7810 Week 9 Part 2: Electrical and Fire Safety Stuff

Different generations of LIM's (3)

1st: alarms set at 2mA, can't detect balanced faults (equal faults in line 1 and 2) 2nd (dynamic): alarms at 2mA and could interfere with monitoring 3rd: preferred, 5mA alarm, correct both previous issues but can't detect loss of equipment ground wire. If there is a broken ground wire plugged into an outlet then the LIM can't detect that

Two types of electrical injury (what are the components that influence severity?)

1) Disruption of normal electrical function of cells (muscle contraction, respiratory paralysis, altered neuronal conduction, cardiac dysfunction/VF) and 2) thermal injury Severity stems from current and duration that electrical stimulus was applied (increased duration = increased severity independent of amperage of the current flow). Current (I) = E/R in which E = voltage and R = skin resistance. Resistance is based on thickness, injury, and water. Skin resistance varies over our body. Calloused hands are much more resistant than other parts of our body that are thinner and have a lower protective coating. If the skin is damaged, broken, or wet, then resistance to electrical injury reduces substantially.

How much micro shock is needed to be harmful to a susceptible patient (what can trigger? What are protections against?)

20micro amps can cause VF in electrically susceptible patient (TVP, swan, anything sticking out of their body). Even stray capacitance can trigger. Thankfully, equipment ground wires (3 prongs) can protect against micro shock because it has a very low-resistance path the current flow can take. Modern monitors place high impedance b/w patient and any device and limits leakage to 10 micro amps. Avoid touching catheter and equipment at the same time, wear gloves.

What is a short circuit?

A connection that allows current to take the path of least resistance

Electrosurgery unit (ESU): what is the typical Hz of an ESU? What is the power formula for ESU? What provides the resistance in this circuit?

A methodology that employs high-frequency current in the approximate range of 0.3 to 2 MHz, which corresponds to the radio frequency region of the electromagnetic spectrum. High frequency (500,000 - 1,000,000 Hz) in which P = I2R (Pav = I2rinsR) where Pav is average power and Irins is a special type of average current known as root mean square current. The resistance is provided by tissue to which the ESU electrode is applied and the power will be dissipated as heat. If the power is distributed over a small area then very large intensities result, giving surgeon to cut or coagulate tissue at a desired location. So current flow is concentrated into the the tip of the device. Heat is produced by the Bovie that is proportional to current squared and inverse to the area through which it passes. Because it has poor tissue penetration its ability to excite contractile cells is limited. So currents can pass right across and through the precordium and not cause VF. BUT it has caused VF before via low-frequency stray current in coagulation mode with surgeon near heart with a device in it.

What is a cheater plug?

A plug that converts a 3 prong to a 2 prong outlet. Modern day 2 prong equipment are insulated on the outside that reduces the amount of current to flow through it and reduce harm. That's what companies will do make 2-prong equipment safe. Ungrounded equipment can be present even when the power is grounded.

Isolated Power System (IPS...What are the 3 components? What principle/law does an IPS operate on? Is there direct contact b/w the primary and secondary circuits? Is the secondary circuit directly connected to the ground? If a first device is shorted and is plugged into IPS, what happens to the circuit? What if a second fault occurs now? Is there a distinction between hot/neutral lines in IPS? What are the benefits of an IPS?)

A system comprising an isolation transformer or its equivalent, a line isolation monitor, and its ungrounded circuit conductors A power system supplied by an isolation transformer, which operates on the principle of electromagnetic induction. Faraday's law of induction is the quantitative relationship that mathematically describes electromagnetic induction, stating that a changing magnetic flux in one coil produces a changing voltage and hence a changing current in a second coil, which can be accomplished using AC in the first coil. Typically consists of a primary circuit connected to an AC power source and a secondary circuit, ea. w/ coils wrapped around a common iron core. No direct contact b/w the primary and secondary circuits and the secondary circuit is not directly connected to the ground so only consists of 2 wires with 120-V potential b/w them. Benefit to this is that one of the wires can be touched and no current will flow 2/2 lack of direct ground connection (no circuit completion with person). So a person would have to touch both wires of the ungrounded system simultaneously before experiencing electrical shock. Outlets in these systems still have dedicated ground wires, but they're also not in direct contact with secondary circuit. So if a device is shorted and is inserted into an ungrounded circuit, the excess current flows through dedicated ground wire and converts the circuit into a grounded circuit, so no significant electrical hazard. A second fault (touching live wire) can lead to electrical shock though. Also no distinction b/w hot/neutral lines. Just line 1 and line 2. So ungrounded can still ground equipment without direct connection to the ground. Short follows the green ground line back to power company. Primary benefits are significant protection from macroshock and faulty equipment will not trip a circuit breaker. It can convert to a grounded system (see above) and a 2nd fault would be needed to create a hazard. 1 faulty equipment piece will not cause a person to get shocked.

