Understanding Mechanical Ventilation: Initiation, Maintenance, and Weaning

[Music] welcome to online anesthesia video of the week today topic is presented by Dr

P nagalakshmi mdda She is currently working as professor in Department of anesthesiology at Shri manula vagar

Medical College pondicheri she did her mbbs in tunal Medical College and da in madurai Medical College she has

completed her MD from tanjavur Medical College she has published eight papers in various National and international

Publications being member and past Secretary of Isa during 20221 she is very much active in conducting academic

activities her area of Interest are Airway management cardiac anesthesia and Regional

anesthesia good morning um uh I would like to thank uh Edward sir for this uh uh opportunity to discuss a session on

initiation uh maintenance and meaning from ventilators I'm Dr nagaki Professor Department of

anesthesiology uh from pacher so uh I would like to discuss about how we put a patient on why we put the patient on uh

mechanical ventilation how do we maintain the patient and how do we ve the patient from the ventilator this is

a basic uh um uh academic session where you understand why the patient has to be put on ventilator what are the clinical

parameters what are the subjective parameters objective parameters to put the patient on

ventilator so the learning objectives of this um presentation is what are the indications what do you define as acute

respiratory failure a few case scenarios the initial ventilator modes and settings and vening protocol spontaneous

breathing trial and what is vening failure so now the objectives of mechanical ventilation why the patient

has to be put on mechanical ventilation can be divided into physiological objectives clinical objectives and

laboratory parameters now what are the physiological objectives or why does the patient require a mechanical ventilation

uh it is initially to support the support or manipulates the pulmonary gas exchange that is alular ventilation or

alular oxygenation alular ventilation is the ability of the patient to achieve an UK CAPIC ventilation that is carbon

dioxide wash out and Alvar oxygen is to maintain the adequate oxygen delivery to the

tissues or to increase the lung volume that is if the patient has an atelectasis to prevent or treat the

atelectasis with adequate inspirator lung inflation we put the patient on mechanical inflation and to reduce the

work of breathing this is in cases of cardiac patients or post anesthesia care patients so the patient will be deeply

sedated or paralyzed and to support and to uh reduce the work of breathing of the patient we put the patient on

mechanical these are the physiological objectives why we put the patient on ventilation so the clinical objectives

are to reverse the acute respiratory failure and respiratory distress to reverse hypoxemia to prevent or reverse

atelectasis and to maintain the F FRC to prevent respiratory uh muscle faake to permit sedation and paralysis and to

reduce the systemic or mardial oxygen uh consumption and to minimize the associated complications and to reduce

the mortality so now how do we Define acute acute respiratory failure acute respiratory failure is

defined as the inability of a patient to maintain his P2 P2 and pH within acceptable limits and hypoxic

respiratory failure is where there is a severe ventilation perfusion mismatch diffusion defects shunting alv or

hypoventilation due to age or inadequate inspired oxygen or it could be because of the hypercapnic respiratory failure

that is the ventilatory failure that is inability to wash out the carbon dioxide and uh because of the failure of the

ventilator third one is the failure of the ventilatory center it is the inability to maintain P2 because of the

central nervous system disorders neuromuscular disorders or disorders that increase the work of breathing so

the increased work of breathing may be due to chest trauma or neox hemothorax so here even though the respiratory

centers in the brain stem are intact the ability to maintain the effort to breathe is seriously compromised so the

patient tries to compensate by increasing the minute ventilation or increasing the respiratory respiratory

rate so minute ventilation is tidal volume into respiratory rate when the tidal volume is not achieved by the

patient then he tries to compensate by increasing the respirator rate so now uh when we talk about the clinical and the

uh physiological parameters we have to have some uh laboratory values to indicate ventilation so those are

defined by the pH P2 and Dead Space to tital volume ratio so these are the measures of ventilation

and the measures of oxygenation are pa2 that is alv arterial oxygen difference and uh ratio of arterial to

alv P2 and PF ratio so the critical values are if the pH is less than 2 7.25 or if the pac2 is more than 55 and

it is increasing and if the Dead Space to tidal volume ratio is more than 6 then we put the patient on mechanical

ventilation we understand that the ventilation is severely compromised and we put the patient on ventilation now

coming on to the oxygen part the pa2 is less than 70 against a normal value of 80 to 100 or if the alv oxygen gradient

is more than 450 with oxygen or if the PF ratio is less than 200 we understand the oxygenation part of respiration is

