Prof. David G. Baxter, School of Rehabilitation Sciences, University of Ulster, Jordanstown, Northern Ireland

 

Abstract

Brief summary of general therapeutic guidelines as per one of the leading world LLLT specialists, dealing with basic principles of clinical LLLT practice. The author explains the importance and advantages of contact application technique in irradiation of deep seated pathologies, as well as of non-contact irradiation in open wounds healing. He stresses the Arndt-Schultz Law, considering optimum effective therapeutic dosage of energy and recommended frequency of treatments.

 

Importance of thorough examination and diagnosis

While low-intensity laser therapy may be regarded in some circles as a magical electrotherapeutic panacea, it can in no way compensate for poor clinical skills. Most importantly, the primary importance of thorough clinical examination and diagnosis remains. The results achieved with any treatment depend upon these basic clinical skills, and this holds equally for laser therapy. Indeed, the potential for good localised therapeutic effects with laser therapy can be severely compromised if the modality  is applied indiscriminately to generalised areas of pain/tenderness/swelling without adequate examination directed at localising the site of the lesion or complaint. To this end good surface anatomy skills are an essential prerequisite to good laser treatments, as they are vital for the accurate targeting of such structures as nerve roots, peripheral nerve trunks and lymph vessels.

 

Contact technique

For the delivery of optimum laser using diode-based treatment systems, or indeed where fibreoptic delivery devices are used in conjunction with He-Ne laser systems, the use of contact technique whenever possible is essential. The reasons for the use and advantages of contact technique are essentially as follows:

1.  The maximisation of power density/irradiance on the target tissue, given the divergence of most therapeutic systems and the predictions of the inverse square law

2. Reflection is minimised where the skin barrier is distended at the tip of the treatment probe, thus more light energy (essentially the number of photons) is delivered to the target tissue

3. Given the exponential attenuation of laser radiation in tissue and the small penetration depths at the wavelengths commonly used in treatment, the depression of tissue between the treatment head and the target tissue helps to minimise attenuation of the beam, and also reduces the perfusion of the tissue. Such decrease in blood perfusion in the treatment area effectively increases the amount of radiation delivered to the underlying tissue, as haemoglobin is a potent chromophore within the red and near infrared wavelength bands.

The only exception to this is the case of open wounds, where patient comfort and aseptic considerations will invariably exclude the possibility of treatment in-contact. However, some clinicians have used proprietary disposable film (clingfilm) pulled over the end of the treatment probe to enable the in-contact laser treatment of wounds with apparent success. Where non-contact treatment technique is used, it is imperative that the treatment head is kept stationary over the target area of tissue, with the distance between the tip of the treatment unit and the tissue being kept as small as possible (< 0.5 cm).

For standard in-contact technique, the treatment probe should be held firmly and perpendicular to the target tissue, with the tip pressed into the skin. The amount of pressure used by the operator (and thus the depth to which the treatment probe is pressed) will primarily depend upon the depth/site of the target tissue; however the tenderness of the area of tissue to which the probe is applied will also obviously be a consideration for the therapist.

Figure 1: Contact techique

 

Figure 2: Irradiation of wound margins

 

The potential therapeutic benefit of manual manipulation of the laser probe during treatment should not be overlooked. Pressure applied through the probe during laser irradiation of such clinically significant areas as acupuncture points or painful musculoskeletal trigger points effectively provides an "acupresure" type treatment in parallel with the laser treatment, the therapeutic benefits of each complementing the other. The most commonly used and recommended type of manipulation involves brisk pecking of the tissue with the treatment probe in a manner not unlike that used during some needle acupuncture treatments.

