Apex Unit 6 Equipment & Monitors Flashcards

Question

Which value exceeds OSHA’s recommended standards for occupational exposure to inhalation anesthetics in the operating room? Sevoflurane 1.0 ppm + Nitrous oxide 15 ppm Sevoflurane 1.8 ppm Desflurane 0.8 ppm Desflurane 0.3 ppm + Nitrous oxide 20 ppm

Answer 1

Sevoflurane 1.0 ppm + Nitrous oxide 15 ppm OSHA recommends that anesthetic gas exposure should not exceed the following: Nitrous oxide alone should be less than 25 ppm. Halogenated agents alone should be less than 2 ppm. Halogenated agents with nitrous oxide should be less than 0.5 ppm. Of all the answers, only sevoflurane 1.0 ppm + nitrous oxide 15 ppm exceeds the maximum.

Answer 2

Open + No rebreathing and no reservoir Semi-open + No rebreathing with a reservoir Semi-closed + Partial rebreathing with a reservoir Closed + Complete rebreathing with a reservoir

Answer 3

Replace the carbon dioxide absorbent. Increase the fresh gas flow in excess of the patient's minute ventilation. This patient is rebreathing CO2. There are 2 ways to fix this. You can either replace the carbon dioxide absorbent or convert the breathing system to a semi-open system by increasing the FGF. Increasing the minute ventilation does not prevent rebreathing. The patient will continue to inspire carbon dioxide, but now only at a faster rate. This is not a problem with the expiratory valve. The trick to diagnosing unidirectional valve malfunction is to look at the beta angle during the inspiratory phase. If you aren't familiar with this term, we have an image for you on the next slide.

Answer 4

Is tested with the Pethick test Delivers fresh gas through the inner tube The Bain system uses a coaxial design, where: Fresh gas is delivered to the patient through the inner tube. Exhaled gas travels through the outer tube. The inner tube is at risk for kinking and disconnection. The Pethick test should be performed as part of the preanesthetic checkout. The Bain system is a modified Mapleson D (not A). It can be used for spontaneous as well as controlled ventilation.

Answer 5

It is based on the Beer-Lambert law Oxygenated hemoglobin absorbs light at 940 nm Why are the other answer choices wrong? The pulse oximeter utilizes the Beer-Lambert law (not the Doppler effect). It emits two wavelengths of light: oxygenated blood better absorbs near-infrared light (940 nm) and deoxygenated blood better absorbs red light (660 nm). The pulse oximeter looks at the ratio of light absorption during the peak of the waveform relative to the trough of the waveform. At the peak of the waveform, the ratio of arterial blood to venous blood is increased (not the other way around).

Answer 6

50 Know these numbers: SpO2 90% = PaO2 60 mmHg SpO2 80% = PaO2 50 mmHg SpO2 70% = PaO2 40 mmHg

Answer 7

Vascular compression You need to know the limitations of your monitors. In the case of the pulse oximeter, it’s not a good monitor of ventilation, anemia, or bronchial intubation. Of the answer choices presented, the pulse oximeter is best for detecting vascular compression. Think about innominate artery compression during mediastinoscopy. Sometimes you're going to look at the answer choices and not love any of them. Learn to reason through why the correct answer is correct, but more importantly, why the wrong answers are wrong.

Answer 8

Jaundice Why are the other answers wrong? Unlike a healthy heart that delivers pulsatile flow to the body, a left ventricular assist device supplements the failing myocardium with non-pulsatile flow. This defeats the mechanism of pulse oximetry. Carboxyhemoglobin absorbs the same wavelength as oxyhemoglobin. This causes the pulse oximeter to overestimate the degree of oxygen bound to hemoglobin. Blue nail polish can cause a false reduction in SpO2.

Answer 9

Infrared absorption Infrared absorption is the most common method of exhaled gas analysis in the operating room. Although the other answer choices are less commonly employed, you still need to understand them.

Answer 10

Requires less pressure to occlude the artery An improperly sized NIBP cuff can produce inaccurate results. The ideal bladder length equals 80 percent of the extremity circumference, while the ideal bladder width equals 40 percent of the extremity circumference. A cuff that is too small overestimates SBP. A cuff that is too large underestimates SBP. Although rare, nerve injury due to NIBP measurement tends to affect the ulnar or median nerve.

Answer 11

15 cm The tip of the central venous catheter should reside at the junction of the vena cava and the right atrium. It should not enter the right atrium! In this example, the correct distance is 15 cm from the skin to the junction of the VC and RA. We’ll show you an easy way to calculate central line distances on the next page.

Answer 12

Increased by PEEP PEEP increases pulmonary vascular resistance. This creates additional resistance against RV ejection, which can increase RVEDP and CVP. Why were the other answers wrong? A transducer above the zero point, underestimates (not overestimates) CVP. Pericardial tamponade produces a compressive force around the heart. This reduces RA compliance and increases (not decreases) CVP. A VSD typically increases RVEDV and CVP (they don't stay the same).

Answer 13

Tricuspid stenosis Diastolic dysfunction If you understand the CVP waveform, then reasoning through this question becomes a whole lot easier! The a wave correlates with atrial contraction. Therefore, if the a wave amplitude increases, it is due to a stenotic tricuspid valve or decreased compliance of the right ventricle. With atrial fibrillation, there is no atrial kick. On the CVP waveform, the a wave is lost. With tricuspid regurgitation, a portion of the RV volume travels through the incompetent tricuspid valve and re-enters the RA. On the CVP waveform, there will be a large v wave.

Answer 14

Dicrotic notch Increased diastolic blood pressure You should be able to explain the pressure changes as the tip of the PAC travels through the heart. When the tip enters the pulmonary artery, the diastolic pressure increases and a dicrotic notch appears. We’ll walk you through all of it on the next page.

Answer 15

Three The tip of the PAC should be in zone III. In this region, there is a continuous column of blood between the tip of the PAC and the left ventricle. This provides the most accurate estimation of LVEDP.

Answer 16

PEEP Diastolic dysfunction You should know when to trust your numbers, and more importantly, you should understand the conditions where your numbers may be inaccurate. Anything that impairs the normal pressure gradient between the PAC tip and the LV can impact your interpretation of the PAOP. PAOP overestimates LVEDV: PEEP and diastolic dysfunction PAOP underestimates LVEDV: Aortic insufficiency

Answer 17

High injectate volume When we measure cardiac output with the thermodilution method, we graph injectate temperature vs. time. Cardiac output is inversely proportional to the the area under the curve. You must know the variables that can skew your results. A high injectate volume underestimates CO, while a low injectate volume overestimates CO. Injectate that is too warm and a partially wedged pulmonary artery catheter overestimate CO. A right-to-left intracardiac shunt has an unpredictable effect on CO measurement.

