Ventilator Modes Flashcards
How are ventilators classified? (3 types)
Reservoir type: Bellows, piston (Fabius), volume
What is the function of the reservoir in ventilators?
it is how gas is delivered to the patient
What two types of drive mechanism are there for reservoirs? What’s their significance?
pneumatic and mechanical
It is how we classify ventilators.
Bellows are almost always ________. And piston is almost always ________.
pneumatic
mechanical
Bellows can be classified as either ________ or ________.
ascending during expiratory phase
descending during expiratory phase
Direction of bellows movement during ________ determines their classification.
expiration
What is the function of the drive gas? What are some significant points about its source and significance?
During inspiration, drive gas is delivered into the space between the bellows and its housing. This causes pressure to be exerted on the bellows, compressing the bellows and closing the exhalation valve (APL valve), preventing escape to scavenging system. The gas inside is 100% O2 (in case of leak in bellows) and is supplied from the pipeline, same source as pt. Cause hypoxic mixture if drive gas is air and cause pt awareness from dilution. If loss of pipeline, it could affect the functioning of the ventilator. Pressure is regulated down to 26 psi. If leak in bellows, can cause barotrauma in pt d/t higher pressures. Think of it like it’s the provider squeezing the reservoir bag.
(If using back up cylinder, the bellows will be driven by the O2 from the cylinder. Therefore it can run out.)
What 4 parameters are used to describe ventilation?
time, pressure, volume, flow rate
How is time divided during ventilation? How is it measured (unit)? How is it expressed/defined? What is a normal I:E for a spontaneously breathing patient?
Inspiration and Expiration
seconds
as a ratio (I:E), defined as number of respiratory cycles w/ in a minute
1:2
How is volume measured in relation to the ventilator and patient? What is Tv? How is it expressed? How is it expressed as VE? How is VE calculated?
Tidal volume, delivered by vent to the pt Volume of gas that pts breathe mL L VE (minute volume) = RR x Tv
What does pressure represent in regards to the ventilator? Where is it encountered? (2)
Impedance to gas flow
breathing circuit, pt’s airway/lungs
Why do we have corrugated tubing as part of the breathing circuit?
helps spread some of impedance of flow rate
What helps lower impedance in tubing? (2)
corrugating and diameter
What creates back pressure in the breathing circuit?
airway resistance
lung-thorax compliance
What type of pt’s do you need to tolerate higher peak pressures? (2)
obese pts
pt’s w/ poor lung compliance (ARDS)
How is pressure expressed on the ventilator? (3)
cmH2O, mmHg, kPA
What is flow rate? Where does it come from and where does it go? What does it refer to? How is it expressed?
rate at which gas volume is delivered to pt
from breathing system to pt
volume change over time
L/sec or L/min
How is an adequate tidal volume calculated? What about on older machines? Why?
5-7 mL/kg
8-10 mL/kg
b/c anesthesia machine were less efficient
Is the exact volume that is dialed in always given to the pt?
Not always, the ventilators are not perfectly efficient. Will get close but not exact.
What is a normal RR?
8-12/min
How is flow rate calculated?
4-6 (use 5 for ease) x minute ventilation (MV = Tv x RR)
How is inspiratory time calculated? (TI) What units do they end up in? What do you need to convert flow rate to?
TI = Tv / flow rate x 60 sec
seconds
from L/min to mL/min
How is expiratory time calculated?
expiratory rate determined by flow rate and RR/min
figure out total time for each ventilation for 1 minute cycle
subtract TI from total time to get TE and ratio.
How do older anesthesia machines function? How is Tv calculated in these machines? What were these types of vents called?
Time triggered and cycled. After certain amount of time vent cycles to expiratory phase.
Tv is calculated as a product of inspiratory time and inspiratory flow rate
“Controller ventilators”
What can modern anesthesia machines do that older ones couldn’t? What are they called?
be triggered by the pt
“Non-controlled ventilators”
What three ventilator modes are there?
AC (Assist control)
PSV (Pressure support ventilation)
SIMV (Synchronized intermittent mandatory ventilation)
On modern machines, how is a ventilation mode selected? (4 steps)
push ventilator
review settings
select mode
select desired mode
Explain volume control mode on the vent (VC)? How much Tv is always lost d/t compliance of system?
Terminates inspiration when a set Tv reached.
Second limit on inspiratory pressure guards against barotrauma.
4-5cc/cmH2O
Explain pressure control mode on the vent (PC)?
Terminates inspiration when aw pressure reaches set level. Tv and inspiratory time vary.
What does the increase in pressure of the bellows during inspiration cause to happen? (2)
APL valve closes - no gas escapes to the scavenger
bellows are compressed and gases delivered to pt
What is the gas made up of in the bellows during inspiratory phase? What about when the gas starts to travel toward the pt? What is added before the gas reaches the pt? What key safety features are downstream of the bellows and their significance (3)?
