A range of different types of bandages or bandage systems are available today, differing in terms of the fabrics used and the way they are manufactured.
To use bandages correctly, it is important to have a sound knowledge of the terminology used to describe these products, in order to understand their mechanism of action, the factors that affect pressure under the bandage and their respective advantages and disadvantages.
Different categories of bandages exist, determined on the basis of:
These physical characteristics describe the yarn, weft, type of manufacture (woven, knit) and the cohesive, adhesive or dry nature of the bandages.
- adhesive bandages. These bandages have one side that has been made adhesive by coating with a sticky substance. Non-removable, non-washable, non-reusable, these can therefore be used once only. Due to their specific manufacturing process, they are elastic in one direction only and are therefore termed one-way stretch bandages.
- cohesive bandages, also known as self-adhesive bandages. These bandages are coated with a substance (natural latex or a synthetic substance) that enables the bandage to adhere to itself without sticking to the patient’s skin or clothing. They are theoretically washable (on average 5 times according to standards), but washing tends to reduce their self-adhesiveness; in addition, the bandage gets tangled up and sticks to itself during washing, making it difficult to unroll. Cohesive bandages are usually one-way stretch (elastic lengthways only).
- dry bandages. Made of an uncoated “dry” knit or fabric, these bandages are washable (25 to 30 times according to standards) and removable, but they require a securing system. They are elastic lengthways or lengthways and widthways and are termed one-way stretch or two-way stretch.
A bandage is defined by measurement of its dynamic characteristics in the laboratory:
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Elasticity . The elasticity of a bandage is the capacity of the stretched textile to return to its initial shape once the deformation force has been removed (in other words, its capacity to resist the stretching force).
In practice, it is not this measurement that has been adopted internationally to determine whether a bandage falls into the category of “elastic” bandages or “non-elastic or low-elasticity” bandages, measurement of extensibility being used instead.
- Extensibility . The extensibility is the capacity of a material to be deformed when it is subjected to a constant traction force . It is expressed as a percentage.
Different national standards are used for this measurement.
In Europe, for example, extensibility is commonly given for a force of 7daN/cm.
The extensibility is a fixed datum for each bandage, generally indicated by the manufacturer on the pack.
IMPORTANT: do not confuse the extensibility of a bandage with the stretching of a bandage, which depends on how it is applied.
The stretching of a bandage is the difference in length between the bandage stretched on application and the unstretched bandage at rest, divided by the length of the unstretched bandage, multiplied by 100.
An application method indicating that a bandage must be stretched to 50% therefore means that the bandage must be stretched by 50% in comparison with its initial length.
- Loss of linear recovery assessed on the basis of a hysteresis graph . To assess the deformation and wear of the textile used for the bandage, it is subjected to stretch and release cycles during which the % extensibility is measured as a function of the force applied. This leads to hysteresis graphs being plotted, showing the loss of linear recovery of the textile following stretch and release cycles.
This leads to the definition of long-stretch bandages and short-stretch bandages.
The standards are far from international and once again can vary depending on the country. However, an international classification system seems to have been emerging in recent years:
- long-stretch, elastic bandages have an extensibility > 100-120% *
- short-stretch bandages have an extensibility <100-120% *
Hysteresis graph profiles of bandages depending on their extensibility
A short-stretch bandage has a low extensibility (<100-120%)
A long-stretch bandage is elastic and has a high extensibility (>100-120%)
* the limit between the two types of bandages ranges from 100% to 120% depending on the publication and the country.
A bandage is also defined by the interface pressures that it exerts on the limbs, i.e. the pressure measured in vivo between the bandage and the skin
The interface pressure is the pressure measured in vivo between the compression system applied to a limb and the skin.
This measurement is performed using sensors applied directly to the patient’s limb, before application of the compression system being assessed, at standardised points (for example, at the base of the calf muscle at point B1, i.e. 10-15 cm above the ankle bone, for assessment of pressure at the ankle).
This measurement still requires international standardisation of the method since it depends primarily on the type of the sensor used and the anatomical zones at which the measurements are taken.
This pressure is expressed in mmHg.
In the past, only technical data produced using laboratory measurements were taken into account to compare bandages. However, in the last few years, the position of international experts has shifted and new international recommendations tend towards in vivo measurement of interface pressures.
Largely overlooked until recently, the interface pressure is now recognised as being the most important biophysical property of compression systems applied to patients.
This pressure varies depending on the type of bandage and whether the limb on which the measurement is being taken is :
- immobile, giving rise to a resting pressure (RP) produced directly by the passive tension exerted by the compression system
- mobile, giving rise to a working pressure (WP) produced intermittently on exertion when the muscle is exercised.
The difference between these 2 pressures corresponds to the static stiffness index of the bandage.
The higher this index is, the more rigid the bandage and the more it fits into the short-stretch (low-elasticity) category.
The lower this index is, the more elastic the bandage it and the more it fits into the long-stretch category.
Resting pressure, working pressure, static stiffness index
Since measurements of the pressure exerted by a compression system are performed in vivo in healthy volunteers or patients, it is necessary to take into account the mobility of the limb on which the measurement is being taken, and hence the status of the muscle pump.
It is therefore necessary to measure the interface pressures at rest and at work.
The resting pressure (RP) is the pressure exerted by the compression system in the absence of any muscle contraction. It is therefore directly dependent on the tension of the system applied to the limb, corresponding to the minimum passive force exerted continuously on the leg by the compression system.
The working pressure (WP) is the pressure exerted during muscle contraction, on exertion. It corresponds to the intermittent active force produced by the compression system exerting a resistance pressure when the muscle contracts and increases in volume.
The stiffness index is the difference between the working pressure and the resting pressure.
Today, a principal method has been defined to measure this index: the Static Stiffness Index (SSI), which is the difference between the pressures measured standing up and lying down.
Other methods are also suggested in the literature today for dynamic pressure measurement (e.g.: ankles flexed and extended or measured on a treadmill).
Since the interface pressures depend on the extensibility of a product, short and long-stretch bandages do not therefore offer the same in vivo interface pressure profiles.
These characteristics will have a direct influence on the expected result on the veno-lymphatic system.
(see chapter on compressive effects as a function of different bandage types)
