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Contents 1 Pressure Mapping Systems Clinical Useage Checklist and Guidelines 1.1 I. Background 1.2 II. Infection Control and mat care 1.3 III. Calibration 1.4 IV. Acquiring data 1.5 V. Interpretation of data 1.6 I. Operational definitions/glossary of terms 1.6.1 Definitions: 1.6.1.1 Pressure 1.6.1.2 Shear 1.6.2 Mat technologies: 1.6.2.1 Resistive 1.6.2.2 Capacitive 1.6.2.3 Pneumatic 1.6.2.4 Hydraulic 1.7 II. Infection Control and mat care 1.7.1 a. Mat storage and handling: 1.7.2 b. Mat cleansing: 1.8 III. Calibration 1.8.1 Calibration: 1.8.2 Equilibration: 1.8.3 Single/Multipoint Equilibration: 1.8.4 “In Situ” Calibration: 1.8.5 Calibration checks: 1.8.6 Clinical calibration check: 1.9 IV. Acquiring data 1.9.1 1) Mat Preparation 1.9.1.1 a) Do a basic system check 1.9.1.2 b) Infection Control 1.9.1.3 c) Select desired software 1.9.2 2) Measurement tools 1.9.2.1 a) Goniometer 1.9.2.2 b) Inclinometer 1.9.2.3 c) Tape measure 1.9.2.4 d) Calipers 1.9.2.5 e) Digital camera 1.9.3 3) File naming 1.9.4 4) Documentation 1.9.4.1 a) ID#/name 1.9.4.2 b) Date 1.9.4.3 c) Equipment set-up 1.9.4.3.1 i) Cushion model, age, w x d 1.9.4.3.2 ii) Backrest model 1.9.4.3.3 iii) Wheelchair model 1.9.4.3.4 iv) Seat to back angle 1.9.4.3.5 v) Seat tilt 1.9.4.4 d) Posture 1.9.4.4.1 i) Note postural 1.9.4.4.2 ii) Upper and lower extremity position 1.9.4.5 e) Determine risk 1.9.5 5) Frame labeling: 1.9.6 6) Photo documentation: 1.9.7 7) Mat set-up 1.9.7.1 a) Consistent Oreintation 1.9.7.2 b) Proper Placement 1.9.7.3 c) Do Not Fold 1.9.7.4 d) Smooth the mat 1.9.7.5 e) Avoid Damage 1.9.7.6 f) Check after transfer 1.9.8 8) Taking the data 1.9.8.1 a) Record Baseline 1.9.8.2 b) Label 1.9.8.3 c) Note Peak and Palpate 1.9.9 9) Recording the actual map 1.9.9.1 a) Time 1.9.9.1.1 i) Tissue and Cushion Creep 1.9.9.1.2 ii) Cushion Material 1.9.9.1.3 iii) Match Time to Creep time during calibration 1.9.9.1.4 iv) Use consistent 5 minute mime 1.9.9.1.5 v) Be Consistent 1.9.9.1.6 vi) Temperature considerations 1.9.10 10) Physical / Postural evaluation 1.9.10.1 a) Transfer 1.9.10.2 b) Asymmetries 1.9.10.3 c) Fixed or Flexible? 1.9.11 11) Skin Inspection 1.9.11.1 a) Assess 1.9.11.2 b) Find the Match 1.9.11.3 c) Note the wounds 1.9.12 12) Confirm or reject current cushion as contributory cause 1.9.12.1 a) Inspect the Cushion 1.9.12.2 b) Check the cushion setup 1.9.12.3 c) Change and redo 1.9.12.4 d) Adjust posture 1.9.12.5 e) Interview 1.9.13 13) Comparative assessment of alternate cushions 1.9.13.1 a) Sample cushions 1.9.13.2 b) Adjust 1.9.13.3 c) Be Consistent 1.9.13.4 d) Of weight 1.9.13.5 e) Find better 1.9.13.6 f) Compare 1.9.13.7 g) Use IPM to rule out options 1.9.13.8 h) Consider other influences 1.9.13.9 i) Check static and Dynamic 1.9.14 14) IPM to assess variable postion seating systems 1.9.14.1 a) Check effectiveness 1.9.14.2 b) Every client is unique 1.9.14.3 c) Label all frames 1.9.15 15) Additional considerations for cushion selection 1.9.15.1 a) Postural stability 1.9.15.2 b) Functional mobility – transfers 1.9.15.3 c) Weight of cushion 1.9.15.4 d) Heat / moisture 1.9.15.5 e) Perceived comfort 1.9.15.6 f) Complexity 1.9.15.7 g) Client’s ability 1.9.15.8 h) Education 1.9.15.9 i) Caregiver 1.9.15.10 j) Follow up 1.9.16 Client Education 1.9.17 Displays 1.9.17.1 1. Isobar View: 1.9.17.2 2. Center of Pressure (CoP): 1.9.17.3 3. 3D mesh: 1.9.17.4 4. Filtering: 1.9.17.5 5. Smoothing: 1.9.17.6 6. Gradient: 1.9.18 Error identification 1.9.18.1 1. Row or column error: 1.9.18.2 2. Artifact identification: 1.9.18.3 3. Usage error: 1.9.18.4 4. Flashing sensor: 1.9.18.5 5. Under or Over Reading: 1.9.18.6 6. Creep: 1.9.18.7 7. Hysteresis: 1.9.19 Video or digital pictures 1.9.20 Remote monitoring: 1.9.21 Databases: 1.9.22 Documentation: 1.10 V. Interpretation of data 1.10.1 Peak Pressure Index 1.10.2 Dispersion Index 1.10.3 Contact area 1.10.4 Gradient 1.10.5 Symmetry

