Equipment and monitors Flashcards
What components are present in the high pressure system of the anesthesia machine? what is the gas pressure in this region?
The high pressure system begins at the cylinder and ends at the cylinder regulators. Components include:
* Hanger yoke
* Yoke block with check valves
* Cylinder pressure gauge
* Cylinder pressure regulators
Gas pressure = cylinder pressure
What components are present in the intermediate pressure system of the anesthesia machine?
The intermediate pressure system begins at the pipeline and ends at the flowmeter valve. Components include:
* pipeline inlets
* pressure gauges
* ventilator power inlet
* oxygen pressure failure system
* oxygen second stage regulator
* Oxygen flush valve
* Flowmeter valve
Gas pressure = 50 psi (if using pipeline) and 45 psi (if using tank)
flush valve is 35-75 L/min, 40- 50 psi
What components are present in the low pressure system of the anesthesia machine?
The low pressure system begins at the flowmeter tubes and ends at the common gas inlet. Components include:
* flowmeter tubes (thorpe tubes)
* vaporizers
* Check valves (if present)
* Common gas outlet
Gas pressure= slightly above atmospheric pressure
What are the 5 tasks of oxygen in the anesthesia machine?
- O2 pressure failure alarm
- O2 pressure failure device (failsafe)
- O2 flowmeter
- O2 flush valve
- Ventilator drive gas (if pneumatic bellows)
Describe the pin index safety system.
The PISS prevents inadvertent misconnections of gas cylinders.
The pin configuration on each hanger yoke assembly is different for each gas, making unintended connections of the wrong gas unlikely, but not impossible.
- The presence of more than one washer between the hanger yoke assembly and the stem of the tank may allow bypassing the PISS.
Describe the diameter index safely system
The DISS prevents inadvertent misconnections of gas hoses. Each gas hose and connector are sized and threaded for each individual gas.
What are the maximum pressures and volumes for cylinders that contain air, oxygen, and nitrous oxide?
Oxygen: 660L, 1900PSI, pin 2,5
Air: 625, 1900PSI, Pin 1,5
Nitrous oxide: 1590L, 745 psi, PIN 3,5
* weight full: 20.7 lb
* weight empty: 14.1 lb
The bourdon pressure gauge on an oxygen cylinder reads 500 psi. If the flow rate is 4L/min, how long will this cylinder provide oxygen to the patient?
Tank capacity/ full tank pressure x contents remaining/ gauge pressure (psi)
how long will it last?
Contents remaining (L)/ FGF rate (L/min) = minutes before tank expires
- 660L/ 1900psi= X/500psi= 174 L
- 174 L/ 4 L/min= 43.5 minutes
if you used 2,000 psi ( as some books do), then the correct answer is 41 minutes
Is it ever safe to use an oxygen cylinder in the MRI suite?
Never take a cylinder into the MRI scanner unless it’s made of a non-magnetic material, such as aluminum.
An MRI safe cylinder will have two colors: most of the tank is silver, and only the top is the color that signifies the gas it contains.
List 3 safety relief devices that prevent a cylinder from exploding when the ambient temperature increases.
Gas cylinders should never be exposed to temperatures higher than 130 F (57 C), as temperatures higher than this may lead to a fire or explosion.
In an environmental fire, there is a safety relief device built into the cylinder that allows the cylinder to empty its contents in a slow and controlled way. Examples of safety relief devices include:
- a fusible plug made of Wood’s metal (melts at elevated temperatures)
- A frangible disk that ruptures under pressure
- a valve that opens at elevated pressures
Give 1 example of how the oxygen pressure failure device (failsafe) might permit the delivery of a hypoxic mixture.
The failsafe device responds to pressure (not flow)
If there is a pipeline crossover, then the pressure of the second gas will produce pressure to defeat the failsafe device. The patient will be exposed to a hypoxic mixture
give 4 examples of how the hypoxia prevention safety device (proportioning device) might allow the delivery of a hypoxic mixture.
proportioning devices will NOT prevent a hypoxic mixture in the following circumstances:
1. Oxygen pipeline crossover
2. Leaks distal to the flowmeter valves
3. administration of a third gas (helium)
4. Defective mechanic or pneumatic components
What is the difference between the oxygen pressure failure device and the hypoxia prevention safety device?
