Sherief's Anesthesia Machine Q's Flashcards

Valve
Terms Definitions
What is the formula for calculating FiO2?

What is the FiO2 for 2 L/min O2 and 3 L/min air?
FiO2 = [Qox + (0.21)Qair]/Qtotal

Where Q = flow in L/min


FiO2 = [2 + (0.21)3]/5 = 0.526 --> 52.6%
If the flow of air and oxygen are equal, what is the FiO2?
~60%
What does the hypoxic guard or proportioning system do?
It prevents the delivery of a hypoxic mixture of N2O & O2. Usually it ensures no less than 25% O2 is delivered with N2O.
What does the proportioning system do?
This O2 failure safety device prevents administration of N2O or other gases when the O2 supply fails. Whenever the O2 pressure is reduced below the manufacturer-specified minimum, the delivered O2 will not fall below 19% at the common gas outlet.
Describe the Link 25.
In the Ohmeda machine, a chain links nitrous oxide and oxygen flow control knobs, allows either to be adjusted independently, yet automatically intercedes to maintain a minimum 1:3 ratio of oxygen to nitrous oxide.

As a result of this link, no less than 25 O2% to 75% N2O (1:3) can be delivered. When the flow control valves are adjusted so that a 25% [O2] is reached, a pin on the O2 sprocket engages the O2 flow control knob and the O2 and N2O become linked.
What are 5 essential safety features of the anesthesia machine?
-Noninterchangeable gas-specific connections to pipeline inlets (DISS)1 with pressure gauges, filter, and check valve
-Pin index safety system for cylinders with pressure gauges, and at least one oxygen cylinder
-Low O2 pressure alarm
-Minimum O2/N2O ratio controller device (hypoxic guard)
-O2 failure safety device (shut-off or proportioning device)
-O2 must enter the common manifold downstream to other gases
-O2 concentration monitor & alarm
-Automatically enabled essential alarms and monitors (eg, oxygen concentration)
-Vaporizer interlock device
-Capnography & anesthetic gas measurement
-O2 flush mechanism that does not pass through vaporizers
-Breathing circuit pressure monitor & alarm
-Exhaled volume monitor
-Pulse oximetry, BP, & ECG monitoring
-Mechanical ventilator
-Scavenger system
What is the purpose of automatically enabled essential alarms and monitors (eg, oxygen concentration)?
Prevent incorrect pipeline attachments; detect failure, depletion, or fluctuation
What is the purpose of the vaporizer interlock device?
Prevent simultaneous administration of more than one volatile agent
What is the purpose of capnography & anesthetic gas measurement?
Guide ventilation; prevent anesthetic overdose; help reduce awareness
What is the purpose of having an O2 flush mechanism that does not pass through vaporizers?
Rapidly refill or flush the breathing circuit
What is the purpose of having breathing circuit pressure monitor & alarm?
Prevent pulmonary barotrauma & detect sustained positive, high peak, & negative airway pressures.
What is the purpose of having an exhaled volume monitor?
Assess ventilation and prevent hypo- or hyperventilation.
What is the purpose of having pulse oximetry, BP, & ECG monitoring?
Provide minimal standard monitoring
What is the purpose of having a mechanical ventilator?
Control alveolar ventilation more accurately and during muscle paralysis for prolonged periods
What is the purpose of the scavenger system?
Prevent contamination of the OR with waste anesthetic gases
What is the purpose of having noninterchangeable gas-specific connections to pipeline inlets (DISS)1 with pressure gauges, filter, and check valve?
Prevent incorrect pipeline attachments; detect failure, depletion, or fluctuation

DISS: diameter index safety system (male/female)
What are the parts of a DISS component?
Body, nipple, nut

small shoulder of nipple mates with small bore

larger shoulder of nipple mates with large bore
What is the purpose of the PISS for cylinders with pressure gauges, and at least one oxygen cylinder?
Prevent incorrect cylinder attachments; provide backup gas supply; detect depletion
What is the purpose of having the low O2 pressure alarm?
Detect O2 supply failure at the common gas inlet
What is the purpose of having O2 enter the common manifold downstream to other gases?
Prevent hypoxia in event of proximal gas leak
What is the purpose of having an O2 concentration monitor & alarm?
Prevent administration of hypoxic gas mixtures in event of a low-pressure system leak; precisely regulate O2 concentration
What are the 5 available volatiles in the US?
-desflurane
-isoflurane
-sevoflurane
-halothane
-enflurane

