So, so far I’ve talked to you about sparking. I’ve said nothing about what happens when you take an electrode and you come in contact with tissue. The rules will change, as you see, when you do contact electrosurgery versus noncontact.
And think about it. Look at this slide and think about the difference in tissue effects just based on the current density. There’s your spark. Think the same electrode, same settings, and now instead of sparking noncontact, take that electrode and put it in contact with the tissue. Look what happens here—you have a much lower current density. You have different thermal effects on tissue. You have much deeper, wider thermal effects, and the rules are different.
So let’s look at a cross-section of liver. Let’s take a roller, sort of ball, electrode, and let’s do some desiccation, coagulation to the surface of the liver. There’s the coag side of the generator. There’s the cutting side of the generator. Remember—high voltage, low voltage—one’s highly interrupted, the others uninterrupted. And look at the visual features that you see here. Here you see cooked, carbonized, high-voltage, high-temperature phenomena, sticky, smoke, but look at the penetration. Relatively minimal, because when you contact with a very high voltage, you penetrate very superficially. On the other hand, look what happens when you use a lower voltage current, which heats the tissue more slowly. That tissue now heats more effectively and more deeply to get a more effective burn. Is this nuance? No, it’s more than nuance. If you happen to be a surgeon who treats endometriosis with electrosurgery and you do electrosurgical ablation of endometriosis with different types of electrodes, realizing that as a disease entity, endometriosis is a retroperitoneal disease. Very commonly you would want to have a depth of penetration that goes beyond the visible portion of the lesion. And you would be compelled to go to a cutting wave form if you wanted to have very thorough, deeper penetration of tissue. So high voltage, rapid desiccation, superficial penetration, lower voltage. Think about it—gradually cook the tissue, more effective, more water in the tissue, and deeper penetration.
And we’re reminded that, regardless of where you are and what kind of instrument you use, there’s one thing that’s always against you when it comes to thermal margins, and that is the longer you’re there, the more injury you produce. So that doesn’t mean that we are frenetic with our movements, but it means that we have a certain amount of alacrity and a certain amount of purposefulness. And we move with intent when we do surgery to minimize the chance for prolonged thermal injury.
So to summarize, we discussed how these variables might impact thermal margins and tissues and the behavior of electrodes. We can manipulate electrodes, which changes their surface area, which completely changes their behavior in the context of current density. We can choose—remember—cutting, blend, or coag waveforms and get different phenomena, different thermal margins. Because, in fact, we’re changing radically the height of the voltage, the output voltage that we’re utilizing. If we change the size of our electrode, you change the surface area, which changes the current density. And then remember, dwell time equals thermal margins. We want to know that we are purposeful with our surgical movements.
So using that information, I want to talk for the rest of this time about bipolar electrosurgery, what I call the basics of bipolar electrosurgery.
Now, not to confuse anyone, but all surgery is bipolar because alternating current means that the current alternates from one pole to the other. What’s really different about bipolar versus monopolar surgery, in the context of using that standard terminology, is the circuit. So think about this—in what we call bipolar electrosurgery, the circuit is the tissue and the 2 tips of the instrument or the 2 electrodes that are close to the tissue. That is the entire circuit. In monopolar electrosurgery, you have a dispersive or return electrode…on the thigh, or the leg, or possibly on the thorax, and you now have the energy going from the tip of the instrument all the way through the patient and back to the generator to complete the circuit.
Think about the energy requirements here. On one, you just have to have energy push through a small piece of tissue between the tips. On the other, you need energy to push all the way through the entire patient back to the generator to complete the circuit. One is much more power consuming. One requires a lot more voltage. Therefore, monopolar electrosurgery, on a power-for-power basis, has much greater requirements. And whether you know it or not, when you take your banana plugs and you plug into an electrosurgical generator—it doesn’t matter what the manufacturer is—and you hit your blue pedal, which is standard throughout the world for the coag output, and it’s set to bipolar, it always by default will put out a pure cut current even though you are putting a coag phenomenon in place. And that’s because, hopefully, it would make sense that if you used very high voltage on a small little area of tissue between 2 tips of an instrument, it literally would fuse and be dysfunctional for you in a surgical sense. So to minimize the chance of adverse thermal effects, it’s always a low-voltage cutting current that’s set off by default by bipolar electrosurgical devices.