Oxygen pressure failure device
* Fail-safe device
* Works by: shuts off and/or proportionately reduces N2O flow if O2 pressure drops below 20psi
Hypoxia prevention safety device:
* proportioning device
* Works by: Prevents you from setting a hypoxic mixture with the flow control valves
* Limits N2O flow to 3 times O2 flow (N2O max around 75%)
Describe the structure and function of the flowmeters.
The annular space is the area between the indicator float and the side wall of the flow tube. The annular space is also the 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.
- laminar flow is dependent on gas viscosity (pouseuille)
- Turbulent flow is dependent of gas density (graham)
What is the safest flowmeter configuration on the anesthesia machine?
The O2 flowmeter should always be the furthest to the right. Here’s why…
Flowmeters are usually made of glass, making them the most delicate part of the anesthesia machine. A leak will allow oxygen to escape the low-pressure system, which could result in the delivery of a hypoxic mixture.
The order of flowmeters is important. The oxygen flowmeter should be positioned closes to the manifold outlet (on the right in the US). If a leak develops in any of the OTHER flowmeters, it won’t reduce the FiO2 delivered to the patient. If, however, a leak develops inside the oxygen flowmeter, all bets are off.
How do you calculate the FiO2 set at the flowmeter?
Equation: FiO2 = ((airflow rate x 21) + (oxygen flow rate x 100))/ total flow rate
ex: FiO2 = (1L/min x 21) + (3L/min x 100)/ 4 L/min = 80.25= 80%
An anesthesia machine uses fresh gas coupling. How do you determine the total tidal volume that will be delivered to the patient?
Vt total= Vt set on a ventilator + FGF during inspiration
you may be asked to include volume lost to compliance
When using a ventilator that couples fresh gas flow to tidal volume, what types of ventilator changes will impact the tidal volume delivered to the patient?
When using a ventilator that couples FGF to Vt, making nearly any change on the ventilator settings will ultimately impact the Vt delivered to the patient.
What is the vaporizer splitting ratio?
Modern variable bypass vaporizers split fresh gas into 2 parts:
1. Some fresh gas enters the vaporizing chamber and becomes 100% saturated with a volatile agent.
2. the rest of the gas bypasses the vaporizing chamber and does not pick up any volatile agent.
Before leaving the vaporizer, these two fractions mix, and this determines the final anesthetic concentration exiting the vaporizer.
By setting the concentration on the dial, you determine the splitting ratio. Setting a higher concentration directs more fresh gas towards the liquid anesthetic, while setting a lower concentration directs less fresh gas towards the liquid anesthetic.
What is the pumping effect?
The pumping effect can increase vaporizer output.
Anything that causes gas that has already left the vaporizer to re-enter the vaporizer chamber can cause the pumping effect. This is generally due to positive pressure ventilation or the use of the oxygen flush valve. Modern anesthesia machine design mitigates this risk.
Compare and contrast the variable bypass vaporizer with the injector-type vaporizer.
What does the oxygen analyzer measure, and where is it located?
The oxygen analyzer monitors oxygen concentration (not pressure) and is the only device downstream of the flowmeters that can detect a hypoxic mixture. Indeed, leaks in the anesthesia machine are most likely to occur in the low-pressure system.
What 2 things must you do in the event of an oxygen supply line crossover?
- Turn ON the oxygen cylinder
- Disconnect the pipeline oxygen supply. This is a key step!
if a crossover occurs, simply turning on the oxygen tank would not save the patient. If an adequate oxygen pipeline pressure is present (regardless of the gas inside), it will prevent the oxygen tank from providing oxygen to the patient.
Pressing the oxygen flush valve exposes the breathing circuit to __ O2 flow and __ O2 pressure.
Oxygen flow = 35-75 L/min
Oxygen pressure = 50 psi (pipeline pressure)
What are the 2 risks of pressing the oxygen flush valve?
Barotrauma and awareness….
Pressing the O2 flush valve during inspiration can cause barotrauma.
Because the gas from the oxygen flush does not pass through the vaporizers, excessive use of the oxygen flush valve adds gas to the breathing circuit that does not contain volatile anesthetic. As a result, it dilutes the partial pressure of the volatile agent and may lead to awareness.
Describe the function of the ventilator spill valve in relation to using the O2 flush valve.
Compare and contrast volume controlled and pressure controlled ventilation
Volume- controlled ventilation delivers a preset tidal volume over a predetermined time. Since the tidal volume is fixed, the inspiratory pressure will vary as the patient’s compliance changes. The inspiratory flow is held constant.
