Apex Unit 6 Equipment & Monitors Flashcards

Question 1

Q

Identify the components of the low pressure system in the anesthesia machine.  (Select 2.)
Common gas outlet
Oxygen flush valve
Flowmeter tubes
Cylinder pressure regulator

Answer

A

Flowmeter tubes

Common gas outlet

The anesthesia machine can be divided into three pressure systems: high, intermediate, and low.

The high pressure system contains the cylinder pressure regulator.
The intermediate pressure system contains the oxygen flush valve.
The low pressure system contains the flowmeter tubes and common gas outlet.

Question 2

Q

Match each component to its proper location in the SPDD model
Supply 
Processing
Delivery
Disposal

Vaporizer
Cylinder
Scavenger
Circle system

Answer

A

Supply + Cylinder
Processing + Vaporizer
Delivery + Circle system
Disposal + Scavenger

Question 3

Q

The PISS system is used to:

filter and exchange air in the operating room.
diagram the pathway of gas through the anesthesia machine.
prevent the use of the wrong gas hose.
prevent the use of the wrong gas cylinder.

Answer

A

Prevent the use of the wrong gas cylinder

The pin index safety system (PISS) prevents the wrong cylinder from being attached to the anesthesia machine.

The diameter index safety system (DISS) prevents the wrong gas hose from being attached to the anesthesia machine.

The SPDD model describes the pathway of gas through the anesthesia machine.

Filtering and exchanging air in the operating room is not a function of the anesthesia machine.

Question 4

Q

The bourdon pressure gauge on an oxygen cylinder reads 500 psi. If the flow rate is 2 L/min, how long will this cylinder provide oxygen to the patient?

(Enter your answer as minutes and round to the nearest whole number)

Answer

A

75 - 87

Some books say a full oxygen e-cylinder contains 1900 psi, while others say 2000 psi. We accepted both values.

We’ll detail the calculation on the next page…

Question 5

Q

Identify the BEST practices for handling gas cylinders. (Select 2.)
Oiling cylinder valves every six months

Laying the cylinder on its side when changing the cylinder on the anesthesia machine

Placing two washers between the cylinder and the hanger yoke assembly

Removing the plastic cover on the port when installing the cylinder

Answer

A

Removing the plastic cover on the port when installing the cylinder

Laying the cylinder on its side when changing the cylinder on the anesthesia machine

Under normal circumstances, gas cylinders must be stored in the upright position AND secured. When changing the cylinder on the anesthesia machine, however, it is appropriate to temporarily place the old cylinder its side until it can be moved to its appropriate storage receptacle.

You should remove the plastic cover from the port before installing the cylinder. Failure to do so may obstruct gas flow when the cylinder is turned on.

The fire triad consists of an oxidizer, a fuel, and an igniter. Oiling the cylinder valve increases the risk of fire by combining oxygen or nitrous with the oil. Only a heat source is needed to complete the triad.

If there is a leak after you install a cylinder, do not be tempted to place more than one washer between the cylinder and the hanger yoke assembly. This may bypass the PISS and allow the wrong cylinder to be matched up with the wrong hanger yoke assembly.

Question 6

Q

The oxygen pressure failure device activates when the: (Select 2.)

oxygen pipeline crossover with nitrous oxide.
FiO2 in the inspiratory limb is less than 21 percent.
oxygen tank is exhausted.
oxygen pressure in the supply line is less than 20 psi.

Answer

A

Oxygen tank is exhausted
Oxygen pressure in the supply line is less than 20 psi

The oxygen pressure failure device monitors oxygen pressure (not concentration). It activates when oxygen pressure in the intermediate pressure system falls below 20 psi. By contrast, the oxygen analyzer monitors oxygen concentration in the low pressure system. It alarms when the FiO2 falls below 21 percent.

If pipeline pressure fails, and the auxiliary oxygen tank is open, the oxygen pressure failure device won’t activate until oxygen pressure (from the tank) is less than 20 psi. This explains why you don’t want to leave the O2 cylinder open if you aren’t using it.

The oxygen pressure failure device is NOT activated by a pipeline crossover or if a leak develops distal to the flowmeters.

