Ventilators and Ventilation Flashcards
how is air drawn into the lungs during spontaneous ventilation?
via negative pressure ventilation
what type of ventilation occurs via negative pressure ventilation?
spontaneous breathing
how does the air move into the lungs during manual/mechanical ventilation?
via positive pressure ventilation
during which type of ventilation is air pushed into the lungs via positive pressure?
manual or mechanical ventilation
which physical factors can affect spontaneous ventilation?
airway obstruction
stenotic nares
excess tissue around airway
hypoplastic trachea
obesity (pressure on diaphragm)
which external factors can affect spontaneous ventilation?
ET tube size
external restriction e.g. sandbags, surgeons hands
what could act as internal restriction against spontaneous breathing?
effusions
what are the indications for assisted ventilation?
reduced drive to ventilate
inability to ventilate/ventilate effectively
why might a patient have decreased ventilatory drive?
anaesthetic drugs (respiratory depression)
CNS disease (raised ICP, encephalopathy)
hypothermia
why might a patient have an inability to ventilate?
open thoracic cavity
muscle failure (NMBAs, myasthenia gravis)
nerve failure
external factors affecting lung inflation (sandbags, surgeons hands)
failure of which nerves might results in an inability to ventilate?
intercostal
diaphragmatic
how might we recognise the need to ventilate our patient?
ventilatory pattern - watch chest movements
tidal/minute volume (spirometry)
blood gases
end tidal CO2
pulse oximetry
what are the advantages of manual ventilation?
easy to perform
cheap - doesn’t require much equipment
what are the disadvantages of manual ventilation?
dependent on the operator
poor control of airway pressures
each breath may be different
operator fatigue
boring and time consuming
what are the advantages of mechanical ventilation?
allows a hands-free anaesthetic
ensures appropriate volumes of gas are administered
what are the disadvantages of mechanical ventilation?
not always available
expensive - initial financial outlay
requires skill
what happens to the large veins of the vena cava during IPPV?
positive pressure in the thoracic cavity exerts pressure on the veins and compresses them
why is cardiac output reduced during mechanical ventilation?
pressure exerted in the thoracic cavity compresses the large veins of the vena cava
results in reduced venous return to the heart and in turn reduced CO
when might cardiac output be even further reduced during mechanical ventilation?
if the patient is hypovolaemic
what are the cardiovascular side effects of IPPV?
decreased venous return and CO
reduced stroke volume, pre-load
reduced BP
what are the other main side effects of IPPV (not directly CVS related)?
reduced hepatic/renal perfusion
possible barotrauma and volutrauma
oxygen toxicity
how can oxygen toxicity due to mechanical ventilation be avoided?
ideally shouldn’t be on 100% oxygen for more than 6 hours
how does extended time on 100% O2 cause damage?
forms damaging free radicals
how can we monitor the efficacy of ventilation?
observation of thoracic movements
auscultation - should hear sounds/air entering both lungs at all areas
capnography
pulse ox
arterial blood gases
what should be considered if we cannot hear sounds/air entering both lungs at all areas during mechanical ventilation?
bronchial intubation
atelectasis
mass affecting lung expansion
fluid/material in pleural space
why doesn’t pulse ox indicate efficacy of ventilation?
only tells you how perfused that specific area is e.g. tongue, toe
what is PaO2?
partial pressure of oxygen in the arterial circulation
what is PaCO2 comparable with?
etCO2 - very close, may be slight difference
what might be happening if there is a large difference between PaCO2 and etCO2?
shunting of blood in the lungs
what might indicate that there is shunting of blood in the lungs?
large difference between etCO2 and PaCO2
what might affect the relationship between PaCO2 and etCO2?
chest cavity open
what might we need to do if the PaCO2 is high?
increase minute volume (usually by changing rate)
what might we need to do if the PaCO2 is low?
look at fresh inspired O2 and amend if necessary
start thinking about possibility of atelectasis
what is peak inspiratory pressure (PIP)?
the highest pressure measured during the respiratory cycle
what is the highest pressure measured during the respiratory cycle known as?
peak inspiratory pressure (PIP
what is positive end pressure ventilation (PEEP)?
pressure applied by the ventilator at the end of each breath to ensure the alveoli are not prone to collapse
what is cycling?
the change from inspiration to expiration
what is the cycling variable?
the variable which determines when and how the ventilator moves from inspiration to expiration
which variable determines when and how the ventilator moves from inspiration to expiration?
the cycling variable
what are the 4 possible cycling variables?
pressure
volume
time
flow
how does pressure controlled ventilation work?
the ventilator maintains a set airway pressure for a set inspiratory time until the max pressure is reached
what can affect pressure controlled ventilation
if lung compliance changes (e.g. open chest) - larger volume of gas delivered before trigger is reached = over-inflation
how does volume controlled ventilation work?
tidal volume, pressure limit, rate/inspiratory time/I:E ratio are all set
check expansion and CO2
what is the advantage of volume controlled ventilation over pressure controlled?
doesn’t rely on airway compliance change - set volume given if chest open or closed
how does time controlled ventilation work?
switches from insp to exp after a set time is reached
done by setting RR, inspiratory time or I:E ratio
how does flow cycling work?
the ventilator delivers a set flow until the total volume has been delivered
useful in paediatrics
what is assist control mode?
where the breath is initiated by the patient?
what is control mode?
where the breath is controlled by the ventilator
what is the standard I:E ratio?
1:2
what types of ventilator are available?
bag squeezer (bellows)
mechanical thumb (similar to t piece)
intermittent blower
volume divider
what should we consider in terms of patient care during long periods of ventilation?
mouth care e.g. rinses, eye care
humidification of gases
ET tube care - suction, deflate cuff and reposition
monitor efficacy of ventilation
physiotherapy, turning patient, limb mobilisation