Exhaled gases: CO2, anesthetic gases, N2O, O2 etc.
When on its way to the pt, CO2 is absorbed by absorbent so no CO2 is rebreathed.
FGF
O2 sensor - ensures right amount O2 reaching pt pressure transducer port - ensures correct pressure being delivered to pt, inspiratory flow sensor - ensures right flow being delivered to pt
Describe what happens during expiration in a pneumatically driven bellows ventilator?
exhaled pt gas fills bellows (must happen before scavenging can occur), drive gas exits bellows, pressure drops to zero, expiratory valve (APL) opens (only time it opens), 2-3 cmH2O back pressure occurs from valve ball, gases go to scavenging
When is the APL valve open in the breathing cycle? Why?
exhalation, to prevent back pressure/barotrauma of pt
Is exhalation active or passive? Why?
Passive, elastic recoil of the lungs
What are advantages/disadvantages of drive gases being 100% O2?
advantage: if leak in bellows occurs it is filled with same gas given to pt
disadvantage: uses up O2 quicker
What are some issues that can occur w/ bellows? (2)
leaks - improper seating
leaks - hole in bellows (can cause hyperinflation d/t drive gas at higher flow rate, and can change O2 concentration)
What are some ventilator relief valve problems (APL)? (3)
hypoventilation caused by disconnection/ruptured valve or other damage - gas goes to scavenger rather than drive
stuck expiratory valve - adds PEEP, excess positive pressure
excess suction from scavenging can cause stuck inhalation valve causing increased pressure
Describe piston ventilators. (5)
computer controlled stepper motor (like plunger on syringe),
single circuit,
uses electricity and therefore less gas,
more accurate Tv delivery d/t piston movement (negligible d/t better technology like feedback technology, circuit compliance compensation and feed back signals),
reservoir for breathing gas is the breathing bag (participates in ventilation of pt)
Describe pneumatic driven bellows ventilator.
bellows separate driving gas from pt gas (ie, double circuit),
bellows are a reservoir for pt breathing gases,
driving force is pressurized gas flowing into bellows housing,
during inspiration driving gas enters chamber and increases pressure,
exhaled pt gas fills bellows (must happen before scavenging can occur), drive gas exits bellows, pressure drops to zero, expiratory valve (APL) opens (only time it opens), 2-3 cmH2O back pressure occurs from valve ball, gases go to scavenging
Describe piston ventilator during inspiratory phase.
inspiration causes PEEP valve in expiratory limb to close, FG coupling valve in inspiratory limb closed via pressure created in breathing circuit, FGF directed toward breathing bag, FGF flows past APL, then exhaust check valve, then to scavenger
Describe piston ventilator during expiratory phase.
Expiratory valve opens and exhaled pt gases go to breathing bag, FGF flows retrograde, piston returns to starting position which draws gases from breathing bag and the FGF supply then performs its stroke with pushes gases retrograde toward breathing bag and absorber where excess gas vents through the exhaust valve and to the scavenger
What are some considerations with piston ventilators? (5)
refill even w/ disconnect
if leak present, RA entrained, lowers O2 concentration (alarm sounds)
hypoxemia
pt awareness
positive pressure relief valve prevents excessive pressure (60-80 cmH2O)
What device is in use in the Maquet FLOW-i ventilator?
volume reflector
Describe Maquet FLOW-i ventilator during inspiration.
Reflector gas module pushes the exhaled gas back out of the volume reflector, through CO2 absorber to the patient. Fresh gas combines with the volume reflector outflow to maintain the desired oxygen and anesthetic concentration. PEEP/APL closed.
Describe Maquet FLOW-i ventilator during expiration.
At the end of exhalation, the volume reflector is filled at its proximal end (nearer the patient) with exhaled gas and is filled distally with a mixture of exhaled gases and reflector gas. PEEP/APL open.
How is oxygen delivery calculated? What does it mean? What is a normal DO2?
DO2 = CO x CaO2 (arterial O2 content/100 mL blood)
[CO = HR x SV]
[CaO2 = (Hgb x 1.34 mL O2 x SaO2 (%)) + (0.0031 mL O2 x PaO2) ]
SaO2 100% = 1, SaO2 80% = 0.8
Amount of gas transported from lungs to microcirculation.
about 1000 mL O2/min.
How many mL of O2 per 100 mL of arterial blood if PO2 100 mmHg?
0.3 mL
How is PaO2 calculated?
PaO2 (%) = PIO2 - PaCO2/R
What can cause PaO2 to be reduced and what helps it?
hypoventilation (medications that reduces RR ie versed)
having pt breathe enriched O2 mixture
In a healthy pt, each time FiO2 is increased by ________ you increase PaO2 by _________.
