Electro and laser surgery: basic principles

Electrosurgery uses high-frequency electrical current that passes through tissue, causing it to heat in the area of high current density. This heating produces two main effects: tissue dissection and coagulation with hemostasis, with the balance between these effects determined by the current parameters and electrode contact technique.

Electrocoagulation and endothermy, in a narrower sense, involve the transfer of heat from a heated instrument to tissue without the passage of current through the patient's body. In practice, this is important for understanding complications: electrosurgery has unique risks associated with the electrical circuit and "alternative paths" of current that are not present with purely thermal treatments.

Laser surgery uses coherent light of a specific wavelength, which is absorbed by tissues differently depending on their composition, primarily water and hemoglobin content. In endoscopy, the laser can be used for precise incision, ablation, or vaporization, and the thermal damage profile depends on the wavelength, power, spot diameter, and exposure time. [3]

Intrauterine electrosurgery and laser are used as part of hysteroscopy, where three things are simultaneously important: quality of vision, a safe cavity expansion environment, and control of energy- and fluid-related complications. Current hysteroscopy guidelines emphasize "see and treat" as the goal, but safety begins with the correct choice of technology for the task. [4]

Table 1. What is the difference between electrosurgery, electrocoagulation and laser?

Technology	Energy source	How the effect is formed	Key risks
Electrosurgery	high-frequency current	heating in the high current density zone, cutting and coagulation	burns from stray energy, burns in the patient's plate area, fires, surgical smoke [5]
Electrocoagulation and endothermy	heated element	direct heat transfer to the tissue	local burns, but no electrical risks
Laser	coherent light	absorption of light by tissue with ablation or coagulation	Thermal damage from improper exposure, smoke, eye damage if unprotected [7]

How current turns into cutting or coagulation: what happens in tissue

Heat is generated where the electrical circuit has its smallest diameter and, therefore, its highest current density. Therefore, a thin electrode heats tissue faster and more accurately than a wide one, while a large patient plate disperses energy over a large area and, under normal conditions, does not overheat.

Cutting mode often uses continuous alternating current with relatively low voltage, which rapidly increases the temperature of the intracellular fluid and causes its evaporation. Microscopically, this appears as cell rupture and "evaporation," which is perceived as a cut with a smaller lateral zone of thermal damage.

In coagulation mode, pulsed current with higher voltage and a shorter active time is often used. Heating occurs more slowly, dehydration and protein denaturation predominate, and a more profound coagulation effect is achieved, which is beneficial for hemostasis, but increases the risk of more pronounced carbonization and thermal spread during prolonged activation.

"Mixed" modes attempt to combine incision and coagulation, but in practice, safety depends more on technique: short activations, working only in the visual field, controlled electrode contact, and avoiding "air activation" near tissue. These principles underlie modern training programs for the safe use of surgical energy. [11]

Table 2. Effects of electrosurgery and typical clinical tasks

Effect on fabric	What predominates physically	What is it most often used for?	A common mistake that increases risk
Section	rapid evaporation and rupture of cells	dissection of septa, tissue resection	long-term activation in situ, increased lateral heating
Coagulation	dehydration and denaturation of protein	hemostasis, vascular coagulation	"cauterization" until a pronounced carbon deposit and deep burn occurs
Fulguration	surface spark coagulation	surface treatment, small bleeding areas	activation out of sight, risk of uncontrolled heat [14]
Mixed mode	balance of heating and dehydration	dissection with simultaneous hemostasis	choosing a mode instead of the correct technique

Monopolar and Bipolar Electrosurgery: Circuit, Differences, and Risks

In a monopolar system, current flows from the active electrode through the patient's tissue to the patient's paddle, completing the electrical circuit. This makes the monopolar technique versatile, but it increases the requirements for correct paddle placement, the integrity of the instrument's insulation, and the prevention of alternate current paths. [16]