Question 7

Q

The hypoxia prevention safety device on the anesthesia machine will:
limit the nitrous oxide flow to three times oxygen flow.
shut off the flow of nitrous oxide if the oxygen supply pressure is less than 30 psi.
alarm if the FiO2 is less than 21 percent.
will prevent a hypoxic mixture if a third gas is used.

Answer

A

Limit the nitrous oxide flow to three times oxygen flow

The hypoxia prevention safety device prevents you from accidently setting a hypoxic mixture with the flow control valves. It’s a pneumatic or mechanical device that limits the nitrous oxide flow to no more than 3 times the oxygen flow.

Question 8

Q

You are administering air 1L/min and oxygen 3 L/min. Calculate the fraction of inspired oxygen.

(Enter your number as a percentage)

Answer

A

80

A fresh gas flow of air 1 L/min and oxygen 3 L/min yields a FiO2 of 80%.

We’ll show you the math on the next page …

Question 9

Q

You are using an anesthesia machine that couples fresh gas flow to tidal volume and fully compensates for circuit compliance. Calculate the total tidal volume delivered to the patient.

Oxygen = 3 L/min
Air = 1 L/min
I:E = 1:2
Bellows = 500 mL
Respiratory rate = 10 bpm

(Enter your answer in mL and as a whole number)

Answer

A

632 or 633

Well done! This is not an easy question.

The correct answer is 632 or 633 mL (depending if how you chose to complete this calculation).

Question 10

Q

A ventilator is programmed to deliver a tidal volume of 600 mL. If the breathing circuit compliance is 5 mL/cm H2O and the peak pressure is 25 cm H2O, what is the total tidal volume that is delivered to the patient?

500 mL
475 mL
450 mL
425 mL

Answer

A

475 mL

When the ventilator produces positive pressure inside the breathing circuit, some of this gas causes the circuit to expand. This quantity of gas does not reach the patient, and therefore does not contribute to the tidal volume that the patient receives.

In this example, 125 mL is lost to the compliance of the circuit. Since the tidal volume is set at 600 mL, the patient will only receive a tidal volume of 475 mL.

Question 11

Q

The isoflurane dial is set to two percent. What percent of fresh gas exiting the vaporizing chamber is saturated with isoflurane?

(Enter your answer as a percentage)

Answer

A

100

Modern variable bypass vaporizers split fresh gas into two parts.

Some fresh gas enters the vaporizing chamber and becomes 100% saturated with volatile agent. Indeed, this was the correct response to this question.
The rest of the fresh gas bypasses the vaporizing chamber and does not pick up anesthetic vapor.

Before leaving the vaporizer, these two fractions mix and determine the final anesthetic concentration exiting the vaporizer.

Question 12

Q

Choose the statement that BEST describes this vaporizer. (Select 2.)

Its output is increased inside a hyperbaric chamber.
It uses a flow-over design.
It is heated to 42 degrees.
It is pressurized to two atmospheres.

Answer

A

It is pressurized to two atmospheres
Its output is increased inside a hyperbaric chamber

The Tec 6 desflurane vaporizer injects anesthetic vapor into the fresh gas (it does not use a flow-over design). The chamber that contains the anesthetic agent is pressured to two atmospheres and heated to 39 (not 42) degrees C.

The vaporizer output varies inversely with elevation. Therefore, the vaporizer should be re-calibrated when it’s going to be used in high altitude locations.

Question 13

Q

Which device will be the FIRST to detect an oxygen pipeline crossover?

Fail-safe device
Oxygen analyzer
Proportioning system
Pulse oximeter

Answer

A

Oxygen analyzer

The oxygen analyzer will be the first monitor to detect an oxygen pipeline crossover.
The pulse oximeter would probably the be second monitor to detect this complication, however it’s unlikely that this complication would be high on your differential.

The oxygen pressure failure device (failsafe) and hypoxia prevention safety device (proportioning system) aren’t designed to detect an oxygen pipeline crossover.

Question 14

Q

Identify the MOST critical actions that should be carried out in the event of an oxygen pipeline crossover. (Select 2.)

Disconnect the pipeline supply.
Turn on the oxygen tank.
Ventilate with an Ambu with the auxiliary oxygen flowmeter.
Replace the oxygen analyzer.