Answer 18

Sodium nitroprusside toxicity Sepsis SvO2 is a function of four variables: cardiac output, arterial oxygen saturation, amount of hemoglobin, and oxygen consumption. ``` Cyanide toxicity (impaired O2 utilization) and sepsis (high cardiac output state + arterial admixture) increase SvO2. Anemia reduces oxygen delivery and decreases SvO2. Thyroid storm increases oxygen demand and decreases SvO2. ```

Answer 19

10 percent As a general rule, preload responsiveness is expected to be present if a 200 - 250 mL fluid bolus increases the stroke volume in excess of 10 percent.

Answer 20

Bachmann bundle There are three internodal tracts that travel from the SA node to the AV node: Bachmann bundle (extends into the left atrium) Wenckebach tract Thorel tract Kent's bundle is a pathologic accessory pathway that is responsible for Wolff-Parkinson-White syndrome.

Answer 21

Phase 0 + QRS complex Phase 2 + QT interval Phase 3 + T wave ``` There are five phases of the ventricular action potential: 0 = Rapid depolarization (QRS) 1 = Initial repolarization (QRS) 2 = Plateau phase (QT interval) 3 = Final repolarization (T wave) 4 = Resting phase (T → QRS) ```

Answer 22

Pericarditis + PR interval depression Hypokalemia + U wave Intracranial hemorrhage + Peaked T wave Wolff-Parkinson-White syndrome + Delta wave

Answer 23

V1 + Septum V3 + Anterior wall aVF + Inferior wall Lead I + Lateral wall

Answer 24

Towards areas of hypertrophy Away from areas of myocardial infarction The mean electrical vector represents the average of all the electrical forces generated by the myocardium. The normal value is between -30 degrees and +90 degrees. The mean electrical vector tends to point: Towards areas of hypertrophy (there is more tissue to depolarize). Away from areas of myocardial infarction (the vector must travel around these areas).

Answer 25

Adenosine Adenosine is an endogenous nucleoside that slows conduction through the AV node. By stimulating the cardiac adenosine-1 receptor, adenosine activates K+ currents, which hyperpolarizes the cell membrane and reduces action potential duration. It is efficacious for supraventricular tachycardia as well as WPW with a narrow QRS. It is not efficacious for atrial fibrillation, atrial flutter, torsades des pointes, or ventricular tachycardia.

Answer 26

Lidocaine + Class I Propranolol + Class II Amiodarone + Class III Verapamil + Class IV Antiarrhythmic drugs can be divided into four classes: Class I drugs inhibit fast sodium channels. Class II drugs decrease the rate of depolarization. Class III drugs inhibit potassium ion channels. Class IV drugs inhibit slow calcium channels.

Answer 27

Atrial-ventricular reentry Wolff-Parkinson-White syndrome occurs when an accessory pathway joins the atrium to the ventricle. This accessory pathway is called Kent's bundle.

Answer 28

Procainamide Amiodarone This is a complex topic, so you may want to read the next page a few time

Answer 29

Metoprolol Patients with long QT syndrome are at risk for developing torsades de pointes. Beta-blocker therapy is associated with a reduction in sudden death in this patient population. Patients with long QT syndrome should not receive drugs known to prolong the QT interval. Methadone is the only narcotic known to increase the QT interval. Furosemide can cause hypokalemia and hypomagnesemia. These metabolic disturbances can prolong the QT interval. Hyperventilation shifts K+ into cells, decreases serum K+, and can prolong the QT interval.

Answer 30

Position I + Chamber paced Position II + Chamber sensed Position III + Response to sensed event Position IV + Programmability

Answer 31

The EtCO2 was 20 mmHg The pacemaker failed to capture, because hypocarbia (which caused hypokalemia) made the myocardium more resistant to depolarization. The same electrical stimulus from the pacemaker was no longer sufficient to depolarize the heart. You'll see the pacer spikes, but you will not see capture. Why the other choices are wrong: When compared to the surgical electrocautery, the use of an ultrasonic Harmonic scalpel decreases the chance of electromagnetic interference. Changing from "coagulation" to "cutting" also reduces the risk of EMI. Hypothermia (not hyper-) makes the myocardium more resistant to depolarization. As an aside, this is why hypothermia causes bradycardia.

Answer 32

A > 25% change from baseline suggests a reduction in cerebral oxygenation. Cerebral oximetry is a noninvasive technique that utilizes near infrared spectroscopy (NIRS) to measure regional (not global) cerebral oxygenation. It is based on the principle that ↓ cerebral oxygen delivery → ↑ cerebral oxygen extraction → ↓ venous hemoglobin saturation. A > 25% change from baseline suggests a reduction in cerebral oxygenation.

Answer 33

1 + Beta 2 + Alpha 3 + Theta 4 + Delta

Answer 34

Ketamine falsely elevates the BIS value. Burst suppression begins at a BIS value of 20. While most general anesthetics reduce high frequency EEG activity, ketamine increases them. This can falsely elevate the BIS value. There is a 20-30 second lag between measuring the EEG and computing the BIS value. Some people argue that titrating your anesthetic to the BIS is akin to driving using only your rear view mirror. The Patient State Index monitor is similar to the BIS in that it measures EEG, runs the data through an algorithm, and displays a number that indicates the level of anesthetic depth. Unlike the BIS where the target for GA is 40-60, the target for the PSA is 25-50. Burst suppression begins at a BIS value around 20.

Answer 35

The alarm sounds when the OR power supply becomes grounded. Unlike where you live, the electrical supply in the OR is NOT grounded. The function of the line isolation monitor is to alert the OR staff when the power supply becomes grounded. This is significant, because a second electrical fault can lead to an electric shock. The line isolation monitor does NOT: Protect the patient from microshock. Isolate the electrical equipment from the ground. Cut off the power supply to a piece of equipment that has become grounded.

Answer 36

Electrocautery can suppress pacemaker function. A return pad that is too small increases the risk of thermal injury. The bipolar cautery is useful if the operative site is near a pacemaker or ICD. Because the current flows from one tip of the instrument to the other, no return pad is required. On a monopolar electrocautery unit, the return pad provides a location for the electrical current to exit the body. If the pad is too small or does not make good contact with the patient, the electrical current will find another way to exit the body. Possible locations include: EKG pads, jewelry, temperature probes, or anything else with conductive properties. As you'll see on the next page, the return pad does not actually "ground" the patient.

