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?
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 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.
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 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
Describe the type of EEG waveforms.
What are the key threshold values for macroshock and microshock?
