WO2003026727A1

WO2003026727A1 - sETHOD AND APPARATUS FOR DELIVERY OF MEDICATION

Info

Publication number: WO2003026727A1
Application number: PCT/NZ2002/000193
Authority: WO
Inventors: Geoffrey Mark Shaw
Original assignee: Lifevent Limited
Priority date: 2001-09-28
Filing date: 2002-09-27
Publication date: 2003-04-03

Abstract

A method for the delivery of medication which involves giving the patient an initial drug dose, supervising the patient to record the patient's reaction to the dose; noting the amount of drug delivered to the patient over a pre-determined review period and at the end of each pre-determined review period, averaging the amount of drug delivered per review period over an averaging period which typically is longer than the review period; adjusting the amount of drug delivered to the patient for the next review period by a pre-determined faction of the total average amount of the drug; the apparatus also relates to apparatus for controlling a drug infusion pump in accordance with the method.

Description

TITLE: METHOD AND APPARATUS FOR DELIVERY OF MEDICATION

TECHNICAL FIELD

The present invention relates to a method and apparatus for the delivery of medication. The method and apparatus of the present invention has been developed for effective sedation delivery, and will be described with particular reference to sedation. However, it will be appreciated that the identical method/apparatus also may be used for delivering other categories of medication which have a measurable effect on the patient.

BACKGROUND ART

Patients may be sedated for a number of reasons, but one of the most common reasons for sedation is to keep a critically ill patient relatively immobile and free of pain. It is to the advantage of both the hospital and the patient to keep the level of sedation to the minimum needed for the patient to be calm and co-operative (if awake) or asleep, not in pain, and not agitated in any way. If the level of sedation is increased beyond that minimum level, expensive drugs are wasted and the unnecessarily heavy sedation is likely to delay the patient's recovery.

At present, patients who require continuous sedation (such as the critically ill) receive one or a mixture of sedative/painkilling drugs from a standard infusion pump of known design which continuously dispenses the drug or mixture of drugs from a reservoir into an intravenous line connected to the patient. As used herein, the term "drug" includes both a single drug and mixtures of two or more drugs. The amount of the drug dispensed by the pump is preset by the nursing staff to a constant rate. It will be appreciated that if this constant rate is set too low, then the patient either may not be efficiently sedated, or may be sedated initially, only for the sedation to wear off as the normal processes of drug redistribution and metabolization by the patient cause the drug levels to fall; the patient may then become undesirably agitated. In contrast, if the constant rate is set too high, the patient will be over sedated, with the drawbacks set out above.

It is therefore an object of the present invention to provide a method and apparatus for optimizing the rate of continuous drug delivery to a patient.

The present invention provides a method for optimizing the rate of continuous drug delivery to a patient including the steps of:

a) delivering to the patient an initial drug dose established in accordance with known criteria;

b) inspecting the patient at predetermined intervals to observe and record one or more preselected criteria;

c) administering to the patient one or more additional medication boluses if required;

d) noting over each predetermined review period both the amount of drug delivered by continuous drug delivery plus the amount of drug delivered as additional medication boluses, to give a total amount of drug delivered for that review period;

e) at the end of each review period, establishing the average amount of drug delivered to the patient per time period equal to said review period, said average being calculated over a predetermined averaging period which is equal in length to, or longer than, said review period;

f) at the end of each said review period, adjusting the amount of drug to be delivered by continuous drug delivery over the next review period to be a predetermined fraction of said average amount of drug established in step (e).

The initial drug dose may be delivered as a single dose or bolus at the outset of the first predetermined review period or may be delivered continuously over said period.

The known criteria used for establishing the initial drug dose are determined by the drug to be administered and by the age and/or other physiological parameters of the patient. The medical condition of the patient also may be a factor. The size of each bolus delivered as an additional medication bolus is determined by the supervisory medical attendant.

Preferably, once medication is well established, (e.g. about four review periods have elapsed), the bolus size is a specified fraction of the amount of drug delivered as a continuous infusion during the corresponding review period.