10%, 50 mmHg
PaO2 FiO2 100 21 150 30 200 40 250 50
What are some key alarms in ventilators?
low pressure alarm (disconnect alarm) - detect drop in pressure
sub-atmospheric (negative) pressure alarm < -10 cm H20
sustained pressure alarm 15 cmH20 > 10 sec
high peak aw pressure - activated at 60 cmH2O (should be set lower)
low O2 supply alarm
ventilator setting alarm - inability to deliver desired MV (older machines)
Which is best pt monitor to detect disconnects and tell how well you are ventilating pt?
etCO2
Which monitor is the most important monitor on the machine? Whats it do?
O2 analyzer, ensures set O2 % is what is actually being given to the pt
Generally speaking, is it better to give more volume or increase RR to achieve better ventilation in pt?
more volume, helps recruit basal alveoli
unless COPD - barotrauma
What is the best overall monitor we have?
vigilance
What is the function of the respirometer? Where is it located? How does it work?
Tv sensor
Expiratory limb
Gas flow translated into electrical pulses
How is exhaled Vt measured?
Vt = Vt set on machine + Vt FGF - Vt lost in system
What is the exhaled volume monitor?
activated automatically once breaths are sensed and always active during mechanical vent
What does the apnea alarm do?
It detects if a sufficient breath is taken by pt w/ 30 sec, based on Tv setting.
What does the low minute volume do?
This alarm will sound when the amount of air taken in per minute drops below a set value. It will act similar to a low pressure alarm and usually indicates some kind of a leak or disconnect in the system.
Compare ICU vs Anesthesia ventilators?
ICU: more powerful, greater insp pressures, greater Tv, more modes of ventilation, gas supplied by ICU ventilator directly ventilates pt
Anesthesia: CO2 absorber, driving gas never reaches pt
What is the content of the driving gas in anesthesia ventilators older vs newer machines?
100% O2 in older
Air and 100% O2 in newer
Describe Intermittent mandatory volume (IMV).
pt spont breathing
vent delivers preset Tv at preset interval, used to wean pt’s.
fixed rate, NOT synced w/ pt.
Describe Synchronized Intermittent mandatory volume (SIMV).
pt spont breathing at a predetermined interval and pt’s breath is assisted by machine
mechanical breath timed w/ beginning of spontaneous effort
good for waking pt up in OR
Describe Assist Control (AC).
pt spont breathing.
intermittent positive pressure. pt’s insp effort creates sub baseline pressure in inspiratory limb of vent circuit which triggers vent to deliver preset Tv.
if pt’s RR drops below minimum set rate, machine takes over.
all breaths are full assisted by vent.
pressure or volume controlled.
Describe Pressure Support (PSV).
pt spont breathing.
aids in normal breathing w/ preset level of positive aw pressure.
senses pt insp. effort (volume or flow) and delivers pressure support. Tv larger than pt would produce on their own (10-12 mL/kg)
Decreases WoB and delays muscle fatigue
Useful for supporting MV and controlling arterial CO2 for spont breathing pt’s during maintenance or emergence.
Describe High Frequency Ventilation. Typical settings? Goal of this mode? Where is this used? Why?
Low Tv, less than dead space, w/ high rate (60-300 bpm).
100-200 bpm, IT 33%, Drive pressure 15-30 psi.
Goal: pulm. gas exchange at lower mean aw pressures
Extracorporeal Shockwave Lithotripsy (ESWL) - breaking up kidney stones
Helps prevent pt from moving from deep breathing and moving the stones.
Describe pressure control ventilation (PCV).
Pt or time triggered, pressure limited, time cycled.
gas flow decreases as aw pressure rises and ceases as aw pressure equals set peak inflation pressure.
Tv is not fixed (volume monitor needed)
Used on pts where pressure could be high.
Useful on neonates and premies.
Describe Continuous Positive Pressure AW Pressure (CPAP). Precautions?
Positive pressure maintained through inspiration and expiration.
Provided via mask.
Pressures > 15 cmH2O can cause regurgitation (gastric insufflation) and subsequent aspiration.
What does the constant 1.36 (1.34-1.39) mL O2 represent?
mL of O2 bound per gram of Hgb .
What does the constant 0.0031 mL of O2 represent?
mL of O2 dissolved in plasma per mmHg of partial pressure.
What is a normal CaO2?
16-22 mL O2/dl or /100 mL blood
What percent of O2 bound to Hgb is released to tissues? How much left attached to Hgb?
25% (therefore 75% attached still to Hgb)
How is venous O2 content of blood calculated? At 100% SaO2? At 95%?
CvO2 = (Hgb x 1.34 mL O2 x SvO2 (%)) + (0.0031 mL O2 x PaO2)
if SaO2 100%, SvO2 75% (25% to tissues)
if SaO2 95%, SvO2 70% (25% to tissues)
How is total time of a breath cycle calculated?
Total = 60 sec / RR
What determines CO2 elimination from lungs?
Mv
How is the Mv (desired) calculated from current Mv?
Mv x CO2 = Mv (desired) x CO2 (desired)
What is controlled ventilation for?
pt’s w/out resp effort
