Interrupt the blood flow. Coaptive vessel sealing using any type of monopolar current may be ineffective if the blood flow remains uninterrupted. Unless a vessel is sufficiently squeezed before electricity is applied, current density is dramatically reduced by conduction in blood, and luminal temperatures undergo little change, as any heat is dissipated by convection. Deceived by the appearance of well-coagulated tissue, a surgeon may discover an alarmingly viable core at the time of incision. Regardless of the selected output current (that is, “cut,” “blend,” or “coag”), coaptive desiccation with monopolar electrosurgery is usually insufficient to reliably secure the uterine or ovarian vessels during hysterectomy and oophorectomy.
Achieve the appropriate cutting arc. Electrosurgical cutting (vaporization/ablation) is possible whenever voltage is sufficient to create an electrical spark between an electrode and underlying tissue; tissue cutting is more apt to occur if the arcing remains unabated. When it does, cellular water is superheated to temperatures greater than 600°C, causing explosive vaporization secondary to the production of highly disruptive pressure (since steam occupies 6 times the volume of liquid water).
Although all of the typical output currents (“cut,” “blend,” and “coag”) provide sufficient voltage to ionize the air gap and arc to tissue, the higher voltages of “blend” and “coag” create progressively wider zones of thermal damage at the margins of the incision (FIGURE 3) These effects are amplified by using broad-surface electrodes.
Wide versus narrow hemostasis. Using “blend” or “coag” current to cut in order to provide wider hemostasis can be helpful during myomectomy, as well as when operating down the broad ligament and along the vaginal fornices during hysterectomy, across vascular adhesions, and to clarify the space of Retzius in preparation for colposuspension and paravaginal repair. Higher-voltage currents also facilitate incision of tissues that have greater impedance, such as fatty or desiccated pedicles and adhesions.
On the other hand, it is more prudent to utilize the lower-voltage “cut” current via the edge of an electrode for electrosurgical incision whenever lateral thermal spread may pose extra liability to adjacent tissues, such as the ovarian cortex during cystectomy and the ureter or rectum during excision of endometriosis from the lateral pelvic sidewall or cul-de-sac.
Deceived by the appearance of well-coagulated tissue, surgeons may discover an alarmingly viable core at the time of incision.
- Fulguration is the use of high-voltage sparking produced by “coag” current to coagulate a broad surface with open bleeders. As opposed to the continuous arcing produced by “cut” current, the highly interrupted output of “coag” current causes the arcs to strike the tissue surface in a widely dispersed and random fashion. This leads to more rapid thermal change, creating a zone of superficial coagulation.
I typically employ fulguration to control small bleeders and vessels cut on end along the undersurface of the ovarian cortex during cystectomy, atop the myometrial bed during myomectomy, and alongside Cooper’s ligament during colposuspension.
Protect vital structures with short bursts of “coag” current. If bleeding near the bowel, bladder, or ureter cannot be controlled with pressure alone, carefully directed short bursts of noncontact “coag” current with a broad-surface electrode may help you attain effective hemostasis with the least-possible amount of electrosurgical penetration.
Despite the high-voltage output involved, fulguration is useless in a wet, conductive surgical field due to the random diffusion of current.
FIGURE 2 Range of output voltages
Relative changes in voltage and average current related to “cut,” “blend,” and “coag” currents.
FIGURE 3Zones of thermal damage related to voltage
Using a conventional electrosurgical generator for tissue cutting, the margin of thermal necrosis expands with increasing voltage.
Bipolar electrosurgery
Mechanism of action. Bipolar electrosurgery consolidates an active electrode and return electrode into an instrument with 2 small poles. These poles can be the tines of a forceps, blades of a scissors, or an electrode matched to a more proximal conductive collar separated by an insulator. The output typically used is the low-voltage “cut” current.
Advantages of bipolar energy. Localization of current between the poles offers distinct advantages. Thermal damage is generally limited to a discrete volume of tissue. A bipolar forceps can be used to coapt and thermally weld blood vessels. The concentrated current and small distance between the poles also make it possible to desiccate tissue that is immersed in fluid. This modality is less useful, however, when open blood vessels are retracted or tissue pedicles are very thick.
Because it tends to promote the flow of energy well beyond desiccation, an ammeter should not be used to determine the treatment endpoint for coagulation of blood vessels in the vicinity of vital tissue.