Typically, a bolus amount would be 50% of the amount of drug delivered by continuous delivery in the corresponding review period. However, an upper limit for each bolus amount is set, for safety, to avoid an overdose; and a lower limit also is set, to ensure that an effective amount of drug is administered.

The length of the predetermined review period is selected to suit the half life of the drug being administered and the patient's requirements. For example, for a patient whose condition presents no unusual features and who requires analgesia/sedation with a mixture of morphine and Midazolam, both of which are relatively slow acting drugs, a suitable review period would be one hour. In contrast, if a patient were being treated with a very short acting anesthetic type drug such as Propofol, a suitable review period could be as short as ten minutes.

The averaging period may be the same length as the review period, but this is not desirable in general, since the selection of such a short averaging period does not sufficiently smooth out periodic fluctuations in the medication administered. For this reason, it is preferable that the averaging period is substantially longer than the review period:- typically, about four times as long. Thus, if the review period were one hour, the averaging period would be four hours.

Preferably, the amount of drug delivered as additional medication boluses over the review period does not include any drug boluses delivered to the patient which are required specifically to provide additional sedation for painful or disturbing processes which have to be carried out on the patient; such boluses are termed "procedural boluses".

The predetermined fraction which is used to adjust the amount of drug delivered by continuous drug delivery for each review period after the first may be experimentally determined or may be established from known drug characteristics.

The means for noting the amount of drug delivered in each review period both by continuous drug delivery plus as additional medication boluses, and the means for establishing the average amount of drug delivered at set out in step (e) above may be manual:- in this case, the medical attendant enters the necessary readings and observations on a chart, performs the necessary calculations and manually adjusts the infusion pump administering the drug. However, this is time-consuming and labour- intensive and it is preferred that the drug quantities are noted and the averages calculated electronically, preferably using an infusion pump controller as described hereinafter, which not only measures the drug quantities and calculates the averages but also controls the infusion pump so as to deliver the correct amount of drug to the patient.

The present invention further provides an infusion pump controller adapted to control an infusion pump of known type connectable to a drug reservoir; said controller including: a microprocessor capable of interfacing with a computer, calculating drug dosages, and of transmitting operating instructions to an infusion pump, said microprocessor providing a programmable memory capable of recording patient and drug data and the quantities of drug dispensed by the pump; and a screen for display of data.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, a preferred embodiment of the present invention, with specific reference to sedation, is described in detail with reference to the accompanying drawings, in which:-

Figure 1 is a flow chart illustrating the method of the present invention;

Figure 2 a-c inclusive is a flow chart illustrating the operation of the infusion pump controller and associated apparatus; and

Figure 3 is a diagrammatic sketch of the infusion pump controller connected to an infusion pump.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiment relates specifically to sedation of a critically ill patient by a mixture of analgesic and sedative drugs, typically a mixture of solutions of morphine at a concentration of 1 mg per ml and Midazolam at a concentration of 0.5 mg per ml.

The rate of administration of the drug mixture (hereinafter referred to as "the drug") is controlled by an infusion pump of known type which is arranged to supply the drug from a reservoir, (e.g. a syringe) to the patient through an intravenous line, in known manner. The infusion pump may be controlled manually or by an infusion pump controller in accordance with the present invention, as hereinafter described.

The infusion pump not only supplies the drug at a predetermined steady rate, but also has the facility for supplying an extra booster amount of the drug, termed a "bolus" as a one- off additional amount when instructed to do so. The amount of drug supplied as a bolus is preset at the same time as the initial infusion rate is calculated. The bolus size is linked to the amount of drug supplied as a continuous infusion as described above, and upper and lower bolus size limits also are set.

The start time of drug administration is noted on the patient's chart. The criteria for sedation and agitation shown on that chart are established clinical criteria, but the usage of these criteria is different in the present invention:- the established scale is a single scale ranging from extreme sedation to dangerous agitation; as used in the present invention, the scale is split into a sedation scale and an agitation scale, and sedation and agitation criteria are noted separately. It is believed that this separate assessment gives a much more accurate picture of the patient's condition.

