoring system

A glucose monitoring system comprising:

• a glucose assembly comprising a plurality of glucose sensors, each glucose sensor comprising an enzymatic glucose sensor adapted to be positioned within a person whose glucose concentration is to be measured, each glucose sensor of the glucose assembly providing a respective sensor signal that varies as a function of sensed glucose;
• and
• a glucose monitor electrically coupled to the glucose assembly, said glucose monitor comprising
• means for receiving the sensor signal from each glucose sensor,
• means for processing the sensor signal received from each glucose sensor, said means for processing including means for comparing the sensor signals obtained from each of said plurality of sensors and generating a composite sensor signal only if the respective sensor signals are within a first prescribed amount of each other,
• means for storing the composite sensor signal,
• means for monitoring the composite sensor signal over a prescribed period of time and generating a rate of change signal that indicates how rapidly the composite sensor signal is changing,
• means for selectively displaying the composite sensor signal and the rate of change signal,
• first alarm means for determining if the composite sensor signal exceeds a preset level limit, and if so, generating a first alarm signal,
• second alarm means for determining if the rate of change signal exceeds a preset trend limit, and if so, generating a second alarm signal,
• calibration means for periodically verifying that each glucose sensor of the sensor assembly provides an accurate measure of the glucose concentration in the blood stream, and
• control means for controlling the monitor so that it performs at least one of a plurality of monitoring functions as selected by a user of said monitor.

A method of measuring a glucose concentration in a patient comprising:

• (a) inserting a plurality of glucose sensor assemblies into a patient, each of said glucose sensor assemblies having a reference electrode, a counter electrode and first and second working electrodes;
• (b) applying a voltage to said electrodes so as to cause first and second electrical currents to flow through said first and second working electrodes, respectively, and measuring said first and second electrical currents, the ratio of said second electrical current to said first electrical current providing a measure of oxygen in the patient;
• (c) placing a glucose oxidase enzyme at said first working electrode, said glucose oxidase enzyme reacting with the oxygen and glucose such that the amount of oxygen measured at said first electrode is inversely proportional to the glucose concentration;
• (d) determining the glucose concentration based on said measure of oxygen and calibration constants associated with each of said glucose sensors;
• (e) comparing the glucose concentration measured by each of said plurality of sensors to determine if the respective plurality of glucose concentration measurements are within a prescribed percentage of each other, and if so, combining the plurality of glucose concentration measurements to form a composite glucose measurement, and if not, rejecting the plurality of glucose measurements as being inaccurate;
• (f) storing the composite glucose measurement as a function of time;
• (g) computing a rate-of-change signal for the composite glucose measurement that indicates how said composite glucose measurement has varied over a specified period of time;
• (h) comparing the composite glucose measurement formed most recently and the rate-of-change signal to preprogrammed limits, and generating an alarm signal in the event the preprogrammed limits are exceeded;
• and
• (i) selectively displaying the composite glucose measurement and rate-of-change signal.

A patient monitoring system comprising:

• an enzymatic sensor adapted to be inserted into a patient in order to make contact between said sensor and a bodily fluid/tissue of said patient, said sensor including means for generating a sensor signal that varies as a function of concentration of a substance sensed in said bodily fluid/tissue, said sensor comprising a detector that detects the amount of said substance in the region of a prescribed enzyme held within said sensor, and wherein said substance in said bodily fluid/tissue reacts with said prescribed enzyme such that the amount of said substance can be measured, and wherein said detector comprises
• a first working electrode, a counter electrode, a reference electrode, and a second working electrode, all of said first and second working electrodes, reference electrode and counter electrode being enclosed within a first membrane wherein an ionic solution is maintained, and said first membrane being enclosed within a second membrane,
• said prescribed enzyme being confined to a window region near said first working electrode,
• electrical means for causing an electrical current to flow between said counter electrode and said first and second working electrodes, and
• means for measuring how much current flows from said first and second working electrodes when a prescribed trim voltage is maintained across said reference electrode and said first and second working electrodes, said measuring means being in communication with said sensor signal generating means, the sensor signal comprising the ratio of said currents and being representative of the substance concentration in said bodily fluid/tissue in the vicinity of said sensor;
• and
• a monitor electrically coupled to the sensor, said monitor comprising
• means for receiving the sensor signal,
• means for processing the sensor signal and generating a substance concentration data signal therefrom,
• means for storing the substance concentration data signal,
• means for monitoring the substance concentration data signal over a prescribed period of time and generating a rate of change signal that indicates how rapidly the substance concentration data signal is changing,
• means for selectively displaying the substance concentration data signal and the rate of change signal,
• first alarm means for determining if the substance concentration data signal exceeds a preset level limit, and if so, generating a first alarm signal,
• second alarm means for determining if the rate of change signal exceeds a preset trend limit, and if so, generating a second alarm signal,
• calibration means for periodically calibrating the sensor so that it provides an accurate measure of the substance concentration in the bodily fluid/tissue, and
• control means for controlling the monitor so that it performs at least one of a plurality of monitoring functions as selected by a user of said monitor.

