Understanding Energy Use in Surgery

Okay, so today's lecture is going to be from chapter 6 in ST4ST. We're discussing energy in the operating room. So when we talk about energy use in the OR, of course energy is used in a lot of places. It powers the lights, it powers some of the systems in the OR, the anesthesia machine, etc. But specifically what we're talking about here in this lesson is energy use to cut and cauterize and coagulate tissue. that the surgeon is going to use to do the procedures themselves and how the surgeon is going to use energy to make that process a lot easier. So if the surgeon is going to cut some tissue, she has two options to choose from. One, she can use a scalpel, which we're familiar with, you can just slice it through and cut the tissue. Or she's going to use some sort of energy source that's going to heat up that material and vaporize it, causing it to cut. Now some advantages to using an energy source over a scalpel come into play, especially if you're deeper in the body. Maybe it's harder to reach with the scalpel. Maybe you want a little bit more fine precision control over what you're burning, what you're cutting through. You can use an energy source to give you that fine control. And especially in difficult to reach areas, those areas might be easier to reach with an energy source than they would be with just a regular metal scalpel. But another advantage that energy offers over a scalpel is that When a scalpel makes an incision, it tends to cut not just the tissue, but of course there are a lot of little blood vessels in that tissue, and it tends to cut those blood vessels as well, which means that they start to bleed and they start to ooze. That's usually not a good thing during surgery. So if we use an energy source, not only does it vaporize that tissue that we're cutting itself, but it also, the heat from that vaporization, spreads out into the tissue nearby. It heats that tissue up, just the tissue right around it, just enough that it causes the proteins to sort of liquefy and denature. And then when that heat source goes away, those proteins settle down, they come together, they solidify and cap off those blood vessels that we just cut. All right. So it's sealing the blood vessels at the same time that it's cutting. So you can make a nice cut and not. have any bleeding. So that's one of the ways that it creates a faster cut using an energy source. And most energy sources allow you to control the depth of that cauterization or that coagulation that you do on either side of that wound that you're creating. So energy use in the OR really started out with a physicist back in the 1920s called W.T. Bovey. That was his name. And he came up with something called a spark gap generator. And this is an example of what a spark gap generator looks like. And it looks completely different from the BOVIs that we use today. Of course, the BOVIs we use today, much more modern version of this. In fact, the technology is completely different from what BOVI used back in the 1920s. But the name sort of stuck. Yeah, officially they're called an ESU or an electrosurgical unit. But many people in the OR, you're going to hear them refer to it as a BOVI because BOVI is a little bit shorter and easier to say. So, in order to understand how electricity works in a Bovey system or an ESU system, and how it works on the patient, we have to understand electricity concepts in general. So at this point, we're going to delve into a little bit of the physics of electricity. So let's take a look at the atom. The atom is the basic building block of all matter. So the atom is composed of a nucleus. That's where most of the mass of the atom is, and that's composed of... protons and neutrons. But going around the nucleus, we have electrons around and around in an orbit around that nucleus. Now the electrons that are nice and close to the nucleus tend to stay right there in the atom. But the electrons a little bit further away from the nucleus, those tend to sort of wander a little bit. Sometimes they'll hang around this atom, but sometimes they'll go and visit some other atoms around. Those are called free electrons. So understanding that atoms have mass. they have a weight, and that the outer electrons, the electrons in those outer orbits, are known as free electrons because they tend to wander around, okay? So, Imagine you have a wire and you have all these electrons that are just sort of wandering around in different directions. That's a typical non-charged wire. Now, if all the electrons suddenly start to flow in the same direction, we've created an electrical current. Now, think of this. This is just like a stream or a river. All the water is flowing in one direction. It creates a current in that water. Well, we're doing exactly the same thing with those electrons. They all start flowing in the same direction and that's creating a current. Now, in physics, current is measured as, it's counted as the number of electrons that we have flowing past any certain point, and it's measured in amps or amperes. So the next component of electricity would be the electrical potential. Now, that's a big fancy word that means, basically, it means the pressure or the strength of those electrons as they move through that wire. So how much force they're able to apply as they move through that wire. That is measured in volts. So when you combine current and electrical potential, when you combine the number of electrons times the strength of each of those electrons, you get the energy that's in that wire. And that is measured in joules. Now I'll use a little gaming analogy here to help you sort of understand what this looks like. Here we've got a couple of characters. You're going on a quest and you get to choose the character you want to be. All right. We have Leo and here's his stats. Not too bad. His strength though is a 4 out of 10. But this character over here, Annabeth, her strength is an 8 out of 10. So let's say we had some work that needs to be done and it would take 12 Leos to do this work in a certain amount of time. Well, because Annabeth electrons are stronger than Leo, they're twice as strong as the Leo electrons. It's only going to take six anabath electrons to do the exact same work as 12 Leo electrons. Because anabath electrons are twice as strong, you only need half as many to do the same amount of work. Does that concept make sense? If it does, if you understand that basic concept there, then you understand what's known as Ohm's Law. Ohm's Law is a way of describing the relationship between Current, electrical potential, resistance, things like that. So the more electrons you have, the weaker they have to be in order to do the same amount of work. Or if you have stronger electrons, you'd need fewer of them in the amount of current that you're using in order to do the same amount of work. So the other element that we can measure would be the power in that wire. And in this case, we're measuring the number and the strength of the electrons every second. So... in a certain amount of time, how many electrons and how strong are they going past any one point. That number is measured in watts. So these are just some different definitions that are used to describe electrical current. Essentially, you're just going to have to memorize these because they will appear probably on a test somewhere, maybe even on the national