What is the typical power supply in the US in V and HZ and A? How does it flow and what kind of circuit?

AC at 120V, frequency of 60 Hz, 120V EMF, and 1A of current. Flows in a sine wave

Line Isolation Monitor (LIM): what does this monitor for? Specifically what does it measure vs. what does it actually display on the LIM? What to do with LIM alarm?

All real AC electrical circuits experience a phenomenon known as leakage current when small amounts of current (on the order of mA) flow to the ground, even though there is no direct ground wire connection. The presence of leakage current results in an ungrounded circuit becoming grounded although to a very minor extent. Contact with such a small leakage current represents no real threat, but it becomes an issue when cumulative large amount of leakage current results 2/2 multiple devices are plugged into an ungrounded circuit. So we have line isolation monitors (LIM) which measure the integrity of an IPS, measuring impedance to the ground. In a perfect system Z is infinite, but in real world there are bits of leakage. LIM's display mA in total leakage POTENTIAL of the system delivered to that OR. It typically alarms at 2 or 5 mA (5 considered a better alarm b/c if you have >5mA of circuit current then it's probably a true short circuit somewhere. If >5 test all equipment for short-circuit. Then take out shorted equipment from room. True fault: test equipment and remove from room when feasible. False fault is too much equipment plugged in. LIM alarm indicates that the ungrounded state of an isolated circuit has been compromised while still allowing circuit to remain on so that vital equipment can continue to be used.

Polarized plugs (Narrow opening has what kind of electrical potential? Wide? What does wide prong communicate with vs. narrow prong?)

Appliance plugs with one blade wider than the other; designed to fit matching outlet and reduce risk of shock. They fit into a polarized receptacle with a wide opening and a narrow opening. By convention, the narrow opening of the receptacle is at a high potential while the wide opening is at a low potential, which forces the plug to be oriented in a specific direction when inserted into an outlet. Manufacturers design these so that the case is connected to the low potential, wide prong of the plug so that when the plug is plugged in, the casing is at a low potential and only the low potential current should reach the outside of the device. When turned off, polarized plug ensures that the high potential current only exists from the receptacle to the power switch on the appliance while the remainder of the appliance is at a low potential.

Effect of frequency on electroshock

At a 60Hz current, 10-20mA is the "let go" point where sustained muscle contraction occurs. At 1MHz (which is a million hertz) - 3A (3000mA) is considered safe (which is substantially higher than a household circuit). So the higher the frequency, the lower the risk of electroshock. Very high frequency doesn't cause dysrhythmias, but this frequency is not feasible for transmission via power lines.

Various OR fire damage; what should you know about laparoscopy fires?

Burns: could be on or in patient either in airway or via laparoscopy and on a patient usually under drapes in head and neck MAC Toxicants from fire could be CO, CN, ammonia, etc. causing direct tissue damage and decreased O2 saturation (competitively bind with hemoglobin and shift curve to left) Laparoscopy fires: N2O can diffuse into bowel and abdominal cavity and ignite, a reason to avoid N2O during laparoscopy...methane gas and hydrogen normally in bowel can be flammable if surgeon accidentally perforates that bowel in the procedure, could cause a fire to occur. So ultimately limit N2O in abdominal cases and in terms of fuel, keep your dry sponges moist (flammable materials in belly need to be moist)

Ground Fault Circuit Interrupter (GFCI): What does the GFCI monitor? What does it do when something changes in what it monitors? what areas is this mandated in by code? What does it have that other outlets do not? Where can it be installed (what does that make the circuit?)? If you're using this for anesthesia, how many items should be plugged into the GFCI?