In a bipolar system, current flows between two electrodes housed in a single instrument, affecting only the tissue between them. This reduces the risk of secondary burns and generally reduces dependence on the patient's paddle. However, bipolar instruments can have limitations in the type of effect and require an understanding of how coagulation varies depending on the volume of tissue in the jaws and the degree of dehydration. [17]

The most dangerous complications of electrosurgery are often related not to "inappropriate power," but to the physics of unintended energy transfer: direct conduction, capacitive conduction, insulation failure, and unintended activation. Current surgical energy safety guidelines highlight these mechanisms as mandatory for training and prevention at the OR team level. [18]

A separate group of risks is associated with surgical smoke and fires in the operating room. Professional guidelines emphasize the need for smoke evacuation, proper oxygen management, and ignition source control, as thermal devices are a key element of the "fire triangle." [19]

Table 3. Monopolar and bipolar electrosurgery

Parameter	Monopolar system	Bipolar system
Current path	through the patient's body to the patient's plate	between 2 electrodes in a tool [20]
Key risk area	alternative current paths, burn in the plate area	local tissue overheating during prolonged activation [21]
Patient plate requirements	mandatory	not usually required [22]
Where it is especially important	resectoscopy, universal incisions and coagulation	precise coagulation, work in an isotonic environment in hysteroscopy [23]

Table 4. Main mechanisms of electrosurgical burns and prevention

Mechanism	What's happening	Practical prevention
Burn in the patient's plate area	poor contact, small contact area, overheating	correct placement, contact control, absence of folds and moisture [24]
Direct guidance	the active electrode accidentally contacts another instrument and transfers energy	Activation only in the line of sight, avoid contact with instruments during activation [25]
Capacitive guidance	energy "passes" through insulation under certain conditions	use compatible systems, minimize airborne activation, check insulation [26]
Insulation breach	microdamage to the insulation causes a hidden burn	regular inspection of instruments, insulation control, personnel training [27]
Unintentional activation	pedal or handle control error	standardization of commands, visual control of active mode [28]

Features of hysteroscopy: the expansion environment of the cavity and “fluid absorption syndrome”

Within the uterine cavity, electrosurgery is closely linked to the dilatation environment, as the fluid determines visibility and simultaneously affects electrical conductivity. Monopolar resectoscopes traditionally require non-electrolyte media, whereas bipolar systems allow operation in 0.9% isotonic sodium chloride solution, which changes the complication profile. [29]

Non-electrolyte hypotonic fluids during intravascular absorption can lead to hyponatremia and water intoxication with the risk of cerebral and pulmonary edema. Therefore, guidelines traditionally set a low threshold for acceptable fluid deficit for hypotonic fluids, and when this threshold is reached, the intervention should be stopped. [30]

Switching to bipolar technologies and isotonic saline significantly reduces the risk of severe hyponatremia, but does not eliminate the risk of volume overload, especially during prolonged surgeries, high intracavitary pressure, and myometrial vascular occlusion. Current guidelines emphasize the need for continuous fluid balance monitoring and predetermined deficit limits, especially in patients with concomitant cardiac and renal disease. [31]

Practical safety is based on three steps: selecting the appropriate fluid for the energy type, limiting pressure and time, and systematically recording the volume of fluid introduced and removed with real-time recording of deficits. These points are described in detail in guidelines for fluid management in surgical hysteroscopy. [32]

Table 5. Uterine cavity expansion environments, energy compatibility and main risks

Wednesday	Compatibility	The main risk in absorption	What needs to be controlled especially strictly
Isotonic sodium chloride solution 0.9%	bipolar energy, part of mechanical systems	volume overload, pulmonary edema	fluid deficiency, pressure, duration [33]
Non-electrolyte hypotonic solutions, such as glycine 1.5%	monopolar energy	hyponatremia, water intoxication	fluid deficit and serum sodium [34]
Non-electrolyte isoosmolar solutions, such as mannitol, sorbitol in protocols	monopolar energy in individual circuits	volume overload and metabolic effects	fluid deficit and clinical signs of overload [35]

