WO2005078439A2

WO2005078439A2 - Wound meter

Info

Publication number: WO2005078439A2
Application number: PCT/GB2005/000442
Authority: WO
Inventors: Francis William Arnold; Wynne Weston-Davies
Original assignee: Francis William Arnold; Wynne Weston-Davies
Priority date: 2004-02-11
Filing date: 2005-02-09
Publication date: 2005-08-25
Also published as: GB0402929D0; WO2005078439A3

Abstract

A method and apparatus is provided, employing a wound meter, for assessing the progress of healing of a wound. A wound is washed with water (or any appropriate solvent), left moist for a predetermined time set by a timer (7) for analytes (in this case, lactate and glucose) to equilibriate with extracellular fluid. The wound meter also permits use of endogenous wound fluid in moist wounds. A dipstick is then applied to the extracellular fluid. The dipstick has active regions (1, 2 )each sensitive to just a respective one of the analytes. The dipstick is inserted into a sheath which individually exposes active regions. The sheath is inserted 11 into the wound meter and the concentrations of the analytes measured and calculated. The ratio between the concentrations of the analytes is calculated and displayed as a result. The dipstick is of known dimensions and the wound meter also comprises a colour camera so that a photograph of the wound can be taken with the dipstick adjacent the wound. The wound meter comprises a memory for storing patient data, all results, the coloured photograph and wound healing time algorithms, the memory being removable and/or down-loadable to a allow retention and/or provision to a central facility. Data can also be up-loaded to the memory. For accurate calculation after sampling and measurement, the wound meter also employs access to algorithms permitting output of predicted 'time to healing'.

Description

Wound Meter

The present invention relates to a method and apparatus for assessing medical progress. In particular, the invention relates to such a method and apparatus for use in assessing healing of wounds.

It is recognised in the medical and nursing arts that chronic wounds are common, often painful and distressing to patients, and that their management by conventional conservative means is often unsatisfactory and expensive. Such wounds most frequently arise through one or more of the following mechanisms, which can co-exist:

1) Venous insufficiency of the lower limb: venous ulcers

2) Loss of sensation of the affected part, due to trauma or consequences of diabetes: pressure sores and diabetic neuropathic ulcers

3) Lack of adequate arterial or capillary blood supply: ischaemic ulcers

4) Pressure and immobility: pressure sores

5) Metabolic abnormalities, including diabetes.

Current conventional conservative clinical management strategies for such chronic wounds vary according the underlying causes and are well established. For example: a) Venous ulcers are treated by a primary dressing, (the nature of which has not been shown at the date of submission to affect time to complete healing) , and by compression to improve venous haemodynamics (which has) . b) Insensate chronic wounds are conventionally treated by debridement and pressure relief. c) Ischaemic ulcers are treated by dressing alone or or in combination with open or minimally invasive revascularisation.

Conservative management carries significant recurring costs for dressing materials and pressure management (bandaging, special footwear, pressure relieving mattresses) , nursing time (whether in the community or in hospital) and transport. For example, it was estimated (in 1992) that the total cost of managing a venous ulcer in the outpatient setting was approximately £2000 per annum. A variety of alternatives to conservative management have become part of clinical practice including: a) Vein surgery, with or without skin grafting, for venous ulcers. b) Bioengineered growth factors for diabetic neuropathic ulcers c) Surgical tissue transfer to cover pressure sores. Other techniques are being developed and validated.

These alternatives involve specialist care, invasive procedures and significant expenditure in the short term, but may be justified in selected cases on grounds of rapid healing, resulting in reduced patient distress and savings of long term costs. For example, approximately 50% of unselected patients with venous ulcers are unhealed at 12 weeks and a similar proportion of diabetic neuropathic ulcers after 20 weeks of optimum conventional care.

The present invention seeks to provide means for accurate and swift assessment, for example, of healing in a wound, thereby allowing a medical practitioner immediate and more accurate information the better to allow perception of the healing state of the wound and selection of appropriate treatment.

