THE CHARTERED SOCIETY OF PHYSIOTHERAPY Safety of Electrotherapy Equipment Working Group

Guide Lines for the Safe Use of Microwave Therapy Equipment 1. Introduction

MICROWAVE therapy apparatus general ly uses electromagnetic radiation at a frequency of 2,450 MHz (12 centimetres), or 4,900 MHz (6 cm). The power output of the equipment should not be more than 250 watts and is normally considerably less than this under operating conditions. Although the technique is not now widely used in this country equipment is found in some centre^.^

2. Equipment Testing Prior t o Acceptance

2.1. Safe performance to the standards laid down in BS 5724 part 1 'General requirements for the safety of medical electrical equipment" or equivalent standards, and in BS 5724 Section 2.6 'Specification for microwave therapy equipment2 or equivalent standards, should be confirmed either by the supplier or, preferably, in the hospital or clinic by suitably trained hospital physicists or engineers. 2.2. Output function should be assessed as indicated in section 3. 2.3 Leakage of microwave radiation from the equipment enclosure should be checked by a qualified engineer on acceptance and following any servicing or damage (eg falling on the floor). Leakage should not exceed 10 mW/cm2.2

3. Calibration

Calibration of radio frequency fields is not easy, as the measuring device will often affect the field being measured. The output of a microwave machine used for physiotherapy will be altered according to the way the applicators are positioned around the patient. However, there are aspects of calibration which can be investigated, usually wi th very specialised field measuring equipment2( '. 3.1 Output power is normally indicated on the front panel of the machine. This normally refers to the drive conditions of the generator, rather than to the power actually delivered to the patient. BS 5724 part 2.6, describes techniques for measuring the output of the equipment.

A resistive load can be applied in place of the applicator and the power delivered to the resistor can then be measured. 3.2 Timer accuracy should be confirmed with the aid of a stopwatch.

4. Maintenance

Regular servicing at intervals of not longer than six months is strongly recommended. Suppliers and/or manufacturers offer various levels of maintenance contract. The value of these compared with 'in-house' servicing (if available) should be examined by an appropriately qualified independent expert before being taken up.9, lo.

5. Routine Care of Equipment

5.1 General care. The generator case, leads and applicator should be kept clean, using a cloth dampened w i th non- abrasive antiseptic cleaning solutions.

The equipment should be kept in a warm, dry environment. If allowed t o become very cold, then it should be allowed

to come to room temperature before being energised to avoid damage to the equipment which would be caused by condensation. 5.2 Visual inspection. All applicator and mains leads and generator casing should be checked visually on a daily basis. Any evidence of damage, cracking or poor connection wi th the plug should result in the equipment being taken out of service and sent for repair without delay. The correct leads should be used with each applicator as 'matched sets' may be provided.

6. Applicator Output Testing

Any suggestion that the power output, as indicated on the front panel display or by the patient response, is different from normal should result in the machine being sent for repair. Access to a microwave power meter is highly desirable in order that correct operation can be confirmed. Special training in the use of this calibration equipment is required.

7. Safety Precautions for the Operator

7.1 Only equipment that is within the specifications for safety as laid down in BS 5724 (parts 1 and 2.3) should be used. 7.2 Occupat ional exposure t o radio f requency electromagnet ic f ie lds in the frequency range 2,000-300,000 MHz should not exceed 5 ~nW/cm ' .~

Exposure of the operator to radio frequency fields can, and should, be minimised by observing the following precaution.

The operator should stay at least 1.5 metres from the applicator during operation of the equipment. During positioning of the applicator the output should be switched off.

8. Safety Precautions for the Patient

Patients should always be tested for impairment of sensation to heat before treatment begins.

8.1 Exposure of the patient to radio frequency energy should be restricted to the minimum dosage required to achieve the benefit desired. 8.2 The treatment should be terminated if the patient shows any signs of distress, such as pain or any uncomfortable sensation. 8.3 Records should be kept for each patient treatment episode. These should include notes on the power, irradiation time, beam application technique and any special features of the treatment - eg patient sensation impairment, pacemaker, pregnancy.

8.4 Contra-indications and precautions4, * Burns and scalds. The skin should be kept dry to avoid scalds from excessive temperature rise occurring in the perspiration as water is preferentially heated by microwave radiation. It is advisable to cover the skin under the applicator wi th a dry towel to absorb any perspiration. Eratogenic effects. Maternal hyperthermia may give rise to

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abnormal fetal development. Consequently it is desirable t o avoid microwave exposure during, or immediately before, pregnancy - especially in the lower abdominal and pelvic regions. Metallic (or conductive) implants. Metal modifies the electromagnetic field, potentially leading t o hazardous temperature rise in the tissues. Patients having metall ic implants in the region requiring treatment should thus no t receive microwave therapy. Similarly metall ic objects such as jewellery should be removed f rom the area o f treatment. Cardiac pacemakers. Strong electromagnetic fields can affect the performance of a pacemaker, especially if o f t he 'demand' type. The risk is greatest if t he thorax is being treated. It is desirable t o swi tch the pacemaker t o a constant mode if one is available, and t o treat only the extremit ies6 Impaired sensation. Patients having impaired sensation in the region being treated should no t be subjected t o this form of therapy. Evidence of cancer. This should be a contra-indication unless the treatment is for t he tumour itself, as part o f t he cancer therapy. This is because temperature rise may accelerate growth o f t he tumour.

