Understanding Diathermy
Diathermy is the use of high-frequency electrical currents to generate heat in bodily tissues, a technique used extensively in surgery for cutting, coagulating, and desiccating tissue. The procedure relies on the principle of current density, where concentrated current at a small point (the active electrode) generates enough heat to achieve the desired effect, while a dispersed current path causes no harm. The key difference between monopolar and bipolar diathermy lies in how the electrical circuit is completed, which directly impacts the risk of burns.
Monopolar Diathermy: A Higher Burn Risk
In a monopolar circuit, the electrical current flows from the active electrode, controlled by the surgeon, through the patient's body, and returns to the generator via a large dispersive pad, also known as a grounding pad. Because the current travels through the patient's body, the potential for unintended burns is significantly higher for several reasons:
- Return Electrode Burns: The most common type of burn in monopolar electrosurgery occurs at the site of the dispersive pad. If the pad's contact with the skin is inadequate—due to improper placement, poor skin preparation, or patient repositioning—the current density at the point of contact increases, leading to a thermal burn. Modern equipment often includes contact quality monitoring systems to mitigate this risk, but human error and patient characteristics can still play a role.
- Alternate Pathway Burns: If the return electrode is disconnected or an earthed metal object (like a patient bed frame) offers an alternative path, the current can seek a new, smaller exit point from the patient's body, causing a burn at that site. This can also happen if the patient has metallic implants, as the current can concentrate around these objects, causing unintended heating.
- Insulation Failure: In laparoscopic and other minimally invasive procedures, the active electrode is insulated to prevent the current from dispersing unintentionally. If there is a microscopic crack or a defect in this insulation, the current can leak and cause a burn to adjacent organs or tissue that the surgeon cannot see.
- Capacitive Coupling: This occurs primarily in laparoscopic procedures when current passes through intact insulation, forming a capacitor with a nearby metal instrument, like a trocar sleeve. If the current induces in the second conductor and is not properly dissipated, it can cause a burn where that instrument touches the patient's tissue.
Bipolar Diathermy: The Safer Alternative
In contrast, a bipolar circuit is much safer regarding burn risk because the current path is highly localized. The surgical instrument, typically a pair of forceps, contains both the active and return electrodes. The electrical current flows only through the tissue held between the tips of the forceps and does not pass through the patient's body to a distant return pad.
This fundamental difference eliminates the major risks associated with monopolar diathermy, such as return electrode burns and alternate pathway burns. The current is concentrated exactly where it needs to be, preventing thermal damage to surrounding tissues. For this reason, bipolar diathermy is the preferred method for delicate procedures, such as neurosurgery, or for use in patients with implanted electronic devices like pacemakers, which could be damaged by stray monopolar currents.
Comparison of Monopolar vs. Bipolar Diathermy
| Feature | Monopolar Diathermy | Bipolar Diathermy |
|---|---|---|
| Current Path | Flows through the patient's entire body from active electrode to distant return pad. | Contained within the tissue grasped between two electrodes on the instrument. |
| Return Electrode | Requires a large dispersive (grounding) pad on the patient's skin. | No dispersive pad is necessary. |
| Risk of Burns | Higher risk, including dispersive pad burns, alternate pathway burns, and risks from insulation failure. | Significantly lower risk, localized to the surgical site. |
| Lateral Thermal Spread | Wider, with potential for damage to adjacent tissue, especially at higher power settings. | Minimal and highly focused, with less risk of damage to surrounding structures. |
| Best For | Procedures requiring a broad, powerful effect over a large surgical area. | Delicate and precise procedures, or use on patients with pacemakers. |
| Operating Environment | Less suitable for use in fluid-filled cavities, as the fluid can cause current dispersal. | Suitable for use in wet or fluid-filled environments, such as urology. |
Reducing Burn Risks in Both Circuits
Regardless of the circuit type, patient safety remains paramount, and proper technique is essential to minimize all risks. For monopolar diathermy, this includes meticulous placement of the dispersive pad on a clean, hairless, and muscular area, and regular inspection of electrode insulation. For both systems, using the lowest effective power setting, short activation times, and ensuring equipment is regularly maintained are key.
The most effective safety measure is proper training and understanding of the technology by all operating room staff. Continuous training can help prevent mishaps and ensure that the appropriate equipment is selected for each patient and procedure. The adoption of advanced technology, such as return electrode monitoring and insulated instruments, has also significantly improved safety over the years, though awareness and vigilance are still the most critical factors in preventing complications.
For more detailed information on surgical safety protocols, visit the National Institutes of Health (NIH) at https://www.ncbi.nlm.nih.gov/.
Conclusion: Prioritizing Safety in Electrosurgery
In summary, the design of the circuit is the primary reason that monopolar diathermy burns are more common than bipolar. While monopolar offers greater versatility in some surgical applications, the need for the current to travel through the patient’s body introduces inherent risks that are eliminated by the localized nature of the bipolar circuit. Bipolar diathermy, by confining the current path, provides a higher degree of safety, particularly for delicate procedures or high-risk patients. However, the ultimate responsibility for preventing diathermy burns lies with the surgical team, who must employ a combination of proper technique, equipment maintenance, and adherence to established safety protocols, regardless of the circuit in use.
