Ventilation Flashcards
what are the 3 different ways ventilation may be achieved during anaesthesia?
spontaneous
manual
mechanical
what pressures are involved in spontaneous ventilation?
negative pressure
what is an example of negative pressure ventilation?
spontaneous ventilation
what pressures are involved in mechanical and manual ventilation?
positive pressure
what happens within the lungs during negative pressure ventilation?
air drawn into the lungs by creating of negative pressure by diaphragm and intercostal muscles
how does air move into the lungs during positive pressure ventilation?
system pushes gas into the lungs
what is the ideal method of ventilation during anaesthesia?
spontaneous
why is spontaneous ventilation the preferred type?
most physiologically normal
what are the 3 overriding factors which affect spontaneous ventilation?
physiological/anatomical
external
internal restriction
what are the main physiological/anatomical factors which affect spontaneous ventilation?
airway obstruction
stenotic nares
excess tissue around the airway
hypoplastic trachea
obesity and associated pressure on the diaphragm
what are the main external factors which affect spontaneous ventilation?
ET tube too small
external restriction (surgeon applying pressure / sandbags)
why can external factors effect spontaneous ventilation?
prevent the thorax from expanding
what are the main internal restriction factors which affect spontaneous ventilation?
effusions
what are the indications for assisted ventilation?
reduced drive to ventilate
inability to ventilate or ventilate effectively
what can decreased respiratory drive be caused by?
anaesthetic drugs
CNS disease
raised ICP
encephalopathy
hypothermia
what can cause an inability to ventilate?
open thoracic cavity
muscle failure
nerve failure
external factors affecting lung inflation
why will an open thoracic cavity lead to an inability to ventilate?
no negative pressure
what types of muscle failure can lead to an inability to ventilate?
NMBA (peri and post)
myasthenia gravis
what nerves may fail leading to an inability to ventilate?
intercostal
diaphragmatic
what are the external factors affecting lung inflation that can lead to an inability to ventilate?
sandbag positioning
surgeon
what can you use to identify if a patient requires ventilation?
ventilatory pattern
tidal or minute volume
blood gases
EtCO2
pulse oximitry
how can a patients ventilatory pattern be assessed?
watching the chest
how can tidal or minute volume be assessed?
spirometry
what is the most useful method for assessing patient ventilation?
looking at the chest
what equipment is required for manual ventilation?
breathing system
ET tube
what are the advantages of manual ventilation?
easy to perform
cheap
not much equipment required
what are the disadvantages of manual ventilation?
dependent on operator knowledge and skills
poor control of airway pressures
each breath may be different
operator fatigue
can be boring!
time consuming
what are the advantages of mechanical ventilation?
hands free anaesthetic
ensures appropriate volumes of gas are administered
what are the disadvantages of mechanical ventilation?
not always available
expensive
requires skill
what forces air into the lungs during ventilation?
positive pressure
what structure within the chest is affected by positive pressure ventilation?
vena cava
what is the role of the vena cava?
returning blood to pulmonary circulation
what is the effect of positive pressure ventilation on the vena cava?
pressure exerted on the veins which are easily collapsible - limits venous return
what is the effect of positive pressure ventilation on cardiac output?
venous return reduced when veins collapse under pressure so CO is reduced
in what patients is the effect of ventilation on the CVS worse?
hypovolaemic
what are the side effects of IPPV on the CVS?
decreased CO
decreased venous return
reduced stroke volume
reduced preload
reduced BP
what are the systemic effects of IPPV?
reduced organ perfusion due to CVS effects
what organs are particularly effected by reduced perfusion?
kidneys
liver
what is the role of the renin angiotensin aldosterone system?
protection of the kidneys and perfusion of the body
what is the main effect of the renin angiotensin aldosterone system?
preservation of water
what triggers the renin angiotensin aldosterone system?
identification of reduced BP by sympathetic nervous system
what is triggered by identification of reduced BP by sympathetic nervous system?
increased HR and cardiac workload
what does increased cardiac workload lead to?
increased oxygen requirement
what effect does the renin angiotensin aldosterone system have on the body?
vasoconstriction
urine retention
ADH release
what are the pulmonary side effects of IPPV?
barotrauma
sheer stress effect (volutrauma)
oxygen toxicity
when can barotrauma be seen in IPPV patients?
if pressures are too high
what causes the sheer stress effect during IPPV?
excessive air
what is oxygen toxicity?
if on 100% O2 for more than 6 hours free radicals can form which cause damage
what is the maximum length of time patients should be left on 100% O2?
up to 6 hours
what are the main ways efficacy of ventilation can be monitored?
observation
auscultation
capnography
pulse oximetry
arterial blood gases
how can observation be used to monitor efficacy of ventilation?
look at thoracic movement
check for anything which may compromise this
look at the abdomen
how can auscultation be used to monitor efficacy of ventilation?
can sounds be heard/is air entering both lungs in all areas
what may be causing reduced lung sounds on auscultation?
bronchial intubation
atelectasis of one lung or area of a lung
mass affecting lung expansion
fluid or other material in pleural space
what information cannot be gained from capnography?
tidal volume
what should be altered about ventilation if EtCO2 is high?
increase minute ventilation
what should be altered about ventilation if EtCO2 is low?
reduce minute volume
how useful is pulse oximetry for ventilation monitoring?
doesn’t indicate efficacy of ventilation and only shows perfusion in the area where it is sited
what is PaO2 a measure of?
O2 in arterial circulation
what is a better indicator of oxygen saturation than SpO2?
arterial blood gases
what should PaCO2 compare to?