DISHEs
What is the pressure of a full cylinder of N2O?
745 psig
What is the pressure of a fully cylinder of O2?
2200 psig
What is the volume of a full cylinder of O2?
625 L
What phase is oxygen in the E cylinder?
gas
What phase is N2O in the E cylinder?
It is part liquid, part gas.
What phase is air in the E cylinder?
gas
What color is the O2 cylinder?
green
What color is the N2O cylinder?
blue
What color is the air cylinder?
yellow
What volume is a full air cylinder?
625 L
At what pressure is a full air cylinder?
2000 psig
What volume is a full cylinder of N2O?
1590 L
How can the volume of N2O in the E cylinder be determined?
By weighing the cylinder (and then doing some math...)
What is the first step of the machine check?
Verify backup ventilation equipment is available and functioning--i.e., check the Ambu bag
What are 8 main components to check in the machine check?
1. Emergency ventilation equipment
2. High pressure system (cylinder, pipeline)
3. Low pressure system (vaporizers, anything to pt)
4. Scavenging system
5. Breathing system (O2 monitor, bag/vent mode, APL)
6. Manual and automatic ventialation systems (breathing bag, uni-directional valves)
7. Monitors
8. Final position
What monitors need to be checked on the anesthesia machine?
-capnometer
-oxygen analyzer
-pressure monitor w/ high and low alarms
-pulse oximeter
-spirometer (resp vol. monitor)
What volume is a full cylinder of N2O?
1590 L
How can the volume of N2O in the E cylinder be determined?
By weighing the cylinder (and then doing some math...)
What is the first step of the machine check?
Verify backup ventilation equipment is available and functioning--i.e., check the Ambu bag
What are 8 main components to check in the machine check?
1. Emergency ventilation equipment
2. High pressure system (cylinder, pipeline)
3. Low pressure system (vaporizers, anything to pt)
4. Scavenging system
5. Breathing system (O2 monitor, bag/vent mode, APL)
6. Manual and automatic ventialation systems (breathing bag, uni-directional valves)
7. Monitors
8. Final position
What monitors need to be checked on the anesthesia machine?
-capnometer
-oxygen analyzer
-pressure monitor w/ high and low alarms
-pulse oximeter
-spirometer (resp vol. monitor)
What pressure is the least acceptable for the oxygen cylinder in the machine check?
1000 psi
What pressure is should the central pipeline read?
About 50
Why is it necessary to perform a negative pressure check on the anesthesia machine?
Also called the universal leak check, this test will identify any leaks in the machine. A high pressure check does not test for leaks upstream of the unidirectional valves (e.g., at the vaporizers). since the high pressure in the breathing circuit will only be transmitted upstream to the check valve, and no further.

The bulb is pumped until it flattens: it will remain flat if no internal leaks are present proximal to the common gas outlet.
What does the high pressure test check?
High pressure test of the breathing circuit ensures there are no leaks distal to common gas outlet
What is meant by the term, "dead space ventilation"?
In normal lungs, apprx. 2/3 of each breath reaches perfused alveoli to take part in gas exchange. This is the alveolar ventilation. The remaining 1/3 of each breath takes no part in gas exchange and is therefore termed the physiologic dead space ventilation (Vd). The relationship is as follows: alveolar ventilation(Va) = frequency (f) (Vt - Vd).

Dead space ventilation involves the volume of the respiratory gases that does not participate in gas exchange. Increasing the proportion of dead space to alveolar ventilation will lead to retention of carbon dioxide by the patient. If mechanical dead space volume equals or exceeds alveolar ventilation volume the patient will not be able to clear carbon dioxide at all.

-Anatomic dead space is comprised of the upper airway structures that do not participate in gas exchange. This includes the gases in the nasal passages, nasopharynx, larynx, trachea, and in the larger airways.
-Alveolar dead space represents those alveoli that are ventilated with fresh gas but not perfused by the pulmonary circulation. Together, anatomic and alveolar dead space is referred to as physiologic dead space.
-Mechanical or equipment dead space is made up of the endotracheal tube extending beyond the patient’s incisors, patient monitor adaptors (ETCO2, apnea alert, etc.), any adaptors used to facilitate patient/system positioning (right-angle or swivel adaptors used to reduce the risk of tracheal trauma during patient rotation), the volume within a mask, humidification management exchangers (HME), and the “Y” piece (defined as the terminal end of an F circuit or noncircle system and the inhalation/exhalation hose connector in a circle system). Exhausted soda lime or malfunctioning one-way valves can also contribute to increasing mechanical dead space.

