week 1 Flashcards
What measures a loss of oxygen pipeline pressure?
The pipeline pressure gauge indicates a loss of oxygen pipeline pressure.
What happens if pressure loss is profound?
The oxygen low-pressure alarm sounds, and the fail-safe valves halt the delivery of all other gases.
Problems with pipeline supply (5)
Pressure loss or excess pressure
Cross-connection of gas delivery pipelines
Contamination
Leaks
Theft of nitrous oxide
Pipeline oxygen is stored at what temperature?
Delivered to the hospital and stored as a liquid, at -184C.
What is pipeline O2 made from?
Made from fractional distillation of liquid air.
What are some Cylinder Safety we need to know?
*No oils or lubricants
*Temperature should be under 130 degrees Fahrenheit (57ºC)
*Keep connections tight
*Don’t interchange regulators/gauges
Keep closed when not using
Open slowly
Don’t stand them up on their own
When attaching to AGM
Crack valve 1st to prevent dust going into machine
New washer for every new tank, never more than 1 washer
What are 3 safety devices on a cylinder?
Frangible disc that bursts under pressure
Valve that opens under extreme pressure
Fusible plug made of Wood’s metal
What does a Hanger Yoke do?
Orients the cylinder
Provides a gas tight seal
Ensures unidirectional flow
Contains a filter required by standard
Check valve to minimize transfilling
The cylinder valve consists of:
body, the outlet port where gas exits, a conical depression for the securing screw, PISS pins, and safety relief devices.
CO2 service pressure is ____ and weighs____
838 psi (full tank is 1,590L)
When CO2 or N2O’s liquid runs out, how much is left in the tank?
Once liquid is gone tank is ¾ empty (~136L left)
International color for oxygen and air?
Oxygen: White, Air: White and black
CO2 psi and temp in cylinder is:
838 psi, < 31 C in gas and liquid
N2O temp in cylinder is:
< 37 C in gas and liquid
Helium psi and weight
2000 psi, 500 L
Nitrogen psi and temp (same as O2)
2000psi, 660L
H-size cylinder is what diameter
H – 4’ x 9” diameter
Bedside when no pipeline available
In OR - N2 compressed gas
How many positions for pins in PISS system?
7
5 tasks of oxygen in the AGM
- O2 supply failure alarm system
If pipeline or cylinder pressure falls less than 30 psig - O2 Pressure Failure Device
AKA Fail-safe valve
Machine will not deliver less than a certain percent of oxygen when also administering a non-life sustaining gas (example nitrous oxide)
Cuts off nitrous oxide or heliox if oxygen concentration gets too low - Ventilator drive Gas
Ventilator power (to bellow)
Auxiliary flowmeter
Jet vent devices- O2 supply line - Flowmeters →circle system → patient
- O2 flush valve → circle system → patient (typically used when not connected to patient, never ever press flush in children, usually used for machine checks)
Bypasses flowmeters
Range between 25-75 L/m directly from pipeline or cylinder depending on model
Open scavenger:
*No risk of barotrauma
*Too much suction = room air entrained
*Too little suction= waste gas goes into OR (expose personnel)
*Contains reservoir
Open to atmosphere
Only used with active systems (suction)
No positive or negative pressure relief valves
Closed scavenger:
*Doesn’t remove excess fresh gas from circuit (because it removes excess exhaled waste anesthetic gases WAG)
*Contains reservoir
Uses pressure valves
If passive system (no suction)- needs positive pressure relief
If active (suction) needs both positive and negative pressure relief
Contains reservoir
Scavenger formula for removing excess gas:
FGF - volume of gas lost to pts O2 consumption
Convenience receptacles are protected by: _____ or _____
Blowing a ____, what would happen?
These convenience receptacles are protected by circuit breakers or fuses. In theory, blowing a fuse in one of these circuits should not affect the operation of the rest of the machine.
Devices which require electric power supply
Cardiopulmonary bypass pump/oxygenators
Air warming blankets
Gas/vapor blenders (Suprane Tec 6) or vaporizers with electronic controls (Aladin cassettes in the ADU or Aisys)
Mechanical ventilators
Electronic monitors
Room and surgical field illumination
Digital flowmeter displays for electronic flowmeters
What devices/techniques do not need electrical power supply?