Answer 37

Less fresh gas to the vaporizing chamber More fresh gas to the bypass chamber Anesthetic vapor pressure is dependent on ambient temperature; the higher the temperature the higher the vapor pressure. Since we need vaporizer output to be consistent over a wide range of ambient temperatures, a temperature compensating bi-metallic strip directs a fraction of the fresh gas to the vaporizing chamber and the remainder of the fresh gas to the bypass chamber. These two fractions combine as fresh gas exits the vaporizing outlet. Since a higher temperature is associated with a higher vapor pressure, it should make sense that we want less fresh gas to enter the vaporizing chamber and more fresh gas to enter the bypass chamber. In this circumstance, the temperature compensating strip expands to accomplish this goal.

Answer 38

Flow control valves to the common gas outlet The low pressure circuit test is conducted by attaching a bulb to the common gas outlet and creating a negative pressure in the low pressure system. Specifically it tests for a leak between the flow control valves to the common gas outlet. The low pressure circuit leak test does not include the anesthesia circuit, which is beyond the common gas outlet. The low pressure circuit leak test is the best method to detect a vaporizer leak. The pipeline is part of the intermediate pressure system.

Answer 39

75 L/min The oxygen flush valve delivers a flow rate between 35 - 75 L/min. It provides a direct link between the oxygen pipeline (50 psi) and the breathing circuit. The O2 flush valve bypasses the flowmeters and the manifold. Using the O2 flush valve can create two problems: 1. Because the ventilator spill valve is closed during inspiration, pressing the O2 flush valve during the inspiratory phase exposes the breathing circuit to pipeline pressure. This increases the risk of barotrauma. 2. Adding a large quantity of oxygen to the breathing circuit dilutes anesthetic vapors. This can increase the risk of awareness.

Answer 40

Is normally observed during periods of nonuse There are two problems that occur with CO2 absorbents: 1) it exhausts its ability to neutralize CO2 and, 2) it dries out - it becomes desiccated. Soda lime is a strong base. As CO2 consumes the basic substrate, the pH of the soda lime decreases (it becomes more acidic). As the pH falls below 10.3 an indicator dye (ethylene violet) changes from colorless to purple. This indicates that the soda lime should be changed. Color reversion means that soda lime that used to be purple has turned back to white. This commonly occurs during periods of nonuse, but it does NOT mean that the soda lime has regenerated. In fact, once it is exposed to CO2, the canister will quickly turn purple. Additionally, the indicator dye does not tell you if the absorbent has become desiccated.

Answer 41

2 ppm When halogenated agents are used alone, the maximum acceptable level of exposure is 2 ppm. When halogenated agents are used in conjunction with nitrous oxide, the maximum acceptable level is 0.5 ppm and 25 ppm respectively.

Answer 42

Na2CO3 + Ca(OH)2 ---> CaCO3 + 2NaOH You should be able to write out the soda lime reaction. CO2 + H2O ---> H2CO3 H2CO3 + 2NaOH ---> Na2CO3 + 2H2O + energy Na2CO3 + Ca(OH)2 ---> CaCO3 + 2NaOH

Answer 43

15% Neutralization of CO2 requires an aqueous environment on the surface of the soda lime granule. This is why soda lime is hydrated to 10-20%.

Answer 44

Endotracheal tube Of the answer choices provided, a properly sized endotracheal tube imposes greater resistance than the anesthesia breathing circuit system. Resistance is any factor within a conduit that restricts flow. And yes, this is but another example of Poiseuille's law in action. Resistance = 8 x viscosity x length of tube 3.14 x radius^4 x pressure difference Since diameter is the most important factor in this equation, you should think about the answer choice with the smallest diameter. In this case, it's the endotracheal tube.

Answer 45

Breathing circuit fire The combination of desiccated Baralyme and sevoflurane has resulted in breathing system fires. Desiccated Baralyme produces flammable by-products such as formaldehyde, methanol, and formic acid. In an oxygen rich environment, the risk of fire is greatly increased. This is why Baralyme is no longer available on the market. Carbon monoxide production is increased with desiccated soda lime (Des > Iso >>> Sevo). Compound A production in increased with sevoflurane in desiccated soda lime.

Answer 46

The annular space is the cross sectional area of the flow tube. The annular space is the area between the indicator float and side wall of the flow tube (not the cross sectional area of the tube). Since the flow tubes are tapered at the base and widen towards the top, the annular space is narrowest at the base and widest at the top. This “variable orifice” architecture provides a constant gas pressure throughout a wide range of flow rates. A higher fresh gas flow creates a turbulent flow pattern. The density of a gas determines whether flow is laminar or turbulent at a given flow rate. A gas of higher density will become turbulent at a given flow rate sooner than a gas of lower density. This is why a helium-oxygen mixture is used to promote laminar flow during an asthmatic attack.

Answer 47

1900, 2000, or 2200 What is the maximum service pressure in an oxygen e-cylinder? Depending on the text you read, you'll see 1900, 2000, and 2200 psi. On the NCE, we hope they'd take multiple answers to a question like this. If you are hard pressed to pick one, then we'd go with 1900. This is the value listed in Nagelhout and Dorsch.

Answer 48

Oxygen - 660 L Nitrous oxide - 1590 L Air - 625 L Each gas is followed by its max capacity (L) and max pressure (psi): Oxygen: 660 L - 1900 psi Nitrous oxide: 1590 L - 745 psi Air: 625 L - 1900 psi

Answer 49

Oxygen - 2, 5 Nitrous Oxide - 3, 5 Air - 1, 5

Answer 50

White Yes, you read that correctly. Oxygen tanks are green in the United States, but in many other countries they are white. We're one of the few countries that still doesn't use the metric system, so the fact that our E cylinders are different colors shouldn't come as a surprise. World Health Organization designed tank colors: Oxygen is white Nitrous oxide is blue Air is black and white

Answer 51

4 - 8 mesh The balance of granule surface area and airflow resistance was derived by heuristic methods over many years. A granule size that is too small provides a very high surface area with a high absorptive capacity. The downside to this is that small granules greatly increase airflow resistance as well as the work of breathing. A granule that is too large has a small surface area and is not an efficient absorber of carbon dioxide. A benefit is that this reduces airflow resistance and the work of breathing. To best balance these conflicting issues, 4 – 8 mesh granules are used. Said another way, each granule is between 1/8 to 1/4 inch in diameter and will pass through a mesh screens with 4 – 8 holes per square inch. This size provides the best combination of absorptive capacity and airflow resistance.

Answer 52

Removal of NaOH Addition of Ca(OH)2 Carbon dioxide absorbents contain NaOH and/or KOH. These strong bases function as activators that facilitate the reaction process. When exposed to volatile anesthetics, these compounds can produce carbon monoxide and compound A. Desiccated CO2 absorbent accelerates the production of these compounds. Calcium hydroxide lime (Amsorb Plus) was formulated to decrease the production of these compounds. This was accomplished by replacing NaOH with Ca(OH)2 (calcium hydroxide).