Pressure control ventilation- delivers a preset inspiratory pressure over a predetermined time. Since the pressure and time are fixed, the tidal volume and inspiratory flow will be variable and dependent on the patient’s lung mechanics. If airway resistance rises or lung compliance decreases, then the tidal volume will suffer, and a high inspiratory flow will be required to achieve the present airway pressure.
A patient is receiving pressure controlled ventilation. What conditions can alter the tidal volume delivered to the patient?
You notice that the soda lime has become exhausted in the middle of a surgical procedure. What is the best action to take at this time?
In the presence of exhausted soda lime, you may want to increase the minute ventilation. While this action will remove a greater amount of carbon dioxide from the body, it does not prevent the patient from rebreathing carbon dioxide and may lead to hypercarbia. Instead, if you cannot replace the CO2 absorbent, the appropriate action is to increase the fresh gas flow to convert the circle system into a semi-open configuration.
what is desiccation, and how does it apply to soda lime?
Water is required to facilitate the reaction of carbon dioxide with CO2 absorbent. The granules are hydrated to 13-20% by weight. When the absorbent is devoid of water, it is said to be desiccated. As and aside, ethyl violet tells you about exhaustion, but it does NOT tell you about the water content of the CO2 absorbent.
In the presence of halogenated anesthetics, desiccated soda lime increases the production of carbon monoxide (desflurane > isoflurane»_space;> sevoflurane) and compound A in the presence of sevoflurane.
- carbon monoxide can cause carboxyhemoglobinemia
- Compound A may cause renal dysfunction
List 7 ways to monitor for disconnection of the breathing circuit.
there are 4 ways to monitor for circuit disconnect. Pressure, volume, ETCO2, and your own vigilance.
- Precordial stethoscope
- visual inspection of chest rise
- Capnography
- respiratory volume monitors
- Low expired volume alarm
- low peak pressure alarm
- Failure of bellows to rise with an ascending bellows (not with descending bellows or piston)
- the oxygen analyzer monitors the concentration of oxygen in the breathing circuit. It’s NOT a disconnect monitor.
What are the OSHA recommendations regarding inhalation anesthetic exposure for health care workers in the operating room?
Halogenated agents alone <2ppm
Nitrous oxide alone< 25ppm
Halogenated agents + nitrous oxide <0.5ppm and 25ppm, respectively
Compare and contrast the four types of breathing circuits, and list examples of each.
what is the purpose of the unidirectional valves in the breathing circuit?
The purpose of the unidirectional valves is to ensure that gas moves in one direction
* if a valve becomes incompetent, then the patient will rebreathe exhaled gas
* if the definitive fix is to correct the valve
* if this cannot be done, then a closed or semi-closed system should be converted to a semi-open system by increasing the FGF in excess of the patient’s minute ventilation
Which Mapleson circuit is most efficient for spontaneous ventilation? which is best for controlled ventilation?
Spontaneous ventilation:
* Best = Mapleson A (A> DFE> CB) all dogs fear every cat bite
* Worst = Mapleson B
Controlled Ventilation
* Best = Mapleson D (DFE> BC>A)
* Worst= A
E and F do not have APL valves
E does not have reservoir bag
what conditions decrease pulmonary compliance? How does this affect the peak pressure and plateau pressure?
A decreased compliance is usually due to a reduction in static compliance (PIP and PP increase)
- Endobronchial intubation
- pulmonary edema
- Pleural effusion
- Tension pneumothorax
- Atelectasis
- chest wall trauma
- abdominal insufflation
- Ascites
- trendelenburg position
- inadequate muscle relaxation
What conditions increase pulmonary resistance? How does this affect the peak pressure and plateau pressure?
Increased pulmonary resistance is usually due to a reduction in dynamic compliance (PIP increases, and PP is unchanged)
- Kinked endotracheal tube
- endotracheal tube cuff herniation
- bronchospasm
- Bronchial secretions
- compression of the airway
- Foreign body aspiration
Describe the 4 phases of the normal capnograph
Phase 1 (A-B): Exhalation of anatomic dead space
Phase II (B-C): exhalation of anatomic dead space + alveolar gas
Phase III (C-D): Exhalation of alveolar gase
Phase IV (D-E): Inspiration of fresh gas that does not contain CO2
Discuss the significance of the alpha and beta angles on the capnograph.