*Mechanical flowmeters
*Scavenging
*Battery operated peripheral nerve stimulators or intravenous
*Monitoring using the anesthetist’s five senses
*Variable bypass vaporizers (Tec 4, 5, 7, Vapor 19 or 2000)
Bag-mask ventilation
Laryngoscope, flashlights
Intravenous bolus or infusion pumps
What is high pressure leak test and how to test for it?
Tests integrity of low-pressure system and breathing circuit
Close APL valve to pressurize circuit to 30cm H2O
Fail = circuit does not remain pressurized ~ 30cm H2O
Should be completed between every patient/ when the circuit is changed
Guideline for Oxygen Pipeline Supply Failure
Do not attempt to fix the oxygen analyzer. It must be trusted until proven inaccurate.
Turn on backup oxygen cylinder on machine fully and disconnect pipeline. If inspired 02 does not increase, ventilate by bag mask and initiate TIVA (total IV anesthetic)
Call for help,
Use low flow of oxygen.
Turn off ventilator and bag manually
Call for help, calculate the time remaining on the cylinder.
Find out details of problem and how long.
DO NOT reconnect patient to pipeline unless it is tested.
Ventilate with an oxygen source or room air via bag valve mask.
Why would Oxygen Pressure Failure Device (Failsafe) alarm?
Depleted O2 tank
Decreased pressure from pipeline
Disconnected O2 hose
When will a Fail safe Device NOT alarm?
Pipeline Crossover
Crack/Leak in the flowmeters (upstream from fail safe device)
How to test if fail safe is working properly?
You turn on O2 and N2O. Then, disconnect the oxygen pipeline and oxygen cylinder and leave the nitrous on until the oxygen reads before 0. It should alarm and stop N2O from running.
When will a hypoxic mixture still occur
*Administration of 3rd gas (Helium)
Pipeline crossover
Leak distal to flowmeter valves
scavenger malfunctioning
Defective mechanic or pneumatic components
Dilution of oxygen due to high concentration of inhaled anesthetics (barash p. 1620)
Minimum FiO2 permitted: 25%
Flowmeter pressure is ____
16 psi
Flowmeter where is the largest diameter
Thorpe tube is gas specific and tapered with largest diameter at top
What is Reynolds number and the formula?
Predicts flow rate through tube; ([DensityDiameterVelocity]/Viscosity)
What is Reynolds number for laminar flow, dependent on ____?
Re< 2,000 = laminar flow (stable, smooth, and predictable)
Depends on gas viscosity
What is Reynolds number for turbulent flow, dependent on ____?
Re> 4,000 = turbulent flow (chaotic, irregular motion and mixing of fluid particles.)
Depends on gas density
What is Reynolds number for transitional flow?
Re 2,000-4,000 = transitional flow
What is fresh gas coupling?
couple fresh gas flow to the set tidal volume
What is fresh gas coupling Tidal volume delivered to the pt?
Vt set on vent + FGF during inspiration- volume lost to circuit compliance
How to calculate fresh gas coupling?
Step 1: Convert Fresh Gas Flow (FGF) from L/min to mL/min (multiply by 1,000)
Example: 4 L/min = 4,000 mL/min.
Step 2: Multiply FGF (ml/min) by the I:E Ratio (If the ratio is 1:2 = 1/3).
This is the amount of FGF delivered during the inspiratory phase.
Ex: 4,000 mL/min×(1/3)=1,333 mL
Step 3: Calculate Tidal Volume per Breath (Divide the insp. FGF by RR)
Ex: 1,333 mL/min/ 10 breathsperminute=133 mL
Step 4: Add set Tidal Volume on ventilator to insp. FGF
Example: 500 mL+133 mL=633 mL
How does an increase in respiratory rate affect delivered tidal volume?
decrease Vt
What decreases Tidal volume delivered in terms of I:E ratio, FGF, bellows height?
decrease I:E (1:2 to 1:3), decrease FGF, decreases bellows height
What increases Tidal volume delivered in terms of I:E ratio, FGF, bellows height?
increase I:E (1:2 to 1:1), increase FGF, increases bellows height
How does a decrease in respiratory rate affect delivered tidal volume?
increase Vt
How does positive pressure in a breathing circuit affect the gas volume delivered to the patient?
causes gas to expand, this will not reach the pt
*This must be subtracted from total Vt
Increase the set tidal volume slightly if circuit compliance and pressure loss are known to reduce the delivered volume.