Common protection from macroshock. Mandated in all wet areas (OR considered wet but we have LIM's so might not see these). Seen in places near sinks, tubs, and swimming pools. If an electrical device is operating as designed, current flowing to the device from high-potential wire should equal the current returning from the device via the low-potential (neutral wire). So GFCI immediately disrupts current in a circuit if an imbalance b/w the two currents is detected. They're designed to detect very small current differences on the order of 5mA or less. Looks similar to ordinary outlet but has two additional buttons for testing functionality of outlet while second button is used to reset the circuit. Can be installed in either individual outlets or installed as a circuit breaker inside a breaker box (in which all outlets might appear to be ordinary, non-GFCI outlets but are protected by the GFCI circuit). Because of these, if you plug anesthesia equipment into GFCI then only plug 1 thing into it so that it doesn't short when something else plugged into that outlet shorts (when GFCI is triggered). A consideration when determining whether you can practice anesthesia in a non-OR setting.

APSF Power Outage OR Recommendations

Continue to use equipment until the battery is gone. Things with battery life include the vent, non-des gas (namely iso and sevo), IV pumps, and pipeline O2. Equipment with poor battery includes etCO2, Desflurane vaporizer, wall suction, video towers, daVinci, CPB, medication system (open all drawers of Pyxis quick in power outage or you won't be able to get meds out), surgeon will lose Bovie soon. Provide an alternate light source (flashlight from anesthesia machine, cell phone flashlight, laryngoscope, etc.)

Current density (a decrease/increase in what 2 variables increase it?)

Current applied per unit area of tissue. It increases with increased current applied and decrease with a greater area of tissue. 100 microamps is voltage applied and even with low or small amount of current could cause VF directly applied to heart.

How safe are current anesthesia gases? Which elements of gas and CO2 absorbent can cause fire?

Current gases are much less flammable than ether and cyclopropane but can still combust. Sevo, soda lime, and baralyme can cause fires. Avoid desiccated CO2 absorbents. Monitor the temperature of the absorbents (on vent circuit). Watch sevoflurane concentration (super rare: would see that amount delivering is much different than what end tidal is--could signal a problem with monitoring device and could be delivering a lot more than necessary = increased r/f fire...)

Circuit Breakers (what do they do? What is the max amount of amperage in a circuit and what is the max amount of wattage? What is a common type of breaker that does not need to be replaced?)

Designed to prevent too much current from flowing because of a short circuit or circuit overload. A fuse contains a thin, metal strip that heats up d/t the resistance of the metal to electrical current. If the current exceeds the rated value of the fuse, the metal strip will become too hot and melt, thus interrupting the current to the circuit. When a fuse has melted it needs to be replaced. Circuit breakers limit amperage of the circuit, max being 15-20A. The power of the circuit is quantified as P = E x I, or 120V (E) x 15A(I) = 1800W. Circuit breaker trips when max wattage is exceeded. A common breaker is a switch and a strip with two metals. The breaker amperage/current is limited by thickness of wire of bimetallic strips in the circuit breaker. If the current is above rated value of circuit breaker, the bimetallic strip will bend enough to open, or trip, the switch and stop the flow of current. Once the strip cools, it will return to its original shape, allowing the circuit breaker to easily reset with the flip of a switch.

What should you do if a fire actually occurs? What's the mnemonic for OR fires if it continues? In the aftermath what should you do?

Disrupt the triad. If it's in airway: Remove ETT and discontinue circuit simultaneously. Pour saline in in airway, BVM, and assess injury, potentially bronchoscope them and reintubate to finish the case. On the patient: turn off gases right away. We don't have to extubate the patient necessarily but remove the burning materials. Extinguish fire with saline or water in the room or with a fire extinguisher, assess and treat burns/inhalation IF fire continues, ERASE it!!! Extinguish (preferably with CO2 fire extinguisher otherwise might introduce chemicals into surgical field) using PASS (pull pin, aim, squeeze, sweep) Rescue patient and staff (evacuate room if needed) Activate fire alarm Shut the doors and gas supply Evaluate patient Preserve the scene: need to determine cause of the fire. Notify risk management and file incident report and treat as adverse event for RCA. Report per requirements, treat as adverse event. Learn from experience, conduct drills, avoid happening in future

What are the requirements for power outages and generators in OR's?

