Negative pressure wound therapy
What is Negative Pressure wound therapy?
Negative pressure wound therapy applies a pressure which is subatmospheric to the wound being treated. The suction is applied to the wound via a controlled machine which nowadays is small enough to carry around with the patient on a shoulder strap or belt.
From this machine which works continuously is an attachment tubing which leads to a small suction drain placed in the wound dressing. To enable the machine to work properly the wound dressing and drain has to be covered by a special transparent adhesive tape which eliminates air from outside of the wound rto enter. If this seal is not properly attached then the possibility to achieve negative pressure in the wound is greatly reduced. Most machines do come with an alarm that allows the patient or carer to know when there is a pressure leak. The optimal pressure for most treatments is between -80mmHg and -120mmHg. The adhesive dressing must be vapor permeable to facilitate gas exchange, an important consideration when treating wounds infected with anaerobic organisms that would thrive in an occlusive, oxygen-depleted environment.
The wound dressing
First clean the wound and the surrounding skin area. Cut the dressing to be used to fit into the wound cavity. There are two types of dressing suitable for this treatment. One is an anti microbial gauze and the other is a special sponge prepared especially for negative pressure therapy or vacuum treatment.
Do not use normal bandages or sponges as these can lead to worsening of the wound. It is important to realise that the bandage is prepared to eliminate bacteria and pus within the wound bed. If the pores are too tight the wound fluid and debris will not be able to be sucked out of the wound and instead be trapped within the dressing.
When applying the dressing it is important that the dressing is applied to all areas which are to be treated. Make sure that undermined areas are properly filled.
Then place the drain either inside the gauze and cover with more gauze before applying the transparent tape. If the sponge method is used then the transparent dressing is applied first and a small snit is made in the tape whereafter a drain is put into place allowing suction in this way. No matter which method is used both of these drain systems will enable negative pressure through the dressing to reach the wound cavity.
When the negative pressure is introduced a continual suction within the wound cavity allows for the elimination of uwanted fluids and bacteria to be sucked out of the area being healed.
Where there is a wound there is usually a build up of interstitial fluid in the surrounding tissue. This appears as swelling filled with fluid. This fluid build up of fluid comprises the circulatory and lymphatic system which in turn reduces the ability of the body to deliver nutrients and oxygen via the blood to help heal the wound. When this happens some bacterias can enter the wound and thrive in this oxygen reduced area causing further problems and ability to heal naturally.
It has also been shown that prolonged fluid which stagnates in the wound can delay wound healing, this is why many wounds have to be cleaned and dressed several times a day when using traditional methods for healing wounds. When the wound is being treated with negative pressure it is this fluid which is being removed from the wound bed continuously together with pus and possible bacteria. When the wound is being treated with negative pressure it is this fluid together with pus and possible bacteria that is being sucked out of the wound cavity. This fluid enters the disposable canister via the connector tubing attached to the drain. When this fluid is removed it has been shown that the circulatory system is not quite so compromised allowing nutrients and oxygen to reach the wound through bloodvessels at the bottom and around the wound cavity. The edema has in otherwords been effectively reduced. With the elimination of bacteria and dead tissue the wound has a better chance to respond to the bodies own healing properties. In some severe cases some patients will also need the added treatment with appropriate antibiotics.When a wound is colonized with bacteria the bacteria actually consume the available nutrients and oxygen which further compromises healing. In addition most release enzymes breaking down the necessary protein needed for wound repair. By sucking out this bacteria negative pressure is helping immensely in the fight for healing the wound cavity. Stagnant wound fluid is part food for some bacterias and it is not surprising that they enjoy colonizing wound beds.
When a wound grows
When a wound grows this is called granulationof the wound. Granulation is filled with new connective tissue and small blood vessels rich in nutrients and oxygen.Granulation should be a rich beefy red colour and not pale pink. It should not have a black or yellow appearance as this can be sign of necrotic dead tissue which needs to be removed.
Contraindications for negative pressure wound therapy
New tissue does not grow on dead tissue. Wounds have to be cleared of this necrotic tissue before negative pressure is applied to get the best results.If a patient has osteomylitis then the infection has to be treated with antibiotics at the same time. Negative pressure wound therapy should never be applied directly to bone tissue or to exposed vessels. This can, however, first be protected by a special fat greasy based dressing or other silicone based dressing which protect the underllying surface.If there is a suspected fistula this is also contraindicated for basic suction methods but there are special techniques which can be applied to help close these wounds too. This is a specialised treatment and should only be treated by a specialist.
Cancer wounds are also a specialised treatment and these should never be treated if cancer cells are still within the wound.
Patients who are not able to receive proper nutrients through feeding will have a much lower chance of wound healing as it is so important for patients to receive protein when wounds are present. It has also been shown that zinc and vitamin C help the wound healing process.
100% pure collagen has also been shown to be effective in the wound healing process and can be applied in the wound bed when treating with negative pressure wound therapy. The patient should be hemodynamically stable any form of bleeding from the wound bed should be investigated and stopped. Sometimes blood thinning medication can be a problem and bruising can appear around the wound if the suction is too intense.
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