However, for ease of description, we will refer to the apparatus in respect of the application of analgesics.

It is nowadays common to have patients, and particularly post-operative patients, but also patients with other conditions where there can be severe pain, control their own analgesic, but these systems have had significant limitations.

These systems are normally adjusted by the patient's doctor or nurse to provide a bolus dose which is fixed and because, generally, a patient's tolerance to a particular analgesic is not known in advance and may change during treatment, nor is a patient's threshhold of pain and the effect of side effects of the medication, it has been conventional for doctors to set the quantities of the bolus to be low so as to be safe with more sensitive of patients.

If one is considering a post-operative situation, the pain felt by a patient, if no analgesic is used, is normally in a curve with respect to time, where the maximum pain can occur in the early hours after the operation and, over a 24 hour period, the level drops substantially.

It is over the first few hours that steps have to be taken to control the patient's pain and it is during this time that normal controlled analgesia is least effective.

The object of the invention is to provide a new method of controlling the delivery of medications, specifically analgesia, to patients, and an apparatus to be used therewith to more closely match the time related pain wave of the patient with appropriately tailored bolus doses, variable lock at times and modified background infusion.

The invention, in its broadest aspect includes a method of controlling the delivery of a medication to a patient to alleviate a condition, including a control device and a pump, the control device enabling the patient to select a pre-determined quantity of medication from one of a possible number of quantities, the selection, initiating the operation of the pump which controls the delivery of the said quantity of medication characterized in that the patient can, over a period, repeatedly operate the control device to maintain the medication at a variable and adaptive value, optimum to maintain control of the condition.

It is preferred that the quantity of medication selected by the patient may be monitored by carers and it is also preferred that the system is so arranged as to prevent the patient from exceeding a predetermined dosage in a specific period called the lockout period.

The invention also includes an apparatus to deliver medication to a patent including a pump and a control system which control system includes a control device which may be operated to deliver different quantities of medication and a control means which receives the signals received from the control device and effects operation of the pump, the control means being able to monitor the operation of the control means and the pump to provide an indication to carers as to the times of operation of the control device and the pump and the quantity of medication passed to the patient.

The invention also relates to a control means for use with an apparatus to deliver medication which includes a handset having a number of positions each of which corresponds to the degree of pain as seen by the patient. The handset also includes a confirmation device to commence the operation of a pump associated with the handset. Each position on the handset may be associated with a tone of a particular pitch to give an audible indication of the position selected.

The control means may also have provision to prevent the operation of the control device to deliver more than a pre-determined quantity of medication over a particular period and to provide to the carer an indication that there had been request (s) for delivery of medication which had not been satisfied.

It may also be preferred that the quantity of medication provided by any particular position of the handset may be modified in respect of time so that, as time passes, the quantity of medication will be such as to provide an apparently equal effect taking into account the position it is expected that the patient will be along the pain curve.

In order that the invention may be more readily understood and put into practice, we shall refer to the accompanying drawings, in which: Figure 1 shows a pain curve where a patient is using a conventional patent controlled analgesic apparatus; Figure 2 shows a similar pain curve for a patient using the apparatus of the invention; Figure 3 shows one form of patient operated control device for the apparatus; and Figure 4 shows a schematic flow chart of the components of the system of the invention, and their interaction.

As mentioned earlier, after, say, major surgery, a patient's pain curve can increase over the first two to three hours as the effects of the anaesthetic wear off and then tends to drop over the next 20 hours. Figure 1 and 2 have as their envelope a typical pain curve 10 which is plotted as pain intensity against time. As mentioned earlier the curve of a particular patient can depart substantially from this idealised curve, but will be of the same general shape.

It is difficult to predict what level of pain a patient may experience or tolerate (and thus the height of the curve). Even more difficult to determine is the patient's tolerance to the analgesic or the likelihood of side effects. Medical staff have had to make those decisions for patients with only rudimentary and subjective input from patients and therefore prescribe conservatively.

