Wound dressings - Adhe-Els

Wound dressings
Nicholas F S Watson
Wendy Hodgkin
The rational use of dressings for wound healing by secondary intention
is the focus of this contribution, which should be read with
‘Classification and management of acute wounds’, page 47.
Practical selection of dressing
There is a lack of high-quality research data regarding the relative
efficacy of the various dressings, so the choice of dressings used in
everyday practice in the UK is often based on familiarity, personal
preference and cost.
Wound care and dressing selection should be a holistic, structured
process involving close cooperation between medical and
nursing staff. Three factors must be considered when assessing
the requirement for a wound dressing:
general health of the patient
local environment of the wound
specific properties of the dressing.
Patient factors
Patients should undergo systematic assessment to address the
underlying cause of their wound. Factors that may delay the healing
process must be addressed, and may include ensuring that:
nutritional intake is sufficient
anaemia and electrolyte imbalances are corrected
diabetic control is optimized
appropriate pressure-relieving equipment is provided
systemic infection is treated
foreign bodies are removed
peripheral oedema is reduced
smoking is stopped.
Some factors may not be easily resolved (e.g. advanced malignancy,
previous radiotherapy), and this should be considered when monitoring
progress of the wound.
If the patient has to manage the wound himself, assessment
should also include factors such as co-ordination, continence and
general cognitive function, any of which may alter the final selection
of the dressing.
Nicholas F S Watson is a Research Fellow in Colorectal Surgery in the
Department of Surgery, Queen’s Medical Centre, Nottingham, UK.
Wendy Hodgkin is a Clinical Nurse Specialist in tissue viability
for Nottingham Primary Care Trusts and Queen’s Medical Centre,
Nottingham, UK.
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The local environment of the wound
Wounds can be divided into four categories (Figure 1) based on
their appearance and stage of healing. Each wound type has slightly
different characteristics and a wound healing by secondary intention
will progress through these different stages over time. There is
no ‘one size fits all’ dressing, hence wounds must be re-evaluated
regularly in order to identify and respond to any changes.
Necrotic wounds (Figure 1a) are usually black or dark green and
contain devitalized tissue. Infected necrotic wounds require sharp
surgical debridement back to viable tissue in order to prevent
systemic sepsis. In the absence of infection, necrotic tissue will
eventually separate from the wound bed by autolysis. Necrotic
wounds are particularly susceptible to dehydration, and autolysis
is inhibited if the wound is allowed to dry out; the main priority
of a dressing is to maintain sufficient moisture in the local environment
of the wound.
Sloughing wounds (Figure 1b) contain a mixture of leukocytes,
wound exudate, dead bacteria and fibrin, typically forming a glutinous
yellow layer of tissue over the wound. The presence of slough
predisposes to wound infection because it provides a nutrient-rich
environment for bacterial proliferation. The formation of granulation
tissue is delayed in a sloughing wound compared with a clean
wound, and hence the optimal dressing will contribute towards
wound debridement and maintenance of a clean wound bed.
Granulating wounds (Figure 1c) are highly vascularized and
are a rich pink or red colour. The amount of exudate produced
is often substantial, and a dressing with the capacity to absorb
excess exudate is desirable. Significant heat loss may occur with
wounds covering large areas, requiring a dressing with insulating
properties.
Overgranulating wounds have the following properties, they:
contain excessive friable granulation tissue
are prone to recurrent episodes of bleeding
suffer from delayed epithelialization.
In this situation, caustic pencils containing silver nitrate or topical
corticosteroid can be applied directly to the affected areas in order
to control the excess tissue.
Epithelializing wounds (Figure 1d) contain new epithelial tissue
(formed by migration of keratinocytes from the wound margins)
or contain islands of tissue (formed from skin appendages in the
wound bed). The main priorities for dressing are the maintenance
of a warm, moist environment around the wound, and the use
of low-adherence dressings (see below) to minimize the trauma
of dressing changes. In addition to the type of wound, the location,
size and depth of the wound may vary considerably. Along
with the condition of the surrounding skin, these should also be
considered when deciding the most suitable dressing.
Dressing factors
The ‘ideal’ properties of a dressing for optimal wound healing are
listed in Figure 2. No product fits this profile exactly, so dressing
selection should address the most important factors identified in
a particular clinical scenario.
Dressings can be grouped into broad categories because many
have similar actions and characteristics (Figure 3).