Answer 53

Flowmeter control valve Oxygen flush valve The anesthesia machine can be divided into 3 systems based on the respective pressures in each. High pressure system - Back up cylinders, cylinder yoke, cylinder gauge, and cylinder regulator Intermediate pressure system - pipeline inlets, check valves, pressure gauges, ventilator power inlet, oxygen pressure system, flowmeter control valve, oxygen 2nd stage regulator, and oxygen flush valve Low pressure system - Flowmeter tubes, vaporizers, common gas outlet, and check valves if present

Answer 54

Hanger yoke Cylinder pressure regulator High pressure system - Back up cylinders, cylinder yoke, cylinder gauge and cylinder regulator Intermediate pressure system - pipeline inlets, check valves, pressure gauges, ventilator power inlet, oxygen pressure system, flowmeter control valve, oxygen 2nd stage regulator, oxygen flush valve Low pressure system - Flowmeter tubes, vaporizers, common gas outlet, check valves if present

Answer 55

Prevent misconnections of gas hoses The DISS (diameter index safety system) system is used to decrease inadvertent misconnections of gas piping. Each gas pipe and connector are sized and threaded differently on the back of the anesthesia machine to avoid catastrophic mistakes. The PISS (pin index safety system) is used to decrease inadvertent misconnections of gas cylinders. The SPDD model is used to understand the pathway of gas through the anesthesia machine.

Answer 56

Inadvertent attachment of a nitrous oxide cylinder The PISS (pin index safety system) is used to prevent the wrong cylinder from being attached to the wrong yoke. Since each pin configuration is specific to a specific gas, it is unlikely (although not impossible) that the wrong tank will be outfitted to the anesthesia machine. Using more than one washer or using a cylinder with missing pins can defeat this safety mechanism. A cylinder leak may have looked like an attractive option, however we can tell you from personal experience that using more than one washer won't create a leak.

Answer 57

GE-Datex-Ohmeda Tec 6 Drager D Vapor The GE-Datex-Ohmeda Tec 6 and a newer version from Drager, the D Vapor, are the only vaporizers approved for the use of desflurane.

Answer 58

Flow control valves to the common gas outlet The low pressure circuit test is conducted by attaching a bulb to the common gas outlet and creating a negative pressure in the low pressure system. Specifically it tests for a leak between the flow control valves to the common gas outlet. The low pressure circuit leak test does not include the anesthesia circuit, which is beyond the common gas outlet. The low pressure circuit leak test is the best method to detect a vaporizer leak. The pipeline is part of the intermediate pressure system.

Answer 59

Less fresh gas to the vaporizing chamber More fresh gas to the bypass chamber Anesthetic vapor pressure is dependent on ambient temperature; the higher the temperature the higher the vapor pressure. Since we need vaporizer output to be consistent over a wide range of ambient temperatures, a temperature compensating bi-metallic strip directs a fraction of the fresh gas to the vaporizing chamber and the remainder of the fresh gas to the bypass chamber. These two fractions combine as fresh gas exits the vaporizing outlet. Since a higher temperature is associated with a higher vapor pressure, it should make sense that we want less fresh gas to enter the vaporizing chamber and more fresh gas to enter the bypass chamber. In this circumstance, the temperature compensating strip expands to accomplish this goal.

Answer 60

Unidirectional valves CO2 absorbent Mapleson devised a classification system for nonrebreathing circuits, which are also known as semi-open circuits. All of the Mapleson circuits lack unidirectional valves and a CO2 absorber. Resistance is low, because there are no unidirectional valves or absorbent granules. This makes these circuits attractive for pediatrics. Since there is no CO2 absorbent, fresh gas flow and the circuit design determine the amount of rebreathing that occurs. The Mapleson D has an APL valve and a reservoir bag. The Mapleson E (Ayre's t-piece) is the only Mapleson design that does not contain an APL valve or reservoir bag.

Answer 61

Open An open circuit is open to the atmosphere and does not contain dead space. All of the other circuits are not open to the atmosphere and contain some degree of dead space.

