ventilators

Question 1

which setting are intermittent blowers found? what are the pros and cons?

Answer 1

ITU
many versatile modes and good for both paeds and adults.

these are not suitable for volatile anaesthetic agents
they are inherently complex.

Question 2

how are ventilators classified

Answer 2

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

Question 3

what is the difference between a flow and pressure generator ventilator?

Answer 3

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)

Question 4

how may a ventilator be powered?

Answer 4

electric or battery powered
some may be pneumatically powered - compressed air, levers and valves
some may be a combination of the above

Question 5

what is the difference between invasive and non-invasive ventilation?

Answer 5

invasive - ET tube / LMA
non-invasive - tight fitting mask

Question 6

what is meant by cycling method..

Answer 6

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

Question 7

give an example of a minute volume divider, intermittent blower and bag squeezer..

are there any other methods of ventilation you know?

Answer 7

min vol divider - manley MP3
intermittent blower - penlon nuffield
bag squeezer - Ohmenda

other methods include - jet ventilation, oscilators, electromagnetic ventilators (found in ITU)

Question 8

what do you know about artificial ventilation?

Answer 8

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

Question 9

Tell me about volume control ventilation

Answer 9

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.

Question 10

tell me about pressure control ventilation…

Answer 10

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.

Question 11

how can ventilator modes be classified?

Answer 11

pressure or volume controlled
type of cycling
manual mode
pressure support or controlled ventilation
more sophisticated modes- APRV, SIMV

Question 12

what is pressure support ventilation?

Answer 12

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

Question 13

what is meant by CPAP?

Answer 13

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

Question 14

what is BiPAP?

Answer 14

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

Question 15

what is SIMV?

Answer 15

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.

Question 16

draw a pressure time graph for VC / PC ventilation showing how it can change with changes to compliance ..

Answer 16

Question 17

what is PEEP?

Answer 17

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

Question 18

what is APRV?

Answer 18

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

Question 19

describe the mechanism behind the iron lung ventilation

Answer 19

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

Question 20

draw and label a pressure time graph for IPPV for pressure control

Answer 20

PIP = PEEP + PS

Question 21

draw a volume pressure curve for IPPV

Answer 21

Question 22

demonstrate what happens to a pressure volume curve with changes to compliance..

Answer 22

Question 23

how does a minute volume divider work?

Answer 23

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

Question 24

explain the following graph..

Answer 24

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.

Question 25

why might the I:E ratio be reversed?

Answer 25

normally 1:2 ratio used sometimes reverse so longer in inspiration - this can help allow time for gases to distribute through lungs without needing to increase pressure to improve oxygenation used in ARDS (similar concept to APRV) also improves CO2 removal by recruiting more alveoli. however only tolerated by anaesthetised patient. and there is a risk of gas trapping if exp not long enough. also has haemodynamic effects - reduces venous return.

Question 26

tell me about the bag in bottle mechanism for ventilation...

Answer 26

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.

Question 27

pros and cons of bag squeezer..

Answer 27

visual indication and simple to use. can add mapleson D or circle breathing system can be used for paeds - varying sizes of bag however needs both FGF and high pressure - wasted bulky

Question 28

what are the safety features of the bag squeezer?

Answer 28

pressure relief valves also pressure in system is fed back to central processing unit to help monitor

Question 29

Tell me about the oxylog ventilators and how they have developed overtime...

Answer 29

commonly used portable ventilator for transfer and emergencies Has developed from oxylog original to oxylog 3000 which is in modern use. the oxylog original was a pneumatically driven and controlled ventilator with flow generation and time cycling. The oxylog 1000 - includes airway and gas pressure monitoring 2000 - pneumatically driven with electronic controls and electronic displays + spon mode 3000 - advanced modes PS, SIMV, CPAP plus graphical display. can be both pressure or flow generated.

Question 30

what are the pros and cons of the oxylog

Answer 30

pros.. portable compact easy to use/ intuitive robust safety features - alarms can operate on battery and the original was pneumatically powered. 3000 can be used for paeds cons needs battery / electricity

Question 31

pros and cons of minute volume divider..

Answer 31

PROS: * does not need pressurised gas flow - uses FGF for operation and for patient - less waste * no electrics needed * simple * can incorportate an APL valve and reservoir bag CONS: * only one mode

Question 32

how do intermittent blowers work?

Answer 32

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

Question 33

pros and cons of intermittent blowers..

Answer 33

PROS * simple, compact * can be used in paeds - newton valve attachment * no electricity needed * can be used with differnet breathing systems * has been developed into more versaltile modes for ITU use CONS * need presurised gas as well as FGF * not suitable for volailtes * more complex

Question 34

why does the driving gas of an intermittent blower never reach the patient?

Answer 34

the expiratory limb is a lot bigger than TV so it simply displaces the volume.

Question 35

compare and constrast the penlon nufflied and manley

Answer 35

Both positive pressure ventilators both pneumatically driven and powered and therefore can be used in remote locations. However the Manley only requires FGF whereas the penlon needs pressurised gas as well as FGF the manley is a minute volume divider whereas penlon is a intermittent blower. both use time cycling. penlon is more versatile can be used in paeds and newer versions have more sophisticated modes. both can be used with different breathing systems.

Question 36

describe the features of an ITU ventilator

Answer 36

needs to be versatile - different modes, for paeds etc alarms for safety features monitoring ability - flow, pressure, temp electronic main disadvantage is its complexity and requires trained staff.

Question 37

tell me about the manual jet ventilator.. e.g. manujet

Answer 37

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.