What do modern ventilators do to circuit compliance?
compensate for circuit compliance when delivering Vt
What is formula for circuit compliance?
Change in volume/change in pressure
How does splitting ratio work?
fresh gas enters vaporizer, some gas encounters the anesthetic, and the rest bypasses it, in the end they mix and create the final concentration
What happens to vaporizer output at low flow rates (<250 mL/min)?
The output is less than the dial setting
Due to low density of liquid – insufficient turbulence is generated to advance molecules upward
What happens to vaporizer output at extremely high flow rates and high concentrations?
The output may be less than the dial setting due to incomplete mixing and saturation of the gas with anesthetic vapor.
Pumping effect is enhanced by 3 things:
Low FGF
Low concentration dial setting
Low levels of liquid anesthetic in vaporizing chamber
Pumping effect is minimized by
modern vaporizers
Pumping effect is caused by (2):
(PPV) positive pressure ventilation or use of O2 flush valve
How does pumping effect cause increase vaporizer output?
Causes gas to re-enter the vaporizing chamber
Where is the most common location for leak in vaporizer? (not most common cause)
internal leak in vaporizer
When can you detect a vaporizer leak?
when its turned on
Calculate amount of anesthetic used; formula
Vol% x FGF (L/min) x 3
Tipping of Vaporizer
Drain vaporizer
Turn dial to highest setting and run it with high FGF for ~ 30min
Why does the TEC 6 vaporizer not rely on fresh gas flow for vaporization?
It uses a dual-circuit design and injector method, where desflurane vapor is injected into the fresh gas flow rather than being vaporized directly by it.
“Gas/Vapor Blender” Injects a precise amount of desflurane directly into the FGF
How does the TEC 6 vaporizer heat desflurane?
Heats liquid to 39 C
increase 2 atmospheres
What adjustment is needed on the TEC 6 vaporizer at lower ambient pressure (e.g., higher altitude)?
A higher setting on the dial is required to achieve the desired anesthetic concentration.
What adjustment is needed on the TEC 6 vaporizer at higher ambient pressure (e.g., in a hyperbaric oxygen tank)?
A lower setting on the dial is required to achieve the desired anesthetic concentration.
Variable bypass models:
Datex-Ohmeda Tec 4, 5, 7ADU
Aladin
Drager Vapor 19, 2000
Injector models:
Datex-Ohmeda Tec 6
Drager D-Vapor
What is the cons for Galvanic Fuel Cell O2 analyzer?
needs calibrated daily and replaced over time
2 functions of Oxygen Analyzer:
detect pipeline crossover and hypoxic mixture from leak in O2 flowmeter
What is the pros for Pragmatic device O2 analyzer?
self-calibrating, no consumable parts, faster response than galvanic fuel-cell
What happens to the ventilator spill valve when its open during exhalation?
When open during exhalation excess gas goes to scavenger after refilling the bag
(Intrinsic PEEP) >2-4 cm H2O
What happens to the ventilator spill valve when its closed during inspiration?
Vt goes to the patient and not the scavenger
Ventilator spill valve only present in ____
Pneumatic ventilators only (ventilator drive gas)
Advantages of Heat and Moisture Exchanger (HME)
No need for water or electrical power source
No risk of hyperthermia
No risk of overhydration
No risk of burns
No risk of electrical shock.
many serve as effective bacterial and viral filters.
How does the effectiveness of HMEs compare to water-based, electrical devices?
not as effective for warming and humidifying the patient’s airway.
What are the cons of HME? (3)
increase dead space
increase the work of breathing
Airway obstruction can occur if the HME becomes blocked with fluid, blood, secretions, or nebulized drugs.
