Patient controlled analgesia system

• US 5,069,668 A
• Filed: 07/12/1990
• Issued: 12/03/1991
• Est. Priority Date: 07/12/1990
• Status: Expired due to Fees

• Current Assignee: Scott A. Boydman
• Original Assignee: Scott A. Boydman
• Inventors: Boydman, Scott A.
• Primary Examiner(s): Grieb, William H.
• Application Number:
  US07/551,886
• Time in Patent Office: 509 Days
• Field of Search: 604/53, 604/121, 604/131, 604/208
• US Class Current: 604/121
• CPC Class Codes: A61M 2005/1405 Patient controlled analgesia [PCA]
• CPC Class Codes: A61M 5/172 electrical or electronic A61M5/16804, A61M5/16831 take precedence

Abstract

A "dynamically" self-adjusting patient-responsive system for administering liquid medicine such as analgesia to patients as by infusion, with the "demand" of each patient for supplemental doses of drug being taken into account both in providing "on demand" "interval dosing" to supplement a "current rate" of background delivery of the drug to the patient, and in modifying the "current rate" of background delivery of the drug to more correctly correspond to the current needs of a particular patient. While "range" parameters (i.e., "limits" that define acceptable ranges of variance for various characteristics of a program of drug delivery that is intended to meet the very changeable current needs of a particular patient) are preset in accordance with the instructions of a physician, the hour-to-hour manner in which a drug is system-delivered to a particular patient principally is determined on a "dynamic" basis by the extent of the patient'"'"'s current "demand" for supplemental drug infusion. By requiring that a "target" level of patient "demand" be maintained in order for a current "dynamically determined" level of drug delivery to be maintained (e.g., a certain number of button presses by the patient per pre-set time interval must be kept up, otherwise the infusion rate will be diminished automatically), infusions are automatically reduced as a patient becomes sedated, as healing progresses, or as patient demand lessens for these and/or other reasons, whereby safety is enhanced and infusion is conformed to a minimum that is consistent with current needs of a patient, within physician-prescribed limits.

Claims

1. A method of administering liquid medicine such as analgesia to a patient as by infusion, comprising the steps of:

a) providing dispensing means having a reservoir for liquid medicine such as analgesia, a tube for delivering the liquid medicine to a patient as by infusion, and pre-settable dispensing means for controllably dispensing a flow of the liquid medicine from the reservoir into the tube, with the pre-settable dispensing means including control means for being operated to input control commands to the pre-settable dispensing means so as to regulate the dispensing of the liquid medicine from the reservoir into the tube, with the control means further including a patient demand control that is operable by a patient who is to be infused with the liquid medicine to register a need felt by the patient for the flow of medicine to continue to be dispensed, and with the control means also being operable to record the operations of the demand control by the patient so that decisions concerning the flow of dispensed liquid medicine can be made based, at least in part, on the record of felt need that has been registered by the patient as by operating the demand control;

b) dispensing liquid medicine from the reservoir through the tube for infusion delivery to the patient at an initial rate of flow, with the initial rate of flow residing within a predetermined range of acceptable flow rates that is bounded by an upper limit beyond which the dispensed flow rate is not to be permitted to rise, and by a lower limit beyond which the dispensed flow rate is not to be permitted to fall;

c) determining a predetermined target number of operations of the demand control per unit of measured time that is to be utilized to maintain an existing rate of flow of liquid medicine dispensed through the tube, and maintaining the then existing rate of flow of liquid medicine being delivered as by infusion to the patient so long as the actual number of operations of the demand control per unit of measured time equals the predetermined target number;

d) determining a first increment in rate of flow of dispensed medicine by which the existing flow rate of dispensed liquid medicine is to be increased in the event that the actual number of operations of the demand control per unit of measured time exceeds the target number by a first predetermined value, and, increasing the rate of flow of dispensed medicine by said first increment of flow rate in response to determining that the actual number of operations of the demand control per unit of measured time exceeds the target number by at least said first predetermined value;

e) determining a second increment in rate of flow of dispensed medicine by which the existing flow rate of dispensed liquid medicine is to be decreased in the event that the actual number of operations of the demand control per unit of measured time falls short of the target number by a second predetermined value, and, decreasing the rate of flow of dispensed medicine by said second increment of flow rate in response to determining that the actual number of operations of the demand control per unit of measured time falls short of the target number by at least said second predetermined value; and

