Patent No. 5791344 Patient monitoring system

 

Patent No. 5791344

Patient monitoring system (Schulman, et al. August 11, 1998)

Assignee: Alfred E. Mann Foundation for Scientific Research (Sylmar, CA)

Abstract

A patient monitoring system measures the concentration of a particular substance in a patient's tissue, blood, or other bodily fluids, provides an indication of the rate of change of such concentration, and determines whether the measured concentration and rate of change are within certain preset limits. If not, an audible and/or visual alarm signal is generated. The patient monitoring system includes at least one enzymatic sensor adapted to be inserted into the patient, where it produces sensor signals related to the concentration of the substance being measured. The sensor signals are delivered through a suitable interconnect cable to a monitor. In one embodiment, the interconnect cable includes a contactless connector that electrically isolates the enzymatic sensor from the monitor, and reduces the number of conductors required to interface with a plurality of sensors. The monitor interprets the sensor signals by applying a previously determined calibration to quantitatively determine the substance concentration value. The substance concentration value thus determined is then processed in order to determine the rate of change, is stored (to create a history or record), and may also be displayed in large, easy-to-read numerals. Rate of change information (trend) may also be numerically or graphically displayed.

 

Notes:

BACKGROUND OF THE INVENTION

The present invention relates to patient monitoring systems and methods, and more particularly to a system that monitors the amount and rate of change of a specified substance, e.g., glucose, in a patient, providing an easy-to-read display of such monitored information, as well as an alarm if either the amount or rate of change exceeds programmable limits.

The monitoring and measuring of glucose concentrations in a patient's blood is one application of the present invention. Glucose is a simple sugar containing six carbon atoms (a hexose). Glucose is an important source of energy in the body and the sole source of energy for the brain. Glucose is stored in the body in the form of glycogen. In a healthy person, the concentration of glucose in the blood is maintained at around 5 mmol/l by a variety of hormones, principally insulin and glucagon. If the blood-glucose concentration falls below this level neurological and other symptoms may result, such as hypoglycemia. Conversely, if the blood-glucose level is raised above its normal level, e.g., to above about 10 mmol/l, the condition of hyperglycemia develops, which is one of the symptoms of diabetes mellitus. It is thus evident that maintaining the concentration of glucose in the blood at a proper level is critically important for wellness and good health.

Unfortunately, some individuals, either through disease, dramatic and/or sudden changes to the body (such as may be caused by injury or surgery), or for other reasons, are unable to maintain the proper level of glucose in their blood. In such instances, the amount of glucose can usually be altered, as required, in order to bring the glucose concentration to a proper level. A shot of insulin, for example, can be administered in order to decrease the glucose concentration (insulin decreases the amount of glucose in the blood). Conversely, glucose may be added directly to the blood through injection, an intravenous (IV) solution, or indirectly by eating or drinking certain foods or liquids.

Before the glucose concentration can be properly adjusted, however, an attending physician (or the patient himself or herself), must know what the present glucose concentration is and whether such concentration is increasing or decreasing. Unfortunately, the only viable technique heretofore available for measuring glucose concentration has been by drawing a blood sample and directly measuring the amount of glucose therein, or by measuring the amount of sugar in the urine. Both measurement techniques are not only inconvenient for the patient, but also may require significant time, manpower, and the use of expensive laboratory instruments, tools or aides to complete. As a result, it is usually not possible for a physician to know immediately what the glucose concentration of a given patient is. Rather, fluid samples must first be obtained, tested or analyzed, and a report issued. Based on such report, appropriate corrective action can then be taken when needed, e.g., through insulin injections or IV supplements, to move the glucose concentration back to an acceptable level. Unfortunately, however, because of the inherent time delay involved with gathering the fluid samples, performing the analysis, and issuing the report, such corrective action may not be possible until several hours after it is first needed. Even after the report is issued, the report results may be misinterpreted, or (e.g., through transcription or analysis error) may simply be wrong. Hence, it is apparent that what is needed is a way to accurately determine the glucose concentration of a patient immediately, effectively communicate such measured concentration to a physician or other interested person (including the patient) with minimum likelihood of error, and provide a clear indication of whether such concentration is within certain prescribed safe limits.

Even after the glucose concentration is known, the physician must still estimate how much corrective action is required until such time as a direction and rate of change of the glucose concentration level has been established. Unfortunately, to identify a trend in the glucose concentration using existing techniques, i.e., to determine whether the glucose concentration is increasing or decreasing, and at what rate, a series of the above-described body fluid measurements must first be made, and the results then analyzed. Such measuring and analyzing process only further delays any appropriate corrective action. What is clearly needed, therefore, is a glucose measurement system that provides a physician, or other medical personnel (or the patient himself or herself) with a rapid measure or indication of the rate of change of the glucose concentration, thereby immediately informing the physician whether any corrective action is needed.

In addition to glucose, there are other substances or elements within a patient that need to be monitored for medical or other reasons. There is thus a need in the art for measurement systems that accurately and rapidly not only measure such other substances, but also provide an indication of the rate of change or such measured substances. The present invention advantageously addresses the above and other needs.

SUMMARY OF THE INVENTION

The present invention provides a patient monitoring system that continuously measures the concentration of a specified substance, e.g., glucose, in a patient, and provides an indication of the rate of change of such concentration. The system further automatically determines whether the measured concentration and rate of change are within certain preset limits, and if not, generates an alarm signal.