Pressure Mapping Systems Clinical Useage

Checklist and Guidelines

Checklist:

Interface Pressure Measurement - Detailed Clinical Usage Guidelines

I. Background

Pressure Ulcers can have multiple contributory causes (shear, temperature, moisture, friction, incontinence, and systemic issues), yet pressure is the defining causative factor. Given its relative importance, seeing how the support surface pressures are being distributed is intuitively valuable for both the clinician and the user.

II. Infection Control and mat care

III. Calibration

IV. Acquiring data

V. Interpretation of data

I. Operational definitions/glossary of terms

Definitions:

Pressure

Pressure is force per unit area. It is the force distribution normal (perpendicular) to the surface. Pressure tends to compress the tissue. The units of pressure are pounds per square inch or Pascals (N/m2) or mmHg, etc. A pressure distribution (pressure map) is a visual representation of the normal forces between two surfaces. It gives a good picture of where the forces are high and how closely they change from high to low.

Shear

Shear (stress/deformation) result from applying forces to cause or tend to cause two contiguous internal parts of the body to deform in transverse planes (i.e. shear force causes shear strain/deformation). Parallel Shear stress is a distortion caused whenever there is sliding or the potential sliding between two surfaces Pinch Shear stress is a distortion whenever there is a pressure gradient. When forces of different magnitudes are applied to neighbouring tissue there is a tendency to move one plane more than another. IPM systems do not measure shear.

Mat technologies:

Resistive

Resistive Sensor Array Sensors are made from two conductors separated by a material that changes resistance when compressed. The electrical resistance is measured between the two conductors as force is applied to compress the material between the conductors. The measurement of a force applied to an area smaller than sensor tends to be measured if is it was applied over the whole sensor. The force range of the sensors is related to the properties of the resistive material.

Resistance changes from very high with no load to very low with high loads in a non linear way. Calibration is required to correlate the load to the output readings. A sensing mat is made up of rows and columns of conductors forming an array of sensors that are read individually through electronic switches. The information is sent to a computer for display.

Capacitive

Capacitive Sensor Array Sensors are made from two conductors separated by a compressible material. The electrical capacitance is measured between the two conductors as force is applied to compress the material between the conductors. The measurement of a force applied to an area smaller than the sensor tends to be measured as if is it was averaged over the whole sensor. The force range of the sensors is related to the properties of the compressible material.

Capacitance changes from very low with no load to very high with high loads in a non linear way. Calibration is required to correlate the load to the output readings. A sensing mat is made up of rows and columns of conductors forming an array of sensors that are read individually through electronic switches. The information is sent to a computer for display.