boards. So just memorize this list, understand that current goes with amps, electrical potential goes with volts, et cetera. And that the relationship between all of these is guided by Ohm's law. Okay. So an electric circuit is made up of three components. First, you have a power source, which in this case we're showing as a battery. We also have a light bulb up here. This is known as the load. This is the stuff that you're trying to get done. This is the whatever's doing the work. In this case, we have a light bulb. We're going to create some light. Sometimes maybe it's a water pump, maybe it's a vacuum cleaner, who knows. Whatever that load is, whatever that's doing the work, that's known as the load. And then the third component is the switch. And this is where you turn the electric power on and off when you make or break that connection. And that turns the load on or off. So, of course, you turn the switch on or off, the light turns on and off, the vacuum cleaner turns on and off. So you have a power source, a load, and a switch. Those are the three components. of an electric circuit. And to connect those three components, usually what we're going to use is a wire. And a wire is composed of both a conductor and an insulator. So in this case, we're showing some copper wire, and the copper itself is the conductor. That's what the electricity likes to flow through. But around that copper conductor, we have an insulator. We have plastic insulator that electricity doesn't like to go flow through. So if I were to grab that copper conductor with my bare hand and it happens to be charged, I'm going to get a shock. But if I hold the plastic insulation, most likely I'm not going to get a shock. I'll be safe because the electricity doesn't flow through that insulation. But conductors and insulators can be lots of different materials. Copper happens to be a really good conductor. Plastic happens to be a really good insulator. But there are other choices that we could use. For example... Air. Air itself happens to be a really good insulator. If I put my hand near this copper wire, but I don't actually touch it, I'm probably not going to get a shock because the air is acting as an insulator between my hand and that wire. Most of the time, but not always. Sometimes, if that charge, if the voltage between two conductors, or say the conductor in my hand, is strong enough. you can get something called dielectric breakdown. So in this case, the air, which is an insulator normally, the elements in the air, the electrons, the atoms, are going to sort of line up in just such a way that they're going to form a bridge from one conductor to the next. And electricity is going to be able to flow right across that bridge. So the insulator, that's normally an insulator, if that voltage gets strong enough, the elements can line up and... instantly that insulator suddenly becomes a conductor. It changes its property from being an insulator to a conductor and electricity can flow across that insulator. That's known as dielectric breakdown. And you've seen this happen. You know a good example of dielectric breakdown. Sure. It's lightning. Lightning, you have a really strong charge up in the cloud. You have a different charge down at the ground. And if that charge gets strong enough, air, which is insulating the tube. suddenly becomes a conductor. You get a little bridge going through that air that the electricity is able to flow through, and you get a big old lightning bolt. So what does all this have to do with surgery? Well, it comes back to this guy, our ESU, our electrosurgical unit. Now, most of the electrosurgical unit, the ESU, is covered in plastic, which is an insulator. But notice right here at the end, you have a metal tip. That's the conductor. If you were to touch that metal tip, obviously you would get a shock. You would get burned. But what happens if you're wearing a glove? Now, if you're wearing a rubber glove, rubber is a good insulator. Electricity doesn't like to flow through rubber. So is it safe to use your rubber glove and just grab on to that metal tip of that ESU unit? Probably not. For one, you know, the metal is kind of sharp and it could actually poke a hole through that rubber and shock you. That would be a bad thing. But even if it doesn't break the integrity of the glove, even if the glove stays intact, the atoms and electrons in that rubber can organize in just such a way, if this electrical potential across there is strong enough, they organize in just such a way that it's going to create a little bridge and that electricity can flow through that insulator. And that way you could indeed get a shock, even if your hand is covered completely, with an intact glove. So for safety reasons, we do not want to touch the metal tip of that ESU, even if we are wearing rubber gloves. So let's talk about different forms of electricity. Electricity can flow all in one direction. The current can continue in one direction constantly. All right, just like water flowing through a hose, it's always going to go in the same direction. That's known as direct current. It's always going the same way. That's the kind of current that we get out of, say, a battery. Something like that. It flows from one end of the battery around the circuit and into the other end of the battery. But another way that electricity can flow would be alternating current. And the difference here is that the electric current, the electrons, are moving this way, and then they switch, and they move this way. And then they switch again, and they move this way. And then they switch, and back and forth. All right? So it's alternating its direction, back and forth, and back and forth. This is the kind of electricity that you will find. in, say, a wall outlet in your house. So a wall outlet has the three prongs. Now, your book actually makes a little mistake here. Your book calls them positive, negative, and ground for the three prongs of your wall outlet. Actually, they're known as hot, neutral, and ground. And the reason for that, the reason we don't have positive and negative when we're talking about alternating current is because when the current's going this way, we have positive and negative. But then it switches, and it goes this way. So... positive and negative have switched places and then it switches again and they switch places. So it keeps going back and forth. So which one's positive and which one's negative at this particular incident? It's hard to tell. So we just call it hot, neutral, and ground. So speaking of electrical outlets, in the hospital you'll often see electrical outlets with different colors. For example, we have white outlets over here, we have red outlets over here, What's the difference? Why is there a different color? They're color coded for a reason. What is that reason? Well, it turns out the reason for that is that electrical outlets that have a red color are connected to an emergency power backup, usually a battery and or a generator. So if, for example, you have a really critical piece of equipment, let's say a ventilator, you want to make sure you're plugging that into a red outlet. Because even if the power goes out to the rest of the building, power is going to continue to flow through those red outlets and into that ventilator and keep that patient alive. So that's important. The red outlets. and have an emergency backup power. So when we think