severely compromised and then the patient might require ventilation so now there are the ventilatory mechanics

which indicate mechanical ventilation these are the parameters which are measured by

spirometry uh so maximum inspiratory pressure expiratory pressure vital capacity tital volume respiratory

frequency or respiratory rate and forced expiratory volume at the first second and Peak expiratory flow rate so these

are the ventilatory mechanics and if they are compromised below a particular value that is the critical value they

may indicate the need for mechanical ventilation also so this can be uh measured by the

spomer a handheld spirometer or a neemo Tachi meter so I would like to share a few

case records so which indicate mechanical ventilation here is a 23y old woman who was taken to the hospital

after ingesting an unknown amount of drugs and alcohol she was found unconscious and in the emergency

department she was unresponsive to verbal commands her pulse rate was racing and 124 beats per minute blood

pressure was 8050 and the respiratory rate is 15 bread Perman it respirations are shallow so the bread sounds uh

reveal Co bilateral Co crackles in the bases and the AGG values indicate P2 of 60 which is lesser P CO2 of 69 mm of

mercury which indicates that is carbon dioxide accumulation and the pH is 7.24 so the second case is a 30-year old

man who is admitted to the hospital emergency uh Department who compl L of weakness of Limbs tingling of hands and

feet and lack of coordination two weeks prior he had been treated for a flu like viral illness the respiratory care

practitioner obtains a b basal ABG value and respiratory mechanics which was initially within normal limits that is

maximum inspiratory pressure is minus 70 cm of water and the vital capacity was 4.3 L against a predicted 4.8 L value

and over a 36 period he started deterior and the uh patient was uh monitored over um every 3 to 4 hours and values

progressively decreased to a vital capacity of 2.5 L which is 44% of the predicted value and a maximum inspir

pressure of minus 32 cm of water and a repeat ABG evaluation on rier shows a po2 of 70 mm of mercury P2 of 48 and a

pH of 7.34 so a worsening um status also indicates mechanical

ventilation to prevent the mortality in the patient so now the third case is a 15year old girl with a life-threatening

exacerbation of asthma who has been treated in the emergency department with oxygen CTIC steroids helos and beta2

adrenergic Bronco diales she has a respiratory rate of 7 37 breaths per minute and her breathing was labored

bilateral inspiratory and expiratory bees were present in both the lungs and the peak EXP flow is 70 L per minute and

F1 was 75 L ABG value shows P2 of 73 mm of mercury P of 28 and a bicarbonate of 19 m per liter and pH of

7.46 so arterial oxygen to alv oxygen ratio is 23 so here the patient has a labored breathing and needs uh

ventilation by cab or mechanical ventilation so now having said all these things what

are the initial modes we start the patient up what are its uh types so the ventilator modes can be either volume

cycled or a pressure cycled ventilation and a combination of both volume or pressure cycled volume cycled is the one

where the ventilator delivers a constant volume with each breath and here the pressures arway pressures may vary and

pressure cycled is the one where the ventilator delivers a constant Conant pressure during each breath and the

volume may vary so this depends on patients body size diagnosis pathophysiology

laboratory recordings and initial ventilatory modes which we put the patient on are only Tre uh served as

starting points and they are tiated to um achieve the required targets the patient might need a full or partial

ventilatory support depending upon those things the patient can be put on initial ventilatory modes so now the startup

modes are volume control ventilation pressure control ventilation synchronized intermittent mandatory

ventilation and pressure support ventilation the last one that is the pressure support ventilation or a

spontaneous mode can also serve as a Ving mode so factors to consider while we set

up the initial ventilator parameters are level of support needed whether the patient needs a full or partial

ventilatory support whether the patient has can trigger their own breath and what is the indication pathophysiology

of the disas and if there is any air flow limitation like an asthma or presence of air leak as in bronol plural

fysa or if there is a neurot truma which has a concern for elevated intracranial pressure so now uh this screen shows you

how a volume control ventilation works here in the volume control ventilation we set up oxygen concentration a PE and

a respiratory rate and a tidal volume so this tidal volume is fixed that is the tital volume is fixed at 6 to 8 ml per

kg and this is fixed so the one in the side panel shows the parameters which is um which the patient parameters so here

if you see so there is a peak pressure that is 34 which is variable because the volume is fixed so this shows the mean

pressure PE respirator oxygen and minute ventilation how much is the tidal inspired volume and how much is the