Emergency power source is mandated (will kick on after 10 seconds primary power off). Regular generator testing is required with a backup in case the generator fails. No elective cases can be performed without two sources of power. IF it's not an emergency then surgeon needs to put in writing that this is an emergency and they can't wait until the power comes back on.

ESU ground plate (return electrode; what does the large return electrode do to the current as it returns through the patient's body? Should the patient be isolated from the ground? how should return plate/pad be placed (return wire status, gel, placement relative to thorax, what to have on hand with external pacing and magnet, where to have pacemaker relative to cautery, etc.)? )

Energy flows through the device tip to the patient but then must return through the patient. Usually, a large surface-area electrode is placed on patient to provide a low current density pathway and provide a safe return path through the body. Large area of the return electrode ensures that the current disperses as it makes its way through the body and by keeping current density low at locations away from the small electrode, little to no tissue damage results as current travels through the body and into return electrode. VITALLY important to ensure that return electrode makes proper physical and electrical contact with the patient's body. Patient should be isolated from the ground (they're not actually grounded by this pad, that's a misnomer). When tip is applied the current density is high but redistributes all over body so grounding pad makes current very low. If there is a problem with how it is applied (like a crease or something ) then current could flow at higher amperage b/c it's flowing back out at a smaller point than is appropriate. Bovie's will now shut off if return plate is improperly applied Ensure that there is appropriate gel on the pad (single patient use usually so gel is already on there) and that the return wire is intact. Place it as close to the site of surgery and as far from EKG leads as possible. If the patient has a demand pacer, place it below the thorax. If they have a demand pacer, have a magnet and external pacing on hand (if you're in outpatient and you don't have these capabilities on hand one should consider recommending surgery in a hospital). Keep the pacemaker out of the path of cautery.

GFCI vs isolated power supply OR requirements

GFCI is permissible if interrupted power would not cause harm. LIM provides more protection to staff, but either GFCI OR IPS are mandatory unless the OR an be classified as a dry area (incredibly unlikely).

Why do we ground equipment? What does the third wire provide for us?

Grounding equipment reduces the shock severity a person receives if they complete that circuit. Because power flows any time the circuit is completed, the neutral wire can connect to neutral, ground wire if present, or to any grounded object/person. The 3rd wire provides alternate, low-resistance path to the ground. Most of the electron flow will go through the ground wire back to ground instead of through a person whose body has a natural resistance to it. If ungrounded, old 2-prong outlet, entire shock will flow through person instead of back to the power company when handling the case. So with a hot case and grounded circuit, person will receive 1-2% of, say, a 500mA flow, making it an acceptable 5-10mA because 90+% of the current will take the least resistance back through ground wire and away from person.

How to best prevent fires

Have equipment ready, run drills, assign tasks Try to prevent: allow skin prep to dry completely (eliminates a fuel) before applying draping (wet draping ignites easier...set a timer for solution drying), communication with team and surgeon, minimizing N2O and FiO2 when using electrocautery (high FiO2 with ENT could cause a massive airway fire), keep gauze wet, avoid head/neck MAC with O2 (considered poor form to do MAC with O2 on a head and neck case...either secure airway or turn of O2 before surgeon applies Bovie) Sometimes O2 is okay in an awake craniotomy or some reason they can't have general anesthesia but you need to have excellent communication with surgeon to drop FiO2 to 35% before they proceed.

What is the OR Fire Triad and who controls each element in the OR primarily?

