Equipment and Monitoring Flashcards
What components are present in the high pressure system of the anesthesia machine?
What is the gas pressure dependent upon?
Begins at cylinder
Ends at cylinder regulators.
Hanger yoke
Yoke block with check valves
cylinder pressure gauge
cylinder pressure regulator
Gas pressure = cylinder pressure
What components are present in the intermediate pressure system of the anesthesia machine?
Begins at pipeline
Ends at the flowmeter valve.
- Pipeline inlets
- Pressure gauges
- Ventilator power inlet
- Oxygen pressure failure system
- Oxygen second stage regulator
- Oxygen flush valve
- Flowmeter valve
Gas pressure = 50psi (if using pipeline) and 45 psi (if using tank)
What components are present in the low pressure system of the anesthesia machine?
Begins at the flowmeter tubes
Ends at common gas inlet
- Flowmeter tubes (Thorpe tubes)
- Vaporizers
- Check valves (if present)
- Common gas outlet (CGO)
Gas pressure = slightly above atmospheric pressure
What are the 5 tasks of oxygen in the anesthesia machine?
see photo in E&M: 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 (PISS)
The PISS prevents inadvertent misconnections of gas cylinders.
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 1 washer between the hanger yoke assembly and the stem of the tank may allow the PISS to be bypassed.
What is the PISS configuration of Air, Oxygen, and N2O?
Air = 1,5 O2= 2,5 N2O= 3,5
Describe the diameter index safety system (DISS):
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, O2, and N2O?
Air:
1900 psi
625 L
O2:
1900 psi
660L
N2O: 745 psi 1590 L wt full 20.7 lbs wt empty 14.1 lbs
The bourdon pressure gauge on an O2 cylinder reads 500psi. if the flow rate is 4 L/min, how long will this cylinder provide O2 to the patient?
- Tank capacity (L) / Full tank pressure (psi) = Contents remaining (L) / gauge pressure (psi)
- Contents remaining (L) / flow rate (L/min) = minutes left before take expires
660 L / 1900 psi = X/500 psi = 174 L
174 L/ 4 L per min = 43.4 minutes
Is it ever safe to use on O2 tank in the MRI suite?
Never take a cylinder into the MRI scanner unless it is made of non-magnetic material, such as aluminum.
An MRI safe cylinder will have 2 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.
In the event of 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.
Ex 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
Gas cylinders should never be exposed to temperatures higher than…
130F (57C) b/c temperature higher than this my lead to fire or explosions
Give 1 example of how the O2 pressure failure device (failsafe) might permit the delivery of a hypoxic mixture. (see photo in E&M Anesthesia machine)
The failsafe device checks pressure (not flow).
If there is a pipeline crossover, then the pressure of the new gas will provide the pressure to defeat the failsafe.
4 examples of how the hypoxia prevention safety device (proportioning device) might permit the delivery of hypoxic mixture:
- Oxygen pipeline crossover
- Leaks distal to the flowmeter valves
- Administration of a third gas (helium)
- 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:
A fail-safe device.
Shuts off and/or proportionately reduces N2O flow if O2 pressure drops below 20 psi.
Hypoxia prevention safety device:
Proportioning device.
Prevents you from setting a hypoxic mixture with the flow control valves.
Limits N2O flow to 3 times O2 flow (N2O max ~75%)
Describe the structure and function of the flow tubes:
Internal diameter of the flow tube is narrowest at the base and progressively widens along its ascent.
The annular space is area between the indicator float and side wall of 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 through out a wide range of flow rates.
- Laminar flow is dependent on gas viscosity (Poiseuille)
- Turbulent flow is dependent on gas density (Graham)
What is the safest flowmeter configuration on the anesthesia machine?
(see photo in E&M: Anesthesia machine)
The O2 flowmeter should always be furthest to the right!
Flowmeters are made of glass. They’re the most delicate part of the machine. A leak will allow O2 to escape the low-pressure system, and could result in hypoxic mixture.
The O2 flowmeter should be closest to manifold outlet (on right in USA). If leak develops in any other flowmeter, ti won’t reduce the FiO2 delivered to pt. If leak is in O2 meter, all bets are off.
How do you calculate the FiO2 set at the flowmeter?
FiO2= (air flow rate x21) + (O2 flow rate x100)/ total flow rate
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 ventilator + FGF during inspiration - Volume lost to compliance
When using a ventilator that couple FGF to Vt, what type of ventilator changes will impact Vt delivered to patient?
Making nearly any changes will ultimately impact the Vt delivered.
Vt increases with:
- decreased RR
- increased I:E ratio (ex 1:2 to 1:1)
- increased FGF
- Increased bellow height
Vt decreases with:
- increased respiratory rate
- decreased I:E ratio (ex 1:2 to 1:3)
- decreased FGF
- decreased bellow height
what is the vaporizer splitting ratio? (see photo in E&M: Anesthesia machine
Modern variable bypass vaporizers split FGF into 2 parts:
- Some fresh gas enters the vaporizing chamber and becomes 100% saturated with VA.
- The rest of the gas bypasses the vaporizing chamber and does not pick up any VA.
Before leaving the vaporizer, these 2 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 FGF towards the liquid anesthetic.
Setting a low concentration directs less FGF towards liquid anesthetic.
What is the pumping effect?
Pumping Effect can increase vaporizer output.
Anything that causes fas that has already left the vaporizer to re-enter the vaporizing chamber can cause the pumping effect. This is generally d/t positive pressure ventilation or use of O2 flush valve.