The invention will be described initially with reference to the manual control system, which is shown in Figure 1. The initial drug dose and bolus amount are calculated by the supervising medical attendant, using known criteria e.g. the patient's age. Alternatively, the initial drug dose and bolus amount may be a "default" dose calculated by the controller from known physiological parameters. The initial drug dose is given as a single bolus, rather than as a continuous administration from the infusion pump. Thus, for the first hour, the infusion rate of the drug continuously supplied by the infusion pump is zero. However, at the discretion of the medical attendant in charge, the initial drug dose may be given as a continuous infusion from the infusion pump over the first hour.

The bolus amount is programmed into the infusion pump such that if the nurse or medical attendant considers that a bolus is required, they manually trigger the pump to supply a bolus of preset size. The patient's condition is observed continuously or at frequent intervals by a nurse. At each observation, the nurse notes the degree of sedation and allocates a figure between 0 and -3 according to the sedation scale, and a figure between 0 and +3 according to the agitation scale. These figures are entered on the patient's chart. If the patient is undesirably agitated, the nurse may use the infusion pump to administer a bolus in addition to the initial drug dose already administered. The total amount of the drug administered to the patient (i.e. the initial dose plus any boluses given) in that first review period (typically one hour) is noted on the chart. Any procedural boluses given (see below) are recorded separately on the chart.

At the end of the first review period, the total amount of drug given to the patient over that period (i.e. the initial dose plus any boluses given, but excluding any procedural boluses) is used to calculate a continuous infusion rate for the next review period, using the algorithm described in detail below. This rate is then administered for the next review period as a continuous infusion. At the end of this next review period, the total amount of the drug given to the patient over that period (i.e. the amount given by continuous infusion plus the amount of any boluses given, but excluding any procedural boluses) is used to calculate the new infusion rate for the subsequent review period, in the manner described below. This sequence is repeated at the end of each review period.

The object in the calculation of the continuous infusion rate of the drug is to reduce the amount of drug infused to the minimum which will provide adequate sedation for the patient. Thus, whenever the new continuous infusion rate is calculated, the new rate is always a fraction of the previous total amount of drug administered. The factor by which the rate is reduced varies depending upon the drug used, and might also vary depending upon the patient's condition. For the specific case discussed in this preferred embodiment, the factor is two-thirds i.e. the new continuous rate is two-thirds of the previous total amount averaged over a predetermined averaging period, as described below. However, the particular reduction factor selected is governed by the drug administered and by the patient's condition.

The effect of this periodic recalculation of the continuous infusion rate is to constantly review and readjust that rate. Thus, over sedation is avoided but the provision of administering additional drug in the form of boluses enables the patient to be maintained at the optimum level of sedation.

Although a review period of one hour has been quoted in the above example, it will be appreciated that this period may be varied to suit both the patient and the drug being administered:- for example, for a relatively slow acting drug and a patient in a comparatively stable condition, a four hourly period might be appropriate. In contrast, if a short term, fast acting drug is being administered, a period a short as ten minutes might be appropriate. Thus, the length of the review period is determined by the half life of the drug administered and by the patient's condition.

For the convenience of hospital administration, the start time for the review periods may be specified. In this case, if sedation is started at any time other than the beginning of one of the specified periods, then the above described calculation procedure does not start until the end of the first specified period.

The method of the present invention also provides for the administration of additional, procedural boluses which are required because some painful or disturbing procedure has to be carried out on the patient. These procedural boluses are not included in the calculation when the continuous infusion rate is calculated.

The nurse records the sedation/agitation observations manually on the chart and performs the necessary calculations for the continuous infusion rate simply from the figures shown on the chart. The nurse then programs the infusion pump appropriately. Although the manually controlled method described above has been found to work well, and to succeed in its objective of providing adequate sedation whilst avoiding over sedation, the method is labour-intensive and requires the nursing staff to carry out frequent calculations to established the correct infusion rates. It therefore is preferred to carry out the method of the present invention using an infusion pump controller to automatically carry out the necessary calculations and control the infusion pump accordingly. This method is carried out as set out in Figure 1 , but the particular features offered by the controller are described in detailed with reference to Figure 2 and 3.

