Ventilators and Ventilation Flashcards by Caitlin Holcombe

how is air drawn into the lungs during spontaneous ventilation?

via negative pressure ventilation

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what type of ventilation occurs via negative pressure ventilation?

spontaneous breathing

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how does the air move into the lungs during manual/mechanical ventilation?

via positive pressure ventilation

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during which type of ventilation is air pushed into the lungs via positive pressure?

manual or mechanical ventilation

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which physical factors can affect spontaneous ventilation?

airway obstruction
stenotic nares
excess tissue around airway
hypoplastic trachea
obesity (pressure on diaphragm)

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which external factors can affect spontaneous ventilation?

ET tube size
external restriction e.g. sandbags, surgeons hands

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what could act as internal restriction against spontaneous breathing?

effusions

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what are the indications for assisted ventilation?

reduced drive to ventilate

inability to ventilate/ventilate effectively

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why might a patient have decreased ventilatory drive?

anaesthetic drugs (respiratory depression)

CNS disease (raised ICP, encephalopathy)

hypothermia

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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)

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failure of which nerves might results in an inability to ventilate?

intercostal

diaphragmatic

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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

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what are the advantages of manual ventilation?

easy to perform

cheap - doesn’t require much equipment

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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

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what are the advantages of mechanical ventilation?

allows a hands-free anaesthetic

ensures appropriate volumes of gas are administered

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what are the disadvantages of mechanical ventilation?

not always available

expensive - initial financial outlay

requires skill

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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

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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

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when might cardiac output be even further reduced during mechanical ventilation?

if the patient is hypovolaemic

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what are the cardiovascular side effects of IPPV?

decreased venous return and CO

reduced stroke volume, pre-load

reduced BP

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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