about alternating current, we're thinking about current that goes this way and then turns this way and then turns this way. And it's going back and forth and back and forth. The rate at which it changes direction and goes back and forth, this is known as its frequency. So sometimes it can go back and forth slowly. Sometimes it can go back and forth very quickly. And that is frequency. And frequency is measured in hertz. So the hertz tell you the frequency at which that electricity flows back and forth and back and forth. So why is that important? Well, it comes back to our ESU again. All right. Notice that on the ESU, there are two buttons. One of these buttons is for cutting. The other one is for coagulating or cauterizing tissue. And the difference has to do with the way that electricity flows from the tip of this ESU. When you press the cut button, You get a nice steady flow of electricity back and forth and back and forth. It's on constantly, 100% of the time. Now what it's doing there is if you have a constant flow of electricity into that tissue, it's going to heat that tissue, heat that tissue, heat it up so much that it vaporizes. And it just goes up into smoke. And that's what's creating the cut. It's vaporizing the tissue, going away, and now you have a gap where that tissue used to be. But the other button is coagulate. And in this case, you have a real sharp high voltage spike, which heats up the material, but not to the point that it vaporizes. It just sort of heats it up so it liquefies. And then the energy shuts off for a little bit. And by doing that, it allows that tissue that was sort of liquefied, all those proteins, to sort of cool down and coagulate and cap off those blood vessels. And then as you move your pencil along, you get another sharp spike in electricity that heats up this spot, and then the tissue sort of cools back down and capsules on. So when you're coagulating, you're not completely vaporizing the tissue and making it go away. You're liquefying it and then letting it solidify over those blood vessels. So the different waveforms coming out of the tip of that ESU control what's happening with the tissue. Now there's a third option that some surgeons use. and so some surgeons swear by their recipe for this they're like little italian grandmothers and they have their special recipe for their sauce they have a blend recipe which is sort of a mixture of cut and coagulate in this case you can take your es you move it through you're cutting maybe a little bit more slowly than you otherwise would on full cut but you're also coagulating at the same time which means as you're cutting you're not going to get the bleeding so different surgeons have different blends that they like to use but basically a blend is a blend and and it's going to cut and coagulate at the same time. So let's look at the ESU itself. We have two versions of ESU. The first version, the one that's used most often, is the monopolar ESU. And we know it's monopolar because mono means one. So we have one wire coming in, and we have one electrode. But wait a minute. In order to create an electric circuit, you need the electricity to both come into the load and then come back out of the load. So where does that happen? So the electricity comes back out of the load. In this case, the load is going to be the patient because we're trying to cauterize the tissue of the patient. So we want the electricity to come out of the patient using a grounding pad. And this is what grounding pads are for. What you're going to do is you're going to place the grounding pad onto the patient's skin somewhere a little bit further away from where you're doing the surgery. And the electricity is going to flow in at the point where you touch the electrosurgical unit to the tissue that's where it's going to be the hottest but at that point the electricity is going to disperse throughout the tissue and throughout the body and as it does it gets weaker and weaker okay it's not so concentrated so it's not going to be hot so the hottest spot is going to be right here a little bit cooler out here and then by the time it gets into the rest of the body it's so weak that it's not doing a whole lot of damage it's so spread out that it's not concentrated in any one area it's going to go through the body and then come to the grounding pad where it's going to exit the body. So using the grounding pad, we're actually creating the complete circuit. The electricity flows in through the ESU tip. It hits the tissue where it gets really hot, and then it disperses through the patient and goes out to the grounding pad, and that's where it leaves the patient and goes back to the bovie unit. So that creates our complete circuit. Now let's imagine we have the patient's skin here. We're going to take the grounding pad. and apply it to the patient's skin. As long as that grounding pad is in full contact with the patient's skin, you've got a wide area for that electricity to leave the body. There's no point where it's actually concentrated enough to cause any damage. So the electricity just flows across this wide area into the grounding pad. But in order for this to work appropriately, you have to make sure that the grounding pad is placed on the patient's body appropriately. If for some reason you get a bubble, between the grounding pad and the patient. Now, what we have is we only have the grounding pad connecting to the patient's body in two spots here and here. And in that case, the electric flow out of the patient is going to be concentrated at these two spots here and here. And if that happens, if it's concentrated enough, you can actually cause an exit burn from the grounding pad. And this is what can happen. A grounding pad was not placed properly on this patient. and you only had two spots where the electricity was coming out and it was concentrated in these two spots enough that the grounding pad itself actually caused a burn on the patient. And the thing is, you don't know this is even happening until the surgery is over and you go and you take your grounding pad off and this is what you see. So grounding pads must be placed exactly right so that you have full contact over a wide area so that you never get a concentrated spot. where the electricity is leaving the patient's body. But grounding pads aren't necessarily the only reason that a patient might have a burn like this somewhere away from the surgical site. If there's any other conductor that happens to be touching the patient's body at the time, the electricity might say, this is a better route to take out. And you could create a burn. For example, if you have a patient lying on a table that happens to have a few pieces of metal in it, well, if the patient's skin is touching those metal points, electricity could flow out through those metal points and create burns on the patient's skin at those points. Or, for example, if the patient's wearing an EKG and you have electrodes all over the patient's chest, well, these electrodes make really nice places for the electricity to leave the body, and you can get burns there if you're using a monopolar ESU. So that's why you would never use monopolar cautery on a patient wearing an EKG or other sort of electrodes attached to their body somewhere. So how can we make monopolar cautery a little bit safer? Can we eliminate the grounding pad? And the answer is yes, with something