An increased alpha angle signifies an expiratory airflow obstruction, such as COPD, bronchospasm, or a kinked endotracheal tube.
The beta angle is increased in some (but not all) etiologies of rebreathing. It is specific to rebreathing caused by a faulty unidirectional valve, but it will appear normal in other instances of rebreathing (exhausted CO2 absorbent). In the case of CO2 absorbent exhaustion, the baseline increases, but the beta angle is normal.
Recall all of the abnormal CO2 waveforms you can (we have 9). Then loo at the answer.
Think of all of the causes of increased and decreased EtCO2 that occur as a result of changes inCO2 production.
Think of all the causes of increased and decreased EtCO2 that occur as a result of changes in alveolar ventilation or equipment malfunction.
What wavelengths of light are emitted by the pulse oximeter? what law is used to make the SpO2 calculation?
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
The pulse oximeter emits 2 wavelengths of light:
* Red light (660 nm) is preferentially absorbed by deoxyhemoglobin (higher in venous blood)
* Near-infrared light (940nm) is preferentially absorbed by oxyhemoglobin (higher in arterial blood)
what conditions impair the reliability of the pulse oximeter?
Decreased perfusion:
* vasoconstriction
* Hypothermia
* Reynaud’s syndrome
Dysfunctional Hgb:
* Carboxyhemoglobin (absorbs 660nm to the same degree as oxygenated hgb)
* Methemoglobin (absorbs 660nm and 990 nm equally)
* NOT HgbS or HgBF
Altered optical characteristics:
* Methylene blue
* Indocyanine green
* Indigo carmine
* NOT fluorescein
Non-pulsatile flow:
* CBP
* LVAD
Motion artifact:
* Shivering/ movement
Other:
* Electrocautery
* Dark skin
* Venous pulsation
* NOT jaundice or polycythemia
what factors affect the accuracy of the noninvasive blood pressure cuff measurement?
The ideal bladder LENGTH is long enough to wrap around 80% of the extremity
The ideal bladder WIDTH is 40% o the circumference of the patient’s arm
Falsely increased BP:
* BP cuff is too small
* BP cuff is too loose
* BP is measured on extremity below the level of the heart
Falsely decreased BP:
* BP cuff is too large
* BP cuff is deflated too rapidly
* BP is measured on extremity above the level of the heart
How does the site of measurement affect the blood pressure reading?
as the pulse moves from the aortic root towards the periphery, the systolic pressure increases, diastolic pressure decreases, and the pulse pressure widens. Mean arterial blood pressure remains constant through the arterial tree.
- At the aortic root: SBP is the lowest, and DBP is the highest, and PP is the narrowest
- At the dorsalis pedis: SBP is highest, DBP is the lowest, and PP is the widest
How does the arm position affect the NIBP reading? How about when an arterial line is used?
Blood in the circulation behaves like a column of fluid and follows the rules of hydrostatic pressure.
* If the BP cuff location is above the heart, the BP will be falsely decreased ( There is less hydrostatic pressure)
* If the BP cuff location is below the heart, the BP reading will be falsely increased (there is more hydrostatic pressure)
* For every 10 cm change, the BP changes by 7.4 mmHg
* For every inch change, the BP changes by 2 mmHg
When an A-line is used, the transducer level is what’s important (the height of the catheter does not matter)
What information ca you learn from the arterial BP waveform?
You can gain a great deal of information by assessing the morphology of the arterial waveform. Here are a few general rules:
* systolic BP= Peak of waveform
* Diastolic BP= Trough of waveform
* Pulse pressure = Peak-trough
* Contractility = upstroke
* Stroke volume= area under the curve
* Closure of aortic valve = dicrotic notch
Discuss damping and the interpretation of the high pressure flush test.
Optimal waveform morphology balances the amount of damping with the amount of distortion from the transducer system. The high-pressure flush test helps us determine this when we flush the system and observe the oscillations that result (if any).
Optimally damped system: The baseline is re-established after 1 oscillation
Under-damped system: The baseline is re-established after several oscillations (SBP is overestimated, DBP is underestimated, and MAP is accurate)
Over damped system: The baseline is re-established with no oscillations (SBP is underestimated, DBP is overestimated, and MAP is accurate). Causes include an air bubble or clot in the pressure tubing or low flush bag
How do you determine the appropriate distance to thread a central line or PA catheter?