The arrangement previously used has been that on initiation of the system, a fixed bolus 11 of analgesia is passed into the patient, usually by a metering pump connected to a cannula or the like.

As mentioned earlier this bolus is usually controlled to set the quantities of the bolus to be low so as to be safe with more sensitive patients.

As can be seen in Figure 1, the bolus selected may leave a substantial pain gap, represented by the height of the curve envelope above the effect of the bolus.

The system of the invention uses a system whereby the patient can operate the introduction of analgesic based on pain level as experienced by the patient. As will be described hereinafter, the pain curve which is sought to be attained by the use of the present invention is illustrated in Figure 2.

In order to do this, the apparatus has a handset 20 which can have, in the particular example, some ten positions 21 which are graded from that for mild pain to severe pain.

Each position can be provided with an indicator light 22 and when a particular value is pressed, the appropriate indicator light for this value is illuminated and, preferably, a tone is sounded which is equivalent to the value selected.

The tones may be selected so that even a patient who is not looking at the handset 20 receives a good indication of the value selected.

That is, the patient has both a visible and audible indication of the quantity of analgesic to be introduced.

Provided the patient believes this is the order of relief required, he or she then presses a confirmation button 23 and the selected bolus dose is infused into the patient by means of a metering infusion pump.

We provide the system in association with a display or recording device, normally a computer which may have a display to indicates the quantity of analgesic used, that is equivalent to the degree of pain being felt by the patient and the time when the material was introduced or which may log this information for examination by medical staff.

If the patient has been effectively correct with his or her evaluation of the pain, then the analgesic shall control the pain for a period, the pain will later return, and subsequently the patient will again operate the handset.

If the patient has underestimated the pain, and received too little analgesic then this will not be fully effective, the pain will continue and the patient will further operate the handset at a greater level.

If successive value above a median value are selected, a constant background infusion of the analgesic is initiated which is then further varied according to activation of the handset.

The background infusion is only sustained according to handset activation. If there is insufficient activation of the handset over time, the rate of background infusion decays with time.

If the patient has overestimated the pain and introduced too much analgesic, this will effectively completely deaden the pain and this situation will remain for some time longer than would normally be expected and there will be a period during which the patient feels no pain and thus uses no analgesic, after which he or she will again wish to have more analgesic.

The system can be adjusted so that as the expected pain curve of the patient reduces, so the quantity of analgesic introduced on the selection of any position of the handset, will be reduced relative to that which would have been provided earlier in the process so that, in general terms, the quantity of analgesic is reduced.

If the patient has a low tolerance to pain, and attempts to use the device more than considered safe by the prescribing doctor, then the subsequent attempt to introduce more analgesia can be rejected and this can also be displayed to the carer.

The displays generated by the device can either be accessible adjacent to the patient or, more usually, at a nurses station or the like so that a degree of monitoring can be maintained without the carer having to visit the bedside of the patient unless they are otherwise called.

The system of the invention is such that the patient should be able to effectively control his or her pain over the period following the operation and the effect of the analgesia can work to provide protection to the current position to the pain curve.

Whilst we have described the present invention in respect of the delivery of analgesic in a post operative situation it will be understood that the invention has other applications.

Including remote control of programming home based Adaptive Patient Controlled Analgesic where device setting may be delivered through telecommunications equipment.

For example, ambulatory patients with chronic pain, such as may occur in patients with cancer may be given a degree of control over their maintenance regime whilst at the same time, being prevented from deliberately overdosing with their medication and patients who go through periods of severe pain, such as when dressings are changed or the like can learn to adapt the level of analgesia to provide good pain control during and after the procedure.

The system can also be used for the control of other medications, for example, control of sedation or anaesthesia or the introduction of blood pressure control medication where the patient's perceived feelings are taken into account in adoption of the control system.

All such variations, together with variations as to the handset or the like are within the scope of the present invention.