Clinical examples of Vdalveolar ventilation include zone 1, pulmonary embolus, and destroyed alveolar septa, and such ventilation therefore does not participate in gas exchange.
What is the difference b/w a single circuit and a dual circuit ventilator?
Most anesthesia machine ventilators are classified as double-circuit, pneumatically driven ventilators. In a double-circuit system, a driving force (i.e., compressed gas) compresses a bag or bellows, which delivers gas to the patient. The driving gas is 100% O2 or an air/oxygen mixture.

With the introduction of circle breathing systems that integrate fresh gas decoupling, a resurgence has been seen in the use of mechanically driven anesthesia ventilators. These piston-type ventilators use a computer controlled stepper motor instead of compressed drive gas to actuate gas movement in the breathing system. In these systems, rather than having dual circuits with gas for the patient in one and the drive gas in another, there is a single gas circuit for the patient. They are classified as piston-driven, single-circuit ventilators. Because the patient's mechanical breath is delivered without the use of compressed gas to actuate the bellows, these systems consume less gas during the ventilator's operation than a traditional pneumatic ventilator.
How long will a nitrous oxide cylinder reading 750 psi last at a 3 L/min flow rate?
If the cylinder is not weighed, there is no way to know.

But, if it can be verified that the cylinder is full (1590 L), then the tank would last ~ 9 h.
Which steps of the machine check should be performed before EVERY case?
Steps 10-14

10. check inital status of breathing system
11. perform leak check of the breathing system
12. Test ventilation systems and unidirectional valves
13. check, calibrate, and/or set alarm limits of all monitors
14. check final status of machine.
What prevents the wrong cylinder from being attached to the oxygen inlet of the machine?
The pin index safety system
What prevents the oxygen hose from being attached to the nitrous pipeline connection?
The DISS components
If the I:E ratio is 1:2 and the RR is 10, how long is the inspiratory time?
-10 breaths/min
-6 s/breath
-6/(1+2) = 2
-I = 2, E = 4

Inspiratory time = 2 s
What prevents a vaporizer from being filled w/ the wrong agent?
The keyed system: filler receptacle only permits the intented bottle adaptor to be inserted. That is, a keyed filler top fits a specific bottle of anesthetic agent, which fits only one vaporizer.

If there is no keyed system, only vigilance will prevent inappropriate agent filling. If the inappropriately added agent has a higher vapor pressure, then the output will be excessive (and v.v.)

There may be color coding
-red: halothane
-orange: enflurane
-purple: isoflurane
-yellow: sevoflurane
-blue: desflurane
What is the difference between an open and a closed scavenging system?
Open interface – open to outside atmosphere & requires no pressure relief valves

Closed interface – closed to outside atmosphere & requires negative & positive pressure relief valves (gases only communicate w/ atomosphere through valves)
What is the Link 25 system?
The Datex-Ohmeda Link-25 Proportion Limiting Control System ensures at least 25% [O2] is delivered with N2O by having the flow controls physically interlinked.
If the fresh gas flow in a machine is 6 L/min, what is the gas flow to the scavenging system?
It should be the same unless there are leaks.
How much does doubling the length of the hose increase mechanical dead space?
Because of the unidirectional valves in a circle system, mechanical dead space consists of equiptment distal to the inspiratory and expiratory gas mixing at the Y piece. Breathing tube length does not directly affect dead space.

This is in contrast to the Mapleston circuit. Here, doubling the length would theoretically double that component's contribution to the mechanical dead space.
What components are part of the high pressure system?
-Hanger Yolk (reserve gas cylinder holder)
-Check valve (prevent reverse flow of gas)
-E Cylinders
-Cylinder Pressure Indicator (Gauge)
-Pressure Reducing Device (Regulator)

The high-pressure circuit is confined to the cylinders and the cylinders' primary pressure regulators. For oxygen, the pressure range of the high-pressure circuit extends from a high of 2200 pounds per square inch gauge (psig) to 45 psig, which is the regulated cylinder pressure. For nitrous oxide in the high-pressure circuit, pressures range from a high of 750 psig in the cylinder to a low of 45 psig.