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Wound appearances in different stages of healing by secondary intention
a Necrotic wound. b Sloughy wound.
c Granulating wound.
Properties of the ‘ideal’ wound dressing
Maintains a moist environment around the wound
Removes excess exudate, but prevents saturation of the dressing
to its outer surface (‘strike through’)
Permits diffusion of gases
Protects wound from micro-organisms
Provides mechanical protection
Controls local temperature and pH
Is easy and comfortable to remove/change
Minimizes pain from the wound
Controls wound odour
Is cosmetically acceptable
Is non-allergenic
Does not contaminate the wound with foreign particles
Is cost effective
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d Epithelializing wound.
Tulle dressings (e.g. Paratulle, Bactigras, Jelonet) are cotton
or viscose gauze dressings impregnated with paraffin (antiseptic
or antibiotic may also be incorporated). Paraffin lowers the dressing
adherence, but this property is lost if the dressing dries out.
The hydrophobic nature of paraffin prevents absorption of moisture
from the wound, and frequent dressing changes are usually
needed. Skin sensitization is also common in medicated types.
Tulle dressings are mainly indicated for superficial clean wounds,
and a secondary dressing is usually needed.
Low-adherence dressings (e.g. Melolin, Mepore, Mepitel)
are manufactured from materials ranging from knitted viscose to
polyester fabric. Built-in perforations reduce adherence between
the dressing and the wound surface. Removal is easy with little
or no trauma, but they have minimal absorptive capacity and are
unsuited for all but lightly exudating and superficial wounds.
Hydrocolloids (e.g. Granuflex, Comfeel, Tegasorb) contain a
hydrocolloid matrix of gelatin, pectin and cellulose mixed together
to form a waterproof adhesive dressing that interacts with the
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Main types of wound dressings
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Tulle dressings
Low-adherence dressings
Hydrocolloids
Hydrofibres
Hydrogels
Films
Foams
Alginates
Mechanical devices
Bioactive/biological dressings
wound bed. Exudates produced by the wound absorb into the
dressing, which dissolves and forms a gel. The moisture from
this gel enhances autolytic debridement of necrotic and sloughing
tissues and promotes the formation of granulation tissue. Hydrocolloid
dressings absorb light-to-moderate levels of exudate, do not
require a secondary dressing, and are shower-proof.
Hydrofibres (e.g. Aquacel) are produced from similar materials
to hydrocolloids and also form a gel on contact with the wound, but
are softer and more fibrous in appearance, with a greater capacity
to absorb exudate. Moisture from the gel assists in debridement
and facilitates non-traumatic removal.
Hydrogels (e.g. Intrasite, Nu-gel, Aquaform) consist of starch
polymers with a very high intrinsic content of water. They conform
to wounds with unusual shapes due to their gel-like nature. In
contrast to hydrofibres, hydrogels are used primarily to donate
fluid to dry necrotic and sloughing wounds, and their absorbency
is limited. A secondary dressing is usually needed.
Films (e.g. Opsite, Tegaderm, Bioclusive) are made from a
thin polyurethane film coated with adhesive. Film dressings are
highly comfortable, shower-proof and their transparency allows for
wound monitoring without dressing removal. Vapour-permeable
films allow diffusion of gases and water vapour, but are minimally
absorbent. Problems can arise if these dressings are applied to
heavily exudating wounds because fluid tends to accumulate
underneath the film, leading to maceration of the wound and
the surrounding skin. Films are thus suited to superficial, lightly
exudating or epithelializing wounds.
Foam dressings (e.g. Lyofoam, Allevyn, Tielle) are constructed
from polyurethane and absorb exudate without interacting
with the wound bed. They absorb low-to-moderate amounts of fluid
and usually have a semi-permeable backing to allow the escape of
moisture. Foams do not require a secondary dressing and are often
used as an outer dressing with other products (e.g. hydrogels).
Alginates (e.g. Sorbsan, Kaltostat, Algisite) are derived
from a calcium salt of alginic acid, producing highly absorbent
dressings suitable for heavily exudating wounds; some alginates
also possess haemostatic properties. As they absorb exudate,
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alginates change from a soft fibrous texture into a gel, facilitating
easy removal and preventing dressing fibres from contaminating
the wound. Alginates are manufactured as flat sheets or as rope,
and are suitable for packing cavities.