like this. Now, some of you might be familiar with what this is. This is a wireless charging device. It's kind of cool. It charges your phone, it charges your earbuds wirelessly. You don't actually have to connect a wire to these things, because what happens, you just set it on this little pad. The pad has some electrical coils in it that... creates a field that is then absorbed by your phone or by your earbuds, and that induces an electric current within the phone itself. So even though there's no wire connecting them, it induces, it creates a current within the phone, and it's that current that actually charges the phone for you. So without connecting a wire, you can still create a current in that phone. Now that's kind of a cool effect, and that effect is known as capacitance. where you have a conductor here, you have insulation, and then maybe another conductor up here. And it's an electric field that flows through the insulation. This is different from dielectric breakdown. The electric field flows through and creates, it induces an electric current in the conductor that's nearby. So how can we use this in surgery? Well, one of the new things that they have out now, and this is not in your book, but it's kind of cool. is a capacitance pad instead of a grounding pad. Now in this case we have a nice electric coil flowing around in this pad but the metal never touches the patient's body. You've got this nice rubber coating that protects the patient. You can even put a sheet over this pad and let the patient lie on this pad. And what you're doing here is you're using this pad to induce an electric current in the patient. Using an electric field you're inducing inducing the electric current in the patient. So what does this mean? It means you've created a wireless charger for your patient. How cool is that? You're wirelessly charging the patient. You don't have an actual wire connected to the patient, so there's no place for a burn to happen at the grounding pad site. You're inducing that electric flow in the patient wirelessly, and that electric flow flows in and out through your ESU tip. Cool. But the idea of capacitance, the idea that you have a conductor and then an insulator and then another conductor and that you can induce an electric current across that insulation, comes into play elsewhere. Let's say, for example, we're running wires from our surgical field back to our BOVI unit, back to the camera system, something like that. And we use a metal clamp as a way of fixing those wires to the drape. Now, the metal clamp might not be actually pinching the wire. Maybe the wire is just sort of wrapped around that metal clamp in some way. Okay. But if that metal clamp is near those wires, there is the possibility, small but not zero chance, that you could end induce an electric current in that metal clamp because that's another conductor. So you're going to induce that electric current over here. You could create a little spark and sparks. We've got enough fuel around, oxygen, drapes, things like that, that could create a fire. So metal clamps holding those wires in place on the drape, probably not the best idea. Probably want to use some sort of a Velcro strap or a plastic clamp, something like that to hold those wires in place. That way we don't get... an induction into those clamps. But there is another option that we can use as well, instead of monopolar cautery. And of course, if we have monopolar, it means one. That means we probably have bipolar, and that means two. And in this case, we do indeed have bipolar cautery forceps. Now notice what we have here. We have two prongs going in, and we have two electrodes at the tip. So here's what's happening. The electricity flows in through one of the prongs, to one of the tips. Then you take those tips and squeeze them together across some tissue. The electricity flows through the tissue to the other tip and then back out through the second prong. So what have we done here? We've created a complete electric circuit within the handpiece. The electricity flows in one side and flows back out the other. So that right there creates a huge safety advantage. We don't have to worry about the grounding pad and any burns that might be formed there. The electricity is concentrated in one point. And that actually gives us another advantage. If we're trying to cauterize a very fine blood vessel here, but let's say we have a nerve running right beside it, and we don't want to affect that nerve, with a monopolar cautery, the electricity comes in and then sort of spreads out and damages the tissue around it. With bipolar cautery, you're able to control very precisely exactly what you're cauterizing and what you're not, because the electricity is only going to flow through the tissue that you happen to be pinching. So that's a real benefit of bipolar cautery. One of the disadvantages, though, is that bipolar isn't very good at cutting because you have to pinch and pinch and pinch and pinch. Bipolar is really good at cauterizing or coagulating tissue, but cutting not so much. So that's why we still use monopolar most of the time in most of the surgeries that you're going to be seeing. You're going to see the monopolar cautery because it cuts and coagulates at the same time. There are a few added risks, but the advantages of being able to cut and cauterize outweigh those risks in most cases. So as you can see, electricity is a popular way of heating up to vaporize and coagulate tissue of cutting and cauterizing. But there are other sources of energy we can use as well. We can use mechanical energy instead of electrical energy. And in this case, we're going to use something called ultrasonic energy. Ultrasonic means very high speed or high frequency sound. So normally we think about sound traveling through air. That's the sound that we hear. The air is vibrating and those vibrations make it to our ear and that's what we hear a sound. But sound can also travel through like a piece of metal and it can make that metal vibrate very quickly as it travels through there. And if you have a very high intensity sound traveling through there, maybe sounds so high you can't hear it, but it's making that metal vibrate back and forth real quick. That vibration can be used to create heat and help cut and cauterize tissue. So this is where the harmonic scalpel comes in. In this case, we have a piece of metal that comes out of the tip of the harmonic scalpel, and it vibrates very quickly, very high speed, back and forth, so fast that you can't really see it. But on a microscopic level, it is vibrating back and forth very quickly. So then you have another pad that comes down on top of it and squeezes the tissue onto this very quickly vibrating piece of metal. And what's happening here? In this case... we get friction. And this friction is going to heat up the tissue so much that it's going to cut and cauterize that tissue. So a harmonic scalpel doesn't use electricity so much to do the heating. It uses the electricity to create the vibrations. But then those vibrations in the metal create friction. And that's where the heat comes from that cauterizes and cuts the tissue. Now, a third way that we can use energy to help cut and cauterize tissue We'll be using instead of electricity, instead of mechanical motion, we can use light. and that's where lasers come in and that's going to be the topic of the next lecture