- You must know the distance from the site of entry to the vena cava junction.
- You must know the distance from the VC junction to where the catheter’s tip should be placed
- Add these two numbers to determine from the insertion site to the tip of the catheter
What are the 3 waves and 2 descents on the CVP waveform? What does each one signify?
How do the waves and descents on the CVP waveform correlate with the electrical events in the heart?
What factors increase or decrease the CVP value?
What conditions cause loss of a wave on the CVP waveform?
Loss of the a wave occurs when synchronized contraction of the right atrium is lost.
* A fib
* V-pacing if the underlying rhythm is asystole
What conditions cause an increased a-wave on the CVP waveform?
A large a wave is produced when the atria contracts and empties against a high resistance (either at the valve or noncompliant ventricle)
* Tricuspid stenosis
* Diastolic dysfunction
* Myocardial ischemia
* Chronic lung disease leading to RV hypertrophy
* AV dissociation
* Junctional rhythm
* V-pacing- asynchronous
* PVC’s
What conditions cause a large v-wave on the CVP waveform?
Tricuspid regurgitation allows a portion of the right ventricular volume to pass through the closed but incompetent tricuspid valve during RV systole. This increases the volume and pressure in the RA and manifests as large v waves.
- Tricuspid regurgitation
- Acute increase in intravascular volume
- RV papillary muscle ischemia
How does the waveform change as a PA catheter is guided into position? what are the normal pressures at each step?
The tip of the PAC should be positioned in West lung zone_?
The tip of the PAC should be in zone 3. In this region, there is a continuous column of blood between the tip of the PAC and the left ventricle. Since LVEDP reflects back through the pulmonary circulation, a tip positioned in zone 3 provides the most accurate estimation of LVED.
Zone 3 is defined as P arterial > P venous> P alveolus
What is the equation for mixed venous oxygen saturation?
CvO2= SaO2 - (VO2/ Q x 1.34 x Hgb x 10)
Mixed venous oxygen saturation is a function of 4 variables:
* Q= Cardiac output (L/min)
* VO2= Oxygen consumption (mL O2/min)
* Hgb= Amount of Hemoglobin (g/dL)
* SaO2= Loading of hemoglobin in arterial blood (%)
What conditions are associated with a decreased SvO2? How about an increased SvO2?
Relate the phase of the cardiac action potential to the EKG.
What region of the myocardial does each EKG lead monitor? What coronary arteries are monitored by each lead?
We commonly use 12 leads to look at the heart’s electrical activity from various angles. We can divide these leads into 3 groups
- Bipolar leads (3)
- Limb leads (3)
- Precordial leads (6)
you should be able to match each lead with he region of the heart it monitors and its corresponding coronary artery.
Recite the heart block poem.
If “R” is far from “P”, then you have a First Degree
Longer, longer ,longer, drop then you have a Wenckeback. (second degree)
If some “P”s don’t get through that you have a mobitz II (second degree)
If “P”s and “Q”s don’t agree then you have a Third Degree.
What is the MOA for each antiarrhythmic class (I-IV)? list examples of each.
What EKG findings are consistent with Wolff-Parkinson- White syndrome?
Delta wave caused by ventricular preexcitation
Short PR interval (<0.12 seconds)
Wide QRS
Possible T wave inversion
What conditions increase the risk of torsades de pointes?
Mnemonic: POINTES
Phenothiazines
Other meds (methadone, droperidol, amiodarone w/hypokalemia)
Intracranial bleed
No known cause
Type I antiarrhythmics
Electrolyte disturbances (low K, Ca, or Mg)
Syndromes (Romano-Ward, Timothy)
What is the treatment for torsades de pointes?
Acute treatment for torsades de pointes includes reversing the underlying cause and/or shorten the QT interval:
* Magnesium sulfate
* Cardiac pacing to increase the heart rate will reduce action potential duration and the QT interval
List 5 indications for cardiac pacemaker insertion.
The cardiac output is dependent on the heart’s ability to generate a normal rate and rhythm. If the heart cannot produce a normal rate and rhythm, a pacemaker can be placed to accomplish this task.
Indications for pacemaker insertion:
* Symptomatic diseases of impulse formation (SA node disease)
* Symptomatic diseases of impulse conduction (AV node disease)
* Long QT syndrome
* Dilated cardiomyopathy
* Hypertrophic obstructive cardiomyopathy
What is the significance of the NBG pacemaker identification code?