A method of measuring the concentration level of a particular substance within a patient, said method comprising the steps of:

• (a) inserting a plurality of sensors into a body location of a patient in order to make contact between said plurality of sensors and body fluid/tissue of the patient, each of said sensors having a reference electrode, a counter electrode and first and second working electrodes, and means for providing a measure of a substance concentration within the patient's body fluid/tissue as a function of the electrical current flowing between said first and second working electrodes;
• (b) applying a voltage to said electrodes so as to cause first and second electrical currents to flow through said first and second working electrodes, respectively, and measuring said first and second electrical currents, said first and second electrical currents providing a measure of the substance concentration within the patient's body fluid/tissue;
• (c) determining the substance concentration in the body fluid/tissue of the patient based on the first and second electrical currents measured in step (b) for each of said plurality of sensors;
• and
• (d) comparing the substance concentration measured by each of said plurality of sensors to determine if the respective plurality of substance concentration measurements are within a prescribed percentage of each other, and if so, combining the plurality of substance concentration measurements to form a composite substance measurement, and if not, rejecting the plurality of substance measurements as being inaccurate.

An enzymatic sensor adapted to be inserted into a patient in order to make contact with body fluid/tissue of said patient, said sensor comprising:

• a first working electrode (W1), a counter electrode (C), a reference electrode (R), and a second working electrode (W2), all of said first and second working electrodes, reference electrode and counter electrode being enclosed within a first membrane wherein an ionic solution is maintained, and said first membrane being enclosed within a second membrane,
• said prescribed enzyme being confined to a window region near said first working electrode,
• electrical means for causing an electrical current to flow between said counter electrode and said first and second working electrodes, and
• means for measuring how much current flows from said first and second working electrodes when a prescribed trim voltage is maintained across said reference electrode and said first and second working electrodes, a ratio of said currents comprising a sensor signal, which sensor signal provides a measure of the substance concentration in said body fluid/tissue in the vicinity of said sensor.

A sensor assembly adapted for implantation into the body of a patient to measure the concentration of one or more substances in the patient's blood, said sensor assembly comprising:

• a substrate;
• first and second sets of sensors spaced apart on said substrate, wherein each set of sensors comprises:
• first and second working electrodes bonded to said substrate;
• a reference electrode bonded to said substrate;
• a counter electrode bonded to said substrate;
• and
• means for making electrical contact with said first and second working electrodes, reference electrode, and counter electrode;
• a layer of insulation deposited on said substrate and means for making electrical contact so as to be interspersed between the electrodes bonded to said substrate, a prescribed surface area of each of said electrodes being exposed through said layer of insulation, whereby said first and second working electrodes, reference electrode and counter electrode are all electrically isolated from each other on said substrate;
• first membrane means covering said substrate and electrodes;
• a saline solution held within said first membrane, said saline solution being in contact with said electrodes bonded to said substrate;
• second membrane means covering said first membrane means, said second membrane means having a window pocket therein above the exposed surface area of said first working electrode;
• a prescribed enzyme placed within said window pocket;
• and
• means for applying a prescribed reference voltage, within each set of sensors, between said counter electrode and said reference electrode, and between said first and second working electrodes and said reference electrode, and for measuring the electrical current that flows from said first and second working electrodes, within each set of sensors;
• whereby when said sensor assembly is inserted in the patient's venous system, oxygen and other substances in the blood of the patient may penetrate said first and second membrane means of each set of sensors and electrochemically react, in the presence of the prescribed enzyme held in said window pocket of each set of sensors, with the current flowing through each of said first working electrodes, and electrochemically react in the absence of said enzyme with the current flowing through each of said second working electrodes;
• said currents flowing through said first and second working electrodes of each set of sensors thereby providing a measure of oxygen and other substances in the blood of the patient as a function of the electrochemical reactions that occur at said first and second working electrodes of each set of sensors.