Electrical Heat Methods Electrocautery

Surgical diathermy is the mainstay of haemostatic control of small vessels and is convenient, quick, and relatively safe to use. The authors favour the use of monopolar diathermy forceps, where current passes through the active electrode, causing a localised heating effect before passing through the patient to the dispersive electrode (patient plate). It is of paramount importance that there is a large surface area contact of the plate electrode to prevent damage to tissues other than where the active electrode is applied. The coagulation setting is preferred, which produces less heat and coagulates proteins and desiccates cells, rather than cell explosion and destruction that occur with the cutting setting. The authors will generally perform a thy-roidectomy using diathermy alone as the haemostatic method, and rarely need to use ties or other aids to haemostasis.

Diathermy is not without potential hazards, however, as high energy electrical currents are passed through the body. The possibilities include interference with pacemaker function, heating effects with metal implants, and superficial burns as a result of spirit-based skin preparation or patient earthing through contact with metal or inappropriately applied patient electrodes.

Bipolar diathermy is inherently safer as current is passed between the tips of a pair of insulated forceps and less energy is required. It has limited efficacy, however, other than in the control of bleeding from very small blood vessels, and cutting is not possible.

Ultrasonic shears

The Harmonic Scalpel (Ethicon Endo-surgery, Cincinatti, Ohio, USA) uses ultrasonic technology that enables both cutting and coagulation at the precise point of impact. This instrument controls bleeding by tamponading the vessel and sealing it with a protein coagulum at temperatures ranging from 50 to 100°C. Coagulation occurs by means of protein denaturation, when the blade, vibrating at 55,000 Hz denatures the protein to form the coagulum seal. In contrast, electrocautery coagulates by burning at much higher temperatures, forming an eschar seal.

The advantage of the harmonic scalpel is that it offers greater precision in tight spaces near important structures, although the authors feel that the currently available hand piece is too large and cumbersome for use in the neck. The Harmonic Scalpel is also currently a relatively expensive piece of disposable equipment. Ultrasonic dissection, however, has a vital place in the abdomen in the laparo-scopic approach to adrenal and pancreatic endocrine surgery. It is the authors' favoured method for dissection and excision of insulinomas and other pancreatic endocrine tumours, and it has made laparoscopic adrenalectomy safe and feasible.

Potential benefits of ultrasonic haemostasis compared with elec-trosurgery include less lateral thermal damage,14 minimal smoke, and no risk of electric shock. The blade of the ultrasonic shears can, however, heat up quickly to high temperatures and damage the recurrent laryngeal nerve during surgery. Therefore, the blade should not be used closer than 3 mm from the nerve.15 The shears should always be used on a lower power setting and with short activation times to prevent collateral damage.16

Ligasure

Ligasure (Valleylab, Boulder, Colorado, USA) is a vessel sealing system that fuses vessels up to 7 mm in diameter without dissection or isolation and with minimal lateral thermal damage. It is a bipolar, computer controlled diathermy system that uses pressure and energy to create a seal by melting the collagen and the elastin in the vessel wall and reforming it into a permanent, plastic-like seal that does not rely on a proximal thrombus. Thermal spread is less than 1 mm with the Ligasure Precise instrument that is used in the neck, but thermal spread increases with vessel size.17 This is important in determining the device's safety around the recurrent laryngeal nerve and external branch of the superior laryngeal nerve. There was no difference in thermal spread between the Ligasure and the Harmonic Scalpel, and both systems have equal efficacy in securing vessels up to 7 mm in size to well above physiological levels of blood pressure.5,18

Studies of its results in thyroid surgery suggest that the Ligasure device is an effective and safe alternative, with faster operating times and possibly a lower risk of hypoparathyroidism when compared with conventional clamp-and-tie thyroidectomy.19--23

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