Odour-reducing dressings (e.g. Clinisorb, Actisorb) are used
primarily for fungating, infected and gangrenous wounds where
malodour is a particular problem. They usually contain charcoal
and should not be cut into because the charcoal fibres may shed
into the wound.
Dressings containing iodine(e.g. Inadine, Iodosorb,
Iodoflex) come in two forms, as povodine–iodine impregnated
into a low-adherent dressing or dressings containing concentrated
cadexomer iodine paste. They possess broad antibacterial activity
and are indicated for infected or heavily colonized wounds.
Iodinated dressings should be removed when they change colour
from brown to white (indicates uptake of available iodine). Systemic
absorption of iodine can be significant with prolonged use,
especially if used in wounds with a large surface area. Hence,
these dressings should be avoided in patients with a history of
thyroid disorders.
Dressings containing silver exist in many different formulations, and
exhibit a broad antibacterial spectrum. They are often used in burn
wounds, and are also indicated for infected and heavily colonized
wounds. Their use is occasionally limited by hypersensitivity.
A summary of the most commonly used primary wound dressings
for different wound types is shown in Figure 4.
Mechanical devices
In the UK, the most commonly used mechanical device in wound
care is the vacuum-assisted closure device, which applies topical
negative pressure (50–125 mmHg) spread evenly over the
wound bed. A specialized open-pore foam dressing is cut to fit
the wound dimensions and is then attached to a vacuum pump
unit via tubing placed under an occlusive secondary dressing.
Vacuum-assisted closure is extremely effective in removing
exudate and reducing oedema in the surrounding tissue, while
leaving the surface of the wound moist. Local blood flow to the
wound is improved, with a subsequent increase in vascularity of
the wound bed and formation of granulation tissue. The wound
is completely sealed to the external environment and, because
exudate is removed, bacteria are drawn away, and the risk of
wound sepsis is reduced.
Vacuum-assisted closure is used in the management of large
or deep wounds where very high levels of exudate are produced
which would quickly overwhelm conventional dressings. Necrotic
wounds or those with thick, dry slough require adequate debridement
before vacuum-assisted closure can be applied.
Vacuum-assisted closure is contraindicated in:
wounds with exposed blood vessels or organs
unexplored fistulas
untreated osteomyelitis
local malignancy.
Biological dressings
Larvae (LarvE) of the common greenbottle fly (Lucilia sericata)
are bred in sterile conditions. These larvae are necrophagous
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Dressings for different wound types
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Dry necrosis
Dry slough
Wet, loose slough
Granulating
Epithelializing
Infected
Malodorous
Fungating
*Requires secondary dressing
(avoiding healthy, viable tissues) and are very effective in treating
sloughing and necrotic wounds. The number of larvae applied is
relative to the size of the wound, and they are usually left in situ
for three days. The larvae feed by a process of extracorporeal digestion,
secreting various enzymes that break down the dead tissue to
an ingestible consistency. Larvae also possess direct antibacterial
activity, although the exact mechanism for this is unknown.
Side-effects (physical discomfort, transient pyrexia, bleeding)
are rare. Larvae therapy is contraindicated in wounds that connect
with body cavities.
‘Skin-substitute’ dressings (e.g. Integra, Alloderm) are
increasingly finding clinical application in the UK, but their use
is restricted to the specialist setting.
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Superficial wound
Cavity wound
Sinus cavity
Treat with systemic
antobiotics
Check for signs of infection
and treat if appropriate with
systemic antibiotics
No infection
Bleeding
Not bleeding
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UK guidelines
Hydrogel*
Hydrocolloid
Saline-soaked hydrofibre*
Dry hydrofibre*
Larvae (seek
specialist advice)
Foam
Hydrocolloid
Hydrofibre
Alginate
Low adherent*
dressing
Hydrocolloid*
Film
Dressing containing
silver or iodine
Deodorizing dressing*
(consider debridement if
appropriate)
Haemostat (i.e. alginate)*
Treat as above, but
consider non-adherent
primary layer to reduce
risk of bleeding
Current guidance from the UK National Institute for Clinical Excellence
on the use of debriding agents and specialist wound care
clinics for difficult-to-heal surgical wounds states that ‘although
there is no randomized controlled trial evidence to support any
particular method, both modern dressings which promote autolytic
debridement and larvae therapy may reduce pain and be more
acceptable to patients when compared with traditional dressings’.
They also advise that the individual choice of dressing should
consider aspects related to patient acceptability, type and location
of wound, and total costs. u
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