Apex unit 6 Flashcards
Identify the components that are absent in a Mapleson D. (Select 2.)
Reservoir bag
APL valve
Unidirectional valves
CO2 absorbent
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.
A patient is receiving controlled ventilation with a fresh gas flow of 5 L/min. Click on the circuit that is MOST likely to cause hypercarbia.
A
Not only do you have to be able to identify each circuit, but you have to know which are best for controlled ventilation.
The Mapleson A is the worst configuration for controlled ventilation (best to worst): DFE > BC > A
Notice the fresh gas flow enters far from the patient and that the APL valve is close to the patient. This combination is what makes the Mapleson A the worst design for controlled ventilation. A fresh gas flow as high as 20 L/min is required to prevent rebreathing!
This specific configuration is also what makes the Mapleson A the best design for spontaneous ventilation (best to worst): A > DFE > CB
Which circuit does not contain dead space?
Open
Semiopen
Closed
Semiclosed
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.
Which Mapleson circuits are MOST likely to be encountered in modern anesthetic practice? (Select 3.)
A B C D E F
DEF
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.
The Mapleson D is an example of a/an: semiopen circuit. open circuit. semiclosed circuit. closed circuit.
Semiopen circuit
Semiopen Circuit (Mapleson A-F, Bain system, circle system w/ FGF > Ve):
Bag reservoir = Yes
Rebreathing = No
Which circuit contains a reservoir bag but does not allow rebreathing of exhaled gases?
Semiopen
Open
Semiclosed
Closed
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
A circle system with a fresh gas flow of 3 L/min is an example of a/an:
closed circuit.
semiclosed circuit.
semiopen circuit.
open circuit.
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
All of the following allow fresh gas to escape into the atmosphere EXCEPT a:
simple face mask.
Bain system.
T-piece.
nasal cannula.
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.
Click on the circuit that is the predecessor to the Bain system.
The Mapleson D (2nd example) is the precursor to the Bain system.
What’s different about the Bain system is that the fresh gas travels towards the patient through a smaller tube INSIDE the corrugated tubing.
Exhaled gas travels inside the corrugated tubing (but outside of the small tube discussed above). This design passively warms the incoming fresh gas.
How do you perform the Pethick test during the pre-anesthetic checkout with a Bain 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.
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.
Click on the phase of the capnograph that BEST correlates with the ventilation-perfusion status of the lung. (Pic is ETCO2 waveform)
between C-D
Phase I = Exhalation of dead space
Phase II = Exhalation of dead space + alveolar gas
Phase III = Exhalation of alveolar gas (best correlates to V/Q status)
Phase IV = Inspiration
Point D = Point of EtCO2 measurement
Click on the beta angle.
There are two angles on the capnograph: alpha and beta
Alpha angle: Between phase II and III Normal = 100-110 degrees Increased by obstruction to expiration, such as COPD, kinked endotracheal tube, etc.
Beta angle:
Between phase III and IV
Normal = 90 degrees
Increased by an inspiratory valve stuck in the open position
Match each event with its MOST likely presentation on the capnograph.
Channeling + Elevated baseline
Incompetent inspiratory valve + Widened beta angle
Sample line leak + Peak at end of phase 3
Tournequet release + Increased EtCO2 with normal return to baseline
All of the following contribute to an increased PaCO2-EtCO2 gradient EXCEPT:
right-to-left shunt.
pulmonary embolism.
sample line leak.
laparoscopy.
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.
Infrared analysis is able to measure: (Select 3.)
carbon dioxide. helium. nitrous oxide. volatile anesthetics. xenon. oxygen.
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.
When compared to a mainstream carbon dioxide sensor, which of the following is an advantage of a sidestream carbon dioxide sensor?
Less apparatus dead space
Absence of a pumping mechanism
Elimination of the water trap
Faster response time
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.
Choose the statement that reflects the MOST complete understanding of pulse oximetry.