The high pressure system receives gases from the cylinders at high, variable pressures and reduces those pressures to a lower, more constant pressure suitable for use in the machine.
What are the components of the intermediate pressure system?
-Pipeline inlet connections
-Pipeline pressure indicators
-Piping
-Gas power outlet
-Master switch
-Oxygen pressure failure devices
-Oxygen flush
-Additional reducing devices
-Flow control valves

It receives gasses from the regulator or the hospital pipeline at pressures of 40-55 psig. The intermediate-pressure circuit begins at the regulated cylinder supply sources at 45 psig, includes the pipeline sources at 50 to 55 psig, and extends to the flow control valves. Depending on the manufacturer and specific machine design, second-stage pressure regulators may be used to decrease the pipeline supply pressures to the flow control valves to even lower pressures, such as 14 or 26 psig within the intermediate-pressure circuit.
What are the components of the low pressure system?
-Flow meters
-Vaporizers
-Vaporizer mounting device
-Check valve
-Tubing b/w check valve and vaporizers
-Common gas outlet

Pressure in this system is only slightly above atmospheric and is variable.
What component is responsible for decreasing the pressure of cylinder gas to a lower, more suitable pressure?
the pressure regulators
An open or a closed scavenging system can be passive?
Only the closed system.
Where are the most likely locations of a breathing-circuit disconnect? A leak?
Frank disconnections occur most frequently between the right angle connector and the tracheal tube.

Leaks are most common in the base plate of the CO2 absorber.

Other common sites for leaks include the tracheal tube (uncuffed) or an indequately filled cuff.
Of what consequence is a malfunction of a unidirectional valve?
Rebreathing of CO2 --> hypercapnia
Which is more common in causing equipment-related adverse outcomes: misuse of anesthesia gas delivery equipment or equipment failure
misuse--with the vast majority involving disconnects or misconnects in the breathing system
Why does fresh gas flow from the common gas outlet normally contribute to the tidal volume delivered to the pt?
Because the ventilator's spill valve is closed during inspiration.
When should the O2 flush valve not be used and why?
It should not be used during the inspiratory cycle of a ventilator becuase the ventilator spill valve will be closed and the APL valve is excluded. The surge of O2 (600-1200 mL/s) and circuit pressure will be transferred to the patient's lungs.
Why might the set and actual tidal volume have large discrepancies during volume controlled ventilation?
-Breathing circuit compliance
-Gas compression
-Ventilator-fresh gas flow coupling
-leaks in the maching, the breathing circuit, or the pt's A/W
What is ventilator-fresh gas flow coupling?
In traditional ventilators, which are not fresh gas decoupled, the delivered tidal volume is the sum of the volume delivered from the ventilator and the fresh gas volume. Thus, delivered tidal volume may change as FGF is changed. Assume a 20 kg patient with a FGF of 4 L/min, a respiratory rate of 20, inspiratory:expiratory ratio of 1:2, and a tidal volume of 200 mL. During each minute, the ventilator spends 20 seconds in inspiratory time and 40 seconds in expiratory time (1:2 ratio). During this 20 seconds, the fresh gas flow is 1,320 mL (4000 mL/min FGF times 1/3). So each of the 20 breaths of 200 mL is augmented by 66 mL of fresh gas flowing while the breath is being delivered, so the total delivered tidal volume is 266 mL/breath. This is a 33% increase above what is set on the ventilator.
An open or a closed scavenging system can be passive?
Only the closed system.
Where are the most likely locations of a breathing-circuit disconnect? A leak?
Frank disconnections occur most frequently between the right angle connector and the tracheal tube.

Leaks are most common in the base plate of the CO2 absorber.

Other common sites for leaks include the tracheal tube (uncuffed) or an indequately filled cuff.
Of what consequence is a malfunction of a unidirectional valve?
Rebreathing of CO2 --> hypercapnia
Which is more common in causing equipment-related adverse outcomes: misuse of anesthesia gas delivery equipment or equipment failure
misuse--with the vast majority involving disconnects or misconnects in the breathing system
Why does fresh gas flow from the common gas outlet normally contribute to the tidal volume delivered to the pt?
Because the ventilator's spill valve is closed during inspiration.
Increasing VT will have what effect on peak A/W pressure?
Increase
What effects will increasing RR have on peak A/W pressure?
Decrease
What effect will increasing the I:E ratio have on peak A/W pressure?
Increasing I:E --> more time spent during inspiration --> greater VT --> increased A/W pressure
What is the difference b/w pressure control and volume control modes of ventilation?
VCV: Most common. Tidal volume and RR or minute volume are preset & the resultant airway pressure is a function of lung compliance & other factors. Inspiratory duration and pressure are varied to deliver a preset volume. (In modern models, there is a pressure-limiting feature to terminate inspiration when a preset pressure limit is reached.)

PCV: Peak airway pressure and I:E ratio are preset & the delivered tidal volume is a product of lung compliance & other factors. The ventiltor does not cycle to inspiration to expiration until until a preset pressure is reached. VT varies.
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