Position 1 = Chamber paced
Position 2= Chamber sensed
Position 3= Response to sensed event
Position 4= programmability
Position 5= pacemaker can pace multiple sites
How does atrial pacing affect the QRS complex? How about ventricular pacing?
If the atrium is paced, the electrical signal travels through the AV node, and the QRS maintains its normal, narrow appearance.
If the ventricle is paced, the electrical signal is delivered beyond the AV node, and the QRS takes on a wide appearance.
What conditions increase the risk of failure to capture?
Failure to capture occurs when the ventricle does not depolarize in response to a pacing stimulus.
* Hyper- and hypokalemia
* Hypocapnia (intracellular K shift)
* Hypothermia
* Myocardial infarction
* Fibrotic tissue buildup around the pacing leads
* Antiarrhythmic medications
How does the cerebral oximeter work? What value is considered a significant change from baseline?
Cerebral oximetry utilizes near-infrared spectroscopy (NIRS) to measure cerebral oxygenation.
* Arterial hemoglobin, venous hemoglobin, and tissue cytochromes absorb different frequencies of infrared light.
* Cerebral oximetry relies on the fact that cerebral blood volume is 1 part arterial to 3 parts venous; 75% of blood in the brain is on the venous side of the circulation
* Since NIRS cannot detect pulsatile blood flow, it is primarily a measure of venous oxyhemoglobin saturation and oxygen extraction
* Decreased cerebral oxygen delivery -> increased cerebral oxygen extraction -> decreased venous hgb saturation
* A >25% change from baseline suggest a reduction in cerebral oxygenation
Describe the type of EEG waveforms.
how do brain waves change during general anesthesia?
General anesthesia causes the following changes in brain activity:
- Induction of general anesthesia is associated with increased beta wave activity
- Light anesthesia is also associated with beta wave activity
- Thea and delta waves predominate during general anesthesia
- Deep anesthesia produces burst suppression
- At 1.5-2 MAC, general anesthetics cause complete suppression or isoelectricity.
Name 2 drugs that are most likely to reduce the reliability of the BIS value
Nitrous oxide increases the amplitude of high-frequency activity and reduces the amplitude of low-frequency activity. This does not affect the BIS value
Ketamine increases high-frequency activity. This can produce a higher BIS value than the level of sedation/anesthesia would otherwise suggest.
What is the difference between macro- and microshock?
Macroshock- is a comparatively larger amount of current that is applied to the external surgace of the body. The skin’s impedance offers a high resistance, so it takes a larger current to induce ventricular fibrillation.
Microshock is a comparatively smaller amount of current that is applied directly to the myocardium. The high resistance of the skin is bypassed, so it takes a significantly smaller amount of current to induce ventricular fibrillation.
- A central line, PA catheter, or pacing wires provide a direct conductive pathway to the heart, so it should make sense that they increase the patient’s susceptibility to microshock.
What are the key threshold values for macroshock and microshock?
What is the role of the line isolation monitor? What should you do if it alarms?
The line isolation monitor assesses the integrity of the ungrounded power system in the OR. It tells you 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.
- The LIM does NOT 9by itself) protect you or the patient from macro- or microshock
- The LIM will alarm when 2-5 mA of leak current is detected
- If the alarm sounds, the last piece of equipment that was plugged in should be unplugged.
What is the water content of soda lime?
10-20%
what creates the GREATEST resistance to airflow?
ETT
the combination of sevo and baralyme increases the risk of:
Breathing circuit fire
Desiccated Baralyme and sevo has resulted in breathing system fires. Desiccated Baralyme produces flammable by-products such as formaldehyde, methanol, and formic acid.
According to the World Health ORganization, what color should the tanks be?
Oxygen- white
Nitrous oxide- blue
Air-black and white
Standard mesh size for soda lime
4-8 holes per square inch- best combination of absorptive capacity and airflow resistance
what actions reduce compound A production
Removal of NaOH
Addition of Ca(OH)2
using more than washer between the cylinder and yoke can lead to:
Inadvertent attachment of a nitrous oxide cylinder
does not create a cylinder leak
The low pressure circuit leak test checks the integrity of the machine from the:
flow control valves to the common gas outlet
the low pressure circuit leak test is the best method to detect a vaporizer leak
when ambient temperature is increased, the bi-metallic strip in a variable bypass vaporizer directs:
more fresh gas to the bypass chamber
less fresh gas to the vaporizing chamber
temp increase then VP increases so for consistency you want less FGF going to the vaporizer
which circuit doe not contain dead space?
open- open to atmosphere
which Mapleson circuits are MOST likely to be encountered in modern anesthetic practice?