,

f) continuing to dispense liquid medicine to the patient for infusion as by periodically adjusting the existing flow rate of dispensed medicine if variances between the actual number of operations of the demand control per unit of measured time exceeds or falls short of the target number by said first and second values, respectively, but with increases and decreases in said flow rate of dispensed medicine being curtailed as may be necessary to maintain the existing flow rate at all times within a predetermined range of safe values for flow rates to be used in dispensing medicine to the patient;

g) whereby, if the actual number of operations of the demand control per unit of measured time falls off due to sedation or diminished need of the patient, the flow rate at which medicine is dispensed to the patient by infusion likewise will diminish to insure safety and to conform the flow rate of medicine delivery to the minimal actual need of the client, but is maintained within said range of safe values for flow rates.

2. The method of claim 1 wherein said first predetermined value equals the number "one," whereby, if the actual number of operations of the demand control per unit of measured time exceeds the target number by even so much as the number "one," the rate of flow of dispensed medicine will be increased by said first increment of flow rate.

3. The method of claim 1 wherein said second predetermined value equals the number "one," whereby, if the actual number of operations of the demand control per unit of measured time falls short of the target number by even so much as the number "one," the rate of flow of dispensed medicine will be decreased by said second increment of flow rate.

4. The method of claim 1 wherein said first predetermined value equals a number greater than the number "one," whereby, if the actual number of operations of the demand control per unit of measured time exceeds the target number by said first predetermined value, the step of dispensing liquid medicine will not be increased until after the demand control has been operated a sufficient number of times to exceed the target number by said first predetermined value, thus the "responsiveness" to increased operations of the demand control as regards increasing the rate of flow of dispensed medicine will be determined and characterized by the selection of said first predetermined value.

5. The method of claim 1 wherein said second predetermined value equals a number greater than the number "one," whereby, if the actual number of operations of the demand control per unit of measured time falls short of the target number by said second predetermined value, the step of dispensing liquid medicine will not be decreased until after the demand control has fallen off to a sufficiently low number of operations per unit of measured time to fall short of the target number by said second predetermined value, thus the "responsiveness" to diminished operation of the demand control as regards decreasing the rate of flow of dispensed medicine will be determined and characterized by the selection of said second predetermined value.

6. The method of claim 1 wherein said first predetermined value and said second predetermined value are set to different numbers so that a) a "first level of responsiveness" to increased operations of the demand control as regards increasing the rate of flow of dispensed medicine will be determined and characterized by the selection of said first predetermined value, b) a "second level of responsiveness" to diminished operation of the demand control as regards decreasing the rate of flow of dispensed medicine will be determined and characterized by the selection of said second predetermined value, and c) said first level of responsiveness will differ from said second level of responsiveness.

7. The method of claim 6 wherein said first predetermined value is set to a number that is less than the number to which the second predetermined value is set, whereby the first level of responsiveness to increased operations of the demand control will cause an increase in the rate at which medicine is dispensed to a patient more readily than the second level of responsiveness to diminished operations of the demand control will cause a decrease in the rate at which medicine is dispensed to the patient.

8. The method of claim 1 for administering liquid medicine such as analgesia to a patient as by infusion, additionally comprising the steps of adding a predetermined dose of medicine to the quantity of liquid that is being dispensed for patient infusion, with said adding of a predetermined dose being done in response to operations of the demand control per unit of measured time when the number of operations of the demand control unit per unit of measured time exceeds said target number by a third predetermined value, but only if a predetermined lock-out interval of time has passed since the most recent earlier added predetermined dose was added to the quantity of liquid medicine that was dispensed, and only if the dispensing of an added dose will not take the amount of dispensed medicine above a safe predetermined limit for a given interval of time.

9. The method of claim 8 wherein the third predetermined value equals the number "one," whereby, if the actual number of operations of the demand control per unit of measured time exceeds the target number by even so much as the number "one," the rate of flow of dispensed medicine will be increased as by adding thereto said added predetermined dose, but only if a predetermined lock-out interval of time has passed since the most recent earlier added predetermined dose was added to the quantity of liquid medicine that was dispensed, and only if the dispensing of an added dose will not take the amount of dispensed medicine above a safe predetermined limit for a given interval of time.

10. The method of claim 8 wherein the third predetermined value equals a number greater than the number "one," and responsivity as by dispensing added predetermined doses of medicine in response to increased operations of the demand control per unit time in excess of the target number is determined, at least in part, by the number to which the third predetermined value is preset, with such responsivity effectively being diminished as by increasing the magnitude of the third predetermined value.