In the assessing the "trajectory of healing" of a chronic wound, a number of factors are considered by individuals skilled in this art. These factors include: the adequacy of wound nutrition relative to the demands of healing and

- the appearance and size of the wound at the present time and over the previous weeks and months . However, in routine practice, these determinations are usually based on experience and qualitative judgements, rather than objective criteria, and there is considerable variation between predictions made by even by experts. There is therefore a need for improved methods to quantify these parameters and to provide them to practitioners in a convenient fashion to help them predict more precisely the outcome of conventional care in individual cases, in terms of rates of healing or time to wound closure. Such methods would facilitate timely referral from primary to specialist care and assist in treatment decisions. They would also assist in the evaluation of novel therapies . The present invention seeks to provide means for objective assessment, for example, of healing in a wound, thereby removing variability in a medical practitioner opinion by providing immediate and more accurate information the better to allow perception of the healing state of the wound.

Wound nutrition can be measured as follows.. Unlike normal skin and subcutaneous tissues, which use very little energy under normal circumstances, the granulation tissue of wounds consumes considerable energy for various purposes, including cell division, synthesis of macromolecules, removal of dead tissue, and killing of colonising or infecting bacteria. This requirement for energy is met through local production of adenosine triphosphate (ATP) from glucose and oxygen. When supply of both nutrients is high (aerobic metabolism) , the production of ATP is coupled with the oxidation of glucose to carbon dioxide and water. When perfusion is inadequate to meet demand, oxygen availability becomes the limiting factor. Under these circumstances (anaerobic metabolism) the oxidation of glucose is incomplete - the intermediate product, lactate is produced in large amounts and ATP in reduced quantities insufficient for rapid healing. Furthermore, bacteria, when present, compete with the body's own cells, further reducing oxygen available for production of ATP; their elimination makes further demands on the energy resources of wounds. Thus the ratio of glucose to lactate in wound fluid is indicative of the adequacy of supply (wound perfusion, nutrition and oxygenation) relative to demand. It has been found that bed rest, a treatment known to increase blood flow to venous ulcers and to accelerate their healing, increases the concentration of glucose and reduces that of lactate in wound exudates.

Glucose is conventionally measured in blood and urine using dipsticks which have a reactive region in which small of volumes of the fluid (<1- 50 microlitres) to be analysed cause either a change in the absorption or emission of light (photo-chemical reaction) or production of an electrical current (electrochemical) by reagents present in the reactive region. At a given time after the fluid is placed in contact with these reagents, the output (electrical or light absorbed or emitted) is proportional to the concentration of glucose present in the sample. When blood is used, methods are commonly employed for separation of cells from blood before contact is made between fluid (plasma) and the reagents. These methods have the disadvantage of requiring, however small, a sample to be obtained from the body of a patient by means of breaching the integrity of the patient's skin or wound surface. The present invention seeks offer the advantage of providing a means of obtaining samples from the patient' s body, the samples having properties which can be accurately measured, without requiring invasion of the patient's body or breaching of the patient's skin or the surface of a wound in any way.

Photochemical reactions can be read by eye. This method is used for qualitative testing of glucose in urine, but is insufficiently precise for self-management of diabetes. Accordingly, a photometer, consisting of a constant light source, a detector for the measurement of light reflected from the dipstick, and appropriate hardware and software suitable for processing and displaying the output as an absolute concentration of glucose are employed.

Alternatively, the reaction on the dipstick can be engineered to directly produce an electrical output or to emit light proportional to glucose concentration in the applied sample. Photochemical and electrochemical dipsticks and readers have also been developed for lactate (for use in sports training) and for other analytes. In the case of dipsticks for testing urine, multiple reactive areas sensitive to various analytes have been placed on a single dipstick, but meters and quantitative measurements are not commonly employed in routine clinical practice for urine samples. For ease of use with blood samples, meters, which are usually only calibrated to read a single type of dipstick are designed to be robust and readily portable. To be of general utility the employment of dipsticks to sample wound fluid must overcome a further, previously unsolved problem. Although the volumes of exudate required for measurement purposes is small, and this fluid is produced continuously, many chronic wounds are too dry to permit direct sampling within a practical time frame. The present invention seeks, also, to provide a means of obtaining and accurately measuring samples from dry wounds, without breaching the patents' skin or the surface of the wound in any way.