D E and F
What circuits are semiopen circuits?
Mapleson A-F, Bain system, circle system w/FGF >Ve
* Has a reservoir bag
* No rebreathing
A circle system with a FGF of 3L.min is a semiclosed circuit
Don’t allow FGF to escape into the atmosphere
* Open circuit do (nasal cannula, simple face, and T-piece)
THe Mapleson D is the precursor to the Bain circuit
Infrared analysis is able to measure:
Carbon dioxide
Volatile anesthetics
Nitrous oxide
Which pulse oximeter location is associated with the slowest response time?
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 T-burg position can cause venous engorgement resulting in a falsely decreased SpO2 measurement
Determinants of dynamic compliance include all of the following except:
Plateau pressure
others were peak inspiratory pressure, Positive end expiratory pressure, and tidal volume
Compliance is a change in volume for a given change in pressure
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- Decreased static compliance
mucus plug- decreased dynamic compliance
pulmonary embolism- No change in dynamic or static compliance
Dynamic compliance is:
* Measured while gas flows into the lungs
* A function of airway resistance and lung/chest wall compliance
* Assessed by Peak pressure
* Decreased by anything that obstructs airflow, such as a kinked ETT, mucus plug, or bronchospasm
Static compliance:
* 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 pulm resistance or compliance
Central venous pressure is MOST accurately measured at the:
End of expiration
Since we measure CVP relative to atmospheric pressure, we dont want changes in intrathoracic pressure to impact the accuracy of our measurement.
* During spontaneous breathing, inhalation creates negative pressure in 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 of expiration. Therefore, CVP should be measured at end expiration during spontaneous or positive pressure breathing.
All of the following are complications of pulmonary artery catheter placement except:
Left BBB
others were pneumothorax, air embolism, and neuropathy- all possible
increased risk of RBBB
obtaining venous access- arterial puncture, air embolism, neuropathy, and pneumo
floating PA catheter- RBBB, complete HB (if pre-existing LBBB), 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
The normal QT interval is:
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)
* 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
Axis deviations
Normal axis: lead I and AVF are positive
Extreme right axis deviation: Leads 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?
it is caused by an ectopic pacemaker
others were: increased venous return increases heart rate, inhalation increases heart rate, it is a consequence of the bainbridge reflex
Sinus arrhythmia occurs when the SA node’s pacing rate varies with respiration.
* Inhalation -> increased heart rate
* Exhalation -> decreased heart rate
Bainbridge reflex 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 -> decreased intrathoracic pressure -> increased venous return -> increased heart rate
- Exhalation -> increased intrathoracic pressure -> decreased venous return -> decreased heart rate
sinus arrhythmia is usually benign
All of the following are appropriate for symptomatic sinus bradycardia in a 70 KG adult except:
Atropine
others were: Dobutamine, glucagon, and transcutaneous pacing
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 HR, contractility, and AV conduction. the initial dose is 50-70 mcg/kg q 3-5 minutes. This can be followed with an infusion at 2-10 mg/hr
which bipolar limb leads are ALWAYS positive
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
Which dysrhythmia is the MOST common cause of acute myocardial infarction?
Sinus tachycardia
Sinus tachy simultaneously increases myocardial oxygen demand while decreasing oxygen supply. In patients with CAD, this can precipitate myocardial ischemia and/or infarction.
When compared to afib, which of the following statements about atrial flutter are true?
It is an organized supraventricular dysrhythmia
Each atrial depolarization is associated with an atrial contraction
characterized by a “sawtooth” 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.
* 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 a flutter should be treated with cardioversion. As little as 50 joules (monophasic) will convert a 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 48hrs. these patients should be anticoagulated and undergo echocardiographic examination to rule out atrial thrombus prior to cardioversion.
Pharmacology therapy aimed at controlling ventricular rate include 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.