Answer

A

Turn on the oxygen tank

Disconnect the pipeline supply

Turn ON the oxygen cylinder, and then disconnect the pipeline oxygen supply. This is a key step! If a crossover occurred, simply turning on the oxygen tank would not fix the problem. If an adequate oxygen pipeline pressure is present (regardless of the gas inside), it will prevent the oxygen tank from releasing its contents.

This is not the time to assume an equipment malfunction. Trust the oxygen analyzer, and do not attempt to fix it. This could waste precious time.

The auxiliary oxygen flowmeter on the anesthesia machine is supplied by the pipeline. If an oxygen crossover occurs, it will supply the wrong gas to the patient. This is why you should use an oxygen tank.

Question 15

Q

Select the true statements regarding the oxygen flush valve. (Select 2.)
Excessive use can lead to awareness.
It will deliver a continuous pressure of 35 – 75 psi.
The risk of barotrauma is minimized by ventilators with fresh gas decoupling.
It will cause the ventilator spill valve to close during inspiration.

Answer

A

Excessive use can lead to awareness

The risk of barotrauma is minimized by ventilators with fresh gas decoupling

Why where the other answer choices wrong?

The oxygen flush valve delivers a continuous oxygen flow of 35 – 75 L/min (not psi).
During inspiration, the ventilator drive gas closes the ventilator spill valve. Pressing the O2 flush valve does not affect this function.

Question 16

Q

Select the true statements about the pneumatic ventilator bellows. (Select 2.)

A leak in the bellows may cause the reading on the oxygen analyzer to increase.
A descending bellows cannot rise and fall with a circuit disconnect.
A hole in the bellows may cause barotrauma.
A descending bellows is made safer by fresh gas coupling.

Answer

A

A hole in the bellows may cause barotrauma.

A leak in the bellows may cause the reading on the oxygen analyzer to increase.

The pneumatic bellows is compressed by the ventilator drive gas. A leak in the bellows creates a direct line of communication between the ventilator drive gas and the breathing circuit. This can cause barotrauma.

If there is a bellows leak and oxygen is used as the ventilator drive gas, the FiO2 in the breathing circuit may increase.

A descending bellows may continue to rise and fall, even with a circuit disconnect. Fresh gas decoupling helps solve this problem.

Question 17

Q

The piston ventilator: (Select 2.)

preserves tank oxygen in the event of oxygen pipeline failure.
allows for more precise delivery of tidal volumes.
removes the risk of barotrauma.
relies on fresh gas flow coupling.

Answer

A

Allows for more precise delivery of tidal volumes

Preserves tank oxygen in the event of oxygen pipeline failure

The piston ventilator offers several advantages over a traditional pneumatic bellows ventilator.

The piston is compressed by an electric motor. Since this type of system doesn’t use oxygen as a drive gas, it won’t consume tank oxygen in the event of oxygen pipeline failure.
It allows for more precise delivery of tidal volumes (fresh gas is decoupled from the ventilator).
Barotrauma remains a risk, however.

Question 18

Q

Which statement regarding pressure control ventilation is true? (Select 2.)

The ventilator switches to expiration after a preset pressure is achieved.
Gas flow decelerates during inspiration.
Increased lung compliance will decrease tidal volume.
The risk of ventilator associated lung injury is decreased.

Answer

A

Gas flow decelerates during inspiration

The risk of ventilator associated lung injury is decreased

Why are the other answer choices wrong?

Because the peak pressure is fixed and the tidal volume is variable, an increase in lung compliance will increase (not decrease) tidal volume.
The ventilator achieves a peak pressure very early in the inspiratory cycle and holds it for a time determined by the I:E ratio. It does not cycle immediately after the peak pressure is achieved.

Question 19

Q

Which modes of mechanical ventilation are BEST suited for a laryngeal mask airway? (Select 2.)

Pressure support ventilation
Inverse ratio ventilation
Controlled mandatory ventilation
Synchronized intermittent mandatory ventilation

Answer

A

Synchronized intermittent mandatory ventilation

Pressure support ventilation

Although not always an accepted practice, mechanical ventilation is now considered a perfectly acceptable technique to use with an LMA. As you’ll see, some modes are better than others.

SIMV and PSV are commonly used with an LMA.
CMV and IMV are best for patients who don’t have a respiratory drive.

Question 20

Q

At what pH does the ethyl violet change to purple?