Answer 62

``` D E F The most common Mapleson circuits include: D, E, and F. You'd be hard pressed to find an A, B, or C. Yes, these circuits are archaic, but they are important in understanding the correlation between fresh gas, dead space, and alveolar gas with circuit design. ``` Mapleson D, E, and F are also labelled the “T piece” group. The fresh gas enters at the proximal end of the circuit and the APL valve is located distally near the reservoir bag. The Mapleson D is actually the reverse set up of a Mapleson A making it an excellent choice for controlled breathing. Although "Basics of Anesthesia" is not listed on the NBCRNA bibliography, it does not mean the content within isn't relevant. It does an excellent job of explaining each Mapleson circuit with a clear voice.

Answer 63

Semiopen circuit Semiopen Circuit (Mapleson A-F, Bain system, circle system w/ FGF > Ve): Bag reservoir = Yes Rebreathing = No

Answer 64

Semiopen A semiopen circuit contains a breathing bag but does not allow rebreathing of exhaled gases. Semiopen Circuit (Mapleson A-F, Bain system, circle system w/ FGF > Ve): Bag reservoir = Yes Rebreathing = No

Answer 65

Semiclosed circuit A circle system with a FGF of 3 L/min is a semiclosed circuit. Semiopen Circuit (Mapleson A-F, Bain system, circle system w/ FGF > Ve): Bag reservoir = Yes Rebreathing = No

Answer 66

Bain System The Bain system is an example of a semiopen circuit. All of the other answer choices are open circuits (nasal cannula, simple face mask and T-piece). Since there is no reservoir bag, an open circuit requires a spontaneously breathing patient. Entrapment of the exhaled gas is also not possible, therefore there is no way to scavenge exhaled gases. This can cause environmental pollution. Since oxygen is pumped into the atmosphere (it's not contained within a circuit), there is a risk of fire if an ignition source and fuel are present.

Answer 67

1st step + Occlude the elbow at the patient end of the circuit. 2nd step + Close the APL valve. 3rd step + Use the oxygen flush valve to fill the circuit. 4th step + Remove the occlusion at the elbow while flushing the circuit. It is possible that the inner tubing of the Bain circuit can become kinked or disconnected. This situation converts the entire length of the corrugated tubing to dead space and greatly increases the risk of hypercarbia if FGF is not increased. The Pethick test should be done as part of the pre-anesthetic checkout. If the inner tubing is patent, the Venturi effect will cause the reservoir bag to collapse. If the inner tubing is occluded, the reservoir bag will remain inflated. This circuit is not safe to use.

Answer 68

Laparoscopy Carbon dioxide follows a concentration gradient as it exits the body: blood > lungs > airway > sample line or atmosphere The normal PaCO2-EtCO2 gradient is 2-5 mmHg. This gradient is increased by any condition that blocks CO2 removal or by a leak in the breathing system. Examples include: Reduced CO2 transport through the lungs Incomplete alveolar emptying Increased dead space Right-to-left shunt Upper airway obstruction Leak in the sample line, endotracheal tube, or LMA Inadequate seal around endotracheal tube, or LMA Insufflation of carbon dioxide during laparoscopy increases blood CO2, however as long as there is nothing preventing its escape, the PaCO2-EtCO2 gradient remains normal.

Answer 69

Carbon dioxide Nitrous oxide Volatile anesthetics Infrared analysis is the most common method of measuring carbon dioxide, nitrous oxide, and halogenated anesthetics. Molecules that contain two or more dissimilar atoms absorb infrared light, and each of these molecules produces a unique infrared absorption footprint. IR analysis cannot measure oxygen, helium, nitrogen, or xenon because these species contain only one type of atom.

Answer 70

Less apparatus dead space There are two sampling methods used for capnography: mainstream and sidestream The mainstream (in-line) measuring device is attached to the endotracheal tube. It provides a faster response time, and doesn't require a water trap or pumping mechanism. Because it's attached to the endotracheal tube, it does increase apparatus dead space as well as adds extra weight. The sidestream (diverting) measuring device is located outside of the airway. A pumping mechanism continuously aspirates the gas sample from the breathing circuit, and for this reason, the response time is slower. Additionally, this arrangement requires a water trap to prevent contamination of the device.

Answer 71

660 nm light is preferentially absorbed by reduced hemoglobin The pulse oximeter is based on the Beer-Lambert law, which relates the intensity of light transmitted through a solution and the concentration of the solute within the solution. In this instance, the solution is blood and solute is hemoglobin. As an aside, the Coanda effect describes the tendency of a jet fluid to be attracted to a nearby surface (think of a wall hugging jet created by mitral regurgitation on TEE). The pulse oximeter emits two wavelengths of light: Red light (660 nm) is preferentially absorbed by reduced Hgb. Near-infrared light (990 nm) is preferentially absorbed by HgbO2. You'll see these numbers vary a bit from book to book. The peak of the waveform contains relatively more arterial blood, while the trough of the waveform contains relatively more venous blood.

Answer 72

Finger As a general rule, the closer the monitoring site is to the central circulation, the faster it will respond to arterial desaturation. Additionally, central monitoring sites are less resistant to the vasoconstrictive effects of SNS stimulation and hypothermia. These sites are ordered from most to least responsive: Fast = Ear, nose, tongue, esophagus, forehead Middle = Finger Slow = Toe When SpO2 is monitored on the head or esophagus, the Trendelenburg position can cause venous engorgement resulting in a falsely decreased SpO2 measurement.

Answer 73

There are no contraindications to pulse oximetry Simply put, there are no contraindications to pulse oximetry. There are times, however, when direct PaO2 measurement better assesses arterial oxygenation than a pulse oximeter alone.

Answer 74

Three year-old toxic from EMLA cream overdose Seven year-old rescued from a basement fire Hemoglobinopathies can contribute to erroneous pulse oximeter measurements: Carbon monoxide poisoning: Overestimates SpO2 Common in smoke inhalation patients Treatment = oxygen therapy Methemoglobinemia: Underestimates SpO2 when oxygen saturation > 85% Overestimates SpO2 when oxygen saturation < 85% Methemoglobin is produced by: prilocaine, EMLA cream (contains prilocaine), benzocaine, cetacaine, nitroprusside, nitroglycerin, sulfonamides, and phenytoin Treatment = methylene blue 1-2 mg/kg over 5 min or exchange transfusion if patient has glucose-6-phosphate dehydrogenase deficiency Neither jaundice nor fluorescein interfere with the accuracy of the pulse oximeter.

Answer 75

Pulse oximeter Endobronchial intubation occurs when the distal end of the endotracheal tube advances into one of the mainstem bronchi. This situation creates a large shunt, as both of the lungs are perfused but only one is ventilated. Depending on the tube position, the Murphy eye may allow ventilation of the contralateral lung even through the endotracheal tube has advanced into the other mainstem bronchi. Of the answer choices provided, the pulse oximeter is the least reliable monitor of endobronchial intubation. If the patient is receiving a high FiO2, then the SpO2 may not decline. Said another way, the absence of arterial desaturation does not rule out endobronchial intubation. To that point, the pulse oximeter is not a reliable monitor for disconnections, leaks, esophageal intubation, or hypercarbia.

Answer 76

40 mmHg It doesn't matter if it's an arterial, venous, or mixed venous sample, the same rule applies. Remember 40, 50, 60 and 70, 80, 90. PO2 40 ~ SpO2 70 PO2 50 ~ SpO2 80 PO2 60 ~ SpO2 90

Answer 77

