DIATHERMY AND THE ANESTHESIOLOGIST

• WHY WE SHOULD KNOW? 1.Anesthesiologist may be blamed if burns occurs due to malposition of the plate 2. It can interfere with monitors e.g. ECG and pulseoximeters 3. It can disrupt pacemaker function in a patient, having it.
• Diathermy depends on the heat generated when a current pass through a tissue and is used to coagulate blood vessels and cut through tissues
• A high frequency current is necessary for this, as myocardium is sensitive to DC and low frequency AC [the usual Mains frequency of 50 Hz will precipitate VF]. Very high frequencies have minimal tissue penetration and pass without harming the myocardium
• A 0.5 MHz alternating sinewave is used for cutting and a 1.0-1.5 MHz pulsed sinewave pattern is used for coagulation
• UNIPOLAR DIATHERMY & PROBLEMS: Here the forceps represent one electrode (small area, high current density and significant heat generation) and the diathermy plate ( indifferent electrode) over the patient represent the other electrode (large area, less heat). If the the plate is malpositioned, the current may pass through any point of metal contact* like ECG electrodes, metal poles of lithotomy, operation table etc, and may result in passage of high current density as the area of contact is small, resulting in a burn. So we should ensure that the plate is in close and proper contact with a large, highly perfused (will dissipate heat) area of skin (adhesive gels are useful). If we place it near to metal prosthesis (e.g. Hip), which has a low resistance than tissue, it will generate a high current density, resulting in burns. A unipolar diathermy can generate 150-400 Watts of energy.
• BIPOLAR DIATHERMY: Current passes between the two blades of the forceps; so requires no plate; safer in patients with pacemaker. But can generate only 40 Watts of energy. So efficacy is less and may be used for coagulation of small blood vessels
• OTHER PROBLEMS: Sometimes diathermies may cause ignition of skin preparation spirit. Newer diathermies dont have earthing; but if your machine is having earthing, an inappropriate earthing will result in current passing through other routes mentioned above*, resulting in burns.
• Cautious use of diathermy is required in patients with pacemakers: