Use of ultrasound in management of wound healing

Dr. Manal R. Salim

Ultrasound is commonly used by physical therapists, but there is no consensus regarding the most effective therapeutic dose for accelerating healing of open or closed wounds (Byl NN etal 1993).

Ultrasound is a mechanical vibration delivered at a frequency above the range of human hearing. Clinical ultrasound units currently being manufactured typically deliver ultrasound at frequencies of 1 and 3 MHz with duty cycles ranging from 20 to 100 percent. Duty cycles less than 100% are usually termed pulsed ultrasound while a 100% duty cycle is referred to as continuous ultrasound.

How does ultrasound benefit wound healing?

Inflammatory Phase - ultrasound causes a degranulation of mast cells resulting in the release of histamine. Histamine and other chemical mediators released from the mast cell are felt to play a role in attracting neutrophils and monocytes to the injured site. These and other events appear to accelerate the acute inflammatory phase and promote healing. Also there will be a pain relief due to inhibition of the transduction of noxious stimuli, but much can be attributed to placebo effect therapeutic ultrasound can alter brain permeability to various ions it is able to affect Ca permeability and as it is known as a secondary messenger can have a profound effect  on cell activities e.g increase synthesis and secretion of wound factors by cells involved in the healing process. This have been shown to occur with macrophages they are on of the key cells in wound healing(Steven Young,1996)

Proliferative Phase - ultrasound has been noted to effect fibroblasts and stimulate them to secrete collagen 1. This can accelerate the process of wound contraction and increase tensile strength of the healing tissue 2. Connective tissue will elongate better if both heat and stretch are combined. Continuous ultrasound at higher therapeutic intensities provides and effective means of heating deeper tissue prior to stretch. (Joseph McCulloch )

Frequency

As the frequency of ultrasound is increased, the penetration of the signal decreases. For most dermal wounds, it is preferable therefore, to utilize a frequency of 3 MHz. 1 MHz wound be more effective on deeper structures or periwound skin.

The basic precautions should be taken:

Treat at the lowest intensity that will produce the desired result.

Assure that the applicator is kept in constant motion throughout treatment and that the proper acoustic coupling medium is used.

Reduce the intensity or terminate treatment if the patient complains of any increase in pain.

Application of ultrasound to wounds

Prior to ultrasound treatment, remove dressings and clean wound of foreign debris or dressing residue. A hydrogel sheet should be placed in direct contact with te wound bed and wound margins, paying special attention to removing any air bubbles that might be present beneath the dressing. Remove any protective plastic covering on the hydrogel sheet.

In cases where a cavity type of wound exists that prevents complete contact between the hydrogel sheet and the wound base, as sterile aqueous hydrogel filler should be used. The cavity is filled with the aqueous gel and then covered wit the hydrogel sheet. Remove all underlying air bubbles between the aqueous hydrogel and hydrogel sheet. Once the hydrogel sheet is in place, apply an ultrasonic coupling gel on top of the sheet. Select the appropriate sized applicator. (the area treated should be no larger than 1.5 to 2 times the size of the applicator. If a relatively large wound is being treated, it would need to be divided into sections.

Set the ultrasound machine to a 20 % duty cycle at a frequency of 3 MHz Applying light pressure, the sound head is placed in contact with the coupling medium on top of the hydrogel sheet and moved in a slow and deliberate manner using either a linear or circular technique. Set the intensity to less than 0.5 watts per square centimeter (usually 0.3 watts/cm 2). Reduce the intensity if the patient experiences pain or heat. Treatment duration is suggested to be about 1 to 2 minutes per zone. Acute wounds are treated 1 to 2 times per day until acute symptoms (inflammation) subside. Treatments can then decrease to 2 to 3 times per week

Application of ultrasound to peri-wound tissue

When it is desired to provide mild heating to the peri wound tissue in order to stimulate circulation, higher intensity ultrasound can be given. Extreme are should be used, however, to assure the tissue is capable of handling the thermal levels delivered.

           To treat peri wound tissue, 1 MHz, continuous ultrasound is usually employed. Again, an ultrasound applicator 1.5 to 2 times the size of the treatment area should be used. With an aqueous coupling medium in place, the sound head is placed lightly against the skin surface and moved in a slow and deliberate manner. The intensity is typically set to between 1 and 1.5 watts per square centimeter. This parameter is extremely variable and depends on the patient's circulatory, sensory and mental status. Thermal ultrasound should never be used in situations where impaired perception prevents the pat