Heat or ignition source, fuel, oxidizer Heat: could be ESU, lasers, light cords, malfunctioning electrical equipment like a short-circuit. But generally these are variables controlled by the surgeon Fuels: any flammable material in the OR like paper drapes, apparel, masks, gown, bonnets, prep agents, ointments, the actual patient's hair or tissue, dressings, anesthesia equipment like tubes, hoses or monitors. These are most often controlled by circulator or techs Oxidizers: this is what we control. O2 (21% takes 12 second to ignite a cotton towel but 95% O2 takes 0.1 seconds to ignite). N2O (burns just as well as O2 does), and air itself because it has atmospheric oxygen although not as easy as a higher fraction of oxygen

Cautery and implanted devices

If unipolar: If the surgery is below umbilicus and cautery is to be used with implanted devices: proceed. If surgery is above the umbilicus and cautery is used and the device is an AICD, use a magnet to disable the tachyarrhythmia therapy. If It's a pacer: are they pacer dependent? If yes, contact rep b/c they might need a magnet or external pacing/reprogramming. If no: contact rep anyways, might just need magnet available. If Bipolar: don't worry about it! No effect on pacemaker or AICD.

How does shock occur? Where must one touch a circuit to complete a circuit? Can we have shock in properly operating equipment and if so under what conditions?

In the absence of safety devices, a person completes an electrical circuit. One touches an energized circuit, a path can be established where the electricity will flow through the body. A person must contact the circuit at TWO points. Voltage source must cause current to flow through. Can result from stray capacitance and inductance in electrical equipment that is properly operating as well.

How to best prevent airway fires (for laser and ESU)

Laser ENT: consider using a laser tube For ESU: low FiO2 possible that is safe for patient. Communicate with surgeon. Can use wet pledgets around the ETT to make sure it's kept moist during case. Avoid using cautery within trachea because it is an oxygen-rich environment.

Macroshock vs. Microshock (What are they? What are #'s for both? What is the Hz and amps of leakage current when designing OR?)

Macroshock occurs when a relatively large amount of current flows through an individual potentially resulting in injury or death. 1mA (0.001A) is threshold of perception. 5mA accepted as maximum harmless current intensity. 10-20mA is "let go" current before sustained muscle contraction. 50mA = pain, fainting, mechanical injury but heart/respiratory function continue 100-300mA = VF starts but respiratory center remains intact 6000mA = sustained myocardial contraction followed by normal heart rhythm with temporary respiratory paralysis and potential burns. Anything >100mA causes damage and can trigger VF. Microshock occurs when an individual who has an external, low-resistance pathway that directly contacts the heart. This person is classified as electrically susceptible. Ex: PA Cath with saline solution or external pacing wires. In microshock, 0.1mA or 100microamps can cause VF. When designing an OR, 10microamps should be the maximum amount of 60Hz leakage current.

What are three environmental hazards in the OR?

Power cords, outlets, and monitors.

What is the difference between grounded and ungrounded equipment? What of the voltage potential that exists between them?

Power is grounded in both circuits, but in ungrounded, there are only 2 wires: hot and neutral in which there is 120V between the hot and neutral line and 120V between the hot and earth. In grounded, there are 3 wires: hot, neutral, and ground. Same voltage b/w hot/neutral and hot/eart but also 120V between hot and ground wires, which add an extra measure of safety. In three-pronged grounded plug, third prong provides a path for current directly to the ground, thus protecting someone who might touch the case of the appliance.

Why is power ungrounded in the OR? Where does the 120V potential exist between in this power setup? How would one become shocked in this setup and why? What increases the risk of electrical accidents in the OR?

Power is isolated from the ground, which protects against macroshock. 120V of potential only exists between two wires, not circuit to ground. There is no connection b/w the power source and the ground. So you can't complete circuit by simply standing on the ground. In order to receive a macro shock in an ungrounded power system, you would have to contact short-circuited equipment at 2 different points. The ground cannot complete the circuit. A high population of electrical equipment + cords/puddles on the floor can increase risk of electrical accidents. So even though grounded electrical systems are designed to minimize shock hazards, these systems can, in certain conditions, present a reasonable possibility of a shock, like in an OR. The abundance of electrical devices and conducting fluids substantially increase the risk of macro shock. So most OR's use isolated, ungrounded electrical circuits or isolated circuits OR ungrounded circuits.

What are the two different ways the concept of grounding is applied?

