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How are anesthesia ventilators classified? What are the 3 classifications?
By power source: gas, electricity, or both
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What are the two different drive mechanisms for the ventilators? What is their power source?
- 1) Pneumatic (bellows) - both
- 2) Piston - electricity
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Where does the air INSIDE the bellow come from?
- 1) Flowmeters
- 2) vaporizers
- 3) gas expired by the patient
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What is the drive gas for the pneumatic system bellow?
100% O2, compressed air, or a mixture of air and O2
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What is the drive gas for the piston system bellows?
It doesn't have one - it uses electricity to drive the bellows
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How does the Piston Ventilator protect against excessive positive pressure and negative end expiratory pressure?
- 1) Positive pressure relief valve which opens at > 75 cm H2O
- 2) Negative pressure relief valve which opens and allows room air in to bellow at < -8 cm H2O
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What are the advantages of a Piston Ventilator?
- 1) Quiet
- 2) No PEEP
- 3) Greater Precision
- 4) Measures compliance and leaks with transducer near piston - eliminates costly sensor close to pt's airway
- 5) Electricity is the driving force for the piston so ok to use during O2 pipeline pressure failure
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How does the piston provide greater precision?
- Compliance and air leak compensation
- Fresh gas flow decoupling
- rigid piston
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What are disadvantages to the Piston Vent?
- 1) loss of visible bellow
- 2) difficult to hear regular cycling
- 3) cannot easily accommodate NRB circuit
- 4) Potential for NEEP if valve is stuck
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What stops the flow of gas during a volume control ventilation mode?
- 1) when the set Vt is delivered
- 2) when a certain pressure is reached
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When does an ascending bellow fill? which direction does it go?
fills during expiration - rises
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What is 1 things that makes an ascending bellow safer than a descending bellow?
It will not fill if there is a disconnect
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What is the ventilator relief valve?
an outlet for excess gas during mechanical ventilation - prevents buildup of volume and pressure in breathing circuit and lungs by popping open and venting excess gas once the bellows is full.
Closed during inspiration.
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Why is it important that the spill valve closes during inspiration?
to prevent volume from entering the scavenger system instead of the patient's lungs
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What is one result on the patient airway of the ventilator relief valve?
It creates 3 cm H20 of PEEP when bellows is completely full prior to end exhalation
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What are the 4 types of pressure alarms?
- 1) High pressure
- 2) Pressure below threshold for 15-30s (apnea, disconnect)
- 3) continuing high pressure
- 4) negative pressure
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What does the reverse flow alarm usually mean?
incompetent expiratory flow unidirectional valve
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How does the machine know to alarm for apnea/disconnect? (3 ways)
1) Chemical Monitoring (ETCO2)
2) Mechanical Monitoring (low peak pressure, failure to return Vt, failure of standing bellows to fill, failure of manual breathing bag to fill during mech ventilation for FG decoupling)
3) Electronic Monitoring (failure of hanging bellows to fill completely sensed by infrared)
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What does PSV absolutely require?
A spontaneously breathing patient
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How does the vent protect from apnea during PSV?
by having a backup mode
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What is the benefit of PSV?
It decreases patient discomfort & bucking while increasing Vt and Vm.
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What is the typical VCV setup?
- Vt 10 ml/kg
- Rate 6-12
- PEEP 0
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What is the solution to most ventilator alarms?
Turn the vent off, manually bag the patient, remedy the cause of the alarm
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What is the typical Peak Airway Pressure alarm limit?
40
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What is the shape of a volume controlled breath?
shark fin
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What is the shape of a pressure controlled breath?
rectangle
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What is the limiting factor in PCV?
pressure - volume is delivered until a set pressure is reached
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What types of patients benefit from PCV? (2 categories, 7 patient populations)
High risk w/ high insp pressures (LMA ventilation, emphysema, neonates/infants)
Low compliance who need higher Vt (pregnancy, laprascopic surgeries, morbid obesity, ARDS)
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What is a typical PCV setting?
- Pressure limit 20
- Rate 6 - 12
- PEEP 0
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What is unique about SIMV?
It has a sensing component which decreases the likelihood of asynchronous breathing
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What is the trigger window during SIMV?
what percentage of the expiratory pause the vent monitors for patient effort (%)
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What is the sensitivity during SIMV?
how much NIF the patient must generate to trigger a breath
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What happens during each PCV-VG breath?
The ventilator delivers a breath while dynamically adjusting the inspiratory pressure to ensure the entire volume is delivered within the Pmax limits
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What 2 things does PCV-VG allow better control of?
- 1) PIP
- 2) arterial CO2 (via Vm control)
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When does the O2/CO2 exchange occur during APRV?
during the release (low pressure) phase
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How does APRV change your anesthetic plan?
- 1) Pt will remain on ICU vent
- 2) Must use TIVA - no vapors
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Under what circumstance would you change the I:E ratio? from what to what?
obstructive type diseases
from 1:2 to ~ 1:3
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What are 4 benefits of PEEP?
- 1) Increases arterial oxygenation
- 2) Increases pulmonary compliance
- 3) Increases Functional Residual Capacity
- 4) Reduces atelectasis
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When do you institute PEEP?
When you cannot maintain a PaO2 > 60 on 50% FiO2
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What are the 4 hazards of PEEP?
- 1) Decreased CO d/t decreased venous return
- 2) barotrauma
- 3) increased extravascular lung water (impede lymph flow)
- 4) V/Q mismatch d/t over distended alveoli
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What is a common fresh gas flow rate? What is the rate for creating a non rebreather?
4 liters/min
1-1.5x Mv = ~ 5-8 liters/min
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When should you use the non rebreather rate for FGF?
- 1) preoxygenation/denitrogenation
- 2) Induction
- 3) Emergence
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What are the advantages of low rate fresh gas flows?
- 1) economy
- 2) decreased pollution
- 3) estimation of agent uptake and O2 consumption
- 4) becomes a closed circuit
- 5) buffers changes in inspired or expired concentration
- 6) conserves heat and humidity
- 7) less danger of barotrauma
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What is the lowest FGF you ever want to use with sevo?
1 liter/min
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What are the disadvantages of low fresh gas flows?
- 1) more attention required
- 2) inability to quickly alter inspired concentrations
- 3) danger of hypercarbia
- 4) absorbent used at faster rate
- 5) accumulation of undesired gases
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What are the undesired gases that accumulate with low fresh gas flow?
- CO
- acetone
- methane
- H2
- ethanol
- anesthetic agent metabolites
- Argon
- N2
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When should you not use low fresh gas flows?
- 1) cases < 15 mins
- 2) old or leaky machine
- 3) mask or LMA anesthesia
- 4) uncuffed ETT
- 5) bronchoscopy
- ABSOLUTELY NOT:
- 1) High oxygen demand
- 2) you are trying to wash out toxic gases
- 3) broken/missing necessary equip (o2 analyzer, agent analyzer, absorbent)
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How do you denitrogenate a patient?
- 1) set FGF to 6-8 liters/min
- 2) Open APL valve fully
- 3) achieve good mask seal and administer 100% FiO2
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What is the most common site of disconnection?
Y Piece
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How can you detect disconnection?
ETCO2 monitoring with audible alarm or with precordial/esophageal stethoscope
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What are some of the causes of obstruction?
- 1) tracheal tube occluded
- 2) incorrect insertion of flow-direction-sensitive components (PEEP valve)
- 3) excess flow in to circuit (flush valve)
- 4) bellows leaks
- 5) malfunction of ventilator relief valve
- 6) APL valve too tight
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