Pneumatic

Pneumatic Sensor

Sensors are a small bladder filled with air or other compressible fluid. Air pressure inside the bladder is measured by a gauge remote from the bladder. The measurement of a force applied to an area smaller than the sensor is measured as if is it was averaged over the whole sensor. Bladder pressure is further reduced by compression in the tube conducting the bladder to a remote gauge. Each sensor must re read individually.

Hydraulic

Hydraulic Sensor

Same as pneumatic except that the fluid is non compressible.

II. Infection Control and mat care

a. Mat storage and handling:

Store in a dry place or per the manufacturer’s suggestions. Care should be taken not to pull on or bend the wires and connections to the mat and electronics.

b. Mat cleansing:

Mat should be protected from contamination using an isolation bag however if the mat does get locally dirty it can typically be cleaned with a mild cleanser. Since all systems involve reading voltages and wetness can affect the readings, care should be taken not to overly wet the dirty area. Be sure to dry the area completely after cleaning using a hair blow drier on low (or no) heat. Re calibrate the mat after cleaning.

III. Calibration

Characterization is a general term applied to sensor response modeling. This process attempts to build a time dependant table to correct for sensor errors.

Calibration:

Calibration is a process wherein the sensing mat is subjected to known forces; the sensor responses are monitored and modeled. A record is kept of the responses (called a calibration file) and whenever the sensors output a similar response, the result is related to the previously known forces. In most cases this is done by placing the mat in a jig with an air filled bladder. The bladder is inflated and the pressure in the bladder is measured. It is assumed to be evenly pressurized over the mat.

Equilibration:

The response of the sensors is assumed and a known weight is applied to the mat. Some sensors experience the known load. The sum of those sensor values multiplied by the area of each sensor is set to be equal to the applied weight. Other sensor readings are then inferred.

Single/Multipoint Equilibration:

If a single data point at the maximum load is used during equilibration and a linear interpolation of data below the maximum is calculated, then it is called a one-point equilibration. If more than one point (generally a minimum of 5 steps are used), then it is called a multi point equilibration.

“In Situ” Calibration:

If the above calibration techniques can be accomplished while the sensing array is deformed approximately as it will be used, then the calibration is said to be “In Situ”. In seating, this would be achieved via having a person sit on the mat atop a cushion, versus placing the mat in a calibration jig. The latter loads the mat in a firm, flat, planar environment, attempting to do so uniformly; conversely, in situ calibration loads the mat via the contours of the buttock and cushion interface. In effect, this tells the system what the total force should add up to given a load profile for a particular cushion. In other words, this provides additional information to the calibration process regarding how many sensors are typically loaded in situ, i.e. on a cushion. Some systems will allow you to make sure that the sensors add up to a known applied weight. Since the errors of the current pressure mapping systems tend to be cumulative (all the same direction) the ability to ensure that the sensors add up to a known weight adds to the accuracy of the readings. When setting the weight, it is important to make sure that all the weight is captured. Make sure that all the weight is captured on the mat and that none is lost on arm rests, foot rests or the back rest.

Follow the manufacturer’s instructions and use the manufacturer’s calibration system.

Recalibrate the mat whenever the readings look suspicious, after excessive use or at the manufacturer’s recommended interval. Keep track of the uses of the mat and the date of the last calibration. You can load old calibration files to see the extent of change over the period.

Calibration checks:

The mat can be placed in the cal jig and the readings compared with the original calibration. However, there will always be a change of readings even if a mat is calibrated and immediately reinstalled in the cal jig and retested. This is due, in part, to the non-repeatability of the bladder in producing a perfectly even pressure distribution.

Clinical calibration check:

A good check for accuracy of a calibration is to take an image of a known person on a known cushion. If the pattern and values look the same as a reference image, then the mat is OK to use.