5
6
3
1

Answer

A

10.3

Ethyl violet is a dye that indicates when soda lime exhausts. It changes from colorless to purple when the pH falls below 10.3.

Question 21

Q

When compared to soda lime, what factor is increased with the use of calcium hydroxide lime (Amsorb Plus)?

Fire risk
Frequency of replacement
CO2 absorption capacity
Carbon monoxide

Answer

A

Frequency of replacement
Benefits of calcium hydroxide lime (Amsorb Plus):

No carbon monoxide production
Very little or no compound A production
Lower risk of fire when compared to soda lime

Drawbacks of calcium hydroxide lime:

Lower CO2 absorption capacity
Requires more frequent replacement
Higher cost

Question 22

Q

What is the MOST common cause of low circuit pressure?

Circuit disconnect
Leak in corrugated tubing
Incompetent ventilator relief valve
Improper fitting of carbon dioxide absorbent

Answer

A

Circuit disconnect

Circuit disconnect (usually at the y-piece) is the most common cause of low circuit pressure.
The second most common cause is a leak around the carbon dioxide absorbent.

Question 23

Q

During a general anesthetic with an endotracheal tube, the high peak pressure alarm sounds. After changing the bag selector switch from ventilator mode to bag mode, the peak inspiratory pressure returns to baseline. Which of the following is the MOST likely explanation for the rise in peak inspiratory pressure?

The endotracheal tube was kinked.
The patient experienced a bronchospasm.
The positive pressure relief valve on the scavenger failed.
The ventilator spill valve malfunctioned.

Answer

A

The ventilator spill valve malfunctioned

This question requires a solid understanding of how the ventilator and scavenger work together.

Changing from ventilator mode to bag mode would not remedy bronchospasm, a kinked endotracheal tube, or a faulty scavenger positive pressure relief valve.

Question 24

Q

While a patient is ventilating spontaneously with an endotracheal tube, you notice that a fresh gas flow of 10 L/min is required to fill the breathing bag and determine that the scavenger is malfunctioning. Which statement must be true?

There is an open scavenging system.
The negative pressure relief valve has failed.
There is a passive scavenging system.
The positive pressure relief valve has failed.

Answer

A

The negative pressure relief valve has failed

A scavenger can be active or passive – an active system uses suction, while a passive system relies on the positive pressure of fresh gas leaving the interface. Since the scavenger in this question is applying excess suction, it must be an active system.

A scavenger can be a closed or open system – a closed system uses valves, while an open system is open to the atmosphere. Since the scavenger in this question is applying excess suction, it must be a closed, active system.

When the negative pressure relief valve fails (closed, active system), it’s possible for the vacuum to remove gas from the breathing circuit.
When the positive pressure relief valve fails (closed, active system), fresh gas can accumulate inside the breathing circuit. This can cause barotrauma.

Question 25

Q

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

A

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.

Question 26

Q

Match each breathing system with its classification.

Answer

A

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

Question 27

Q

While providing an anesthetic with a circle system, you observe this waveform. What is the BEST course of action at this time? (Select 2.)

Increase the fresh gas flow in excess of the patient’s minute ventilation.
Repair the expiratory valve.
Increase the patient’s minute ventilation.
Replace the carbon dioxide absorbent.

Answer

A

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.

Question 28

Q

The Bain circuit: (Select 2.)

is a modified Mapleson A.
delivers fresh gas through the inner tube.
is best for spontaneous but not controlled ventilation.
is tested with the Pethick test.

Answer

A

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.

Question 29

Q

Select the statements that MOST accurately describe pulse oximetry. (Select 2.)

Oxygenated hemoglobin absorbs light at 940 nm.
At the peak of the waveform, the ratio of arterial blood to venous blood is reduced.
It is based on the Doppler effect.
It is based on the Beer-Lambert law.

Answer

A

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).

Question 30

Q

The pulse oximeter reads 80 percent. You estimate the PaO2 is approximately:

(Enter your answer as mmHg)

Answer

A

50

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

Question 31

Q

The pulse oximeter is a useful monitor of:

ventilation.
bronchial intubation.
vascular compression.
anemia.

Answer

A

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.

Question 32

Q

Which condition is LEAST likely to affect the reliability of the pulse oximeter?
Blue nail polish
Jaundice
Carboxyhemoglobin
Left ventricular assist device

Answer

A

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.