In the method using the infusion pump controller, the initial infusion rate of the drug and the bolus amount either may be preset by criteria already entered on the controller (typically based on the patient's age) or, preferably, the initial infusion rate of the drug is zero, with the initial dose of the drug being given as a single initial bolus, and only the bolus amount is preset. As with the manual system, the patient is continuously or very frequently observed, and the nurse administers boluses (simply by pressing the appropriate button on the pump controller) as necessary. The amount of all boluses (other than procedural boluses as described above) is recorded by the controller and the end of the first hour period the total recorded drug delivery is used to calculate the new continuous infusion rate; the pump is adjusted accordingly. Procedural boluses are separately recorded by the controller.

For both manual and automatic methods, the continuous infusion rate for each review period after the first is calculated as follows:-

Once the first review period has been completed, a continuous infusion rate is calculated by taking a specified fraction of the average total recorded drug delivery for a predetermined averaging period which may be equal in length to, but preferably is longer than, the review period. This may be expressed as:- 2 1 " y„ + 1 = — x — ^ y_m + Xm

^•J " m=n—3

¹ V¹

.^■. y_n + ι = — y^{m J χ,n}

" m=n—3 where : n = number of hours that the algorithm has been run y = the background rate (ml/hour) x = the amount given as boluses (excluding procedural boluses) (ml) m = specific hour.

2/3 is the specified fraction

The averaging period is four hours and the review period is one hour.

For the first such calculation, since only one hour of sedation has been completed, the drug delivery for the preceding three hours is zero.

The table given below gives a sample calculation for the first five hours of sedation, with an initial dose of 10 ml.

Bolus (ml) infusion rate (ml) hour

10 0 0

0 10/6= 1.7 1

0 ( 10+1.7)/6=1.95 2

0 (10+1.7+1.95)/6=2.3 3

0 (10+1.7+1.95+2.3)/6 =2.66 4

0 (1.7+1.95+2.3+2.66)/6=1.44 5 The amount of the drug which can be administered by a bolus, and the number of boluses which can be given to the patient within a specified time, are limited by the controller in accordance with criteria programmed in to the controller. For example, the bolus size may be set at 50% of the background infusion rate. Both the pump and the controller are designed to be safe, i.e. programmed to limit the rate of administration of the drug, the total amount of drug administered in any one review period, and the total amount of the drug administered overall, with appropriate alarms.

Figure 2 illustrates the use of the infusion pump controller. The infusion pump controller 2 (Figure 3) incorporates a microprocessor which provides a programmable memory and also is able to control the operation of a known infusion pump and to record the quantities of drug dispensed by the infusion pump. The microprocessor is adapted to interface with a computer, to receive data from the computer. The controller also incorporates a screen 3 upon which data can be displayed.

It would of course be possible to construct an infusion pump controller which incorporated a computer and which also incorporated a infusion pump. However, electronic equipment is expensive and it is preferable for economic reasons to provide an infusion pump controller which can interface with the existing computers already available in a hospital and which also can control known types of infusion pumps such as the Graseby 3500 Syringe Pump, which is widely available and which is provided with a communications port and thus able to receive external commands from the controller without modification.

At the start of the procedure, the controller is connected to a computer and is initialized to erase all previously stored information from the previous patient. This ensures that the wrong data cannot be used. Next, the computer downloads into the microprocessor's memory basic patient and drug data:- the patient' s name, date of birth, age, allocated number, and medical attendant; the drug name, concentration, bolus volume, maximum infusion rate, maximum bolus volume and procedural bolus volume. The controller is then disconnected from the computer.

Alternatively, the controller 2 could be permanently linked to a remote computer by a wired or wireless link. The programmed controller is connected to a known type of infusion pump 4, (e.g. Graseby 3500) using the pump's communications port. The medical attendant prepares a syringe 5 containing the required drug to be administered, at the correct concentration, and inserts the loaded syringe into the infusion pump.

The medical attendant then checks on the patient's ID bracelet against the patient's ID number displayed on the controller's screen 3, as a precaution against incorrect drug administration.