Power: power is always grounded in the home and usually ungrounded in the OR Equipment: may or may not be grounded in the home but always grounded in the OR

Laser surgery safety; what are some different types of lasers? What laser is similar to argon, what are they absorbed by and what is their tissue penetration? What is the most powerful and what is it used for? Which has little penetration and is considered most precise/what is it used for? Which one is used for aiming?

Protect eyes of the staff and patient. N95 mask appropriate (plume). Warning signs so they know lasers are in use. Consider laser-resistant ETT. Keep FiO2 if they're in airway. Consider using rigid metal branch or jet ventilator for this. Argon laser is absorbed by hgb and has a modest tissue penetration. KTP is similar to Argon laser Most powerful is Nd:YAG used for tumor debulking especially in airway. CO2 has little penetration and is most precise. Used for OP, vocal cord surgery He-Ne: red light used for aiming...no precautions for this.

T/F: power is ungrounded in an isolated power system in the OR (IPS) and is monitored by line isolation monitors (LIM)

TRUE (all equipment is grounded, providing a low-resistance pathway to limit macro and micro shock. This information is provided to LIM. Ground wire is hospital grade and can be inspected. If you plug something two-pronged in then you're potentially bypassing your LIM.

T/F: equipment should always be grounded in ungrounded IPS (why)

TRUE (if equipment is ungrounded, then it circumvents the LIM and shorts can't be detected. Equipment ground wire provides low-resistance alternate route for shock in case of second fault occurring at the same time)

Bipolar cautery

The active and return electrodes are two blades of a forceps; requires less power, frequently used for neuro, ocular, ENT. No return pad needed. Lot safer but less power.

Impedance (r/t LIM's): High impedance results in what current and vice versa? Does the displayed LIM value correspond to the amount of current actually flowing through at that moment?

The generalization of the concept of resistance, which is simply the opposition of a circuit to the flow of current. High impedance results in very little current while low impedance can result in large currents. To calculate impedance Z, do Z = E/I in which E is the volts in the circuit and I is current. So 120V and a 2mA current flow (0.002A) leads to 120V/0.002A = 60,000ohm in impedance. LIM's display the current that corresponds to the measured impedance to ground in an isolated circuit. The displayed value is the current that would result if a fault were to occur, NOT the current actually flowing at that moment. A short on a piece of equipment plugged into an isolated circuit reduces the impedance to the ground. This will trigger LIM alarm, indicating first fault is present. If a second fault occurs, then a shock could occur.

How is a typical power cord set up? How many conductors are there? What is the current flow inversely proportional to and what is a short circuit with that knowledge in mind?

Two conductors: Hot that carries current to impedance and a neutral that returns the current to the source. The difference between them is 120V. The current flow (load) is inversely proportional to impedance (resistance for AC circuits). A short circuit is a situation in which there is high current flow and zero impedance Ex: typical home circuit has 120V with 0.5A (originating from 60W bulb and 120V circuit of current flowing throughout the circuit. Given a 60W bulb and a circuit with 120V, can compute the resistance to be R = E/I = 120V/0.5A = 240ohm

Electromagnetic Interference

Unlesss you have 2G phone, this is not a thing anymore for "no cell phone use intros area." From cellular, internet, and walkie-talkies. If you do have it then it could possibly interfere with equipment causing ventilator malfunction, pacemaker interference, distance restriction (1m). Technological improvements have mitigated this.

Double insulation (what is it designed to do to live wires?)

Used for appliances without an earth wire Have plastic casings Designed so that the live wire cannot touch the casing Cannot give an electric shock. Some equipment may safely have 2-pronged plug that contains 2 layers of insulation + plastic exterior (power tools, IV pumps). Permissible in the OR. Hazard could occur if the inside gets wet.

Neutral Grounded Power System (what are the lines from power co to fuse box and from fuse box to outlet?)

Utility power is always "grounded" in that it comes from the power company to your house and is grounded in the earth. There will be hot and neutral lines to a fuse box with a hot to hot distribution strip and neutral to neutral strip and to ground. The hot line is 120V (black), the neutral is white and connected to ground pipe, and ground is green/bare and connected to ground pipe as well. So in 3-prong outlets, one of the long slits (right side) originates from the hot line, the neutral line is the other vertical slit (left), and the hole below them is the ground line.