Plateau pressure Compliance is a change in volume for a given change in pressure (C = ∆V / ∆P). We can measure compliance when gas is moving into the lung (dynamic compliance), or we can measure compliance when there is no gas flow at the inspiratory pause (static compliance). Dynamic compliance is a function of airway resistance + lung/chest compliance. Static compliance is a function of lung/chest compliance only.

Answer 78

Mucus plug + Decreased dynamic compliance Endobronchial intubation + Decreased static compliance Pulmonary embolism + No change in dynamic or static compliance Compliance is a change in volume for a given change in pressure (C = ∆V / ∆P). Dynamic Compliance is: Measured while gas flows into the lungs. A function of airway resistance + lung/chest wall compliance. Assessed by peak pressure. Decreased by anything that obstructs airflow, such as a kinked endotracheal tube, mucus plug, and bronchospasm. Static compliance is: Measured when there is no gas flow (during the inspiratory pause). A function of lung/chest wall compliance only (resistance only occurs during gas flow). Assessed by plateau pressure. Decreased by anything that reduces lung compliance, such as endobronchial intubation, tension pneumothorax, pneumonia, and pulmonary edema. Pulmonary embolism does not affect pulmonary resistance or compliance.

Answer 79

Systolic BP increases Diastolic BP decreases Pulse pressure increases As the pulse moves from the aortic root towards the periphery, the SBP increases, DBP decreases, and the pulse pressure widens. MAP remains constant. At the aortic root: SBP is lowest, DBP is highest, and PP is narrowest At the dorsalis pedis: SBP is highest, DBP is lowest, and PP is widest Be sure to understand how moving the cuff to a different location affects your measurement. The automated noninvasive blood pressure cuff works equally well when used to measure blood pressure in the upper arm, forearm, wrist, or ankle. The exception here is its unreliability when placed on the calf for patients undergoing c-section.

Answer 80

P wave + a wave QRS complex + c wave ST segment + x descent T wave + v wave

Answer 81

End of expiration CVP is measured relative to atmospheric pressure. For example, a CVP reading of 7 mmHg means that it is 7 mmHg above ambient pressure. This also explains why CVP can never truly be negative; a CVP of -1 is 1 mmHg below ambient pressure and NOT a negative pressure. Since we measure CVP relative to atmospheric pressure, we don't want changes in intrathoracic pressure to impact the accuracy of our measurement. During spontaneous breathing, inhalation creates negative pressure in the thorax and reduces intrathoracic pressure. During positive pressure ventilation, inhalation increases intrathoracic pressure. For both spontaneous and positive pressure ventilation, intrathoracic pressure is zero at end expiration. Therefore, CVP should be measured at end expiration during spontaneous or positive pressure breathing.

Answer 82

a wave + Right atrial contraction c wave + Right ventricular contraction x descent + Right atrial relaxation v wave + Passive filling of right atrium On the CVP waveform, there are three positive deflections (a, c, v) and 2 negative deflections (x, y). Here are the mechanical events of the right heart as they correspond to the CVP waveform. a wave - Right atrial contraction c wave - Right ventricular contraction x descent - Right atrial relaxation v wave - Passive filling of right atrium y descent - Right atrium empties through open tricuspid valve

Answer 83

Tricuspid regurgitation Papillary muscle ischemia The CVP waveform is a measure of the right atrial pressure. It has three peaks (a, c, v) and two troughs (x, y). You should understand how pathology influences the CVP waveform. Large v wave (enhanced RA filling): During tricuspid regurgitation, a portion of the RV volume flows retrograde across the incompetent tricuspid valve. Papillary muscle ischemia can cause tricuspid regurgitation. On the CVP waveform, there will be a large v wave. Lost a wave (loss of RA contraction): Atrial kick is lost during atrial fibrillation. On the CVP waveform, the a wave is lost. Cannon a wave (increased resistance to atrial ejection): The a wave correlates with atrial contraction. A canon a wave is present when there is an increased resistance to atrial ejection. Examples include complete heart block, nodal rhythm, tricuspid stenosis, and decreased right ventricular compliance (RVH and RV ischemia).

Answer 84

20 cm The tip of the catheter should reside at the junction of the vena cava and right atrium. It should not rest inside the right atrium, as this can induce dysrhythmias or perforate the myocardium. Here are the distances that you should know (access site to junction of vena cava and RA): ``` Left or right subclavian: 10 cm Right internal jugular: 15 cm Left internal jugular: 20 cm Femoral: 40 cm Right median basilic: 40 cm Left median basilic: 50 cm ```

Answer 85

20 cm (It's usually 15-30 cm, but 20 cm was the only answer choice in this range) We made this question easier than we could have, but in case you're not so lucky on the NCE, here's a simple way to calculate the distance from any insertion site to the tip of the PA catheter anywhere in the heart. To do this, you'll need to know two pieces of information: the distance from the insertion site to the junction of the VC and then the distance from the junction of the VC and RA to the tip of the catheter. Then add these numbers together. ``` Distance from the insertion site to the junction of the VC and RA: Left or right subclavian: 10 cm Right internal jugular: 15 cm Left internal jugular: 20 cm Femoral: 40 cm Right median basilic: 40 cm Left medial basilic: 50 cm Distance from the junction of the VC and RA to the tip of the catheter: Right atrium: 0-10 cm Right ventricle: 10-15 cm Pulmonary artery: 15-30 cm PAOP position: 25-35 cm ```

Answer 86

The systolic pressure increases The pulse pressure increases The PA catheter has advanced from the right atrium into the right ventricle. Here, the systolic pressure increases, and this increases the pulse pressure. As you advance the PA catheter further, it will transverse the pulmonic valve and enter the pulmonary artery. You'll know you've arrived when you notice a dicrotic notch and a rise in diastolic pressure. When reviewing questions, don't just learn the question and move on. Quiz yourself about other key ideas related to the topic being addressed. For example, here you might want to consider intracardiac distances, the pressures in each chamber, or complications of PA catheter placement.

Answer 87

Left bundle branch block The PA catheter does not increase the risk of a left BBB, but it does increase the risk of creating a right BBB. If you place a PA catheter in a patient with a pre-existing left BBB, there is a risk of inducing a right BBB thereby creating complete heart block. Complications of PA catheter can be grouped according to when they occur during placement: Obtaining venous access: arterial puncture, air embolism, neuropathy, and pneumothorax. Floating the PA catheter: Right BBB, complete heart block (if pre-existing left BBB), PA rupture, and dysrhythmias such as PVCs, VT, and VF. Catheter residence: bacterial colonization, sepsis, thrombus formation, thrombophlebitis, pulmonary infarction, and myocardial or valvular injury.

Answer 88

Fever Seizure SvO2 is reduced by anything that increases oxygen consumption or decreases oxygen delivery. ``` Increased VO2: Fever Stress Seizures Shivering Thyrotoxicosis Pain Decreased DO2: ``` ``` Hemorrhage Anemia Low CO Hypoxia SvO2 is increased by cyanide toxicity, sepsis, increased cardiac output, a wedged PA catheter, hypothermia, and a left-to-right shunt. ```

Answer 89

0.40 seconds Key facts about the QT interval: It extends from the beginning of the Q wave (or R wave if there is no Q wave) through the end of the T wave. It corresponds with the beginning of ventricular depolarization to the end of repolarization. Hypercalcemia makes it shorter. Hypocalcemia makes it longer. It is inversely related to heart rate (faster heart rate = shorter QT interval). Normal value = 0.35 - 0.45 seconds. When it exceeds 0.5 seconds, there is an increased risk of torsades de pointes.

Answer 90

