ventilators Flashcards
which setting are intermittent blowers found? what are the pros and cons?
ITU
many versatile modes and good for both paeds and adults.
these are not suitable for volatile anaesthetic agents
they are inherently complex.
how are ventilators classified
positive or negative pressure - negative pressure include the iron lung and not used anymore. Modern ventilators use positive pressure ventilation.
further classified by their mechanism …
intermittent blowers, bag squeezer or minute volume dividers
OR by their cycling method - volume, time or pressure cycled.
OR via their generation - pressure generation or flow generation. However most modern ventilators can switch between these.
can also be classified as invasive vs non invasive
what is the difference between a flow and pressure generator ventilator?
flow - constant flow generated until a volume is given (closely linked to vol control ventilation). presure will vary depending on compliance of lungs.
pressure - constant pressure given for set time. volume will vary depending on compliance of lungs. (closely linked to pressure control ventilation)
how may a ventilator be powered?
electric or battery powered
some may be pneumatically powered - compressed air, levers and valves
some may be a combination of the above
what is the difference between invasive and non-invasive ventilation?
invasive - ET tube / LMA
non-invasive - tight fitting mask
what is meant by cycling method..
the method that flicks between inspiration and expiration. e.g. volume cycled when a certain volume is reached it switches
time cycling is usually used and there is a set inspiratory and expiratory time.
others include pressure and flow cycling
manual cycling is used by jet ventilators
give an example of a minute volume divider, intermittent blower and bag squeezer..
are there any other methods of ventilation you know?
min vol divider - manley MP3
intermittent blower - penlon nuffield
bag squeezer - Ohmenda
other methods include - jet ventilation, oscilators, electromagnetic ventilators (found in ITU)
what do you know about artificial ventilation?
movement of air into a persons lungs through either applying positive or negative pressure
to replace or support a patients breathing
useful in critically ill in ITU, in theatre and emergencies
Tell me about volume control ventilation
a constant flow is delivered until volume is reached. then flow stops and lungs allowed to recoil to move air out.
Pressure builds up during inspiration which will depend on lung compliance.
volume will gradually rise as lungs fill and then drop during exhalation
usually inspiratory pause before expiration.
flow rate will depend on volume set and time needed to get to that.
does not compensate well for leaks.
risk of barotrauma if non-compliant lungs.
tell me about pressure control ventilation…
gas at a constant pressure is delivered for certain inspiratory time.
flow rate and volume will vary depending on lung compliance.
higher mean airway pressure than vol control so better at recruiting alveoli and better oxygenation. And less risk of barotruama and compensates for leaks
however may not get volumes required or too much volume depending on compliance.
how can ventilator modes be classified?
pressure or volume controlled
type of cycling
manual mode
pressure support or controlled ventilation
more sophisticated modes- APRV, SIMV
what is pressure support ventilation?
ventilator senses inspiration from patient and then supports this by applying postive pressure to drive volume in.
better tolerated by patients if not paralysed/ not deep and helps with weaning
what is meant by CPAP?
continuous positive airway pressure
positive pressure applied and patient allowed to spontaneously breath over this.
can be used in NIV as well as invasive.
good for OSA as splints open airways
good for pulmonary oedema
what is BiPAP?
bilevel positive airway pressure for NIV
Inspiratory Positive Airway Pressure (IPAP): A higher pressure is applied when the patient inhales, helping to keep the airways open and making it easier to breathe in.
Expiratory Positive Airway Pressure (EPAP): (PEEP) A lower pressure is applied when the patient exhales, allowing easier exhalation while still maintaining airway support
good for COPD
remember BiPAP = ventilation
CPAP = oxygenation
what is SIMV?
synchronised intermittent mandatory ventilation..
PS with PC
when no inspiratory efforts - a min resp rate is sets and delivers via PC
when inspiratory effort sensed - ventilator supports.
draw a pressure time graph for VC / PC ventilation showing how it can change with changes to compliance ..
what is PEEP?
positive end expiratory pressure
physiological PEEP is applied by vocal cords to help splint open alveoli at end of expiration also brings lungs up to the steep part of compliance curve.
after intubation this is lost
PEEP applied to replicate - set at 5cmH20
PEEP can be increased to help open collapsed alveoli and improve oxygenation e.g. in laparoscopic surgery, head down, COPD
what is APRV?
airway pressure release ventilaiton
pressure controlled ventilation varient
used in patients with ARDS on ITU
to improve oxygenation
high pressure maintained during long inspiratory phase
then pressure released for short expiratory phase to allow CO2 removal.
theory is consistent high pressure keeps lung open for longer and alveoli recruitment
describe the mechanism behind the iron lung ventilation
patient lies in a iron box with head outside and a tight seal. air is removed from the box to create a negative pressure
this causes negative intrapleural pressure
this causes lungs to inflate - as air enters from surroundings outside the box down pressure gradient
draw and label a pressure time graph for IPPV for pressure control
PIP = PEEP + PS
draw a volume pressure curve for IPPV
demonstrate what happens to a pressure volume curve with changes to compliance..
how does a minute volume divider work?
2 sets of bellows
during inspiration..
main bellow delivers a set volume to the patient and FGF is directed to fill a smaller bellow
during expiration..
when the small bellow is filled, it triggers a valve to switch such that the main bellow is closed off at the patient end and open to allow small bellow to fill this. During this phase the patient expires whilst the large bellow is filling.
when the small bellow is empty a valve swictches again and the cycle repeats.
hence small bellow size and FGF rate determines the RR and time for inspiration/expiration
the size of large bellow determines TV
e.g. manley mp3
explain the following graph..
this graph is for volume controlled ventilation. the pressure rises gradually until a peak - A
there is then an inspiratory pause which allows airflow to distribute - pendeluft effect
this causes a drop in pressure - B - Pplateau pressure
this occurs because different alveoli units take different times to fill.
tell me about the bag in bottle mechanism for ventilation…
pneumatically powered ventilator with electronic controls.
most common seen on anaesthetic machines
uses both FGF and pressurised gas.
the bag is allowed to fill with FGF and then during inspiration phase, high pressure gas fills the compartment surrounding the bag to ‘squeeze’ and empty this into the patient.
central processing unit switches valves on and off for cycling between inspiration and expiration.
during expiration, the flow of high pressure is blocked and instead the bag fills with FGF.
how do intermittent blowers work?
positive pressure ventilator used in penlon nuffield.
pneumatically powered using high pressure source
flow generating and time cycling.
there are 2 limbs (exp and insp) and a shuttle valve that switches between the two limbs. when the valve is pushed across, it allows high pressure gas to push and displace space such that FGF is pushed into patient during inspiration.
the valve switches to occlude the inspiratory limb and patient can expire.
the inspiratory time is controlled via a valve (on the right of image) the more screwed down the longer it takes the pressurised gas to fill this right hand part of chamber. once it fills this and exceeds a pressure it will push the shuttle across.
there is also a flow control valve which will alter the rate of pressurised gas going towards breathing circuit and pushing FGF
why does the driving gas of an intermittent blower never reach the patient?
the expiratory limb is a lot bigger than TV so it simply displaces the volume.
tell me about the manual jet ventilator.. e.g. manujet
positive pressure ventilator
pneumatically powered flow generator
with manual cycling.
these are also known as low frequency jet ventilators
long thin tube connected to pipeline gas at 4bar pressure 02. and at the other end connected to a canula/bronchoscope.
trigger available to control gas flow
by the time it reaches the patient, pressure drops to 25cmH20 due to narrow tubing.
Some entrainment of air too due to bernoulli
TV is a combination of entrained air and injected air. can never be 100% O2.