tidal expiratory volume so this is about the volume control ventilation now coming on to the pressure control

ventilation pressure control ventilation if you see the lower panel here we set up um the oxygen concentration Peep And

respirat as in the volume control mode and the pressure control above the peep is set so here the pressure is fixed and

the side panel shows the respiratory rate is almost varying according to the breathing pattern or according to the

compliance of the lung so the pressure is fixed and the volume is variable so if you see here the pressure is the peak

pressure is 22 which is an addition of uh the peep and the pressure control which we have Set uh and also you can

see the varying tidal inspiratory volume and the tidal expiratory volume this is about the pressure control ventilation

now coming on to synchronized intermittent manditory ventilation here the ventilator allows the patient to

breathe himself also the patient might need a partial ventilatory support and the ventilator allows the patient to

breathe and support the ventilation which the patient triggers and if the patient is not

breathing the ventilator uh delivers a uh machine breath so this is synchronized intermittent mandatory

ventilation so there is an S period where the Meine delivers a breath and there is a spontaneous period where the

patient takes a breath and then comes the uh sa

period so the synchronized intermittent mandatory ventilation can be pressure

supported or volume supported so here if you see the first breath is the machine breath where the trigger is time

triggered or the machine triggered and the second breath uh if you notice the pink line is the patient triggered

breath so and the uh ventilation is supported by the machine so now coming on to the fourth

mode which is the pressure control mode of the spontaneous mode here the patient needs a partial ventilator support and

the patient can breathe on his own so all the breaths are patient triggered here and the breath is supported by the

ventilator so here we set up only the oxygen concentration peep that oxygen concentration is F2 the peep and the

pressure support above the peep and patient uh triggers the breath if support if suppose the patient

does not breathe on a pressure support then we set up the backup ventilation so backup ventilation mode is the mode

where the machine falls back to pressure control mode or a volume control mode as we

set if the patient falls into apnea so we set up an apnea time if the patient has an apnea of more than 20 seconds or

30 seconds as we said then it falls back to a backup ventilation mode which acts like a volume control or a pressure

control mode so what are the initial parameters which we set up um while starting up the patient on mechanical

ventilation those are the respiratory tidal volume sensitivity if the patient is put on partial ventilatory support

flow rate flow waveform and inspiratory and expiratory ratio so there are few triggers triggers

um are the ones which start up each breath so what are those triggers they can be either time triggered or patient

triggered time triggered is the one where the ventilator breaths ventilator initiates a bre breath and the patient

triggered breaths can be either flow triggered or pressure trigger so what triggers a breath is

what is called as trigger sensitivity see the time triggered or patient triggered so time triggered is the one

where the machine initiates a breath at a particular interval so if we keep a respiratory rate of 15 which spans over

60 seconds that is 1 minute then the machine triggers breath at every 4th second so this is time triggered

breathing which we set up in the control modes so what is pressure triggering both pressure triggering and flow

triggering are uh when the patient initiates a breath so pressure triggering is the one where the the

pressure drop at the beginning of inspiration is sensed by the ventilator and it is triggered it is supported so

this is this is pressure triggering so if you see here in the inspirated tubing there is no negative pressure which is

developed and in the expiratory tubing there is a minus 3 cm of water which is sensed by the ventilator and the breath

is initiated now flow triggering is one where there is a constant flow of air flow and if the patient takes a breath

the drop in the air flow in The Returned limb is calculated by the ventilator and is sensed as a

breath so now these are the settings tidal volume ventilator rate p uh fa2 inspiratory flow trigger

sensitivity and pressure support levels inspiratory pressures so if you see here tidal

volume is set between 6 ml per 6 to 8 ml per kg in uh volume limited ventilation and in pressure limited ventilation the

inspiratory pressure is set to Target uh to achieve a desire tidal volume according to the pressure support and

respiratory rate PE are all the same and uh fa2 we set according to the requirement or if it is hypoxemic

respiratory failure we put the patient on higher F2 and inspiratory flow rate pattern to Target an inspiratory

expiratory ratio of 1 is to 2 or 1 is to3 and trigger sensitivity can be flow triggered or pressure triggered and

pressure support levels as we desire so this are the initial parameters which we set the patient on

ventilator and they can be titrated as and when required to achieve the target SP2 P2 and

pco2 so now coming on to the P what setting up an optimal peep what is a Peep Peep is the application of pressure

at the end of expiration to prevent the airway collapse so p is positive end expiratory pressure where we sit up uh