But specifically what we're talking about here in this lesson is energy use to cut and cauterize and coagulate tissue. that the surgeon is going to use to do the procedures themselves and how the surgeon is going to use energy to make that process a lot easier. So if the surgeon is going to cut some tissue, she has two options to choose from.

One, she can use a scalpel, which we're familiar with, you can just slice it through and cut the tissue. Or she's going to use some sort of energy source that's going to heat up that material and vaporize it, causing it to cut. Now some advantages to using an energy source over a scalpel come into play, especially if you're deeper in the body.

Maybe it's harder to reach with the scalpel. Maybe you want a little bit more fine precision control over what you're burning, what you're cutting through. You can use an energy source to give you that fine control. And especially in difficult to reach areas, those areas might be easier to reach with an energy source than they would be with just a regular metal scalpel.

But another advantage that energy offers over a scalpel is that When a scalpel makes an incision, it tends to cut not just the tissue, but of course there are a lot of little blood vessels in that tissue, and it tends to cut those blood vessels as well, which means that they start to bleed and they start to ooze. That's usually not a good thing during surgery. So if we use an energy source, not only does it vaporize that tissue that we're cutting itself, but it also, the heat from that vaporization, spreads out into the tissue nearby.

It heats that tissue up, just the tissue right around it, just enough that it causes the proteins to sort of liquefy and denature. And then when that heat source goes away, those proteins settle down, they come together, they solidify and cap off those blood vessels that we just cut. All right. So it's sealing the blood vessels at the same time that it's cutting.

So you can make a nice cut and not. have any bleeding. So that's one of the ways that it creates a faster cut using an energy source.

And most energy sources allow you to control the depth of that cauterization or that coagulation that you do on either side of that wound that you're creating. So energy use in the OR really started out with a physicist back in the 1920s called W.T. Bovey. That was his name. And he came up with something called a spark gap generator.

And this is an example of what a spark gap generator looks like. And it looks completely different from the BOVIs that we use today. Of course, the BOVIs we use today, much more modern version of this. In fact, the technology is completely different from what BOVI used back in the 1920s.

But the name sort of stuck. Yeah, officially they're called an ESU or an electrosurgical unit. But many people in the OR, you're going to hear them refer to it as a BOVI because BOVI is a little bit shorter and easier to say.

So, in order to understand how electricity works in a Bovey system or an ESU system, and how it works on the patient, we have to understand electricity concepts in general. So at this point, we're going to delve into a little bit of the physics of electricity. So let's take a look at the atom. The atom is the basic building block of all matter.

So the atom is composed of a nucleus. That's where most of the mass of the atom is, and that's composed of... protons and neutrons. But going around the nucleus, we have electrons around and around in an orbit around that nucleus. Now the electrons that are nice and close to the nucleus tend to stay right there in the atom.

But the electrons a little bit further away from the nucleus, those tend to sort of wander a little bit. Sometimes they'll hang around this atom, but sometimes they'll go and visit some other atoms around. Those are called free electrons.

So understanding that atoms have mass. they have a weight, and that the outer electrons, the electrons in those outer orbits, are known as free electrons because they tend to wander around, okay? So, Imagine you have a wire and you have all these electrons that are just sort of wandering around in different directions. That's a typical non-charged wire.

Now, if all the electrons suddenly start to flow in the same direction, we've created an electrical current. Now, think of this. This is just like a stream or a river. All the water is flowing in one direction.

It creates a current in that water. Well, we're doing exactly the same thing with those electrons. They all start flowing in the same direction and that's creating a current.

Now, in physics, current is measured as, it's counted as the number of electrons that we have flowing past any certain point, and it's measured in amps or amperes. So the next component of electricity would be the electrical potential. Now, that's a big fancy word that means, basically, it means the pressure or the strength of those electrons as they move through that wire. So how much force they're able to apply as they move through that wire.

That is measured in volts. So when you combine current and electrical potential, when you combine the number of electrons times the strength of each of those electrons, you get the energy that's in that wire. And that is measured in joules. Now I'll use a little gaming analogy here to help you sort of understand what this looks like.

Here we've got a couple of characters. You're going on a quest and you get to choose the character you want to be. All right. We have Leo and here's his stats. Not too bad.

His strength though is a 4 out of 10. But this character over here, Annabeth, her strength is an 8 out of 10. So let's say we had some work that needs to be done and it would take 12 Leos to do this work in a certain amount of time. Well, because Annabeth electrons are stronger than Leo, they're twice as strong as the Leo electrons. It's only going to take six anabath electrons to do the exact same work as 12 Leo electrons. Because anabath electrons are twice as strong, you only need half as many to do the same amount of work.

Does that concept make sense? If it does, if you understand that basic concept there, then you understand what's known as Ohm's Law. Ohm's Law is a way of describing the relationship between Current, electrical potential, resistance, things like that.

So the more electrons you have, the weaker they have to be in order to do the same amount of work. Or if you have stronger electrons, you'd need fewer of them in the amount of current that you're using in order to do the same amount of work. So the other element that we can measure would be the power in that wire. And in this case, we're measuring the number and the strength of the electrons every second.

So... in a certain amount of time, how many electrons and how strong are they going past any one point. That number is measured in watts. So these are just some different definitions that are used to describe electrical current. Essentially, you're just going to have to memorize these because they will appear probably on a test somewhere, maybe even on the national boards.

So just memorize this list, understand that current goes with amps, electrical potential goes with volts, et cetera. And that the relationship between all of these is guided by Ohm's law. Okay. So an electric circuit is made up of three components. First, you have a power source, which in this case we're showing as a battery.