To start the administration of the drug to the patient, the infusion pump is connected to the patient in known manner and the "continue" button 6 on the controller is pressed.

If the patient is observed to be agitated or in pain, the attendant can use the controller to give an additional medication bolus by pressing the "bolus" button 7 on the controller. As described above, for the first review period of the medication the continuous infusion rate of the drug is zero, and the initial dose of the drug is given as a single bolus at the start of the medication period. This initial dose is administered using the "bolus" button; any additional medication required is given in the same manner.

In the event that the medical attendant anticipates pain or discomfort for the patient (e.g. because of some procedure which is about to be performed on the patient), the attendant can give a procedural bolus by pressing the "procedural bolus" button 8 on the controller.

If a break in sedation is needed e.g. to change the syringe 5 on the infusion pump, then the attendant presses the "stop" button 9 on the controller once, to pause sedation. Sedation is continued by pressing the "continue" button 6.

At the end of each predetermined review period, the controller display screen 3 flashes to remind the attendant, and displays the total quantity of the drug delivered to the patient for that period:- the drug supplied by continuous infusion and the drug supplied as one or more boluses are treated together for calculation purposes, as described above; any drug supplied as a procedural bolus is omitted from the calculation of the average quantity of drug supplied over the averaging period. The medical attendant records the drug totals.

When the period of sedation ends, the attendant presses the "stop" button 9 three times; this stops the infusion pump 4. The data stored in the controller can now be downloaded to the computer for recordal.

All the data relating to the amount of drug administered and the times at which the drug was administered are stored on the controller and can be used in conjunction with the observed sedation/agitation readings to give a complete sedation profile. Profiles of this type are invaluable for research and audit purposes and also may form the basis for research into modeling the kinetics of sedation and other drug reactions in patients. Further, if access to the controller is by means of a recorded password or swipe card, the patterns of medication used by individual medical attendants can readily be established; this can be valuable in carrying out a medical audit.

Claims

1. A method for optimizing the rate of continuous drug delivery to a patient, including the steps of:

2. The method as claimed in claim one wherein said initial drug dose is administered to the patient as a single bolus at the start of medication.

3. The method as claimed in claim one wherein said initial drug dose is administered to the patient as a continuous drug delivery over the first review period.

4. The method as claimed in any one of the preceding claims further including the administration of one or more procedural boluses at the discretion of the medical attendants, the or each procedural bolus being excluded from the average drug calculation in step (e) .

5. The method as claimed in claim 4, wherein an upper limit is set for the total amount of drug which can be administered to a patient by any means in any one review period.

6. The method as claimed in any one of the preceding claims wherein the amount of drug which can be administered by each additional medication bolus during a review period is set as a predetermined fraction of the amount of drug delivered to the patient by continuous drug delivery during that review period.

7. The method as claimed in claim 6 wherein the amount of drug which can be administered by each additional medication bolus has preset upper and lower limits.

8. The method as claimed in any one of the preceding claims wherein said drug is a mixture of a sedative drug and an analgesic drug.

9. The method as claimed in claim 8 wherein said review period is one hour and said averaging period is four hours.

10. The method as claimed in claim 8 or claim 9 wherein said predetermined fraction is two-thirds.

11. An infusion pump controller adapted to control an infusion pump of known type connectable to a drug reservoir; said controller including: a microprocessor capable of interfacing with a computer, calculating drug dosages, and of transmitting operating instructions to an infusion pump, said microprocessor providing a programmable memory capable of recording patient and drug data and the quantities of drug dispensed by the pump; and a screen for display of data.

12. The infusion pump controller as claimed in claim 11 wherein said controller also includes manually operable controls for starting the infusion pump, stopping the infusion pump, pausing operation of the infusion pump, and causing the infusion pump to supply to the patient a bolus of drug of predetermined size.

13. The combination of an infusion pump controller as claimed in claim 11 or claim 12 and a computer permanently linked to said controller by a wired or wireless link.

14 The combination of an infusion pump controller as claimed in any one of claims 11 - 13 and an infusion pump.