Wound size and colour are also features indicating the healing progress of a wound. The dimensions of chronic wounds over preceding weeks and months is an important predictor of subsequent healing. However, it is difficult for practitioners to remember previous appearances and relate these to the present situation, even when (as commonly does not occur) the patient is seen by the same practitioner on sequential visits. A permanent record and measurement therefrom of wound area (or indices of same) is therefore of value in determining whether current treatment is effective, and should be continued or altered. The present invention also seeks to solve this, problem by providing an accurate and rapid means of obtaining and recording the dimensions of a wound.

Similarly the colour of wounds (red, yellow, black) is indicative of the processes going on within them (eg necrosis and infection) . The extent of each colour/process is held by many practitioners to be of value in predicting outcomes and choosing treatment. There is therefore a utility to being able to record and analyse wound colour. The present invention also seeks to solve this problem by providing an accurate and rapid means of obtaining and recording the appearance and colour of a wound.

In hospitals and clinics, a patient may be attended by different practitioners on different occasions for treatment of the same wound. The particular practitioner may not have clear recollection of the state of a wound when last seen, perhaps by another practitioner. Records in patients' notes may require effort to be included and may not have sufficient detail to give a clear and immediate impression of the changes experienced by the wound. The present invention seeks to provide means whereby an easy, direct, immediate and complete retrievable record of the condition of a wound can be readily stored for later retrieval and display.

Although the present invention is disclosed hereafter with reference to assessing the condition of a wound, it is to be appreciated that the invention can equally be applied to assessment of other conditions or manifestations where samples can be obtained in the same way and the same measurement technique can be employed.

One aspect of the invention relates to methods and devices for sampling fluid produced by, or in contact with open wounds, for measuring the concentration of chemical entities present within such fluids, and for reporting these concentrations and ratios between them. Other desirable functions of the embodiment are also described.

The preferred embodiment of the invention features a device for measuring, displaying, recording and transmitting critical determinants of the rate at which chronic wounds will heal, and for predicting the probability of successful healing within an interval acceptable to patients and their care providers, so that the most appropriate and cost-effect treatments can be selected.

According to another aspect of the invention, there is provided a device (dipstick) which allows: safe and representative sampling of fluid exuded from, or in contact, with chronic wounds, biochemical reactions between specific constituents of the fluids and reagents present on the active area of the dipstick resulting in a colour change, electrical output, or other quantifiable reaction whose rate or extent is proportional to the concentration of those constituents; and scaling of wound size and colour for purposes of standardised photographic recording and subsequent quantitation.

Further, according to the present invention, there is provided a device (meter) capable of: - measuring, calculating, displaying, storing and transmitting data about the concentration of analytes in wound eluate and ratios between them; performing digital photography of wounds, and outputting them to a suitably programmed computer, or having internally the processing capacity to analyse wound area and colour, and changes with respect to previous determined areas of individual wounds .

Particular advantages of the present invention include: capacity to rapidly, conveniently, and safely produce data directly relevant to prediction of healing; utility in both the hospital and community (including the patient's home) by virtue of portability; output of ratios of analytes, allowing useful measurements to be made from "dry" wounds; ability to record scaled data regarding wound size and colour; and capacity to display and transmit data for integration with the rest of the patient's medical records and with that of other patients for purposes of audit and research.