We also have a light bulb up here. This is known as the load. This is the stuff that you're trying to get done. This is the whatever's doing the work. In this case, we have a light bulb.

We're going to create some light. Sometimes maybe it's a water pump, maybe it's a vacuum cleaner, who knows. Whatever that load is, whatever that's doing the work, that's known as the load. And then the third component is the switch. And this is where you turn the electric power on and off when you make or break that connection.

And that turns the load on or off. So, of course, you turn the switch on or off, the light turns on and off, the vacuum cleaner turns on and off. So you have a power source, a load, and a switch.

Those are the three components. of an electric circuit. And to connect those three components, usually what we're going to use is a wire.

And a wire is composed of both a conductor and an insulator. So in this case, we're showing some copper wire, and the copper itself is the conductor. That's what the electricity likes to flow through.

But around that copper conductor, we have an insulator. We have plastic insulator that electricity doesn't like to go flow through. So if I were to grab that copper conductor with my bare hand and it happens to be charged, I'm going to get a shock. But if I hold the plastic insulation, most likely I'm not going to get a shock. I'll be safe because the electricity doesn't flow through that insulation.

But conductors and insulators can be lots of different materials. Copper happens to be a really good conductor. Plastic happens to be a really good insulator.

But there are other choices that we could use. For example... Air.

Air itself happens to be a really good insulator. If I put my hand near this copper wire, but I don't actually touch it, I'm probably not going to get a shock because the air is acting as an insulator between my hand and that wire. Most of the time, but not always. Sometimes, if that charge, if the voltage between two conductors, or say the conductor in my hand, is strong enough.

you can get something called dielectric breakdown. So in this case, the air, which is an insulator normally, the elements in the air, the electrons, the atoms, are going to sort of line up in just such a way that they're going to form a bridge from one conductor to the next. And electricity is going to be able to flow right across that bridge.

So the insulator, that's normally an insulator, if that voltage gets strong enough, the elements can line up and... instantly that insulator suddenly becomes a conductor. It changes its property from being an insulator to a conductor and electricity can flow across that insulator.

That's known as dielectric breakdown. And you've seen this happen. You know a good example of dielectric breakdown. Sure. It's lightning.

Lightning, you have a really strong charge up in the cloud. You have a different charge down at the ground. And if that charge gets strong enough, air, which is insulating the tube.

suddenly becomes a conductor. You get a little bridge going through that air that the electricity is able to flow through, and you get a big old lightning bolt. So what does all this have to do with surgery?

Well, it comes back to this guy, our ESU, our electrosurgical unit. Now, most of the electrosurgical unit, the ESU, is covered in plastic, which is an insulator. But notice right here at the end, you have a metal tip. That's the conductor.

If you were to touch that metal tip, obviously you would get a shock. You would get burned. But what happens if you're wearing a glove? Now, if you're wearing a rubber glove, rubber is a good insulator.

Electricity doesn't like to flow through rubber. So is it safe to use your rubber glove and just grab on to that metal tip of that ESU unit? Probably not. For one, you know, the metal is kind of sharp and it could actually poke a hole through that rubber and shock you.

That would be a bad thing. But even if it doesn't break the integrity of the glove, even if the glove stays intact, the atoms and electrons in that rubber can organize in just such a way, if this electrical potential across there is strong enough, they organize in just such a way that it's going to create a little bridge and that electricity can flow through that insulator. And that way you could indeed get a shock, even if your hand is covered completely, with an intact glove. So for safety reasons, we do not want to touch the metal tip of that ESU, even if we are wearing rubber gloves. So let's talk about different forms of electricity.

Electricity can flow all in one direction. The current can continue in one direction constantly. All right, just like water flowing through a hose, it's always going to go in the same direction.

That's known as direct current. It's always going the same way. That's the kind of current that we get out of, say, a battery. Something like that.

It flows from one end of the battery around the circuit and into the other end of the battery. But another way that electricity can flow would be alternating current. And the difference here is that the electric current, the electrons, are moving this way, and then they switch, and they move this way. And then they switch again, and they move this way. And then they switch, and back and forth.

All right? So it's alternating its direction, back and forth, and back and forth. This is the kind of electricity that you will find.

in, say, a wall outlet in your house. So a wall outlet has the three prongs. Now, your book actually makes a little mistake here.

Your book calls them positive, negative, and ground for the three prongs of your wall outlet. Actually, they're known as hot, neutral, and ground. And the reason for that, the reason we don't have positive and negative when we're talking about alternating current is because when the current's going this way, we have positive and negative.

But then it switches, and it goes this way. So... positive and negative have switched places and then it switches again and they switch places.

So it keeps going back and forth. So which one's positive and which one's negative at this particular incident? It's hard to tell.

So we just call it hot, neutral, and ground. So speaking of electrical outlets, in the hospital you'll often see electrical outlets with different colors. For example, we have white outlets over here, we have red outlets over here, What's the difference? Why is there a different color? They're color coded for a reason.

What is that reason? Well, it turns out the reason for that is that electrical outlets that have a red color are connected to an emergency power backup, usually a battery and or a generator. So if, for example, you have a really critical piece of equipment, let's say a ventilator, you want to make sure you're plugging that into a red outlet.

Because even if the power goes out to the rest of the building, power is going to continue to flow through those red outlets and into that ventilator and keep that patient alive. So that's important. The red outlets. and have an emergency backup power. So when we think about alternating current, we're thinking about current that goes this way and then turns this way and then turns this way.

And it's going back and forth and back and forth. The rate at which it changes direction and goes back and forth, this is known as its frequency. So sometimes it can go back and forth slowly.