EtCO2
what may a large difference between PaCO2 and EtCO2 indicate?
blood shunting within the lungs
when may a difference between PaCO2 and EtCO2 be seen in surgical patients?
if the chest is open
what should be done about ventilation if PaCO2 is high?
increase minute volume
how can minute volume be increased on a ventilator?
increase volume or rate (usually rate)
what should be done about ventilation if PaO2 is low?
look at Fi and consider increasing
potential for atelectasis
what is a ventilator?
machine designed to provide mechanical ventilation to a patient by moving air into and out of the lungs
why may a ventilator be needed?
apnoeic patient
poorly ventilated
thoracotomy
diaphragmatic rupture
NMBAs
where did the main drive to develop ventilators originate?
polio epidemic in the 50s
when may mechanical ventilation be used?
anaesthesia
ICU
why must ventilator use be justified?
is not a benign procedure
what are the main ventilator settings?
frequency of breathing
tidal volume / minute volume
I:E ratio
inspiratory flow rate
PIP
PEEP
what is described by inspiratory flow rate?
flow of gas per minute
what does PIP stand for?
peak inspiratory pressure
what does PEEP stand for?
positive end expiratory pressure
what does PIP describe?
highest pressure measured during the respiratory cycle
what does PEEP describe?
pressure applied by the ventilator at the end of each breath to ensure that alvioli are not prone to collapse
what is ventilator cycling?
the change from inspiration to expiration
what is determined by the cycling variable?
when and how the ventilator moves from inspiration to expiration
how many variables are used to determine when to cycle to expiration?
4
what are the four variables used to determine when to cycle to expiration?
pressure
volume
time
flow
how do the variables used to determine when to cycle to expiration work?
maximum parameter level before cycling to expiration
how does pressure controlled ventilation work?
ventilator maintains set airway pressure for set inspiratory time
when does pressure controlled ventilation cycle to expiration?
max pressure is pre-set by user and ventilator delivers volume of gas until this pressure is reached
how is the expiratory cycle triggered during pressure controlled ventilation?
inspiratory flow of gas is delivered until a trigger pressure is reached. This causes inspiratory cut off and will begin the expiratory cycle
when is pressure controlled ventilation unsuitable?
if lung compliance changes
when may lung compliance change?
if the chest is opened
why is pressure controlled ventilation not suitable for thoracotomy patients?
lung compliance changes so a much larger volume of gas will be delivered before the trigger is reached which cn cause over inflation of the lungs
what must be set before volume controlled ventilation can be started?
tidal volume
pressure limit
rate
inspiratory time or I:E ratio
what is the calculation for tidal volume
10-15 ml/kg
once VCV is started what should be checked?
chest expansion
CO2
what is illustrated about VCV by assessing chest expansion?
tidal volume
what is illustrated about VCV by assessing CO2?
ventilation
what is a key benefit of VCV?
doesn’t rely on airway compliance change to trigger cut off (like PCV) so set volume is given whether the chest is open or closed
what may be needed in VCV to avoid over inflation?
pressure cut off
how does time cycling ventilation work?
ventilator breath switches from inspiration to expiration after a certain time reached
how is time controlled ventilation set up?
setting respiratory rate
inspiratory time or I:E ratio
how do flow cycling ventilators work?
ventilator delivers a set flow until the total volume has been delivered then it switches to expiration
when is flow cycling ventilation often used?
paediatrics
what are the two ventilator control modes?
assist control
control
what is assist control mode?
breath is initiated by the patient
what is control mode?
breath is controlled fully by the machine
what does the I:E ratio refer to?
ratio of inspiratory to expiratory time in normal spontaneous breathing
what is the standard I:E ratio?
1:2
how do expiratory and inspiratory time compare in a I:E ratio?
expiratory is usually twice the inspiratory time
what is the total breath time of an I:E ratio of 1:2?
breath lasts 3 seconds
what does I:E ratio drive?
RR
what are the main types of ventilators?
bag squeezer
mechanical thumb
intermittent blower
volume divider
what are the types of bag squeezer ventilator?
ascending bellow
descending bellow
horizontal bellow
what is a mechanical thumb ventilator similar to?
t-piece
how does an intermittent blower ventilator work?
no bag, gas is blown in
what are bag squeezer ventilators made up of?
bag in bottle bellow
connected to a bag port
what can be set on a bag squeezer ventilator?
volume
I:E time
TV
inspiratory time
what cycling is used on mechanical thumb ventilators?
pressure
inspiratory time
where are mechanical thumb ventilators often used?
small animal anaesthesia
how do intermittent blower ventilators work?
takes driving gas and divides into smaller volumes which are used to push the gas into the patient
what are the 2 main types of intermittent blowers?
merlin
nuffield
what cycling is used on a merlin ventilator?
time
pressure
volume
what are two types of bag squeezer ventilators?
hallowell EMC 2000
JD medical (equine)
what cycling is used on hallowell EMC 2000 ventilators?
time
what cycling is used on JD medical ventilators?
pressure
how do minute volume divider ventilators work?
collect continuous flow of gas into reservoir within unit
delivered to patient under positive pressure
how is fresh gas flow calculated within minute volume divider ventilators?
intended minute volume divided into required breaths per min
what is a negative of minute volume divider ventilators?
expensive in terms of FGF
what is the main minute volume divider ventilator type?
manley MP3
what cycling is the manley MP3 run on?
VCV
what bellows are on the manley MP3?
main and storage
what can be set on manley MP3 ventilators?
TV
inspiratory time
what is involved in patient care during long periods of ventilation?
oral care
humidification of gases
ET tube care
monitoring efficacy of ventilation
periodic ‘sigh’
physiotherapy
turning patient
eye care
limb mobilisation
managing excretion
what is involved in ET tube care of patients undergoing long periods of ventilation?
suctioning
deflation of cuff
repositioning of tube
what is the benefit of a periodic sigh in longer term ventilator patients?
larger breath given every now and then
prevents lung atelectasis
