EUROPEAN PRESSURE ULCER ADVISORY PANEL

DEFORMATION ANALYSIS OF A SUPPORTED BUTTOCK CONTACT

C.W.J. Oomens1, E.M.H. Bosboom1, C.V.C.Bouten1 and D.L. Bader2
1. Eindhoven University of Technology, The Netherlands
2. Queen Mary, University of London, England

Introduction

For a breakthrough in the prevention and treatment of pressure sores it is necessary to obtain a better understanding of the aetiology. Biomechanical studies may be a valuable tool in the chain of activities necessary to reach this goal. Mechanical models are used to find the association between global external loads and the internal mechanical condition of the tissue. Until the present day interface pressure measurements play a major role in the evaluation of tissue support systems, although they represent only a small part of the problem.

The objective is to study the mechanical condition and interface pressure of a supported buttock contact, depending on cushion properties, relative properties of tissue layers and friction. The results are relevant for the design of seat supports for patients at risk of developing pressure sores.

Methods

Numerical, mechanical simulations of a buttock on a supporting cushion are described. The ischial tuberosity is modelled as a rigid body, whereas the overlying muscle, fat and skin layers are modelled as a non-linear Ogden material. Material parameters and thickness of the fat layer are varied. Coulomb friction between buttock and cushion is modelled with different values of the friction coefficient. Moreover, the thickness and properties of the cushion are varied.

Results

Even a simple geometry, with simple loading conditions but inhomogeneous material properties leads to a complicated stress/strain field in the tissues. High shear strains are found in the muscle near the bony prominence and the fat layer near the symmetry line. The performed parameter variations lead to large differences in shear strain in the fat layer, but relatively small variations in the skeletal muscle. This is an important result, considering the fact that many pressure sores start in deeper tissue layers. There have been many reports in literature, which suggest that it is difficult to perform reproducible and accurate measurements of interface pressure. The present simulation model questions their validity, indicating that interface pressures alone do not reflect the internal stress/strain state existing in loaded soft biological materials.

REPORT ON ACTIVITIES OF EPUAP WORKING GROUP 2 - Laboratory Evaluation of Support Surfaces

Alastair McLeod
Huntleigh Healthcare, 310-312 Dallow Road, Luton, Beds LU1 1TD, England

Two meetings took place in the UK and Holland in 2001, building on the work reported at last year's EPUAP open meeting. Attendees were mostly from industry, instrumentation manufacturers, academic establishments and hospitals.

The narrow objective set by the group was to build a set of guidelines for the acquisition and reporting of interface pressure (IP) measurements. This objective is also shared by the EPUAP's sister organisation, the NPUAP. Eventually, it is hoped that this work will contribute towards the development of an international standard, similar to that currently being developed for wheelchair seat cushion assessment, under the auspices of ISO TC173 SC1 WG11.

Since there are additional complexities in measuring and analysing IP on moving (e.g., alternating) surfaces, it was decided to focus initially on a protocol for assessing surfaces which do not vary IP in a cyclic manner (e.g., foams, non-alternating air, fibre-filled and water-filled mattresses).

This presentation will outline some of the issues still under discussion, including:

• Whole body mapping: is it necessary to measure anywhere except the bony prominences?
• Mannequin design: is it necessary for the mannequin to have complex, flesh-like properties for comparative testing against a standard foam surface?
• How do we analyse the potentially large amount of data from sensors?
• IP measurement instrumentation: is it accurate enough to detect 'clinically significant' differences?
• What are 'clinically significant' differences in calculated parameters as opposed to 'statistically signilicant'?

A draft protocol based on discussions to date will be available for comment. From discussions and work conducted thus far, it is obvious that new research is needed in order to clarity some of the issues raised above. It is therefore recommended that the EPUAP part-funds a programme of work in collaboration with the NPUAP and other interested parties to answer remaining questions.

UP-DATE OF THE PAN-EUROPEAN PRESSURE ULCER STUDY (PEPUS)

Christina Lindholm PhD
Assistant Professor, Karolinska Hospital, Stockholm, Sweden. (European research coordinator / EPUAP / PEPUS)

It was decided by the EPUAP Council that a reseach project regarding pressure ulcers should be started in Europe. The aim of the project was to generate european data on patients of high risk of developing pressure ulcers.

The PEPUS study was designed to collect data from populations of patients undergoing surgery for hip fracture, which is reported to be one of the major groups at risk of pressure sores. The overall aim was to follow the patients closely throughout the entire episode of care, to detect potential risk factors both in the environment (the care process) and in the individual patients. These riskfactors, recorded throughout Europe were believed to give a relevant picture of factors associated with hip fracture and pressure ulcer development, give the individual centres useful information regarding possible shortcomings in the chain of events, and to detect patient-related parameters related to developing these ulcers. The ultimate outcome is planned to be the development a risk assessment instrument for this specific group of patients.

Inclusion

Twenty consecutive patients with hip fracture admitted to A&E Departments in five hospitals in each country. Patients are followed up until discharge or for seven days. A total of fourteen countries volunteered to participate.

Method

Patients are inspected upon arrival to A&E Department for pressure ulcers. Parameters suh as: time of accident, time of ambulance transportation, time/duration of surgery, complications, nutritional/hydrational status, Braden Scale-parameters, pain, type of mattersses in A&E Dept, radiological Department (if different), ward and theatre. Patients are closely monitored throughout their hospital stay, and altogether 250 parameters are studied.

Results

Of the initially fourteen countries who volunteered to participate, three have completed the study (Sweden, Portugal and Finland), and another three (Great Britain, Italy and Greece) have commenced. It is hoped that the remaining countries will be inspired to participate after the presentation of the study and the preliminary results.

DEBRIDEMENT IN DETAIL WITH A FOCUS ON SHARP DEBRIDEMENT

Mr Mark O'Brien
The Royal London Hospital, London, England

Debridement describes the removal of dead or devitalised tissue, particulate matter and foreign bodies from a wound bed (Vowden and Vowden, 1999) and is generally accepted as a necessary precursor to the formation of new tissue.

The methods of debridement, including mechanical, autolytic, biological, chemical, are discussed but with an emphasis upon the controversial area of conservative sharp debridement. This procedure though widely practised by senior nurses, and recognised as a valuable tool in promoting the healing process, is currenfly not supported by an educational framework to guide practise. This has led to the development of a debridement course combining theory, essential cadaveric anatomy and basic surgical techniques.

Reference

Vowden KR, Vowden P. (1999) 'Wound debridement, Part 2: Sharp techniques.' J Wound Care. 8, 6, 291-4.