It emits two wavelengths of ultraviolet light.
At the trough of the waveform, the sample contains more arterial blood.
It is based on the Coanda effect.
660 nm light is preferentially absorbed by reduced hemoglobin.
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.
Which pulse oximeter location is associated with the SLOWEST response time?
Ear
Tongue
Nose
Finger
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.
Which of the following is a contraindication to pulse oximetry?
Raynaud’s disease
Takayasu arteritis
Cardiopulmonary resuscitation
There are no contraindications to pulse oximetry.
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.
In which patients is the pulse oximeter MOST likely to provide an inaccurate measurement? (Select 2.)
7 year-old rescued from a basement fire
10 year-old with jaundice
15 year-old who received fluorescein
3 year-old toxic from EMLA cream overdose
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.
Which of the following is the LEAST reliable monitor of endobronchial intubation?
Fiberoptic bronchoscope
Pulse oximeter
Pressure-volume loop
Lung auscultation
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.
The mixed venous oxygen saturation monitor reads 70%. Estimate the PvO2.
(Enter your answer as a whole number in mmHg)
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
Determinants of dynamic compliance include all of the following EXCEPT:
tidal volume.
peak inspiratory pressure.
plateau pressure.
positive end-expiratory pressure
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.
Match each condition with its MOST likely effect on pulmonary pressure monitoring.
Endobronchial intubation
Mucus plug
Pulmonary embolism
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.
The normal QT interval is:
- 10 seconds.
- 25 seconds.
- 40 seconds.
- 55 seconds.
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.
This EKG indicates:
normal axis.
left axis deviation.
right axis deviation.
extreme right axis deviation.
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
All of the following are true of sinus arrhythmia EXCEPT:
inhalation increases heart rate.
it is caused by an ectopic pacemaker.
increased venous return increases heart rate.
it is a consequence of the Bainbridge reflex.
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.
This EKG tracing represents a:
antidromic pathway.
sinus arrhythmia.
Mobitz type II block.
non-compensatory pause.
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.
All of the following are appropriate treatments for symptomatic sinus bradycardia in a 70 kg adult EXCEPT:
dobutamine 5 mcg/kg/min.
atropine 0.2 mg.
glucagon 3 mg.
transcutaneous pacing.
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.
Click on the bipolar limb lead that is ALWAYS positive.
bottom left
There are three bipolar limb leads, and each one has a positive and a negative pole. The mean electrical vector travels away from the negative pole and towards the positive pole.
Lead I: Right arm (-) to Left arm (+)
Lead II: Right arm (-) to Left leg (+)
Lead III: Left arm (-) to Left leg (+)
Notice that the left leg is always positive and the right arm is always negative.
Click on the area of the hexagonal reference system that correlates with left axis deviation.
-90 to - 30 degrees
The electrical axis depicts the path of the mean electrical vector. This vector tends to move towards areas of hypertrophy and away from areas of infarction.
The normal axis is -30 to +90 degrees.
Here are an easy set of ranges to remember:
Left axis deviation = < -30 degrees
Right axis deviation = > 90 degrees
You will find some books that describe superior right axis deviation (+180 to - 90).
Which dysrhythmia is the MOST common cause of acute myocardial infarction?
Atrial fibrillation with rapid ventricular rate
Paroxysmal atrial tachycardia
Atrial flutter
Sinus tachycardia
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.
Match each dysrhythmia with its EKG tracing.
VT
SVT
ST
AFlutter
When compared to atrial fibrillation, which of the following statements about atrial flutter are true? (Select 2.)
Amiodarone is more likely to restore normal sinus rhythm.
It is an organized supraventricular dysrhythmia.
Each atrial depolarization is associated with an atrial contraction.
More current is required for synchronized cardioversion.
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.
Which conditions are MOST closely associated with the following abnormality? (Select 2.) Parasympathetic stimulation Hypokalemia Digitalis toxicity Hypermagnesemia
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)