Sometimes it can go back and forth very quickly. And that is frequency. And frequency is measured in hertz.

So the hertz tell you the frequency at which that electricity flows back and forth and back and forth. So why is that important? Well, it comes back to our ESU again.

All right. Notice that on the ESU, there are two buttons. One of these buttons is for cutting.

The other one is for coagulating or cauterizing tissue. And the difference has to do with the way that electricity flows from the tip of this ESU. When you press the cut button, You get a nice steady flow of electricity back and forth and back and forth. It's on constantly, 100% of the time.

Now what it's doing there is if you have a constant flow of electricity into that tissue, it's going to heat that tissue, heat that tissue, heat it up so much that it vaporizes. And it just goes up into smoke. And that's what's creating the cut. It's vaporizing the tissue, going away, and now you have a gap where that tissue used to be.

But the other button is coagulate. And in this case, you have a real sharp high voltage spike, which heats up the material, but not to the point that it vaporizes. It just sort of heats it up so it liquefies. And then the energy shuts off for a little bit.

And by doing that, it allows that tissue that was sort of liquefied, all those proteins, to sort of cool down and coagulate and cap off those blood vessels. And then as you move your pencil along, you get another sharp spike in electricity that heats up this spot, and then the tissue sort of cools back down and capsules on. So when you're coagulating, you're not completely vaporizing the tissue and making it go away.

You're liquefying it and then letting it solidify over those blood vessels. So the different waveforms coming out of the tip of that ESU control what's happening with the tissue. Now there's a third option that some surgeons use. and so some surgeons swear by their recipe for this they're like little italian grandmothers and they have their special recipe for their sauce they have a blend recipe which is sort of a mixture of cut and coagulate in this case you can take your es you move it through you're cutting maybe a little bit more slowly than you otherwise would on full cut but you're also coagulating at the same time which means as you're cutting you're not going to get the bleeding so different surgeons have different blends that they like to use but basically a blend is a blend and and it's going to cut and coagulate at the same time.

So let's look at the ESU itself. We have two versions of ESU. The first version, the one that's used most often, is the monopolar ESU.

And we know it's monopolar because mono means one. So we have one wire coming in, and we have one electrode. But wait a minute. In order to create an electric circuit, you need the electricity to both come into the load and then come back out of the load. So where does that happen?

So the electricity comes back out of the load. In this case, the load is going to be the patient because we're trying to cauterize the tissue of the patient. So we want the electricity to come out of the patient using a grounding pad.

And this is what grounding pads are for. What you're going to do is you're going to place the grounding pad onto the patient's skin somewhere a little bit further away from where you're doing the surgery. And the electricity is going to flow in at the point where you touch the electrosurgical unit to the tissue that's where it's going to be the hottest but at that point the electricity is going to disperse throughout the tissue and throughout the body and as it does it gets weaker and weaker okay it's not so concentrated so it's not going to be hot so the hottest spot is going to be right here a little bit cooler out here and then by the time it gets into the rest of the body it's so weak that it's not doing a whole lot of damage it's so spread out that it's not concentrated in any one area it's going to go through the body and then come to the grounding pad where it's going to exit the body. So using the grounding pad, we're actually creating the complete circuit. The electricity flows in through the ESU tip.

It hits the tissue where it gets really hot, and then it disperses through the patient and goes out to the grounding pad, and that's where it leaves the patient and goes back to the bovie unit. So that creates our complete circuit. Now let's imagine we have the patient's skin here. We're going to take the grounding pad.

and apply it to the patient's skin. As long as that grounding pad is in full contact with the patient's skin, you've got a wide area for that electricity to leave the body. There's no point where it's actually concentrated enough to cause any damage. So the electricity just flows across this wide area into the grounding pad. But in order for this to work appropriately, you have to make sure that the grounding pad is placed on the patient's body appropriately.

If for some reason you get a bubble, between the grounding pad and the patient. Now, what we have is we only have the grounding pad connecting to the patient's body in two spots here and here. And in that case, the electric flow out of the patient is going to be concentrated at these two spots here and here. And if that happens, if it's concentrated enough, you can actually cause an exit burn from the grounding pad. And this is what can happen.

A grounding pad was not placed properly on this patient. and you only had two spots where the electricity was coming out and it was concentrated in these two spots enough that the grounding pad itself actually caused a burn on the patient. And the thing is, you don't know this is even happening until the surgery is over and you go and you take your grounding pad off and this is what you see.

So grounding pads must be placed exactly right so that you have full contact over a wide area so that you never get a concentrated spot. where the electricity is leaving the patient's body. But grounding pads aren't necessarily the only reason that a patient might have a burn like this somewhere away from the surgical site.

If there's any other conductor that happens to be touching the patient's body at the time, the electricity might say, this is a better route to take out. And you could create a burn. For example, if you have a patient lying on a table that happens to have a few pieces of metal in it, well, if the patient's skin is touching those metal points, electricity could flow out through those metal points and create burns on the patient's skin at those points. Or, for example, if the patient's wearing an EKG and you have electrodes all over the patient's chest, well, these electrodes make really nice places for the electricity to leave the body, and you can get burns there if you're using a monopolar ESU. So that's why you would never use monopolar cautery on a patient wearing an EKG or other sort of electrodes attached to their body somewhere.

So how can we make monopolar cautery a little bit safer? Can we eliminate the grounding pad? And the answer is yes, with something like this.

Now, some of you might be familiar with what this is. This is a wireless charging device. It's kind of cool.

