Electrosurgical hysteroscopy: Principles and expert techniques for optimizing the resectoscope loop

How monopolar energy works

When first developed, all resectoscopes used monopolar energy. As such, throughout the 1990s, the monopolar resectoscope was the gold standard for performing electrosurgical hysteroscopy. Because the current travels a long distance between the active and the return electrode in a monopolar setup, a hypotonic, nonelectrolyte-rich medium (a poor conductor), such as glycine 1.5%, mannitol 5%, or sorbitol 3%, must be used. If an electrolyte-rich medium, such as normal saline, is used with a monopolar device, the current would be dispersed throughout the medium outside the operative field, causing unwanted tissue effects.

Although nonelectrolyte distension media improve visibility when encountering bleeding, they can be associated with hyponatremia, hyperglycemia, and even lifethreatening cerebral edema. Furthermore, glycine use is contraindicated in patients with renal or hepatic failure since oxidative deamination may cause hyperammonemia. Because of these numerous risk factors, the fluid deficit for hypotonic, nonelectrolyte distension media is limited to 1,000 mL, with a suggested maximum fluid deficit of 750 mL for elderly or fragile patients. Additionally, because the return electrode is off the surgical field in monopolar surgery, there is a risk of current diversion to the cervix, vagina, or vulva because the current travels between the active electrode on the surgical field to the return electrode on the patient’s thigh. The risk of current diversion is greater if there is damage to electrode insulation, loss of contact between the external sheath and the cervix, or direct coupling between the electrode and the surrounding tissue.

Advantages of the bipolar resectoscope

Because of the potential risks associated with the monopolar resectoscope, over the past 25 years the bipolar resectoscope emerged as an alternative due to its numerous benefits (TABLE 1).

Unlike monopolar resectoscopes, bipolar resectoscopes require an electrolyte-rich distension medium such as 0.9% normal saline or lactated Ringer’s. These isotonic distension media allow a much higher fluid deficit (2,500 mL for healthy patients, 1,500 mL for elderly patients or patients with comorbidities) as the isotonic solution is safer to use. Furthermore, it allows for lower voltage settings and decreased electrical spread compared to the monopolar resectoscope since the current stays between the 2 electrodes. Because isotonic media are miscible with blood, however, a potential drawback is that in cases with bleeding, visibility may be more limited compared to hypotonic distension media.

Evidence on fertility outcomes

Several studies have compared operative and fertility outcomes with the use of monopolar versus bipolar hysteroscopy.

In a randomized controlled trial (RCT) comparing outcomes after hysteroscopy with a monopolar (glycine 1.5%) versus bipolar (0.9% normal saline) 26 French resectoscope loop, Berg and colleagues found that the only significant difference between the 2 groups was that the change in serum sodium pre and postoperatively was greater in the monopolar group despite having a smaller mean fluid deficit (765 mL vs 1,227 mL).¹

Similarly, in a study of fertility outcomes after monopolar versus bipolar hysteroscopic myomectomy with use of a 26 French resectoscope Collins knife, Roy and colleagues found no significant differences in postoperative pregnancy rates or successful pregnancy outcomes, operative time, fluid deficit, or improvement in menstrual symptoms.² However, the monopolar group had a much higher incidence of postoperative hyponatremia (30% vs 0%) that required additional days of hospitalization despite similar fluid deficits of between 600 and 700 mL.²

Similar findings were noted in another RCT that compared operative outcomes between monopolar and bipolar resectoscope usage during metroplasty for infertility, with a postoperative hyponatremia incidence of 17.1% in the monopolar group versus 0% in the bipolar group despite similar fluid deficits.³ Energy type had no effect on reproductive outcomes in either group.³

Continue to: How does the resectoscope compare with mechanical tissue removal systems?...