Open wounds, haemorrhage, ischaemic tissue, acute infection in the treatment site are all contra-indications. Regions of poor vascularity should n o t be subjected t o microwave irridiation. The eyes should n o t be treated with microwave energy. Particular care should be exercised i f areas near t o the eyes are being treated. The patient should then wear protective eye goggles t o avoid heating the lens of t he eye, a particularly sensitive structure. The testes should n o t be subjected t o microwave radiation. Microwave energy should be used with extreme caution when applied via a body orifice.

9. Training of Personnel

Operators applying microwave therapy equipment t o patients should hold an appropriate professional qualification and have completed a course in microwave therapy wh ich should include instruction in the basic physics and biological effects o f microwave radiation, instrumentation, indications and contra-indications, dosages and applications. It is recommended tha t short revision courses be attended a t least once every f ive years, and tha t all physiotherapists should keep up to date by reading appropriate professional journals.

10. References 1. BS 5724 (1989). Safety of medical electrical equipment. Part 1.

General Requirements. British Standards Institution. London, England.

2. BS 5724 (1985). Section 2.6 Specification for microwave therapy equipment. British Standards Institution. London, England.

3. IRPA (1988). 'Guide lines on limits of exposure to radiofrequency electromagnetic fields in the frequency range from 100 kHz to 300 GHz', Health Physics, 54, 115-123.

4. Delpizzo, V and Joyner, K H (1987). 'On the safe use of microwave and shortwave diathermy units', Australian Journal of Physiotherapy, 33, 152-162.

5. Health Equipment Information Number 88 (1980), 77/80. 'Microwave diathermy is safe in normal use' (DHSS 14 Russell Square, London WClB 5EP).

6. Health Notice (Hazard) (80)lO (1980). 'Implantable cardiac pacemakers - Interference generated by diathermy equipment' (DHSS).

7. 'Practical aspects of nonionising radiation protection' (1982). Hospital Physicists Association, Conference Report Series - 36.

8. Australian Physiotherapy Association (1982). 'Clinical standards for the use of electrophysical agents', Practice ,Accreditation Manual, Appendix 11.

9. Safety Action Bulletin 61, SAB(90)49 (1990). 'Physiotherapy equipment: Care and maintenance', Department of Health.

10. Health Equipment Information 98 (1990). 'Management of medical equipment and devices', Department of Health.

The Cervical and Thoracic Spine - Mechanical diagnosis and therapy, by R A McKenzie. Spinal Publications Ltd, PO Box 275, West Byfleet, Surrey KT14 6ET, 1990 (ISBN 0 9597746 7 X). Illus. 320 pages. €46.50.

The original principles that Robin McKenzie advocates for manual therapy of the lumbar spine have now, in this volume, been applied to the diagnosis and treatment of cervical and thoracic spine disorders. The chapters on the cervical spine constitute the main bulk of the book, which only five of a total of 26 chapters referring to the thoracic spine. This is a reflection of the low percentage of patients with mechanical disorders of the thoracic spine and hence the limited opportunity the author had to observe and treat them.

The book briefly describes the anatomy of the cervical and thoracic spine and discusses the biomechanics and pathophysiology associated with these regions. Central to the author's concept of mechanical diagnosis and therapy are the biomechanics of the intervertebral disc and this is reflected in the text. However, the majority of the papers that he quotes in

support of his concept refer to studies of the lumbar intervertebral disc.

Three specific subgroups are identified: postural, dysfunction and derangement models. Each one is described in detail, highlighting predisposing and precipitating factors in each of the groups. A system of classification by pain patterns, based on the recommendations of 'The Report of the Quebec Task Force on Activity Related Spinal Disorders' forms the basis of the diagnosis.

The chapters on interviewing the patient and the clinical examination are clearly set out with each movement in the sequence of the examination accompanied by a photograph to illustrate the text. This also applies to the descriptions of the procedures and techniques of mechanical therapy. Having provided the reader with the theory and techniques, the author then proceeds to illustrate the cervical and thoracic models by outlining the aims of treatment and prescribing a sequence of management that includes exercises and if necessary special techniques. Asthe author states in his book 'The emphasis in the McKenzie philosophy of patient care is self-treatment' so in all

cases the initial management of the patient's problem is by exercise although Mr McKenzie does acknowledge that of the 70% of patients who can self-treat, improvement in a significant number will be accelerated by the application of mobilising procedures.

This approach to patients is reliant on identifying syndromes and classifying patterns of pain; in clinical practice many of these patients do exist but there are also a significant number who present with less well-defined problems. In view of this and also because some of the exercises and techniques described in the book, particularly where there is extension and rotation of the cervical spine, with or without traction, demand more caution than the author implies. I suggest the book should be used by more experienced manual therapists.

It provides a useful approach to the management of patients with cervical and thoracic spine problems and will be a very useful reference book for those people who have attended courses on mechanical diagnosis and therapy. SUSAN M WEEKS BA MCSP DipTP

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