What should be done to assess for a mechanical defect in the HME?
The peak pressure should be measured both with and without the HME in place to assess for a mechanical defect in the device. If defect, can cause airway resistance
What are Hydrophobic HMEs? Pros vs Cons
Pros:
Have a hydrophobic membrane with small pores that is pleated to provide a greater surface area.
Hydrophobic HME’s may also be more effective at preventing the transmission of the hepatitis C virus than hygroscopic HME’s.
The airway resistance of hydrophobic HME’s increases only slightly if wet.
Cons:
High ambient temperature may decrease the effectiveness
What are Hygroscopic HMEs? Pros vs Cons
Pros:
Contain a wool, foam, or paper like material that is coated with a chemical that helps it to retain moisture.
more effective at preserving heat and humidity
Cons:
If become wet, they may lose their ability to filter airborne pathogens and airway resistance may increase substantially
What occurs when there is a leak in bellows (with driving gas)?
Diluted gas
Hypoxia (if bellows are driven of air)
Increased FiO2 (if bellows are driven on O2)
Loss of agent – risk of awareness
Pneumatic Bellows Ventilator is a single or double circuit why?
Double circuit
What must a descending bellow have? Why?
Must have a CO2/apnea alarm because it can still move even after disconnected.
Piston ventilator has 2 pressure relief valves:
Positive – valve opens when pressure is too high in circuit
Negative- entrains air when too much negative pressure occurs
Pros of Piston ventilator:
Decouples FGF from ventilator
Consistent tidal volumes
Does not add intrinsic PEEP
Use an electric motor to compress the piston to generate positive pressure, it doesn’t use oxygen to run the ventilator
Doesn’t deplete O2 tank in pipeline failure situation
Breathing bag in ventilator circuit during mechanical ventilation
VCV; what is variable?
Inspiratory pressure depends on pts pulmonary compliance
Inspiratory flow on VCV is ____?
constant
In VCV, Increase in airway resistance or decreased lung compliance can increase_____
increased peak inspiratory pressure (PIP)
PCV; what is variable?
Vt & inspiratory flow
In PCV, decrease in lung compliance or rise in airway resistance =
decreased Vt
Inspiratory flow on PCV is ____?
decelerating pattern, starts high to achieve pressure and then slows to maintain pressure
In PCV, Name two factors that can decrease compliance and reduce VT.
Pneumoperitoneum and the Trendelenburg position
In PCV, What are two examples of increased resistance that can decrease VT?
Bronchospasm and a kinked ETT increase resistance and decrease VT.
In PCV, Name two factors that can increase compliance and increase VT.
Release of pneumoperitoneum and transitioning from the Trendelenburg position to supine increase compliance and VT.
In PCV, What interventions can decrease resistance and increase VT?
Bronchodilator therapy and removing airway secretions decrease resistance and increase VT.
Why is PCV preferred in patients with low lung compliance?
PCV delivers tidal volumes at lower peak inspiratory pressures, which is beneficial in patients with low compliance, such as in pregnancy, obesity, laparoscopy, or ARDS.
In which conditions is high peak inspiratory pressure (PIP) particularly dangerous, making PCV a better option?
High PIP is dangerous in patients with LMAs, neonates, or emphysema, where PCV helps limit peak pressures.
Why is PCV good in cases where there is a need to compensate for a leak in the ventilation system?
PCV maintains consistent pressure despite leaks, making it suitable for cases with LMAs or uncuffed ETTs in children. (Limits PIP)
How does PCV improve ventilation in laparoscopic surgeries or patients in the Trendelenburg position?
PCV improves alveolar recruitment and maintains ventilation by compensating for reduced compliance caused by increased intra-abdominal pressure.
Why is PCV preferred for ventilating neonates or patients with fragile lungs?
PCV avoids high peak inspiratory pressures, reducing the risk of barotrauma in fragile lungs, such as in neonates or emphysema patients.
Cons for Controlled Mandatory Ventilation (CMV)
Doesn’t compensate for pt initiating breaths
Vent asynchrony can occur
Which mode is best for apneic patients?