In an exemplary preferred embodiment of the invention, chronic wounds, which are conventionally cleaned after dressing removal by gentle rinsing, often with sterile physiological saline solution, have excess fluid is removed after cleaning (by aspiration from cavity wounds and by gentle blotting from superficial wounds) . Residual moisture is permitted to equilibrate with extracellular fluid within the wound for a sufficient period (usually of the order of 3-5 minutes . ) Although the absolute concentrations of lactate and glucose in the surplus moisture will be less than that within the wound proper, the ratios between them in the two fluids will be essentially identical, because both are highly water soluble and readily diffusible small molecules. The ratio of concentrations between the lactate and glucose is then measured and the measured ratio provided as output. By expressing and providing readings as the ratio of these analytes, clinically useful results can be obtained from drier or dry .wounds .

One embodiment of the present invention will now be described, operating on the principle of absorption spectrophotometry, by way of example only, with reference to the accompanying illustrative drawings, in which: -

Figure 1 diagrammatically illustrates a device (dipstick) whose active regions undergo chemical reactions following contact with wound fluid resulting in a change in light absorption in proportion to the concentration of the relevant analytes (glucose and lactate) present in the fluid.,

Figure 2 diagrammatically illustrates a device (sheath) which serves to hold the dipstick, and

Figures 3 - 6 diagrammatically illustrate a device (meter) into which the dipstick and sheath are inserted for purposes of measuring, displaying, storing, manipulating and transmitting data regarding concentrations of these analytes.

The present embodiment will be considered in relation to the actions of a skilled clinical practitioner in assessing a chronic wound. Dressings are removed and the wound is cleansed if required with physiological saline solution. Residual moisture after cleansing, or that exuding from the unwashed wound, is allowed to equilibrate with extracellular fluid present within the wound for a pre-selected time (optimally less than 5 minutes.)

The active regions 1 and 2 of the dipstick are brought into contact with moisture on the wound surface. A labelled control button 7 is pressed to start the timer within the meter. The dipstick is inserted into the sheath, so that active regions 1 and 2 are aligned with the apertures 5 to permit the unimpeded passage of light to and from them. The sheath containing the dipstick is inserted into the snugly fitting insertion point 11 on the meter. The sheath serves to locate the dipstick in proper alignment, to prevent ingress of ambient light, to protect the interior of the meter from microbiological contamination, and to lock the sheath in position by means of the bayonet fitting 4. At a predetermined time (optimally 1 minute or less) after the timer has been started, a microprocessor activates light emitting diodes (LEDs) which expose the active regions of the stick (1 and 2) to light of pre-selected frequencies. This light is reflected onto the surfaces of photo-detectors, which output a digital electrical signal proportional to the difference between the amount of light emitted by the LEDs and the amount of light reflected by the active regions 1 and 2. This signal is stored in on-board memory and a concentration for each analyte calculated with reference to look-up tables also stored in memory. The concentrations of the analytes and the ratio between them are displayed on the liquid crystal display screen 6 and stored in on-board memory.

Following successful measurement, an alert is sounded via the speaker 9, to inform the practitioner that the sheath and dipstick can be removed. The stick can then be placed adjacent to the wound for use of the scale 3 for standardising photographs taken by the digital camera 8, controlled by means of control buttons 7.

The preferred embodiment of the present invention there is also provided with one or more power sources, for example a battery (within the battery housing 10) and a socket 12 for a mains transformer; a removable onboard memory 14 sufficient to hold data generated by operation of the meter; digital photographs and/or scaled area measurements of same, patient data relevant to the probable time to healing (age, sex, wound type) ; and algorithms for computing the probable time to healing. The memory provides facilities to upload stored data and to download data including algorithms via the input/output port 13.

The wound meter comprises on-board software (which can be downloaded and upgraded) to calculate "probability of healing within a fixed period" (conventionally, 3 months for venous ulcer, 5 months for diabetic neuropathic foot ulcers, but in principle over any predetermined interval), by a method incorporating the steps of: calculating the value of the ration between Lactate and Glucose; and employing a database comprising a look-up table, correlating the lactate to glucose ratio with healing times of wounds of the same class, to find the probability of healing.