What causes PVCs
there are many conditions that are associated with PVCs:
* SNS stimulation (hypoxia, hypercarbia, acidosis, light anesthesia)
* Myocardial ischemia and/or infarcion
* Valvular heart disease
* Cardiomyopathy
* Prolonged QT interval
* Hypokalemia
* Hypomagnesemia
* Digitalis toxicity
* Caffeine
* Cocaine
* Alcohol
* Mechanical irritation (central line insertion)
Best drug of treatment for symptomatic premature ventricular contractions
Lidocaine
what is the safest med of the following to administer to a pt with prolonged QT syndrome?
Metoprolol*
not quinidine, procainamide, or amiodarone
BB’s are shown to reduce the incidence of torsades de pointes. the other meds mentioned may cause it.
Which syndromes are MOST likely to cause prolonged QT syndrome?
Romano- ward and Timothy syndrome
not king denborough (MH) or brugada (pseudo RBBB and ST elevation in V1-V3)
potential causes of first degree heart block include:
PR >0.20 seconds
- Degenerative changes that accompany aging
- Posterior wall MI (a branch of the right coronary artery usually supplies the AV node)
- Parasympathetic stimulation
- Amiodarone
- Digoxin
usually benign
anesthetic considerations: preventing situations that increase vagal tone or slow AV conduction
What should be used to treat for third degree block?
Transcutaneous pacing and isoproterenol (chemical pacemaker)
Cerebral oximetry
75% venous 25% arterial
Measures venous oxygen in cerebral blood
utilizes near infrared spectroscopy (NIRS) to measure regional (not global) cerebral oxygenation
A > 25% change from baseline suggests a reduction in cerebral oxygenation
during anesthetic maintenance, the appearance of delta waves should raise suspicion of:
Cerebral ischemia
the following circumstances mimic cerebral ischemia: Deep anesthesia, hypothermia, and hypocarbia
In the OR:
Power is not grounded
Equipment is grounded
What are the characteristics of volume-controlled ventilation?
Tidal volume delivered at constant flow
Inspiration terminated when desired tidal volume delivered
Peak inspiratory pressure controlled….but then states peak pressure is monitored but not controlled
5 Oxygen pathways in the anesthesia machine:
- Flowing through the fresh-gas glow meter
- powering the oxygen fail-safe valve
- activating the oxygen fail-safe system
- Activating the oxygen low-pressure alarm
- Compressing the bellows for mechanical ventilation
Components of anesthesia machine flowmeters?
- Control knobs
- Needle valve
- Float indicator
- Valve stops (may not be on all machines)
What component reduces the cylinder pressure to a pressure suitable for the anesthesia machine?
Pressure regulator
Why is a contemporary variable bypass vaporizer unacceptable for the vaporization of desflurane?
High rate of evaporation- would require excessive FGF (73L/min), and would result in excessive cooling and decreasing the concentration output
Desflurane’s high volatility- concentration output would be uncontrolled in variable bypass
Which is correct regarding the use of an auxiliary oxygen flowmeter?
Readily available source of O2 for controlled ventilation
Allows supplemental oxygen administration
Which activators in soda lime are associated with the formation of compound A?
Potassium hydroxide and sodium hydroxide
Newer absorbents such as Amsorb, Litholyme, and Spiralith lack NaOH and KOH and avoid the formation of Compound A and Carbon monoxide
The water content of soda lime is what percent by weight?
13-20% by weight
What are the advantages of a mechanically driven piston ventilator?
Accurate tidal volume deliver (without compressed gas)
Mechanical breaths delivered without compressed gas
A hazard of the piston ventilator is that in the event of a circuit disconnect, the piston will continue to refill and, in the presence of a circuit leak, will entrain room air diluting the desired anesthetic and oxygen concentration
The designation of ascending or descending bellows ventilators is determined by:
bellows movement on expiration
an ascending bellows rises during expiration, whereas a descending bellows falls during expiration. In the even of a circuit leak or disconnect, the ascending bellows would fail to fill, whereas the descending bellows would fill despite a circuit leak or disconnect
What is the function of the interlock/vaporizer system on the contemporary anesthesia machine?
Prevent fresh gas from passing through more than one vaporizer.
prevents cross-contamination of the contents of one vaporizer with another by isolating the vaporizers from one another.
Proportioning/hypoxic guard systems on contemporary anesthesia machines are designed to provide a common gas outlet oxygen percentage of at LEAST:
23% - 25%
3:1 mixture of nitrous oxide to oxygen