11. A method of administering liquid medicine such as analgesia to a patient through a tube, comprising the steps of:

a) dispensing liquid medicine at an initial rate of flow through a tube to a patient, with the rate of flow being held substantially constant for at least a predetermined interval of time, and with the rate of flow being selected to reside within a range of flow rates that is bounded at its upper and lower ends by maximum and minimum rates of flow that are predetermined as defining safe limits for said patient;

b) monitoring signals from an input device that is provided to the patient to enable the patient to periodically enter discrete requests for medicine;

c) adjusting the rate of flow of liquid medicine that is being dispensed through the tube, with the adjustment being made on a step-by-step basis in response to whether the number of monitored signals from the input device is less than, equal to, or greater than a predetermined target value during a measured unit of time, with the rate of flow being incrementally diminished at predetermined increments of flow rate so long as each successive number of monitored signals during each successive unit of time continues to remain lower than said target value, with the rate of flow being incrementally increased at predetermined increments of flow rate so long as each successive number of monitored signals during each successive unit of time continues to remain higher than said target value, but with no adjustment of flow rate being made so long as each successive number of monitored signals during each successive unit of time continues to equal said target value; and

,

d) maintaining a continuous flow rate of medicine being dispensed to the patient through the tube in accordance with steps a), b) and c) above, but assuring that the rate of flow does not exceed said maximum rate of flow, or fall below said minimum rate of flow, with a portion of said step of maintaining a continuous flow including the step of curtailing any adjustments that are implemented as the result of step c) to assure that the flow rate is maintained within said predetermined range of flow rates that are safe for said patient.

12. The method of claim 11 for dispensing liquid medicine to a patient through a tube, additionally comprising the step of adding a predetermined dose of medicine to the quantity of liquid that is being dispensed through the tube to the patient, with said adding of a predetermined dose being effected in response to monitored signals from the input device that exceed a predetermined value that is at least as large in magnitude as said target value, but only if a predetermined lock-out interval of time has passed since the most recent earlier added predetermined dose was added to the quantity of liquid medicine that is being dispensed to the patient, and only if the dispensing of the predetermined dose will not exceed said maximum rate of flow that defines the upper boundary said predetermined range of flow rates.

13. In a method of administering liquid analgesia to a patient as by intravenous infusion wherein a dispensing means is provided that is of the type having a reservoir for liquid analgesia, a tube for delivering the liquid analgesia to a patient as by intravenous infusion, and pre-settable control means for controllably dispensing a flow of the liquid analgesia from the reservoir into the tube, with the pre-settable control means being operable to receive, store and execute at instructed times an inputted series of commands so as to regulate the dispensing of the liquid analgesia from the reservoir into the tube, with the control means further including a patient demand control that is operable by a patient who is to be infused with the liquid analgesia to register a need felt by the patient for the flow of analgesia to continue to be dispensed, and with the control means also being operable to record the operations of the demand control by the patient so that decisions concerning the flow of dispensed liquid analgesia can be made based, at least in part, on the felt need that has been registered by the patient, wherein the improvement comprises the step of operating the dispensing means to carry out the following steps, comprising:

a) dispensing liquid analgesia from the reservoir of the dispensing means through the tube of the dispensing means for intravenous infusion delivery to the patient at an initial rate of flow, with the initial rate of flow residing within a predetermined range of acceptable flow rates that is bounded by an upper limit beyond which the dispensed flow rate is not to be permitted to rise, and a lower limit beyond which the dispensed flow rate is not to be permitted to fall;

b) determining a predetermined target number of operations of the demand control per unit of measured time that is to be utilized by the dispensing means to maintain an existing rate of flow of liquid analgesia dispensed through the tube, and maintaining the then existing rate of flow of liquid analgesia that is being delivered as by intravenous infusion to the patient so long as the actual number of operations of the demand control per unit of measured time equals the predetermined target number;

c) determining a first increment in rate of flow of dispensed analgesia by which the existing flow rate of dispensed liquid analgesia is to be increased in the event that the actual number of operations of the demand control per unit of measured time exceeds the target number by a first predetermined value, and, increasing the rate of flow of dispensed analgesia by said first increment of flow rate in response to determining that the actual number of operations of the demand control per unit of measured time exceeds the target number by at least said first predetermined value;

d) determining a second increment in rate of flow of dispensed analgesia by which the existing flow rate of dispensed liquid analgesia is to be decreased in the event that the actual number of operations of the demand control per unit of measured time falls short of the target number by a second predetermined value, and, decreasing the rate of flow of dispensed analgesia by said second increment of flow rate in response to determining that the actual number of operations of the demand control per unit of measured time falls short of the target number by at least said second predetermined value; and

