Ventilators Flashcards
How are bellows classified?
Direction of bellows movement during expiration
Ascending- ascends during expiratory phase
Descending- descends during expiration
Classification of reservoirs?
Bellows
Piston
Volume
Drive mechanisms of reservoir?
Pneumatic
Mechanical
Bellows uses what drive mechanism?
Pneumatic
Piston uses what drive mechanism?
Mechanical
Equation for MV
MV= TV x RR.
Volume control ventilation (VCV)
- Terminates when preselected TV delivered
- Percentage of TV is lost to compliance of system (4-5 cc/cmh2o)
Pressure control ventilation? When is it used, what is held constant, what changes?
Used with COPD, ARDS
-cycle into expiratory phase when airway pressure reaches predetermined level
- Pressure constant
- Volume and inspiratory time vary
Talk about relationship of drive gas and patient gas circuit with the bellows?
It’s a double circuit
DRIVE gas is separated and send to bellows to drive the bellows (usually 100%o2)
Pt gas circuit is inside bellows
What 2 things happen when drive gas enters the bellows?
- Pop off valve closes so no gas can escape into scavenger
- Bellows compressed and gases in bellows are delivered to patient
Is the reservoir bag included in a bellows system?
No, it is completely separated
When is pop off valve open?
Only during expiration AFTER bellows have been filled with patient gases.
Issues with bellows? (3)
1) Leaks
2) Hole in bellows
- causes hyperinflation of lungs
- o2 concentration changes
3) Ventilator relieve valve problems
- Valve open- Hypoventiatlion (going to scavenger rather than drive)
- Caused by-disconnection, ruptured valve’
- Stuck valve in closed position which causes increased PEEP and excess pressure
- Excess suction from scavenging can close the valve and cause increased pressure
What is piston ventilation similar to?
Syringe
Describe the piston ventilator circuit?
Single circuit
Which uses more gases, bellows or piston?
Bellows
Which has more accurate TV delivery, bellows or piston?
Piston
What is the reservoir bag roll during a piston ventilator?
Involved in circuit during expiration.
What happens with the peep valve during inspiratory phase of piston ventilator?
Held close
How does the fresh gas decoupling valve work?
Allows gases from piston ventilator to flow into patient and not back into CO2 scrubber/res our bag
What happens during the first step exhalation of piston ventilators?
Gas flows through CO2 scrubber into reservoir bag. Fresh gas continue to flow into reservoir bag as well. Decoupling valve is closed
What happens during second step exhalation of piston ventilator?
Breathing gases stored in reservoir bag go into the piston ventilator through open decoupling valve. Once piston fills, it reverses, CLOSING decoupling valve and sending excess gas to the scavenger.
Fresh gas inflow sends excess gas to the scavenger.
Issues with pistons
Refill even if circuit disconnection occurs
— piston ventilators May entail RA during leak, thereby diluting O2 and anesthetic agent
— may cause hypoxemia and awareness, but an alarm will alert operator
-positive pressure relief valve prevents excessively high breathing circuit pressure (60-80)
Briefly describe reflector ventilators
Drive gas and patient gas mix and acts like piston.
What is pressure?
Impedance to gas flow rate
Where is impendance encountered?
Breathing circuit
Pt airway and lungs
The backpressure generated during ventilation is a result of?
Airway resistance
Lung-thorax compliance
What is flow rate, how is it described?
Rate at which the gas volume is delivered to pt
Refers to volume change/time
Expressed in L/sec of L/min
Gotta get air in quick to get it out
Standard TV?
5-7 mL/kg
Standard RR?
8-12/min
Flow rate standard?
4-6 X MV
MV =?
TV*RR
What is physiologic I:E ratio?
1:2
How do we calculate I:E ratio?
TI = TV/flow rate (TV in L)
Ex 0.5mL/30,000mL/min=0.0167 minx60 sec= 1 second
Answer in min, change to second x60
TE
Total time for ventilation 60seconds/12 bpm= 5 second/breath
5 seconds total-1 for inhale= 4 for exhale
1:4
Oxygen content equation
Oxygen content= (hgb x %sat x 1.39mLo2)+ (PaO2 X0.0031mL o2)
Calculate paO2?
PIO2- PaCO2/ (R+F)
R= EXTRACTION RATIO 0.8
F= correction factor
F is very small number
Thus
PaO2=PIO2-Paco2/R
Relationship between Fio2 and pao2?
10% increase FIO2= increase PaO2 ~50mmHg
Low pressure alarm (disconnect alarm)
Detected by a drop in peak circuit pressure
Sub atmospheric pressure alarm
PRESSURE OF < OF = -10 CMh20.
Inhaling against machine
High peak airway pressure alarm
Detects excess pressure in system, activated at 60 cmH2o or set by practitioner
What is the best monitor to reveal a disconnect?
ETCO2 monitor
What is the most important monitor on the machine?
Oxygen analyzer. How much o2 delivering to machine
Where is the TV sensor?
Expiratory limb
Formula for exhaled TV on respirometer?
VT= VT set on vent +VT fresh gas flow- VT lost in system
Describe SIMV
Ventilator delivers preset TV at predetermined interval, patient allowed to breath spontaneously in addition to ventilator. Patient’s breaths will be supported by ventilator.
Good for waking up pt in OR.
Good for when patient may lack ability to take full breath.
If patient not reaching certain MV, the vent will assist; otherwise, breaths on own
Describe A/C ventilation.
Intermittent mode positive pressure ventilation.
Patient’s inspiratory effort creates “sub baseline” pressure in inspiratory limb and triggers vent to deliver predetermined TV
If patient’s rate doesn’t meet min rate, ventilator takes over with controlled vent mode
- all breaths are full assisted ventilator breaths
- can be pressure/volume controlled
Describe PSV?
Pressure support ventilation aids in normal breathing with predetermined level of positive a/w pressure.
Pt must be spontaneously breathing
Vent senses inspiratory effort and delivers pressure support, resulting in larger TV than pt would get on own
PSV useful to support minute ventilation and control CO2 for spontaneously-breathing pt
Good for emergence with residual NMB
Describe high frequency ventilation.. What are typical settings? When is it used?
Low tidal
What is disadvantage to O2 used for drive gas in bellows?
O2 can be depleted quickly
What happens during inspiration on piston ventilators?
1) PEEP/PMax valve closed.
2) Pressure in breathing circuit generated by the ventilator closes fresh gas decoupling valve.
3) This directs fresh gas flow toward breathing bag during inspiration so it doesnt’ interfere with TV accuracy
4) Excess gas flows past open APL bypass valve, through exhaust check valve, to the scavenger.
Breathing bag integral to circuit function
TI=?
TV/flow rate
Total time for cycle?
TI+TE
Total time (seconds) for cycle?
60/RR
Flow rate=?
4-6 xMV