 

Effective therapeutic dosage

The difficulty in deciding upon what represents an effective dosage for a given condition should be apparent ... results from the work completed to date are unclear in this respect. In general, however, poor results, whether found in routine clinical practice or in research trials, are typically associated with the use of inappropriately low dosages. Nonetheless, the situation is not as simple as it first might appear, as some practitioners and researchers have reported considerable success using regimes based upon relatively low dosages. One explanation for these apparent conflicting observations lies in the so-called Arndt-Shultz law of photobiological activation (see Ohshiro & Calderhead 1988). This essentially predicts that:

1. a threshold amount of stimulation (in this case: dosage of laser) is required to demonstrate an effect or enhanced activation of the biological system or process under consideration,
2. a dosage-dependent effect will be demonstrated at relatively low dosages above threshold, so that increasing dosage will increase the degree of activation of the biological system or process,
3. immadiately above these relatively low levels of stimulation (laser dosage) a plateau effect will be observed. Hence many workers in the field sometimes argue that it is for all practical purposes impossible to overdose with laser treatment,
4. at the highest dosage levels, there is an inhibitory effect the given biological process or system.

The Arndt-Schulz law thus provides a useful theoretical basis to explain the varying photobiostimulatory and  photobioinhibitory effects observed in the laboratory; however it also goes some way to accounting for the apparently conflicting results that are sometimes achieved with low-intensity laser therapy. Unfortunately, while the general operation of the law may be adequately described schematically, the precise relationship(s) existing for the treatment of those conditions encountered in clinical practice is as yet unclear.

Figure 3: Arndt-Schultz Law

 

Wound Healing

Laser therapy can be an effective therapeutic modality in the management of a range of wounds of various aetiologies. Apart from burns, gun shot, stab and surgical wounds, including skin graft donor areas, such distressing and chronic conditions as diabetic ulcers, pressure sores and venous leg ulcers can also benefit significantly from laser treatment. Initiation of laser treatment at the earliest possible opportunity is essential to minimise patient suffering and to maximise the potential benefit. Timing and frequency of treatment seem to be less critical: in the early stages laser may be used twice per day without danger of overtreatment. In this, liaison with the rest of the health care team can ensure that provision of laser treatment is synchronised with changes of dressing and other ward or wound management routine. In particular, treatment should usually only be carried out after the wound has been cleaned/desloughed, as the presence of such slough will significantly attenuate the laser beam.

Laser treatment of wounds (and indeed conditions that may be usefully regarded as ‘closed’ wounds such as bruising/haematoma etc.) can be considered in two stages. For the first stage, contact technique is used to treat a series of points around  the whole sound margin, approximately 1 cm from the edge of the wound (see Figure 2), using a standard dosage. For this an initial dosage of  0.5-1 J/point or approximately 4-8 J/cm² is usually sufficient with which to begin treatment. Laser treatments at 2 cm intervals around the edge of the wound will usually be sufficient, with alternation of the position of points between treatment sessions. While the primary aim of such treatment is to accelerate margination and eventually wound closure, promotion of increased blood flow to the wound area as well as angiogenesis are also important objectives.

As already indicated, during this first stage of wound treatment contact technique is used; for this a light but firm pressure is required to maintain adequate contact of the treatment head. Excessive/deep pressure for such laser treatments is unnecessary and will usually not be well tolerated by the patient.

During the second stage of treatment, the wound bed is treated using non-contact technique. For this a number of devices can be employed to simplify treatment including scanning devices, multisource ‘cluster’ treatment units and flexible arms to support and maintain the position of the treatment head and thus the area of irradiation.

 

Manual treatment techniques

These consist of variations of two distinct techniques: manual scanning and ‘gridding’. Manual scanning is essentially a manual version of what can be achieved using the purpose built scanning devices outlined above. However, as scanning of the laser radiation in this case is achieved by the motion of the operator’s hand, considerable care is required to ensure that a reasonably uniform dosage is delivered to all areas of the wound. For this, a steady slow movement of the treatment probe back and forth across the surface of the wound is required, the operator taking care to maintain a standard distance (<0.5-1 cm) between the tip of the probe and the surface of the wound bed. A pattern for the manual scanning treatment of a wound is suggested in Figure 4. 