IV. Acquiring data

1) Mat Preparation

a) Do a basic system check

Place the IPM mat on a firm, flat surface, such as a plinth/mat table. The clinician sits briefly on the mat with feet lifted off the floor and arms across chest. With clinician’s known weight, one can compare force input to output. Check to make sure a proper buttock profile is represented (i.e. does it look like a buttock?). Check for defective rows/columns, irregular peaks or flashing values. If the display looks suspiscious, first check mat set-up, e.g. no wrinkles. If the set-up appears okay, consider the need for re-calibration.

b) Infection Control

Wash hands and wear gloves for infection control. Remove gloves when you stop touching the client, i.e. to use the laptop or digital camera. Encase the IPM mat in a thin protective bag (e.g. thin plastic) to ensure that infection control is maintained for patient safety. This also protects the IPM mat from urine, feces, wound drainage or other spills and is in compliance with Universal Precaution guidelines, especially if the client’s history is positive for infectious disease such as MRSA. Some mats may withstand topical medical grade cleansers, and thus cleansing could be done in lieu of the plastic bag. However, this must be done between each client. Some spray cleansers require the mat be set aside to air dry before the next use. Thus, there may not be adequate time between clients, in which case the plastic bag should be used. Note: Use of a plastic bag may affect the mat performance, e.g. it may promote hamocking, especially if the mat’s ability to conform into the cushion contour is hindered. As a rule of thumb, if your mat has a stretchy matrix, use a bag that is stretchy also.

c) Select desired software

Select the desired statistic features and be consistent for comparison.

2) Measurement tools

Gather additional tools needed for the seating assessment

a) Goniometer

b) Inclinometer

c) Tape measure

Metal is preferred over cloth. Cloth tape measures can be errantly bent around the body’s contour resulting in higher than actual linear measurement values.

d) Calipers

Calipers can be used in place of tape measure for many measurements

e) Digital camera

Use it to capture reference images. Store them with the file if possible.

3) File naming

Use a consistent file naming protocol for each client. Incorporate client ID or name abbreviation (observe privacy guidelines) together with the date. This allows efficient retrieval for comparison at follow-up assessments.

4) Documentation

Enter client information (use note or evaluation section in IPM software)

a) ID#/name

Observe privacy guidelines

b) Date

c) Equipment set-up

Establish a basseline.

i) Cushion model, age, w x d

ii) Backrest model

iii) Wheelchair model

Record specifics w x d

iv) Seat to back angle

v) Seat tilt

d) Posture

i) Note postural

Note deformities or asymmetries

ii) Upper and lower extremity position

Be consistent

e) Determine risk

Determine the risk level via standardized scale (e.g. Braden Scale) or use low, medium, high based on sensation, mobility, history of pressure ulcer and frequency of pressure relief.

5) Frame labeling:

Label every frame (or group of frames) that you want to use for documentation. Describe thoroughly, e.g. baseline, cushion type and size, changes in equipment set-up.

6) Photo documentation:

Use correlative photo documentation to reflect posture and seating set-up – before and after photos.

7) Mat set-up

a) Consistent Oreintation

Consistently orient the mat on the cushion, per client session. This avoids confusion during map interpretation.

b) Proper Placement

Place the mat on the cushion to assure the buttocks will be fully captured by the mat. This usually is accomplished by having the rear row of mat sensors behind the posterior edge of the cushion.

c) Do Not Fold

If the wheelchair is small, use caution regarding mat folds at the edges.

d) Smooth the mat

Make sure the mat is relaxing into the contour of the cushion to avoid hammocking. Use hands to smooth the mat into the contour as needed.

e) Avoid Damage

Avoid the use of transfer boards if there is risk of damaging the sensors – check with manufacturer.

f) Check after transfer

Make sure the mat is still in place after the transfer – squared on the cushion, without wrinkles. Re-adjust as needed. Note: use of a plastic isolation bag often contributes to the mat sliding out of place during the transfer.

8) Taking the data

a) Record Baseline

Record baseline data (how client rolled in) to capture usual posture and equipment set-up. Note: If the client sits on a transfer sling of incontinence pad, leave these in place for the base-line reading if possible. Additional layers such as these could be contributory to IP problems.

b) Label

Label the frame as baseline per #5.

c) Note Peak and Palpate

Note the peak pressures and palpate to verify matching of bony prominence to peak(s). Palpating can be done by placing the hand either under the mat or between the mat and body. The thinner and more pliable the mat, the easier the former method is. Side entries are generally easiest for palpation of the greater trochanters or ischial tuberosities. The client may need to lean (or be leaned) to the side slightly to position the hand. Once the bony prominence is located, the client resumes an upright position, sitting on the clinician’s hand. This must be done otherwise the prominence will not correlate with the original peak on the mat. Label the frame with the coordinate that represents the peak and matching bony prominence. Note: All peaks are not always caused by a bony prominence. Other causes could be a clothing seams, pocket, wallet, etc.