Question 33

Q

What is the MOST common method of measuring exhaled gases inside the breathing circuit?

Mass spectrometry
Infrared absorption
Raman scattering
Piezoelectric crystals

Answer

A

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.

Question 34

Q

A blood pressure cuff that is too large:
requires less pressure to occlude the artery.
has a bladder width less than 40 percent of the circumference of the extremity.
falsely increases the blood pressure measurement.
increases the risk of radial neuropathy.

Answer

A

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.

Question 35

Q

When inserting a central line in the right internal jugular vein, how far should the catheter be advanced to achieve correct placement?

10 cm
15 cm
20 cm
25 cm

Answer

A

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.

Question 36

Q

Central venous pressure is:

unchanged by a ventricular septal defect.
increased by PEEP.
falsely increased by placing the transducer above the zero point.
decreased by pericardial tamponade.

Answer

A

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).

Question 37

Q

Which conditions increase the amplitude of the a wave on the CVP waveform? (Select 2.)

Tricuspid stenosis
Atrial fibrillation
Diastolic dysfunction
Tricuspid regurgitation

Answer

A

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.

Question 38

Q

Which findings are observed when the tip of the pulmonary artery catheter enters the highlighted area? (Select 2.)

Dicrotic notch
Increased systolic blood pressure
Increased pulse pressure
Increased diastolic blood pressure

Answer

A

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.

Question 39

Q

In which lung zone should the tip of the pulmonary artery catheter be placed?

(Enter your answer as a whole number)

Answer

A

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.

Question 40

Q

When does pulmonary artery occlusion pressure overestimate left ventricular end diastolic volume?  (Select 2.)
Aortic insufficiency
PA catheter tip in West zone III
PEEP
Diastolic dysfunction

Answer

A

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

Question 41

Q

Which situation underestimates cardiac output obtained by the thermodilution method?
Right-to-left intracardiac shunt
Over warmed injectate
High injectate volume
Partially wedged pulmonary artery catheter

Answer

A

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.

Question 42

Q

Factors that increase mixed venous oxygen saturation include: (Select 2.)

sepsis.
thyroid storm.
anemia.
sodium nitroprusside toxicity.

Answer

A

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.

Question 43

Q

Preload responsiveness is expected to be present if a 250 mL fluid bolus increases the stroke volume in excess of:

(Enter your answer as a percentage)

Answer

A

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.

Question 44

Q

Which pathway depolarizes the left atrium?
Kent bundle
Thorel tract
Wenckebach tract
Bachmann bundle

Answer

A

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.

Question 45

Q

Match each phase of the ventricular action potential to its corresponding component on the EKG waveform.

Answer

A

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)

Question 46

Q

Match each disease with the EKG abnormality that it is MOST likely to cause.

Answer

A

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

Question 47

Q

Match each lead to the cardiac region that it monitors.

Answer

A

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

Question 48

Q

The mean electrical vector tends to point: (Select 2.)

towards areas of hypertrophy.
towards areas of myocardial infarction.
away from areas of hypertrophy.
away from areas of myocardial infarction.

Answer

A

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).

Question 49

Q

All of the following are effective for the treatment of atrial fibrillation EXCEPT:

metoprolol.
adenosine.
digoxin.
verapamil.

Answer

A

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.

Question 50

Q

Match each antiarrhythmic agent with its drug class.

Answer

A

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.

Question 51

Q

Wolff Parkinson White syndrome is associated with:

atrial-ventricular reentry.
SA nodal reentry.
atrial reentry.
ventricular reentry.

Answer

A

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.

Question 52

Q

A patient with Wolff Parkinson White syndrome develops atrial fibrillation during surgery. Select the BEST treatment for this situation. (Select 2.)

Digoxin
Amiodarone
Procainamide
Verapamil

Answer

A

Procainamide
Amiodarone

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

Question 53

Q

All of the following increase the likelihood of torsades de pointes in the patient with long QT syndrome EXCEPT:

furosemide.
metoprolol.
methadone.
hyperventilation.

Answer

A

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.

Question 54

Q

Match the NBG pacemaker identification code to its designated function.