The database is preferably held "onboard" the device, or, as an alternative, downloaded (and updated) from a dedicated central server, or, as another alternative, anonymised patient data sent to a central server for calculation through a data connection such as via the USB or any other communication ports provided.

The data base and the calculating algorithms in the wound meter (or central server) also provide that relevant categories of data can be input to the wound healing probability calculation process to improve the precision the prediction, such relevant data being, for example but not restricted to, such data as: patient age, wound area, change of wound area over a known previous interval, and any other predictive features.

The wound meter is operative to provide output either as ^• an indication of the ratio between lactate and glucose; or as a probability of healing at a defined time in the future (with or without confidence intervals) ; or both. As an option, when the wound meter is used for remote computation, anonymised data is downloaded to the server to permit refinement of the algorithms by which predictions are made.

Claims

1. A method for clinical assessment; said method comprising the steps of: obtaining a sample of comprising a plurality of soluble analytes from a patient; measuring the relative concentrations of at least two analytes in the sample; and employing the respective measured relative proportional concentrations as clinical indication.

2. A method according to claims 1, wherein said step of obtaining a sample comprises the steps of: providing a dipstick; providing, on the dipstick, a plurality of separate areas each sensitive to being changed by a single one of the plurality of analytes whose relative concentrations are to be measured; and exposing the dipstick to the soluble analytes from the patient.

3. A method, according to claim 2, wherein said step of obtaining a sample comprises the steps of: moistening the surface of a patient with solvent; waiting for the solvent to equilibriate with the soluble analytes with the analytes in underlying surface; and coating the equilibriated solvent onto the dipstick.

4. A method, according to claim 2 or claim 3, wherein said step of measuring the relative concentrations of at least two analytes in the sample comprises the steps of: measuring a changed physical property in each of the separate areas each sensitive to being changed by a single one of the plurality of analytes whose relative concentrations are to be measured; relating each measured change physical property to a particular concentration of the respective analyte whose concentration is to be measured; and calculating the relative proportions of the analytes whose relative concentrations are to be measured.

5. A method, according to claim 4, wherein the changed physical property comprises at least one of: optical reflectivity; colour; ultra-violet fluorescence; generated electrical potential; electrical conductivity; optical opacity; and optical transparency.

6. A method, according to any one of the preceding claims, including the steps of: providing a dipstick of predetermined known discernable dimensions; and taking and storing a colour photograph of the wound with the dipstick adjacent to the wound and within the photograph.

7. A method according to any one of the preceding claims, including the steps of recording the relative proportional concentrations of the respective analytes in a memory.

8. A method, according to claim 7 when dependent upon claim 6, including recording the colour photograph in the memory.

9. A method, according to claim 7 or claim 8, wherein said memory is at least one of: removable; and down-loadable to a larger data storage system.

10. A method, according to any one of the preceding claims, for use with wounds; wherein said at least two analytes are glucose and lactate; and wherein said solvent is water.

11. A method of clinical assessment comprising the steps of; moistening the surface of a patient with solvent; waiting for the solvent to equilibriate with soluble analytes with the analytes in underlying surface of the patient; obtaining a sample of equilibriated solvent; and measuring the relative proportional concentrations of at least two analytes.

12. A method, according to claim 11, wherein said step of obtaining a sample of equilibriated solvent comprises the steps of: providing a dipstick having a plurality of separate areas each sensitive to being changed by a single analyte; and exposing the dipstick to the equilibrated solvent.

13. A method, according to claim 11 or 12, wherein said step of measuring the relative proportional concentrations of two or more analytes comprises the steps of: measuring a changed physical property in each of the separate areas each sensitive to being changed by a single one of the plurality of analytes whose relative concentrations are to be measured; relating each measured changed physical property to a particular concentration of the respective analyte whose concentration is to be measured; and calculating the relative proportions of the analytes whose relative concentrations are to be measured.