Controlled Mandatory Ventilation (CMV)
Assist control (ACV)
Spontaneous breaths receive full preset Vt
If pt over breaths it my lead to hyperventilation
Which mode is great for LMA and weaning?
Synchronized Intermittent Mandatory Ventilation (SIMV)
PSV
PSV-Pro
What is Synchronized Intermittent Mandatory Ventilation (SIMV) ?
Machine initiates breaths and gives a preset Vt and RR, but pt can breathe in between machine breaths
Machine breaths will coordinate with patient’s spontaneous respirations
Better synchrony between vent and pt
Spontaneous breaths can be augmented with pressure support
Guarantees minimum minute ventilation
What is PCV-VG good for?
Great for cases with compliance changes( example- laparoscopic surgery)
Only uses the amount of pressure needed to achieve set tidal volume
Difference between CPAP and PSV
PSV only gives pressure during inspiration
Airway Pressure Release Ventilation (APRV)
Used for spontaneous ventilation
Like BiPAP, but high level of CPAP throughout most of the respiratory cycle
High level of pressure is released at preset intervals to facilitate exhalation
What mode is good for ARDS?
Airway Pressure Release Ventilation (APRV)
Inverse Ratio Ventilation (IRV) - must be paralyzed
High-Frequency Ventilation delivers ____
small tidal volumes below dead space at very high respiratory rates
High-Frequency Ventilation: gas transport occurs by ____
molecular diffusion, coaxial flow, and high velocity flow
3 types of High-Frequency Ventilation:
High frequency oscillation
High frequency jet ventilation
High frequency percussive ventilation
How does soda lime work?
base neutralizes an acid (CO2)
Soda lime exists in what kind of circuits?
closed and semi-closed circuits
What is the first reaction in the interaction of carbon dioxide with soda lime?
CO₂ + H₂O → H₂CO₃
Carbon dioxide reacts with water to form carbonic acid
In the second step of the reaction, what does carbonic acid react with, and what are the products?
H₂CO₃ + 2 NaOH → Na₂CO₃ + 2 H₂O + heat
Carbonic acid reacts with sodium hydroxide to form sodium carbonate, water, and heat
What is the final step in the reaction between sodium carbonate and calcium hydroxide?
Na₂CO₃ + Ca(OH)₂ → CaCO₃ + 2 NaOH
Sodium carbonate reacts with calcium hydroxide to produce calcium carbonate and sodium hydroxide
How to Minimize Risk of CO and Compound A
Low FGF
Turn off FGF between cases
Change all absorbent at once
Change canister when they turn purple
Change canister if unsure about level of hydration
Downside of Calcium Hydroxide Lime (Amsorb Plus) :
Absorbs less CO2 (10.6L/100g absorbent vs 26L/100g soda lime)
More expensive
If circuit disconnect is the 1st common reason for low pressure circuit, what is the 2nd common reason?
CO2 absorber
Poor seal
Defective canister- cracked
What is the first step in the reaction between carbon dioxide and calcium hydroxide lime (Amsorb Plus)?
CO₂ + H₂O → H₂CO₃
Carbon dioxide reacts with water to form carbonic acid
In the second step of AmSorb, what does carbonic acid react with, and what are the products?
H₂CO₃ + Ca(OH)₂ → CaCO₃ + 2 H₂O + heat
Carbonic acid reacts with calcium hydroxide to form calcium carbonate, water, and heat
What are the monitors/devices for Circuit Disconnect?
Pressure
Volume
ETCO2
Your vigilance
Why would there be a sustained high circuit pressure during manual ventilation?
Scavenger obstructed
Scavenger relief valves have failed
Disconnect scavenging system if possible
Use Ambu bag to ventilate patient
What happens if high circuit pressure is relieved after removing ventilator from system?
Ventilator relief valve is malfunctioning
Ventilator must be repaired and is NOT TO BE USED!!
How to respond to sustained high circuit pressure?
Switch to “bag mode” or manual ventilation
Try manually ventilating the patient
Assess and treat patient related causes