It charges your phone, it charges your earbuds wirelessly. You don't actually have to connect a wire to these things, because what happens, you just set it on this little pad. The pad has some electrical coils in it that... creates a field that is then absorbed by your phone or by your earbuds, and that induces an electric current within the phone itself. So even though there's no wire connecting them, it induces, it creates a current within the phone, and it's that current that actually charges the phone for you.

So without connecting a wire, you can still create a current in that phone. Now that's kind of a cool effect, and that effect is known as capacitance. where you have a conductor here, you have insulation, and then maybe another conductor up here.

And it's an electric field that flows through the insulation. This is different from dielectric breakdown. The electric field flows through and creates, it induces an electric current in the conductor that's nearby. So how can we use this in surgery? Well, one of the new things that they have out now, and this is not in your book, but it's kind of cool.

is a capacitance pad instead of a grounding pad. Now in this case we have a nice electric coil flowing around in this pad but the metal never touches the patient's body. You've got this nice rubber coating that protects the patient. You can even put a sheet over this pad and let the patient lie on this pad. And what you're doing here is you're using this pad to induce an electric current in the patient.

Using an electric field you're inducing inducing the electric current in the patient. So what does this mean? It means you've created a wireless charger for your patient.

How cool is that? You're wirelessly charging the patient. You don't have an actual wire connected to the patient, so there's no place for a burn to happen at the grounding pad site. You're inducing that electric flow in the patient wirelessly, and that electric flow flows in and out through your ESU tip. Cool.

But the idea of capacitance, the idea that you have a conductor and then an insulator and then another conductor and that you can induce an electric current across that insulation, comes into play elsewhere. Let's say, for example, we're running wires from our surgical field back to our BOVI unit, back to the camera system, something like that. And we use a metal clamp as a way of fixing those wires to the drape.

Now, the metal clamp might not be actually pinching the wire. Maybe the wire is just sort of wrapped around that metal clamp in some way. Okay.

But if that metal clamp is near those wires, there is the possibility, small but not zero chance, that you could end induce an electric current in that metal clamp because that's another conductor. So you're going to induce that electric current over here. You could create a little spark and sparks.

We've got enough fuel around, oxygen, drapes, things like that, that could create a fire. So metal clamps holding those wires in place on the drape, probably not the best idea. Probably want to use some sort of a Velcro strap or a plastic clamp, something like that to hold those wires in place.

That way we don't get... an induction into those clamps. But there is another option that we can use as well, instead of monopolar cautery.

And of course, if we have monopolar, it means one. That means we probably have bipolar, and that means two. And in this case, we do indeed have bipolar cautery forceps.

Now notice what we have here. We have two prongs going in, and we have two electrodes at the tip. So here's what's happening. The electricity flows in through one of the prongs, to one of the tips.

Then you take those tips and squeeze them together across some tissue. The electricity flows through the tissue to the other tip and then back out through the second prong. So what have we done here?

We've created a complete electric circuit within the handpiece. The electricity flows in one side and flows back out the other. So that right there creates a huge safety advantage. We don't have to worry about the grounding pad and any burns that might be formed there. The electricity is concentrated in one point.

And that actually gives us another advantage. If we're trying to cauterize a very fine blood vessel here, but let's say we have a nerve running right beside it, and we don't want to affect that nerve, with a monopolar cautery, the electricity comes in and then sort of spreads out and damages the tissue around it. With bipolar cautery, you're able to control very precisely exactly what you're cauterizing and what you're not, because the electricity is only going to flow through the tissue that you happen to be pinching.

So that's a real benefit of bipolar cautery. One of the disadvantages, though, is that bipolar isn't very good at cutting because you have to pinch and pinch and pinch and pinch. Bipolar is really good at cauterizing or coagulating tissue, but cutting not so much.

So that's why we still use monopolar most of the time in most of the surgeries that you're going to be seeing. You're going to see the monopolar cautery because it cuts and coagulates at the same time. There are a few added risks, but the advantages of being able to cut and cauterize outweigh those risks in most cases. So as you can see, electricity is a popular way of heating up to vaporize and coagulate tissue of cutting and cauterizing.

But there are other sources of energy we can use as well. We can use mechanical energy instead of electrical energy. And in this case, we're going to use something called ultrasonic energy.

Ultrasonic means very high speed or high frequency sound. So normally we think about sound traveling through air. That's the sound that we hear. The air is vibrating and those vibrations make it to our ear and that's what we hear a sound. But sound can also travel through like a piece of metal and it can make that metal vibrate very quickly as it travels through there.

And if you have a very high intensity sound traveling through there, maybe sounds so high you can't hear it, but it's making that metal vibrate back and forth real quick. That vibration can be used to create heat and help cut and cauterize tissue. So this is where the harmonic scalpel comes in. In this case, we have a piece of metal that comes out of the tip of the harmonic scalpel, and it vibrates very quickly, very high speed, back and forth, so fast that you can't really see it. But on a microscopic level, it is vibrating back and forth very quickly.

So then you have another pad that comes down on top of it and squeezes the tissue onto this very quickly vibrating piece of metal. And what's happening here? In this case...

we get friction. And this friction is going to heat up the tissue so much that it's going to cut and cauterize that tissue. So a harmonic scalpel doesn't use electricity so much to do the heating. It uses the electricity to create the vibrations.

But then those vibrations in the metal create friction. And that's where the heat comes from that cauterizes and cuts the tissue. Now, a third way that we can use energy to help cut and cauterize tissue We'll be using instead of electricity, instead of mechanical motion, we can use light.

and that's where lasers come in and that's going to be the topic of the next lecture

Transcript for:Understanding Energy Use in Surgery

Transcript for:
Understanding Energy Use in Surgery