Left axis deviation The electrical axis indicates the direction of depolarization as it travels through the myocardium. We can illustrate the general direction of the movement of depolarization by using a vector. The mean electrical vector is the summation of all of the vectors of ventricular depolarization. The mean electrical vector tends to point towards ventricular hypertrophy and point away from myocardial infarction. To determine the axis or the direction of the mean electrical vector, you have to look at the QRS complex in lead I and AVF. Normal axis: lead I and AVF are positive Extreme right axis: lead I and AVF are negative Right axis: lead I is negative and AVF is positive Left axis: lead I is positive and AVF is negative

Answer 91

It is caused by an ectopic pacemaker Sinus arrhythmia occurs when the SA node's pacing rate varies with respiration. Inhalation → ↑ heart rate Exhalation → ↓ heart rate Remember the Bainbridge reflex? This is the one where an increased venous return stretches the right atrium and SA node causing the heart rate to increase. It should also make sense that the Bainbridge reflex causes sinus arrhythmia. Inhalation → ↓intrathoracic pressure → ↑venous return → ↑heart rate Exhalation → ↑intrathoracic pressure → ↓ venous return → ↓ heart rate Sinus arrhythmia is usually benign.

Answer 92

Non-compensatory pause This EKG shows an example of a premature atrial contraction. A PAC originates from an ectopic focus in the atria. The P wave comes early and has a different morphology. The PAC is followed by a non-compensatory pause. In this tracing, the QRS complexes are orthodromic (they are conducted through the AV node). The QRS morphology is normal. An antidromic pathway is an accessory pathway that bypasses the AV node (think of the Bundle of Kent and Wolff-Parkinson-White syndrome). The QRS morphology is abnormally wide.

Answer 93

Atropine 0.2 mg Increased vagal tone is often the source of bradycardia. While atropine is a first-line treatment, not giving enough (< 0.5 mg IV) can cause paradoxical bradycardia. This is probably mediated by presynaptic muscarinic receptors. Severely symptomatic patients (syncope or chest pain) should receive immediate transcutaneous pacing. Glucagon is useful in the setting of beta blocker or calcium channel blocker overdose. By stimulating glucagon receptors on the myocardium, glucagon effectively increases cAMP leading to increased heart rate, contractility, and AV conduction. The initial dose is 50 - 70 mcg/kg q 3-5 min. This can be followed with an infusion at 2 - 10 mg/hr.

Answer 94

Sinus tachycardia. Sinus tachycardia simultaneously increases myocardial oxygen demand while decreasing oxygen supply. In patients with CAD, this can precipitate myocardial ischemia and/or infarction. While any condition that increases heart rate can stress the heart, the most common rhythm associated with myocardial infarction is sinus tachycardia.

Answer 95

It (atrial flutter) is an organized supraventricular rhythm Each atrial depolarization is associated with an atrial contraction Unlike atrial fibrillation, atrial flutter is an organized supraventricular rhythm. You should recognize it by its characteristic "saw tooth" pattern. The atrial rate is usually very fast (250-350 bpm). Each atrial depolarization is associated with an atrial contraction, but not all atrial depolarizations are conducted past the AV node. There is usually a defined ratio of atrial to ventricular contractions. For example, there may be 2 atrial contractions for every 1 ventricular contraction (2:1 ratio) or 3 atrial contractions for every 1 ventricular contraction (3:1 ratio). The effective refractory period prevents all atrial impulses from being transmitted to the ventricles. A rapid ventricular rate significantly reduces diastolic filling time, and this can lead to hemodynamic instability. Hemodynamically unstable atrial flutter should be treated with cardioversion. As little as 50 joules (monophasic) will convert atrial flutter to normal sinus rhythm. By contrast, cardioversion for atrial fibrillation begins with 100 joules. There is an increased risk of atrial thrombus formation if afib/aflutter lasts longer than 48 hours. These patients should be anticoagulated and undergo echocardiographic examination to rule out atrial thrombus prior to cardioversion. Pharmacology therapy aimed at controlling ventricular rate includes amiodarone, diltiazem and verapamil. While these drugs can reduce the ventricular rate, they are unlikely to convert atrial flutter to normal sinus rhythm. By contrast, they are more effective at converting atrial fibrillation to NSR.

Answer 96

Hypokalemia Digitalis toxicity Premature ventricular contractions originate from foci below the AV node. As such, the QRS complex is wide. PVCs that arise from a single location are unifocal (the morphology is the same on the EKG). PVCs that arise from multiple locations are multifocal (there are different QRS morphologies on the EKG). There are many conditions that are associated with the development of PVCs. Examples include: ``` SNS stimulation (hypoxia, hypercarbia, acidosis, light anesthesia) Myocardial ischemia and/or infarction Valvular heart disease Cardiomyopathy Prolonged QT interval Hypokalemia Hypomagnesemia Digitalis toxicity Caffeine Cocaine Alcohol Mechanical irritation (central line insertion) ```

Answer 97

Lidocaine Premature ventricular contractions can precipitate the R on T phenomenon. They should be treated when they are: Frequent (> 6 per min) In runs of 3 or more Polymorphic (they arise from multiple foci) The first step in treatment targets the underlying cause. This includes reversal of hypoxia/hypercarbia, correction of electrolyte imbalances, discontinuation of QT prolonging drugs, and repositioning a central line that's tickling the atrium. Symptomatic PVCs are treated with lidocaine 1.0 - 1.5 mg/kg. If PVCs continue, follow with an infusion of 1 - 4 mg/min.

Answer 98

Metoprolol Beta blockers are shown to reduce the incidence of torsades de pointes. The other antiarrhythmics mentioned may cause torsades de pointes in patients with a prolonged QT interval.

Answer 99

Romano-Ward Timothy Romano-Ward and Timothy syndrome are associated with a prolonged QT interval. King Denborough syndrome is a genetic disorder linked to malignant hyperthermia. Brugada syndrome is characterized by a pseudo right bundle branch block and ST elevation in V1-V3.

Answer 100

Delta wave In the patient with Wolff-Parkinson-White syndrome, atrial depolarization is conducted to the ventricles via the bundle of Kent. This accessory pathway bypasses the AV node. Since the ventricles are prematurely excited, there is a short PR interval and an upsloping of the R wave. This is called a delta wave.

Answer 101

Advanced age Amiodarone A first degree heart block occurs when there is a conduction delay at the AV node. It is defined as a PR interval > 0.20 seconds. Each P wave is conducted There is 1 QRS for every 1 P wave Causes of first degree heart block include: Degenerative changes that accompany aging Posterior wall MI (a branch of the right coronary artery usually supplies the AV node) Parasympathetic stimulation Amiodarone Digoxin First degree heart block is usually benign and does not require treatment or additional work-up. Anesthetic considerations include preventing situations that increase vagal tone or slow AV conduction.

Answer 102

Transcutaneous pacing Isoproterenol This EKG is an example of third degree (complete) heart block. No conduction occurs through the AV node. Because of this, the atria and the ventricles depolarize at their own rates - that is to say that the atria and ventricles each have their own pacemaker. Third degree heart block is an indication for transcutaneous or transvenous pacing. If heart block does not resolve, the patient should receive an implantable pacemaker. Isoproterenol can be used as a "chemical pacemaker" until other forms of pacing are available. Antidysrhythmic medications should be avoided. They might suppress the rescue ventricular pacemaker that is responsible for maintaining the ventricular rate. A slow rate is better than no rate at all!

Answer 103