14. A method, according to claim 13, wherein the changed physical property comprises at least one of: optical reflectivity; colour; ultra-violet fluorescence; generated electrical potential; electrical conductivity; optical opacity; and optical transparency.

15. A method, according to claim 12, or according to claim 13 or 14 when dependent upon claim 12, including the steps of: providing that the dipstick of predetermined discernable dimensions; and taking and storing a colour photograph of the wound with the dipstick within the photograph.

16. A method according to any one of claims 11 to 15, including the steps of recording the relative proportional concentrations of the respective analytes in a memory.

17. A method, according to claim 16 when dependent upon claim 15, including the step of recording the colour photograph in said memory.

18. A method, according to claim 16 or claim 17, wherein said memory is at least one of: removable; and down-loadable to a larger data storage system.

19. A method, according to any one of claims 13 to 20, for use ^" with wounds; wherein said at least two analytes are glucose and lactate; and wherein said solvent is water.

20. A dipstick, for gathering samples for assesment of the condition of a wound, characterised in that the dipstick is of predetermined dimensions, said dipstick being includable in a photograph taken of the wound, the dipstick providing an indication of the size of the wound.

21. A method for assessing the progress a wound, said method comprising the steps of: employing a dipstick of known dimensions for gathering samples for assessment of the condition of wound; and photographing the wound with the dipstick within the photograph adjacent to the wound to measure and record the dimensions of the wound.

22. A method, according to claim 21, wherein the photograph is a colour photograph for recording the appearance of the wound.

23. An apparatus for clinical assessment comprising: a sampling device: means for accepting insertion of said sampling device, said sampling device comprising a plurality of areas of separate areas each sensitive to being changed by a respective single specie of analyte from among a plurality of analytes whose relative concentrations are to be measured; means for measuring the extent of change in each of said plurality of areas; means for relating each measured physical change to a concentration of each respective analyte; means for calculating the relative proportions of the concentrations of the analytes; and means for providing the calculated relative proportions of the concentrations of the analytes as output.

24. An apparatus, according to claim 23, wherein said means for measuring the extent of change in each of said plurality of areas is comprised within a meter; wherein said sampling device is a dipstick; wherein said means for accepting insertion of said sampling device comprised a sheath for accepting and locating said dipstick within said sheath; wherein said meter comprises means to accept said sheath; wherein said sheath comprises means for locating said sheath within said meter; and wherein said sheath provides for separate exposure, within said meter, of each of said plurality of separate areas .

25. An apparatus, according to claim 23 or 24, said means for measuring the extent of change in each of said plurality of areas comprises at least one of: means to measure optical reflectivity; means to measure colour; means to measure ultra-violet fluorescence; means to measure generated electrical potential; means to measure electrical conductivity; means to measure optical opacity; and means to measure optical transparency.

26. An apparatus, according to claim 24, or according to claim 25 when dependent upon claim 24, for use in assessment of a wound, wherein: said dipstick is of known dimensions; and wherein said meter comprises a camera for taking and recording a photograph of wound with the dipstick, adjacent to the wound, also in the photograph, to record the dimensions of the wound.

27. An apparatus, according to claim 26, wherein said camera is a colour camera, for recording the appearance of the wound.

28. An apparatus, according to claim 24, or according to any one of claims 25 to 27 when dependent upon claim 24, wherein said meter comprises a memory for recording the relative proportional concentrations of the respective analytes in a memory.

29. An apparatus, according to claim 26 or 27, or according to claim 28 when dependent upon claim 26 or 27, wherein said memory is operative to store said photograph.

30. An apparatus, according to any one of claims 26 to 30, wherein said memory is at least one of: removable; and down-loadable to a larger data storage system.

31. A method, substantially as described and claimed in claims 1 to 10, with reference to the drawings.

32. A method, substantially as described and claimed in claims 11 to 19, with reference to the drawings.

33. An apparatus, substantially as described and claimed in claims 23 to 30, with reference to the drawings.