,

e) continuing to dispense liquid analgesia to the patient for infusion as by periodically adjusting the existing flow rate of dispensed analgesia if variances between the actual number of operations of the demand control per unit of measured time exceeds or falls short of the target number by said first and second values, respectively, but with increases and decreases in said flow rate of dispensed analgesia being curtailed as may be necessary to maintain the existing flow rate at all times within a predetermined range of safe values for flow rates to be used in dispensing analgesia to the patient;

f) whereby, if the actual number of operations of the demand control per unit of measured time falls off due to sedation or diminished need of the patient, the flow rate at which analgesia is dispensed to the patient by infusion likewise will diminish to insure safety and to conform the flow rate of analgesia delivery to the minimal actual need of the client, but is maintained within said range of safe values for flow rates.

14. The method of claim 13 wherein said first predetermined value equals the number "one," whereby, if the actual number of operations of the demand control per unit of measured time exceeds the target number by even so much as the number "one," the rate of flow of dispensed medicine will be increased by said first increment of flow rate.

15. The method of claim 13 wherein said second predetermined value equals the number "one," whereby, if the actual number of operations of the demand control per unit of measured time falls short of the target number by even so much as the number "one," the rate of flow of dispensed medicine will be decreased by said second increment of flow rate.

16. The method of claim 13 wherein said first predetermined value equals a number greater than the number "one," whereby, if the actual number of operations of the demand control per unit of measured time exceeds the target number by said first predetermined value, the step of dispensing liquid medicine will not be increased until after the demand control has been operated a sufficient number of times to exceed the target number by said first predetermined value, thus the "responsiveness" to increased operations of the demand control as regards increasing the rate of flow of dispensed medicine will be determined and characterized by the selection of said first predetermined value.

17. The method of claim 13 wherein said second predetermined value equals a number greater than the number "one," whereby, if the actual number of operations of the demand control per unit of measured time falls short of the target number by said second predetermined value, the step of dispensing liquid medicine will not be decreased until after the demand control has fallen off to a sufficiently low number of operations per unit of measured time to fall short of the target number by said second predetermined value, thus the "responsiveness" to diminished operation of the demand control as regards decreasing the rate of flow of dispensed medicine will be determined and characterized by the selection of said second predetermined value.

18. The method of claim 13 wherein said first predetermined value and said second predetermined value are set to different numbers so that a) a "first level of responsiveness" to increased operations of the demand control as regards increasing the rate of flow of dispensed medicine will be determined and characterized by the selection of said first predetermined value, b) a "second level of responsiveness" to diminished operation of the demand control as regards decreasing the rate of flow of dispensed medicine will be determined and characterized by the selection of said second predetermined value, and c) said first level of responsiveness will differ from said second level of responsiveness.

19. The method of claim 18 wherein said first predetermined value is set to a number that is less than the number to which the second predetermined value is set, whereby the first level of responsiveness to increased operations of the demand control will cause an increase in the rate at which medicine is dispensed to a patient more readily than the second level of responsiveness to diminished operations of the demand control will cause a decrease in the rate at which medicine is dispensed to the patient.

20. The method of claim 13 for administering liquid analgesia to a patient as by intravenous infusion, additionally comprising the step of adding a predetermined dose of analgesia to the quantity of liquid analgesia that is being dispensed for patient infusion, with said adding of a predetermined dose being done in response to operations of the demand control per unit of measured time when the number of operations of the demand control unit per unit of measured time exceeds said target number by a third predetermined value, but only if a predetermined lock-out interval of time has passed since the most recent earlier added predetermined dose was added to the quantity of liquid analgesia that was dispensed, and only if the dispensing of an added dose will not take the amount of dispensed analgesia above a safe predetermined limit for a given interval of time.