The preferred embodiment of the invention relates to a monitoring system that continuously measures the glucose concentration in the blood of a patient. However, it is to be understood that the invention is not so limited, but also applies to systems, apparatus, and methods for monitoring and measuring the concentration of any substance or element found in a patient's tissue, blood, or other body fluids that needs to be monitored and measured with an appropriate sensor.

The preferred glucose monitoring system includes a glucose sensor that may be inserted into an appropriate body location, such as the venous system, the peritoneal system, or other location of the patient, where it responds to blood glucose or other elements or substances and produces electrical signals that are related to the concentration of glucose or other substances. The electrical signals generated by the sensor ("sensor signals") are delivered through a suitable interconnect cable to a monitor. The monitor interprets the sensor signals by applying a previously determined calibration to quantitatively determine the concentration value of the blood glucose or other substance. The concentration value thus determined is then processed in order to determine the rate of change, is stored (to create a history or record), and may also be displayed. One selectable display mode displays the measured concentration in large, easy-to-read numerals, with selectable units, e.g., milligrams (mg) per deciliter (dl), or mg/dl. Another selectable display mode displays a graph of the rate of change (trend) in accordance with selected units, such as mg/dl/hr. Such graph provides an easy-to-see representation of the concentration values over a past period of time, e.g., three hours.

The preferred glucose monitor stores the blood glucose value and other data (including the patient name, sensor identification number, start date, etc.) in memory and displays the measured glucose level, updating the displayed level periodically (e.g., once per minute). Such stored data may also advantageously be viewed, as selected, as a graphic display that indicates the last several hours of recorded values, thereby clearly showing any trends in the data over such time period.

In accordance with one aspect of the invention, a plurality of glucose or other sensors, e.g., at least two sensors, are inserted into a vein or other appropriate location of the patient and are coupled to the monitor, with a concentration measurement being provided by each sensor. A prescribed degree of correlation must exist between the readings from each sensor in order to validate the correctness of the concentration measurement that is made. If the prescribed degree of correlation does not exist, then the monitor automatically indicates that a recalibration and/or new sensor(s) is required.

In accordance with a further aspect of the invention, some of the plurality of sensors coupled to the monitor may be other than glucose sensors, e.g., a sensor to detect oxygen, hydrogen peroxide, or other substances or elements of interest that are present in the patient's tissue, blood, or other bodily fluids. The monitor, in such instances, may process and combine the measurements from each sensor, e.g., by combining the measurement from one sensor with the measurement from another sensor, as required, in order to provide an overall evaluation of the condition, well-being and/or health of the patient.

In accordance with another aspect of the invention, the monitor includes a data card port that allows the current data to be stored in a data card that can be selectively removed from the monitor in order to indirectly make such data available to another computer or processor, or to make such data available for analysis at a later time. The monitor may further include, in one embodiment, an RS-232 (serial) port that allows the monitor to be connected directly to a computer network, or other computer equipment, to facilitate the direct transfer of the data to such other computer network or equipment.

In accordance with an additional aspect of the invention, the monitor is controlled via on-screen menus that define the various subroutines or processes carried out by the monitor at any given time. The screen menus are readily accessed, in a preferred embodiment, by simply touching a designated area of a touch sensitive screen. A user of the monitor may readily "jump" between the main menu and any of the subroutines or processes by merely pressing or touching an appropriate MENU button or key displayed on the touch sensitive screen.

In accordance with yet a further aspect of the invention, the patient monitoring system is calibrated with each new sensor. Further, periodically, e.g., once every 24 hours, the system is calibrated against a blood or other tissue sample that has been independently analyzed by a certified reference method for measuring the concentration of a particular element or substance, e.g., glucose, therein.

It is therefore a feature of the invention to provide a monitoring system that continuously monitors the concentration of a specified substance or element within a patient, providing real-time readings and a history of concentration levels of that substance or element for the patient, including the rate at which the concentration is changing. Such system is particularly suited for use in a hospital environment or other in-patient setting. Such system is also adaptable to any language or units of measure.

It is another feature of the invention to provide such a monitoring system that displays the measured concentration in large, easy-to-read numerals that can be seen from across the room, or even from outside of the room (e.g., just by looking into the room where the patient is situated).

It is an additional feature of the invention to provide such a monitoring system that has setable limits above or below which the measured concentration, or the rate of change (trend) of the concentration, may not go without flashing and/or sounding an alarm.

It is a further feature of the invention to provide a glucose or other sensor that is designed to be implanted in the patient, e.g., into the venous system, the peritoneal system, or exposed to other tissue or fluids of the patient, to continuously monitor the presence of a specified substance, e.g., the glucose concentration, and to provide a measurement thereof without having to withdraw a blood or tissue sample (except for an occasional calibration check). Such sensor advantageously provides electrical signals (an electrical current) from which the concentration can be derived.

It is another feature of the invention, in accordance with one embodiment thereof, to provide a monitoring system that couples an implanted or external sensor, e.g., a sensor placed in the venous or peritoneal system of a patient, through a "contactless" connector and two- or three-conductor cable with a monitor. Advantageously, the contactless connector may be purposefully or inadvertently disconnected without harming the patient or the sensor, and without disrupting operation of the sensor (thereby preventing the need for restabilization or recalibration).

It is yet an additional feature of the invention to provide a monitoring system that monitors the blood or other tissue/fluids for the presence of certain substances, and that utilizes the measurements from a plurality of venous, interperitoneal, or other implanted sensors, in order to confirm the correctness of a given determination or measurement. Such system requires, e.g., that the measurements from two or three separate sensors be within certain prescribed limits of each other before a measurement is considered accurate or reliable, or before identifying or confirming the presence and/or concentration of certain substances within the blood or other tissue.