9) Recording the actual map

a) Time

Time to sit prior to recording the map:

i) Tissue and Cushion Creep

This takes into account the time to settle into the cushion (effect of tissue and cushion creep) and the creep of the sensor.

ii) Cushion Material

Settling time varies based on differences in tissue and cushion material – cushions composed of time-dependent materials take longer to settle into. Cushions which are air-filled or comprised of elastic foam have a short settling time (by ~one minute) in contrast to cushions with viscous materials – viscous fluid or viscoelastic foam which take longer (up to 5 minutes or more).

iii) Match Time to Creep time during calibration

For IPM systems which allow in-field versus factory only calibration, the creep correction time factor for the calibration should be set to match the outer margin of cushion creep for a given set of cushions typically assessed. Five minutes is recommended for this setting.

iv) Use consistent 5 minute mime

This five minute creep correction should match the time at which each map reading is taken. Thus the client sits on each cushion to be tested for five minutes of settling time at which point the actual recording is taken. The aim is to have at least one frame of data at this 5 minute time point. Either a single

frame or a series of frames can be taken. This will keep the effects of sensor and tissue creep consistent across the comparison of products.

v) Be Consistent

Be consistent per client session across cushions, unless client safety is compromised. For example, if a client’s skin is currently compromised and high peak pressures are immediately evident, clinical judgement would advise against having the client remain on this unsafe surface for the full five minutes. Client pain would be another obvious reason to abort the five minute settling time. The clinician must then be mindful that pressure values tend to rise over time to do sensor creep. Thus it will not be an apples-to-apples comparison between the cushions sat upon for 1 minute versus 5 minutes. Taking all data at the same time point (e.g. post 5 minutes) will keep the effects of sensor creep consistent across the comparison of products.

vi) Temperature considerations

Variations in temperature can affect certain cushion materials’ response to loading. For example, a viscoelastic foam cushion which has been stored in cold temperatures may initially be stiffer and take longer to settle into. For this reason it is best to have all cushions at room temperature before undergoing IPM assessment.

10) Physical / Postural evaluation

a) Transfer

Transfer the client to a mat table.

b) Asymmetries

Perform supine and sitting evaluations to determine asymmetries – confirm/compare initial findings noted with client in wheelchair.

c) Fixed or Flexible?

May use IPM in sitting on edge of mat table to precisely define weight bearing areas, check if asymmetries are fixed or flexible, determine location of postural supports (using hands) and amount of force needed to correct / reduce asymmetries. In this way, the clinician is capitalizing on the visual feedback utility of IPM to guide clinical decision making.

11) Skin Inspection

a) Assess

Recommend assessment versus verbal report as client is not always fully aware of extent of skin involvement.

b) Find the Match

Note at-risk /involved sites – match to IPM findings re: peak pressures.

c) Note the wounds

Note that wound dressings can affect pressure readings, often elevating values.

12) Confirm or reject current cushion as contributory cause

a) Inspect the Cushion

Inspect cushion for defects or excessive wear.

b) Check the cushion setup

If cushion is in good condition, first determine that problem is not merely a set-up issue with the cushion itself or with the wheelchair / seating configuration.

c) Change and redo

Make changes in cushion as needed/appropriate, then re-do IPM.

d) Adjust posture

Assess for other postural changes or seating adjustments needed before abandoning original cushion (need to rule it out).

e) Interview

Interview client – consider additional surfaces and out of the ordinary behaviors as contributing / causative factors.

