2 The technology

Description of the technology


The Mega Soft Patient Return Electrode (Megadyne Medical Products) is a reusable dispersive capacitive electrode designed for use during monopolar electrosurgery. The electrode, which is incorporated into a pad, is intended to reduce the risk of burns and to provide pressure relief.


Electrosurgery uses high frequency current to achieve surgical effects such as cutting and coagulation. It is commonly referred to as diathermy. Monopolar electrosurgery (monopolar diathermy) specifically relies on the patient forming part of the electrical circuit. In addition to the patient's tissue, the electrical circuit also includes the electrosurgical unit, which generates the electrical current, an active electrode and a patient return electrode. High frequency electrical current is conducted from the target tissue to an electrosurgical unit, or generator. When the surgeon touches a selected area of the patient's tissue with the electrosurgery tool (the active electrode), current passes from the tool, is distributed widely throughout the patient's body and then returns to the electrosurgical unit via a patient return (dispersive) electrode. In current NHS clinical practice, the electrical circuit is completed by using an adhesive disposable single-use pad with an integral return electrode, which is attached directly to the patient's skin (patient return electrode). These electrodes consist of a conductive foil covered by a polymer. The Mega Soft Patient Return Electrode is incorporated into a large pressure-relieving pad (approximately 117 cm x 51 cm x 1.25 cm) that is placed on the operating table on which the patient lies. When the patient lies on the pad containing the Mega Soft Patient Return Electrode the electrical circuit is completed.


A standard disposable single-use patient return electrode measures approximately 12 cm x 13 cm. The area covered by the pad needs to be large enough to maximise conduction of electrical energy away from the patient (disperse the electrical current) and so minimise the rise in skin temperature. A standard patient return electrode is therefore also known as a dispersive electrode. It may also be called a neutral electrode, and this is the name used in the relevant technical standard specification, for example the IEC 60601-2-2-2009. In clinical practice, the standard patient return electrode is commonly referred to as a diathermy pad.


A standard disposable single-use patient return electrode forms a resistive circuit and the direct electrical connection relies on good contact with the patient. The Mega Soft Patient Return Electrode does not rely on direct contact with the patient and forms a capacitive circuit. The Mega Soft Patient Return Electrode is much larger than a standard disposable single-use patient return electrode and the sponsor states that this leads to a reduction in current density when compared with the disposable single-use patient return electrode. It should be noted that this will depend on the position of the patient and is likely to be true when the patient is lying supine and is in contact with a large area of the mat.


Most adverse events related to electrosurgery are patient burns. During electrosurgery, patients are at risk of 2 types of burn: return electrode site burns and alternative site burns. Return electrode site burns can occur when the contact area is reduced (for example, when a disposable pad partially peels off during surgery) and the current density increases. Some split disposable single-use patient return electrodes are designed to set off an alarm and cause the electrosurgical unit to cease to function when they start to peel off. Alternative site burns occur when some of the current does not follow the main circuit route, but finds an alternative path to earth rather than returning to the generator. If the alternative path is unintentionally directed towards the patient then a burn can occur. Most electrosurgical generators are isolated, which means the high frequency circuit is not referenced to earth directly. However, whenever high frequency currents are used, there is some leakage to earth, even in an isolated circuit. If the main circuit becomes harder to complete (for example, because of reduced patient contact with the return electrode), there is, in theory, an increased possibility of alternative current pathways that can result in alternative site burns.


During 2009/10 approximately 9.7 million inpatient surgical procedures were performed in the UK. It has been estimated that 2.81 million of these (29% of the total) involved general anaesthesia and lasted for more than 30 minutes. It is thought likely that monopolar electrosurgery is used in at least half of all surgical procedures; therefore, patient return electrodes are used in around 1.4 million procedures per year.


The cost of the Mega Soft Patient Return Electrode given in the sponsor's submission is £1,900 without VAT. The Mega Soft Patient Return Electrode can be used with all electrosurgical generators, with the exception of the ERBE generator when that is used on the High Cut and Endo Cut mode (as stated in the Mega Soft Patient Return Electrode instructions for use). It is recommended that each Mega Soft Patient Return Electrode is used for a maximum of 24 months.


The claimed benefits of the Mega Soft Patient Return Electrode presented by the sponsor are:

  • reduction in the incidence of burns in patients having monopolar electrosurgery, with a consequent drop in treatment and litigation costs

  • avoidance of skin shaving

  • reduction in skin irritation because the Mega Soft Patient Return Electrode is not attached directly to the patient's skin; this may be particularly applicable to patients with burns or other skin conditions as well as to paediatric patients and older patients with fragile skin

  • reduction in the risk of pressure-related injury resulting from immobility during surgery

  • reduction in staff time because the Mega Soft Patient Return Electrode is reusable, is not attached directly to the patient and therefore staff do not need to consider avoiding bony prominences, scar tissue and tattoos as they would when placing a disposable patient return electrode

  • cost saving and improved sustainability compared with current practice because the electrode is reusable and a separate pressure-relieving device may not be needed.

Current management


Current practice is to apply a disposable single-use patient return electrode to the skin before monopolar electrosurgery. If electrical conduction is impaired at the skin-to-pad surface interface, the current density increases and this can lead to an increase in skin temperature, which exposes the patient to a risk of return electrode site burns. Electrical conduction can be impaired when the contact area of the standard disposable single-use patient return electrode is reduced by body hair, adipose tissue, bony prominences, fluid invasion, peeling or failure of the electrode to adhere to the patient, or scar tissue. To optimise electrode contact, care must be taken to place the electrode on hair-free areas without bony prominences. This may mean that the skin needs to be shaved before the electrode is applied.


Patient return electrodes used in current practice are single-use and disposable: they vary in 2 main respects. First, they may have split (dual) and non-split (single) electrodes. Second, they may have integral lead wires to attach them to the generator or they may be supplied without lead wires. If a patient return electrode has integral lead wires then these are discarded with the disposable electrode after use. Patient return electrodes without attached lead wires are connected to the generator by reusable lead wires. All types of patient return electrode are available in a range of sizes for adults and children. NHS procurement data indicate that the most commonly used type of patient return electrode in the NHS in England is the split adult disposable single-use patient return electrode without a lead wire.