PR segment The PR segment is an isoelectric line. Because of this, it is used as the reference point for measuring ST elevation and depression. The J point is where the QRS complex ends and the ST segment begins. By measuring this point relative to the PR segment, we can quantify the amount of ST elevation and depression.

Answer 104

Supraventricular tachycardia Adenosine is an endogenous nucleoside that slows conduction through the AV node. By stimulating the cardiac adenosine-1 receptor, adenosine causes potassium to exit the cell. This hyperpolarizes the cell membrane and reduces action potential duration. It is efficacious for supraventricular tachycardia as well as WPW with a narrow QRS. It is not efficacious for atrial fibrillation, atrial flutter, torsades des pointes, or ventricular tachycardia.

Answer 105

Hypokalemia + Flat T wave and presence of U wave Hyperkalemia + Wide QRS and peaked T wave Hypocalcemia + Prolonged QT interval Hypercalcemia + Short QT interval

Answer 106

Place the return electrode as far as possible from the pulse generator Use a harmonic scalpel instead of a monopolar cautery Before we get to the answer, we first need to clear up a huge source of confusion. Nobody in the OR should be grounded - not even the patient! But what about the grounding pad you say? Read on grasshopper... When you are at home, all of your electrical devices plugged into the wall are grounded. If you touch a live wire, you'll complete the circuit and you'll receive a macroshock. In the OR, isolation transformers are used to isolate the equipment from the ground. This provides a margin of safety. If there is one fault and you come into contact with it, you'll become grounded, but since the circuit isn't complete you won't get shocked. If there is a second fault and you come into contact with both faults, then the current will flow from the equipment → first fault → you → back through the second fault to complete the circuit. The line isolation monitor alarms when it detects the first fault (usually > 2 - 5 mA). If it alarms, unplug the last piece of equipment that was plugged in. When a monopolar device is used, electricity flows through the tip of the electrocautery, through the patient, and exits the patient's body through the return electrode. Indeed, that cold sticky pad is a return electrode and NOT a grounding pad. We're not suggesting that you boast your newfound knowledge to the old school nurses in the OR, but it's ok to smirk behind your mask when you hear it called something that might actually harm the patient! And now back to the topic... Here are some ways to reduce the risk of inadvertent AICD discharge: Deactivate the AICD's defibrillation function by placing a magnet over the pulse generator. Always consult with the manufacturer before doing this. Use a harmonic scalpel or bipolar cautery instead of a monopolar cautery. Keep the electrocautery at least 15 cm away (not 5 cm) from the pulse generator. Place the return electrode as far from the pulse generator as possible, while making sure the current doesn't cross the chest.

Answer 107

The coagulation setting of a monopolar cautery The coagulation setting of a monopolar cautery causes the greatest risk of electromagnetic interference. This is followed by the cut setting of the monopolar cautery. The bipolar cautery and Harmonic scalpel create the least amount of EMI.

Answer 108

Measures venous oxygen saturation in cerebral blood Cerebral oximetry is a noninvasive technique that utilizes near infrared spectroscopy (NIRS) to measure regional (not global) cerebral oxygenation. It is based on the principle that ↓ cerebral oxygen delivery → ↑ cerebral oxygen extraction → ↓ venous hemoglobin saturation. Because it measures venous oxygen saturation, it does not require pulsatile flow. A > 25 percent change from baseline suggests a reduction in cerebral oxygenation.

Answer 109

Cerebral ischemia EEG provides a sensitive measure of brain tissue at risk of infarction. The brain requires an adequate perfusion pressure to provide a steady supply of oxygen and glucose. In the absence of these substrates, the brain is unable maintain its electrical function. The development of new delta waves during anesthetic maintenance may signify that brain is at risk for ischemia. The following circumstances mimic cerebral ischemia: deep anesthesia, hypothermia, and hypocarbia.

Answer 110

40 - 60 The bispectral index monitor (BIS) uses a computer algorithm to translate raw EEG data into a number between 0 – 100. This algorithm is proprietary, so it only applies to the BIS. It's recommended that the depth of anesthesia is titrated to 40 - 60 during maintenance. 0 = Absence of cerebral activity (isoelectric) 20 = Burst suppression 40 = Deep hypnotic state 60 = Upper limit of low probability of explicit recall 80 = Moderate sedation 100 = Fully awake

Answer 111

25 - 50 Like the BIS, the patient safety index monitor (PSA) uses a computer algorithm to translate raw EEG data into a number between 0 – 100. It uses a different proprietary algorithm, so the interpretation o the reading is also different. It is recommended that the depth of anesthesia is titrated to 25 - 50 during maintenance.

Answer 112

Voltage + Blood pressure Current + Cardiac output Impedance + Systemic vascular resistance Ohm's law can be applied to electricity as well as hemodynamics. Applied to electricity: Voltage = Current x Impedance Applied to hemodynamics: BP = CO x SVR

Answer 113

100 mA Macroshock is the amount of current that is applied to the external surface of the body. The impedance of the skin offers a high resistance, so it takes a larger current to induce ventricular fibrillation. 1 mA = Threshold for touch perception of shock 5 mA = Max current for harmless shock 10 - 20 mA = "Let go" current occurs before sustained contraction 50 mA = Loss of consciousness 100 mA = Ventricular fibrillation

Answer 114

100 µA Microshock is the amount of current that is applied directly to the myocardium. The high resistance of the skin is bypassed, so it take a significantly smaller amount of current to induce ventricular fibrillation (ex: pacing wires or central line). 10 µA = Max allowable current leak in the OR 100 µA = Ventricular fibrillation

Answer 115

Power is not grounded Equipment is grounded The electrical systems in the OR are designed to reduce the risk of electric shock. For an electric shock to occur, there must be two faults in the system: After the first fault, the system becomes grounded. There is no completed circuit and there is no shock. After the second fault, the circuit is complete and electric shock occurs. When you're at home, an electric shock can occur with the first fault.

Answer 116

Alarms when the operating room is grounded The line isolation monitor assesses the integrity of the ungrounded power system in the OR. It tells you when the OR becomes grounded and how much current could potentially flow through you or a patient if a second fault occurs. The primary purpose of the LIM is to alert the OR staff of the first fault (this means the OR has become grounded). The LIM does NOT (by itself) protect you or the patient from macro- or microshock. If the alarm sounds, the last piece of equipment that was plugged in should be unplugged. The LIM will alarm when 2 - 5 mA of leak current is detected. All electrical devices leak a small amount of current. If the sum of all the currents exceeds 2 - 5 mA, the alarm will sound, however there is no risk of electric shock in this situation and no corrective action is required.

Answer 117

Forceps The surgical electrocautery device delivers a high frequency current (500,000 - 1 million Hz) that is used to cut, coagulate, dissect, or destroy tissue. When using a monopolar device, electricity travels from the probe, through the patient, and then exits via the return pad to complete the circuit. It's not a grounding pad! Remember, patients and OR staff aren't grounded. When using a bipolar device, the electricity travels from the active electrode, through the local tissue, and then exits the patient through the return electrode. Because the electricity leaves from and returns to the handheld component of the device, there is no need for a return pad.