13) Comparative assessment of alternate cushions

a) Sample cushions

Select a small sample of cushions (2-3) based on client needs (risk level, pressure distribution goal – envelopment vs off-loading, posture, balance, temperature, continence).

b) Adjust

Adjust postural supports as needed to accommodate differences in trial cushion(s).

c) Be Consistent

Be consistent with postural support across cushions (thighs supported, arms on armrests or lap, etc).

d) Of weight

Completely off-weight mat between readings. This re-sets the sensors to minimize the effects of sensor creep.

e) Find better

Goal is to beat the current cushion.

f) Compare

Perform relative comparisons. There is no magic pressure threshold beyond which pressure ulcer formation occurs. 32mmHg is not, repeat NOT, a valid threshold and should not be used.

g) Use IPM to rule out options

Use IPM primarily to rule out versus make definitive selection.

h) Consider other influences

IPM should not be sole deciding factor.

i) Check static and Dynamic

Use IPM to assess both static and dynamic loading (e.g. take movie during propulsion, transfer, etc)

14) IPM to assess variable postion seating systems

a) Check effectiveness

Pressure mapping can also be used to assess the effectiveness of tilt, recline, tilt/recline combinations or lateral tilt. It might also be used to assess the offloading of a standing feature.

b) Every client is unique

Remember that there is no one angle threshold that provides effective pressure redistribution off the buttocks across a population. Just as with pressure thresholds, an effective tilt or recline angle is unique to the individual.

c) Label all frames

When taking recordings at different angles/positions in space, remember to clearly label all pertinent frames.

15) Additional considerations for cushion selection

a) Postural stability

b) Functional mobility – transfers

c) Weight of cushion

d) Heat / moisture

e) Perceived comfort

f) Complexity

- maintenance and set-up requirements

g) Client’s ability

Client's ability to perform or direct care

h) Education

Ability to provide client and care-giver education

i) Caregiver

Number of care-givers / staff turnover

j) Follow up

Ability to provide follow-up as needed

Client Education

IPM is also useful as a visual feedback mechanism for client education. Seeing one’s own pressure distribution and peak areas drives home the message of the importance of pressure management. It is also a very valuable tool to demonstrate the effectiveness of pressure relief techniques. For this application, the sampling rate should be set as close to “real time” as possible (~ 24 frames/second), so that client’s weight shifts are represented with minimal lag time – when they move, they should see an immediate shift in pressures.

Displays

1. Isobar View:

This type of view displays the pressures of the same or similar values as a single colour. Note: Most IPM systems allow the user to adjust the scale which correlates colour to a specific pressure range; thus, great caution should be taken in automatically assuming a certain colour is good or bad. Always check the scale.

2. Center of Pressure (CoP):

This type of view displays a marker which represents where the load on the mat (i.e. body weight) is concentrated. This marker can be used to assess symmetry. For example, a client presents with a flexible left pelvic obliquity. The baseline map would likely show a shift in the CoP to the left. Different cushions and seating set-ups will have variable effectiveness in reducing the obliquity. Noting which intervention shifts the CoP toward a midline point will aid in choosing the best solution.

3. 3D mesh:

This type of view displays lines that connect points of equal pressure. The areas between the lines are often colored. High pressures are represented by peaks in the 3D display.

4. Filtering:

Filtering is a mathematical manipulation of the values to: eliminate a sensor that is not reading or is reading grossly different from neighbouring sensors.

5. Smoothing:

Smoothing is a mathematical technique to reduce the high and/or raise the low values. In other words the software identifies these values as outliers and thus probable sources of error. From an isobar display perspective, smoothing blends the colours and margins of adjacent sensors. In some cases (e.g. FSA) the smoothing preserves the highest value. Note that smoothing changes the actual values, so if you choose the smoothing for one cushion, you should also use smoothing for all cushions in a given client evaluation session to perform a fair relative comparison of the cushions.

6. Gradient:

Gradient displays the spatial changes in pressure. High gradients occur where the pressures quickly change from high to low on neighbouring sensors. 3D mesh display is useful in assessing gradient. The steeper the “slope of the hill” created by the peaks, the higher the gradient. High gradients are indicative of either poor envelopment or off-loading of the bony prominences.

Error identification

1. Row or column error:

Entire rows or columns could be maxed out or not reading at all. Most electrical systems that use a matrix array scanning process, suffer from some form of spill over of the readings from a sensor a neighbouring sensor. This is often due to the capacitance of the neighbouring sensors.

2. Artifact identification:

If a reading is suspect the mat can be rotated such that a different sensor is at the suspect location. If the reading moves with the sensor then the mat is suspect.

3. Usage error:

The buttocks not on mat; mat not on top of the cushion; edge folded over, etc. A diagonal “hot spot” line is usually indicative of a wrinkle in the mat. This is more commonly seen in cushions which are highly contoured.