When manual scanning is employed, the calculation of dosage becomes less accurate. Where care is taken to provide a uniform irradiation to cover the whole surface of the wound, the total average radiant exposure can be estimated by dividing the product of the machine’s output (in watts or milliwatts) and time of irradiation in seconds by the area of the wound in square centimetres. This latter can be best estimated by using manual tracing techniques and graph paper. For the initial or early stages of treatment an initial radiant exposure of no less than 1.5 J/cm² is recommended.

Figure 4: Manual scanning of the wound	Figure 5: Manual griding

A more practical and usually less time-consuming alternative to manual scanning is the use of a grid technique. For this, the area of the wound bed is visualised as being covered with a gridwork of squares measuring 1 cm x 1 cm as depicted diagrammatically in Figure 5. Using the grid as reference, treatment is then applied systematically to each square using a single diode or fibreoptic applicator from a distance of no more than ~0.5-1 cm. For such treatments of the wound bed, an energy density of 1,5-2.5 J/cm² (in each irradiated grid square) is recommended as a minimum for the early stages of wound management. Where time is limited, the grid can be visualised as a draught- or chequerboard and irradiation on subsequent treatment sessions alternated between ‘black’ and ‘white’ squares. Under such circumstances, as only half the squares are irradiated during any one session, it is recommended that the frequency of laser treatment is increased.  

A note on supplementary treatment of the lymphatic system

In addition to the direct irradiation of the margins and bed of the wound, it has also been claimed that therapeutic laser units can also be used to stimulate the functioning of the lymphatic system and thus improve the rate of wound healing. Although not widely used for such treatments, at least in the British Isles, the reported clinical successes in Japan (Ohshiro 1991) and positive results from in vitro cellular research would suggest this as a potentially effective method of treatment in the management of chronic wounds.

For these treatments, the laser is used to irradiate the main lymphatic vessels and nodes associated with the site of the wound or lesion. Thus for the lower limb, the laser would be applied to the lymph nodes in the ipsilateral groin area and at a few points along the course of the main vessels serving these nodes. Contact technique using a firm pressure is necessary if such treatments are to be successful and energy densities of around 3-5 J/cm²; it is further recommended that treatment of the lymph nodes and vessels is completed before irradiation if the wound. It should also be stressed that even where the lymph nodes are found to be swollen, the athermic nature of laser treatment means that the treatment is safe and can be delivered with confidence. Where the therapists is in any doubt, a test dosage of 1 J/cm² can be applied and the condition monitored over the subsequent 24 hours.

 

Dosage/energy density

The difficulties inherent in recommending treatment parameters for any laser treatment have already been identified. However, based upon research findings and clinical experiences to date, it is recommended that in-contact treatments of wound margins should usually  initiated using energy densities of no less than ~4 J/cm² or about 0.5 J/point. Where wound closure progresses well, it should not normally be necessary to consider increasing the dosage. However, where the rate healing is poor or reaches a plateau, dosage can be increased and the effect monitored. Under such circumstances, healing may be enhanced with dosages of up to 12 J/cm². While there is little evidence to suggest that dosages above this value applied in contact whit intact skin will adversely affect the rate of healing or indeed cause any serious side effects, the practical constraints (not least of which is the time of treatment) inherent in increasing the dosage above this value exclude unlimited progression of treatment.

In contrast, there is some evidence to suggest that the application of dosages of over 3-4 J/cm² directly to the wound bed may well inhibit the overall progression of wound healing. Consequently, such treatment is usually commenced with dosages of not less than ~1.5 J/cm² and progressed, where healing is considered to be slow, to dosages of up to 4 J/cm² maximum. Where only minimal or marginal effects are produced with such dosages, it is unlikely that laser therapy will be indicated for the particular patient.

 

Frequency of treatment

In the early stages of treatment, daily irradiation is recommended; however twice- and trice daily treatments have also been used without affecting therapeutic benefit. Where improvement has been established, frequency of treatment can usually be reduced to irradiation on alternate days, or to irradiation on several days per week. In such cases, it is important to monitor and re-assess the progression of wound healing while reducing the frequency of treatment.

 

Literature

G. David Baxter: Therapeutic Lasers Theory and Practice, Churchill Livingstone, Edinburgh, 1994.