Diathermy is electrically induced heat or the use of high-frequency electromagnetic currents as a form of physical or occupational therapy and in surgical procedures. The field was pioneered in 1907 by German physician Karl Franz Nagelschmidt, who coined the term diathermy from the Greek words dia and θέρμη therma, literally meaning “heating through” (adj., diather´mal, diather´mic).
Diathermy is commonly used for muscle relaxation, and to induce deep heating in tissue for therapeutic purposes in medicine. It is used in physical therapy and occupational therapy to deliver moderate heat directly to pathologic lesions in the deeper tissues of the body.
Diathermy is produced by three techniques: ultrasound (ultrasonic diathermy), short-wave radio frequencies in the range 1–100 MHz (shortwave diathermy) or microwaves typically in the 915 MHz or 2.45 GHz bands (microwave diathermy), the methods differing mainly in their penetration capability. It exerts physical effects and elicits a spectrum of physiological responses.
The same techniques are also used to create higher tissue temperatures to destroy neoplasms (cancer and tumors), warts, and infected tissues; this is called hyperthermia treatment. In surgery diathermy is used to cauterize blood vessels to prevent excessive bleeding. The technique is particularly valuable in neurosurgery and surgery of the eye.
Short wave diathermy machines use two condenser plates that are placed on either side of the body part to be treated. Another mode of application is by induction coils that are pliable and can be molded to fit the part of the body under treatment. As the high-frequency waves travel through the body tissues between the condensers or the coils, they are converted into heat. The degree of heat and depth of penetration depend in part on the absorptive and resistance properties of the tissues that the waves encounter.
Short wave diathermy operations use the ISM band frequencies of 13.56, 27.12, and 40.68 megahertz. Most commercial machines operate at a frequency of 27.12 MHz, a wavelength of approximately 11 meters.
Short wave diathermy usually is prescribed for treatment of deep muscles and joints that are covered with a heavy soft-tissue mass, for example, the hip. In some instances short wave diathermy may be applied to localize deep inflammatory processes, as in pelvic inflammatory disease. Short wave diathermy can also be used for hyperthermia therapy, as an adjuvant to radiation in cancer treatment.
PHYSIOLOGY EFFECT OF DIATHERMY
Short Wave Diathermy
Short wave diathermy utilizes electromagnetic radio waves to convert energy to deep heat. As with ultrasound, short wave diathermy is thought to exert its therapeutic effects by both thermal and nonthermal mechanisms. The primary nonthermal mechanism associated with the use of therapeutic short wave diathermy occurs via vibration induction of tissue molecules when exposed to radio waves. By changing the characteristics of the shortwave applicator, the clinician can target the specific type of tissue he or she wants to heat. By using an inductive applicator that generates a magnetically induced eddy of radio wave currents in the tissues, selective heating of water-rich tissues such as muscle can be obtained. By using a capacity coupled applicator that generates heat via generation of an electrical field, selective heating of water poor tissues such as subcutaneous fat and adjacent soft tissues can be accomplished. With either type of short wave diathermy, metal must be avoided, so the patient must remove all jewelry and treatment must be carried out on a nonconductive treatment table, such as one made of wood. Furthermore, implanted pacemakers, spinal cord stimulators, surgical implants, and copper-containing IUDs should never be exposed to short wave diathermy, to avoid excessive heating and thermal injury. Indications for short wave diathermy mirror those listed for ultrasound, although the ability to heat subcutaneous fat and adjacent soft tissues not reached by superficial heat modalities and less well heated by ultrasound may lead the clinician to choose short wave diathermy to treat painful conditions and other pathologic processes that are thought to find their nidus in more superficial tissues.
Diathermy used in surgery is of typically two types.
where electric current passes from one electrode near the tissue to be treated to other fixed electrode (indifferent electrode) elsewhere in the body. Usually this type of electrode is placed in contact with buttocks or around the leg.
where both electrodes are mounted on same pen-like device and electric current passes only through the tissue being treated. Advantage of bipolar electrosurgery is that it prevents the flow of current through other tissues of the body and focuses only on the tissue in contact. This is useful in microsurgery and in patients with cardiac pacemaker.
TYPES OF ELECTRODS
1 CABLE ELECTROD
2 DISC ELECTROD
3 PAD ELECTROD
Burns from electrocautery generally arise from a faulty grounding pad or from an outbreak of a fire. Monopolar electrocautery works because radio frequency energy is concentrated by the surgical instrument’s small surface area. The electrical circuit is completed by passing current through the patient’s body to a conductive pad that is connectd to the radio frequency generator. Because the pad’s surface area is large relative to the instrument’s tip, energy density across the pad is reliably low enough that no tissue injury occurs at the pad site. Electrical shocks and burns are possible, however, if the circuit is interrupted or energy is concentrated in some way. This can happen if the pad surface in contact is small, e.g. if the pad’s electrolytic gel is dry, if the pad becomes disconnected from the radio frequency generator, or via a metal implant. Modern electrocautery systems are equipped with sensors to detect high resistance in the circuit that can prevent some injuries.
As with all forms of heat applications, care must be taken to avoid burns during diathermy treatments, especially in patients with decreased sensitivity to heat and cold. With electrocautery there have been reported cases of flash fires in the operating theatre related to heat generation meeting chemical flash points, especially in the presence of increased oxygen concentrations associated with anaesthetic.
Concerns have also been raised regarding the toxicity of surgical smoke produced by electrocautery. This has been shown to contain chemicals which may cause harm to patients, surgeons and/or operating theatre staff.
For patients that have a surgically implanted Spinal Cord Stimulator (SCS) system, diathermy can cause tissue damage through energy that is transferred into the implanted SCS components resulting in severe injury or death.
Short-wave Diathermy can be effective in providing some relief and treatment of symptoms related to:
sprains and strains
Similar to other methods for applying energy to the body, short wave diathermy can be applied in two distinct modes: continuous or pulsed. When continuous mode is used, the tissue being targeted becomes heated as the waves constantly convey energy to them. Pulsed mode is used when less heat is desired for the affected tissue. When short wave diathermy is applied in pulse mode, the mechanical effects of the treatment are applied independent of the thermally affecting (heating) the tissue. One of the most promising applications of pulsed mode is it is able to facilitate increased flexibility and joint mobilization for restoration of joint range of motion. Short-wave diathermy includes non-thermal benefits as well including:
- Acceleration of cell growth
Enabling damaged cells to return to normal function
Increase wound healing
Contraindication of Short Wave Diathermy
Over wet dressing
Infected open wound
Impaired thermal sensation
Severe cardiac abnormality
Blood pressure abnormality
Tendency of bleeding
Danger/Precaution of Short Wave Diathermy
Proper connection of machine and electrodes
Ensure the earthing of machine
Do not allow the patient to touch the unit.
Not over cloth
Not over wet area
Check the thermal sensitivity
Skin surface separated by towel
Ensure even pattern of heat
Wait for 2-3 minutes after setting
Proper position of the patient.