21. The method of claim 20 wherein the third predetermined value equals the number "one," whereby, if the actual number of operations of the demand control per unit of measured time exceeds the target number by even so much as the number "one," the rate of flow of dispensed medicine will be increased as by adding thereto said added predetermined dose, but only if a predetermined lock-out interval of time has passed since the most recent earlier added predetermined dose was added to the quantity of liquid medicine that was dispensed, and only if the dispensing of an added dose will not take the amount of dispensed medicine above a safe predetermined limit for a given interval of time.

22. The method of claim 20 wherein the third predetermined value equals a number greater than the number "one," and responsivity as by dispensing added predetermined doses of medicine in response to increased operations of the demand control per unit time in excess of the target number is determined, at least in part, by the number to which the third predetermined value is preset, with such responsivity effectively being diminished as by increasing the magnitude of the third predetermined value.

23. A method for dispensing liquid medicine through a tube to a patient, a) wherein the medicine is of a type such as analgesia that is given to the patient for "relief" of an affliction, b) wherein the adequacy of the "relief" that is provided to the patient tends to increase as, within a safe range of dosages of medicine, the rate at which medicine is dispensed to the patient increases, and tends to decrease as the rate at which medicine is dispensed decreases, c) wherein the patient unto whom the "medicine is dispensed is provides "signals" as to the adequacy of the relief that he experiences as the result of the rate at which medicine is dispensed to the patient, and d) wherein the method of dispensing medicine comprises the steps of:

a) providing the patient with a patient operable signaling device that the patient is to operate during each of a series of consecutive intervals of time that are of equal length, wherein the signals that are provided by the patient as the result of the operation of the signaling device during each of the intervals are counted an are interpreted such that;

i) if the counted number of signals during a particular time interval is equal to a "target" number, the rate at which medicine is being dispensed to the patient is deemed to be adequate;

ii) if the counted number of signals during a particular time interval is greater than said "target" number, the rate at which medicine is being dispensed to the patient is deemed to be inadequate; and

,

iii) if the counted number of signals during a particular time interval is less than said "target" number, the rate at which medicine is being dispensed to the patient is deemed to be excessive;

b) determining a safe range of rates for dispensing medicine to the patient that is deemed to be desirable for use with the particular patient, and, initiating a continuous-flow dispensing rate of medicine to the patient that is well within said safe range of rates;

c) utilizing the counted signal information that is provided by the patient'"'"'s operation of the signalling device to determine not only how the continuous-flow dispensing of the medicine to the patient is to be adjusted within said safe range of rates, but also to determine when a supplemental interval dose of medicine of a predetermined magnitude is to be dispensed through the tube to the patient, wherein;

i) if the counted number of signals within a particular time interval is equal to said "target" number, A) the rate at which medicine is being dispensed to the patient is maintained, and B) the rate at which medicine is being dispensed to the patient is not supplemented by any supplemental interval doses--whereby, the dispensing of medicine through the tube to the patient is held at a rate that the patient has signalled is adequate;

ii) if the counted number of signals within a particular time interval is greater by a first predetermined value than said "target" number, A) the rate at which medicine is being dispensed to the patient is increased as by a predetermined incremental amount except that, if the upper end value of the safe range of rates is reached, the upper end value is not exceeded, and B) the rate at which medicine is being dispensed to the patient briefly is supplemented as by dispensing a supplemental interval dose of a predetermined quantity of medicine through the tube to the patient--whereby the dispensing of medicine through the tube to the patient is increased to a rate of flow that is more in conformance with what the patient has signalled that he deems is needed; and

,

iii) if the counted number of signals within a particular time interval is less by a second predetermined value than said "target" number, A) the rate at which medicine is being dispensed to the patient is decreased as by a predetermined incremental amount except that, if the lower end value of the safe range of rates is reached, the lower end value is not exceeded, and B) the rate at which medicine is being dispensed to the patient briefly is not supplemented as by dispensing a supplemental interval dose of a predetermined quantity of medicine through the tube to the patient--whereby the dispensing of medicine through the tube to the patient is decreased to a rate of flow that is more in conformance with what the patient has signalled that he deems is needed.

24. The method of claim 23 wherein the first predetermined value and the second predetermined value are set so as to suitably govern the degree of responsiveness to which changes are made in the rate at which medicine is dispensed to the patient as variations in counted signals per interval of time from the target number are encountered during the dispensing of medicine to the patient.

25. The method of claim 24 wherein the first and second predetermined values are set to provide different degrees of responsiveness to govern increases as opposed to decreases in the rates at which medicine is dispensed to the patient.