Answer

A

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

Question 55

Q

A patient undergoing a bunionectomy has a VOO pacemaker with a rate of 80 bpm. During the procedure, there is failure to capture and the heart rate decreases to 50 beats per minute. Which of the following BEST explains why this complication occurred?

The patient was hyperthermic.
The EtCO2 was 20 mmHg.
An ultrasonic Harmonic scalpel was used.
The electrocautery setting was changed from “coagulation” to “cutting.”

Answer

A

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.

Question 56

Q

Select the statement that BEST describes cerebral oximetry.

A > 25% change from baseline suggests a reduction in cerebral oxygenation.
It monitors arterial oxygen saturation in cerebral blood.
It monitors global cerebral oxygenation.
It is invasive.

Answer

A

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.

Question 57

Q

Rank the EEG waveforms from highest to lowest frequency.

One is the highest frequency and four is the lowest frequency

Answer

A

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

Question 58

Q

Choose the statements that MOST accurately describe the Bispectral Index monitor. (Select 2.)

Burst suppression begins at a BIS value of 20.
Ketamine falsely elevates the BIS value.
The BIS value is calculated in real time.
The BIS value and Patient Safety Index value are interpreted in the same way.

Answer

A

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.

Question 59

Q

Select the statement that MOST accurately describes the function of the line isolation monitor.

It protects the patient from microshock.
It isolates electrical equipment from the ground.
The alarm sounds when the OR power supply becomes grounded.
If a piece of equipment becomes grounded, it cuts off the power supply to that piece of equipment.

Answer

A

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.

Question 60

Q

Choose the statements that BEST describe the surgical electrocautery unit. (Select 2.)

Electrocautery can suppress pacemaker function.
Bipolar electrocautery requires a return pad.
A return pad that is too small increases the risk of thermal injury.
The return pad grounds the patient.

Answer

A

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.

Question 61

Q

When the ambient temperature is increased, the bi-metallic strip in a variable bypass vaporizer directs: (Select 2.)

Less fresh gas to the vaporizing chamber.
More fresh gas to the bypass chamber.
More fresh gas to the vaporizing chamber.
Less fresh gas to the bypass chamber.

Answer

A

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.

Question 62

Q

The low pressure circuit leak test checks the integrity of the machine from the:

vaporizers to the oxygen analyzer.
pipeline supply to the flowmeters.
flow control valves to the common gas outlet.
pipeline supply to the common gas outlet.

Answer

A

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.

Question 63

Q

What is the MAXIMUM flow rate delivered by the oxygen flush valve?

(Enter your answer as L/min)

Answer

A

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.

Question 64

Q

Soda lime that has changed color from purple to white:

indicates the pH has increased.
has regenerated.
is normally observed during periods of nonuse
is most common at the end of the day.

Answer

A

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 65

A

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 66

A

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 67

A

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 68

A

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 69

A

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&raquo_space;> Sevo).

Compound A production in increased with sevoflurane in desiccated soda lime.

Answer 70

A

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 71

A

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 72

A

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 73

A

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

Answer 74

A

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 75

A

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 76

A

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 77

A

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 78

A

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 79

A

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 80

A

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 81

A

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 82

A

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 83

A

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 84

A

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 85

A

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 86

A

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 87

A

Semiopen circuit

Semiopen Circuit (Mapleson A-F, Bain system, circle system w/ FGF > Ve):

Bag reservoir = Yes
Rebreathing = No

Answer 88

A

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 89

A

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 90

A

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 91

A

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 92

A

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 93

A

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 94

A

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 95

A

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 96

A

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 97

A

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 98

A

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 99

A

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 100

A

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 101

A

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 102

A

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 103

A

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 104

A

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

Answer 105

A

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 106

A

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 107

A

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 108

A

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 109

A

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 110

A

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 111

A

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 112

A

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 113

A

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 114

A

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 115

A

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 116

A

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 117

A

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 118

A

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 119

A

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 120

A

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 121

A

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 122

A

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 123

A

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 124

A

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 125

A

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 126

A

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 127

A

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 128

A

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 129

A

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 130

A

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 131

A

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 132

A

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 133

A

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 134

A

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 135

A

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 136

A

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 137

A

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 138

A

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 139

A

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 140

A

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 141

A

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.

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Apex Unit 6 Equipment & Monitors Flashcards

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