Variable Bypass Vaporizer:
- Model
- Splitting ratio
- Method of vaporization
- Temperature compensation
- Calibration
- Position
- Elevation compensation
1. Datex-Ohmeda Tec 4, 5, 7ADU Aldain Drager Vapor 19, 2000 2. Variable bypass (slits FGF) 3. Flow over 4. Automatic 5. Agent specific 6. out of circuit 7. Yes
Injector (Desflurane) vaporizer:
- Model
- Splitting ratio
- Method of vaporization
- Temperature compensation
- Calibration
- Position
- Elevation compensation
1. Datex-Ohmeda Tec6 Drager D-Vapor 2. Dual circuit (fresh gas is not split) 3. Gas/vapor blender (heat creates vapor that is injected into FGF) 4. Electronically heated to 39C 5. Agent specific 6. Out of circuit 7. NO
What does the oxygen analyzer measure and where is it located?
Monitors O2 concentration (not pressure) and its the only device downstream of the flowmeters that can detect a hypoxic mixture. Indeed, leaks in 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 oxygen cylinder
- disconnect the pipeline oxygen supply. THIS IS KEY STEP!
Simply turning on O2 tank would not save the patient. If an adequate O2 pipeline pressure is present (regardless of the gas inside), it will prevent O2 tank from providing O2.
Pressing the O2 flush valve exposes the breathing circuit to _____ O2 flow and _____ O2 pressure.
flow = 35-75 L/min pressure = 50psi
2 risks of pressing O2 flush valve?
Barotrauma and awareness.
Pressing it during inspiration can cause barotrauma.
B/c gas from O2 flush doesn’t pass through vaporizer, excessive use of O2 flush adds gas to breathing circuit that doesn’t contain VA. It dilutes the PP of VA and may lead to awareness.
Describe the function of the ventilator spill valve in relation to using the O2 flush valve. (see photo in E&M: anesthesia machine)
If the O2 flush is pushed during expiration, the excess flow will first fill the bellows then the rest is vented out the scavenger.
Drive gas compresses the bellows. The flow rate of the drive gas is controlled by the inspiratory flow. This gas is outside the breathing circuit.
Inspiration: Drive gas compresses bellows–> drive gas closes spill valve–> FGF from the ventilator goes to pt.
Expiration: Expired gas refills bellows–> bellows fill completely–> when circuit pressure > 2-4 cmH2O expired gas is directed through the spill valve to the scavenger.
What is volume controlled ventilation?
VC delivers a preset Vt over a predetermined time. Since Vt is fixed, the inspiratory pressure will vary as the patient’s compliance changes. The inspiratory flow is held constant during inspiration.
Fixed: Vt, inspiratory flow rate, inspiratory time
Variable: peak inspiratory pressure
What is pressure controlled ventilation?
PC delivers a preset inspiratory pressure over a predetermined time. Since pressure and time are fixed, the Vt and inspiratory flow will be variable and dependent on the patient’s lung mechanics.
If airway resistance rises or lung compliance decreases, the Vt will suffer and a higher inspiratory flow will be required to achieve the preset airway pressure.
Fixed: Peak inspiratory pressure, inspiratory time
Variable: Vt, inspiratory flow
What decreases Vt during pressure controlled ventilation?
Decreased compliance:
- Pneumoperitoneum
- Trendelenburg position
Increased resistance:
- Bronchospasm
- Kinked ETT
What increases Vt during pressure controlled ventilation?
Increased compliance:
- Release of pneumoperitoneum
- Going from Tburg to supine
Decreased resistance:
- Bronchodilator therapy
- removing airway secretions
Soda lime has become exhausted in the middle of a surgical procedure. what is the best action to take next?
You maybe tempted to increase minute ventilation. While it will remove a greater amount of CO2 from the body, it doesn’t prevent the patient from rebreathing CO2 and may lead to hypercarbia. Instead, if you are unable to replace CO2 absorbent, the appropriate action is to increase the FGF to convert the circle system into a semi-open system.
what is desiccation, and how does it apply to soda lime?
Water is required to facilitate the reaction of CO2 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. Ethyl violet informs you about exhaustion but it does NOT provide information regarding the water content of the CO2 absorbent.
In the presence of halogenated anesthetics, desiccated SL increases the production of carbon monoxide (des> iso»>sevo) and compound A in the presence of sevo.
- CO can cause carboxyhemoglobinemia
- CA can cause renal dysfunction
7 ways to monitor for disconnection of the breathing circuit:
(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)
*O2 analyzer monitors the concentration of O2 in the breathing circuit. it is NOT a disconnect monitor
What are the OSHA recommendations regarding inhalation anesthetic exposure for health care workers in the operating room?
Halogenated agents alone < or = 2 ppm
N2O alone < or = 25 ppm
Halogenated agents + N2O < or = 0.5 ppm and 25ppm respectively
Open breathing circuit:
No rebreathing
No reservoir
EX: Insufflation
Simple face mask
NC
open drop
Semi-open circuit:
No rebreathing
Has reservoir
EX: Mapleson circuit (FGF dependent on design) circle system (FGF > minute ventilation)
Semi-closed circuit:
Yes (partial) rebreathing
Has reservoir
EX: Circle system (FGF < Minute ventilation)
Closed circuit:
Yes (complete) rebreathing
Has reservoir
EX: circle system with very low FGF and APL closed
What is the purpose of the unidirectional valves in the breathing circuit?
(see photo in E&M: breathing circuits)
To ensure that gas moves in one direction.
- If a valve becomes incompetent, then the patient will rebreathe exhaled gas.
- 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.
Which mapleson circuit is most efficient for spontaneous ventilation? (see photo in E&M: breathing circuits)
Best: Mapleson A (A > DFE> CB)
Worst: B
Which mapleson circuit is most efficient for controlled ventilation? (see photo in E&M: breathing circuits)
Best: D (DFE > BC > A)
Worst: A