Table 6. Typical fluid deficit thresholds after which intervention should be stopped

Type of environment	Deficiency threshold in a healthy patient	Deficiency threshold for concomitant diseases
Hypotonic non-electrolyte media	1000 ml	750 ml [36]
Isotonic electrolyte solutions	2500 ml	1500 ml [37]

Laser Surgery in Hysteroscopy: Benefits and Limitations

Lasers differ from electrosurgery in that energy is delivered by light rather than current, and tissue responds depending on which chromophore absorbs the wave. Some lasers target water, resulting in very superficial ablation, while others penetrate deeper, increasing the risk of deep thermal damage if the settings are incorrect. [38]

In hysteroscopy, the diode laser has attracted considerable interest in recent years as a tool for the outpatient "see and treat" approach to intrauterine pathology. A 2024 systematic review describes the use of the diode laser for endometrial polyps and certain types of leiomyomas, noting overall feasibility and low complication rates in the available studies. [39]

The potential advantages of lasers in the uterine cavity are usually summarized as follows: precision of action, the ability to work with fine instruments, controlled ablation, and sometimes a reduced need for "rough" electrical incisions. However, the quality of evidence depends on the design of the studies, and the choice of technology should take into account equipment availability, surgeon experience, and the specific task, such as the FIGO nodule type and fertility plans. [40]

Lasers do not replace basic safety requirements: eye protection, smoke control, prevention of burns from prolonged exposure, proper operation in liquid environments, and adherence to laser safety regulations in the operating room. Guidelines for the safe use of energy devices consider these measures a mandatory element of operating room culture. [41]

Table 7. Lasers most commonly discussed in gynecological endoscopy

Laser type	Key takeover target	Typical exposure profile	Application notes
Carbon dioxide laser	water	very superficial ablation	requires strict laser safety [42]
Neodymium laser	deeper penetrating radiation	deeper heating	higher requirements for exposure control [43]
Diode laser	depends on the wavelength, often closer to hemoglobin and water	controlled ablation in “see and treat”	2024 systematic reviews describe use in intrauterine pathology [44]

A practical solution map: how to choose energy and avoid complications

The choice of mode begins with the clinical task: septal dissection, polyp removal, submucosal node resection, hemostasis, or endometrial ablation. For each task, it is safer to determine in advance which effect is primarily needed—incision or coagulation—and use the minimum necessary power with short activations. [45]

In hysteroscopy, it is critical that the energy type be appropriate for the cavity expansion environment. The error "monopolar energy in an electrolyte environment" or "loss of fluid deficit control" is considered a systemic cause of complications, so modern guidelines emphasize checklists, continuous deficit monitoring, and predetermined stopping thresholds. [46]

Electrosurgical safety generally focuses on preventing injuries from unintended energy. Training programs and guidelines describe insulation testing, proper patient pad placement, visual activation only, and pedal handling discipline as basic standards. [47]

Specific requirements for lasers include standardized laser hazard zones, eye protection, personnel training, and strict smoke removal policies. Modern documents on the safe use of energy devices include laser safety as a separate set of practical measures. [48]

Table 8. Safety checklist before turning on the power during hysteroscopy

Step	What to check	For what
1	the energy type is selected and is compatible with the expansion environment	prevention of electrolyte complications and technical errors [49]
2	a fluid deficit limit has been set and a person responsible for accounting has been appointed	early stopping before complications [50]
3	the electrode is activated only in the field of vision	reducing the risk of hidden burns [51]
4	The isolation of instruments and the correct placement of the patient plate in a monopolar system were checked	prevention of alternative burns [52]
5	smoke removal is enabled and fire safety regulations are observed	reducing the risk of exposure to smoke and fires [53]
6	When using a laser, eye protection and laser zone rules must be used.	eye injury prevention [54]