Question 38

pros and cons of a manujet - i.e. low fre jet ventilator..

Answer 38

pros: practical for emergencies and short airway proceedures e.g. bronchoscopy. and rescue ventilation - CICO when canula in cricoid simple to use cons * cant use anaesthetic gas * cant deliver 100% O2 and FiO2 is variable and unknown depending on entrainment * no humidification * risk of baro/ volutrauma - doesnt measure volumes and presures. * movement of vocal cords can affect airway surgery

Question 39

what is high frequency jet ventilation?

Answer 39

pneumatically powered, flow generating ventilator v. high frequency RR = 600 breaths/ min ( 10Hz) , low tidal volume. delivers via cannula, entrainment of air. works by diffusion, convection currents and pendeluft effect

Question 40

what are the features of an ideal portable ventilator..

Answer 40

small and lightweight battery powered with good life intuitive and easy to use robust - more likely to get dropped many modes of ventilation paeds and adults can be used with different breathing circuits.

Question 41

pros and cons of high freq jet ventilation..

Answer 41

pros: * less alveolar distension and airway pressures - good for ards * airway vibration from high frequency can help clear secretions cons * risk of gas trapping * unable to humidify * no volatiles * hard to measure gas concs and pressure.

Question 41

what are high frequency jet ventilators?

Answer 41

pneumatically powered flow generating ventilators use low TV and very high frequency (12 to 600 cycles/min) - time cycling. gas exchange achieved via * simple diffusion * connective streaming - high velocity jet from ventilation travels down centre of airway * pendeluft - small TV enter larger airways and slowly filter to smaller.

Question 42

what are high frequency oscilating ventilators?

Answer 42

type of high freq ventilator that uses an oscilating diaphragm with v. high resp rate (180 to 900 cycles/min) and low volumes. (time cycled) unlike jet ventilators uses an ET tube, sealed and no entrainment of air. gas exchange achieved via * simple diffusion * connective streaming - high velocity jet from ventilation travels down centre of airway * pendeluft - small TV enter larger airways and slowly filter to smaller.

Question 43

features of an ideal ventilator..

Answer 43

user friendly.. easy to use, transportable, light weight uses - versatile modes, paeds and adults cost - cheap and robust safety features - measures gases, volumes, pressures. and has alarms.

Question 44

what is volume control autoflow ?

Answer 44

volume delivered but variable flow to reduce peak airway pressures.

Question 45

what checks should be completed before transporting a patient on a ventilator?

Answer 45

check ventilator setting and alarm setting check O2 cylinders - how much left, back up water circuit available other airway equiptment ongoing sedation emergency drugs monitoring - including capnography trained assistant

Question 46

what are the physiological effects of positive pressure ventilation?

Answer 46

Respiratory... * barotrauma, volutrauma and gas trapping --> pneumothorax * ventilator dependancy - weakening of diaphragm - hard to wean Cardiovascular.. * reduced venous return and hence preload * reduced venous drainage from head and neck * increased PVR and hence afterload on RV * LV unloading - increased thoracic pressure means LV needs to generate less pressure to eject blood - hence less work * reduced preload may be beneficial if at particular point on starling renal - reduced CO - reduced renal perfusion and AKI - RAAS activated - water retention neuro - increased ICP hepatice - reduced CO, poor blood flow, reduced drug metabolism

Question 47

benefits of PEEP?

Answer 47

splints open alveoli - reduces atelectasis and shunting - improves oxygenation shifts volumes to steeper part of compliance curve reduces gas trapping as keeps alveoli open for long i.e. reduces closing volume. reduces alveolar oedema

Question 48

describe the safety features of most modern ventilators...

Answer 48

most modern ventilators have pre-set volumes, pressures and alarms for the input data e.g. age, height, weight alarms - low and high pressure alarms e.g. low if theres a leak. gas supply alarms pressure relief valves - protect machine and patient although safety features are present it is the role of the anaesthetist to ensure appropriate settings (volume, pressures, alarm limits)

Question 49

what methods can be employed to lower CO2?

Answer 49

increase minute volume check soda lime not exhausted can increase FGF increase I:E ratio

Question 50

what is permissive hypercapnia?

Answer 50

allowing someone to have high PaCO2 within reason to compromise airway pressures and baro/volutrauama

Question 51

you get an ABG and PaO2 is low what do you do?

Answer 51

check saturations and clinically assess patient if sats are okay, PaO2 is only small proportion should also check Hb

Question 52

What is CMV mode ?

Answer 52

Continous mandatory ventilation Set volume/ pressure and resp rate No regard to patients ventilation Will breathe over any patient efforts (Unlike SIMV)

Question 53

What are the causes of ventilator associated lung injury

Answer 53

Volutruama Barotruama May lead to pneumothorax Atelectotrauma - alveolar sheer stress caused by repeated opening and closing - can be fixed by using lower volumes and maintaining peep to keep them open

Question 54

How is ventilator associated lung injury minimised ?

Answer 54

Keeping airway pressure below 30cmH20 - alarms Keep volumes 6ml/kg -8ml/kg (lower than 6 in ARDS) PEEP Permissive hypercapnia Avoid hyperoxia

Question 55

How is ventilator associated lung injury minimised ?

Answer 55

Keeping airway pressure below 30cmH20 - alarms Keep volumes 6ml/kg -8ml/kg (lower than 6 in ARDS) PEEP Permissive hypercapnia Avoid hyperoxia

Question 56

What is automatic tube compensation?

Answer 56

The ventilator produces a higher pressure than what is set to compensate for resistance of tubing