4. Flashing sensor:

A sensor appears to fluctuate between very high and low values when the client is sitting statically. Mat error can be ruled out via rotating the mat, as described above.

5. Under or Over Reading:

Evident under/over-reading and/or the map does not reflect a buttock shape– re-calibration of the mat should be considered.

6. Creep:

Creep is the tendency for sensors to increase their reading over time. Since all sensors have this tendency it must be modeled and corrected for. In the calibration process a load in applied to the sensors and the changes over time are recorded. Time/creep corrections can then be added to the calibration. To the extent the

time in the calibration reflects the time during use the calibration will be accurate however if the times are substantially different this may be a source of error. Most accurate numbers are achieved when the time of reading matches the creep correction time used during calibration. Note that there is creep in the pressure mapping system, the cushion and the human tissue. Consistent time and temperature are important to be able to compare different cushions. Try to match the creep correction time from the calibration process.

7. Hysteresis:

Hysteresis is the tendency to under read when forces are increasing (e.g. when body weight is being loaded onto the mat) and to over read when forces are dropping (e.g. when weight is being lifted off the mat). During the calibration process the force differences are known and the differences modeled. During reading, the system monitors the changes and correlates to the appropriate increasing or decreasing reading. Clinically, hysteresis could come into play when the client performs a partial or full weight-shift or when air pressure is being adjusted in an air-filled cushion. Thus, hysteresis correction should always be included in the calibration process.

Video or digital pictures

Often it is possible to take a video or digital picture at the time the pressure are being taken. This is very useful and will help with future understanding of the pressure patterns.

Remote monitoring:

It is possible with most systems to gather the data while not connected to the computer so tat the user is free to propel or perform other functions that may cause unwanted pressures. An example of this would be transferring to a commode.

Databases:

Although some statistics are displayed in the software, the pressure data can often be exported to a spread sheet and further analyzed. For example an average of several frames of data can be attained. Much information can be extracted from the data however it is important to understand the influence that the acquisition and manipulation of the data has on the results. For example the averages of the pressures of a person leaning forward and backward may be meaningless.

Documentation:

The single most important thing when taking pressure data are the notes on the position, posture and circumstances existing when the data was taken. It is easy to take lots of data but difficult to remember the details of exactly what the conditions were when the data was taken.

V. Interpretation of data

The following are considered to be the most useful indicators for pressure ulcer risk.

Peak Pressure Index

– The highest pressure within a 9-10 cm2 in the ischial region or other bony prominence. Try to achieve the lowest possible PPI. Single sensor peak values are not recommended to rate maps, as they are not reliable (repeatable).

Dispersion Index

– percentage of the pressure from the total rectangular sensing area compared to the combined area under the ischial and sacro-coccygeal region. Otherwise stated, it is the sum of the pressure distributed over the IT and sacral regions divided by the sum of pressure readings over the entire mat – expressed as a percentage. Try to achieve the lowest possible DI. Evidence supports that a DI > 50% indicates high pressure ulcer risk (Drummond 1985)

DI = A/ A+B (expressed as a percentage):

Contact area

– area of the sensors with pressures above 10mmHg. Try to get the largest possible contact area. Note that when comparing a cushion which redistributes pressure via envelopment with one that off-loads, contact area by itself is not an adequate means to rate the cushions.

Gradient

- change in pressures per inch or cm (how close the high pressures are to the low pressures). Try to get the lowest possible gradient.

Symmetry

– Optimization of pressure distribution symmetry, comparing right and left sides, is a key goal. Focus is placed on symmetry of at-risk sites: the IT’s and greater trochanters. This parameter highlights the importance of integrating IPM findings which a comprehensive seating evaluation. Problem solving with

respect to asymmetrical IPM results cannot be accomplished absent of a postural evaluation. In fact, mapping the client while seated on a mat table is a useful means of to combine the two techniques: bony prominences can be clearly matched to peak pressures, asymmetries can be elucidated and the effect of manually providing postural support/correction can be assessed. The goal is to have even weight distribution on the right and left sides of the map. This would reflect optimally addressing any postural asymmetry which needs to be either corrected/reduced or accommodated.