required amount of pressure at the end of expiration to prevent the collapse of the alveol so if you see the respiratory

bre pattern breath pattern this is the pressure volume Loop where the pressure is plotted and volume is in the y- axis

the initial zone is the zone of ectasis this is the list compant Zone and then uh this point is called as a lower

inflection point after which there is a steep race in the volume and uh the change in volume per change in pressure

will be very high and then comes the upper inflection point and upper in after the upper inflection point is the

less comp less compliant area where almost all the Alvi are kept open so these are the three phases in a

inspirated limb and the the next one is the expirat Lim expirat Lim here is the uh upper deflection point and lower

deflection point so how to set up an optimal peep so we can go for an incremental peep titration or a

decremental peep titration so the incremental peep titration we monitor the complaints driving pressure spo2 and

other hemodynamic parameters we set up an initial Peep and then monitor all these things and increase the peep level

every 5 minutes by 2 to 5 C of water until the PE Peak reaches to 40 or 50 cm of water and decremental Peep dition is

we initially set up to a high peep that is 40 to 50 cm of water and then decrease by every 2 to 5 cm of water uh

every 5 minutes monitoring the uh complains driving pressure and other hemodynamic

parameters so then comes the maintenance part we maintain the patient on mechanical ventilation uh with sedation

analysis delivia management hemodynamic IC monitoring nutritional support glucose control uh and we take measures

to prevent the ventilator Associated pneumonia to prevent Venus thromboembolism gastrointestinal

prophylaxis uh required Venus and arterial axis and temperature management so coming to the last part

that is a weaning from mechanical ventilation how do we Define weaning from mechanical ventilation this is the

liberation of patient from the mechanical ventilation and it involves a three-step process so first is the

Readiness testing and then the waning and extubation Readiness testing is the objective clinical criteria to determine

whether the patient is ready to be weaned from the mechanical ventilation and weaning is the process of decreasing

the degree of ventilatory support we have provided and allowing the patient to take over the greater proportion of

their own ventilation and extubation is removal of the endot trical tube and is the final step so uh this is how a

patient who is put on ventilator looks like uh the patient is admitted for treatment of acute respiratory failure

then the patient is maintained on ventilator and the Clin suspects if the patient can be weaned and assess the

Readiness to we and we perform a spontaneous breathing test and exate the patient attempted only if the patient

passes the SBT and if if it is required then the patient is reintubated or the patient might be discharged almost

40% of this process is a veening process and uh it requires a careful plan so now when do we

consider Ving when there is an improvement in the underlying cause of respiratory failure when there is

adequate oxygen and if arterial pH stabilizes and hemodynamic stability and ability of the patient to take

spontaneous respiration so thinking of all these things what are the clinical criteria as we started ventilation we

have a few criteria where we can assess the Readiness for spontaneous breathing so the cause for respiratory failure has

improved the PF ratio is more than 150 or 200 and the SP2 is 90% with an fa2 of 4% and Peep is less than 5 cm of water

hemodynamic St stability with low or no vasod Vaso supressor medications and ability to initiate a inspiratory effort

so additional criteria can be the hemoglobin level should be more than 7 G per deciliter temperature should be

maintained and the patient should be awake and alert and easily rousable so subjective assessment if the

patient has an adequate cough there is no neuromuscular blocking agents absence of excessive trob bronch C secretions

and reversal of the underling cause so objective criteria is pac2 of less than 50 mm of mercury with normal pH the

vital capacity is more than 10 ml per kg a spontaneous tidal volume of more than 5 ml per kg and uh patient can generate

a respiratory rate of less than 35 per minute and F by V it is less than 100 breads per minute per liter and minute

ventilation is less than 10 lit with a satisfactory blood gases so this is the weaning path ready weaning if there

there is reversal of respiratory failure GCS is more than eight spontaneous breathing PF ratio is more than 200 is

hemodynamic stability if this is achieved then they pass on to the next step which is ready breathing where the

patient is able to cough AO saturation is more than 9 respiratory rate is less than 35 peep is less than 8 and rsbi is

less than 105 if this conditions are fulfilled then comes the phase of ready extubation

that is successful 30 minutes SBT that is spontaneous breathing trial when the patient passes the spontaneous breathing

trial then the patient is ready for extubation and extb so these are the Ving predictors

there are measures of oxygenation and gas exchange simple measures of respiratory system load integrative

indices and complex measurements which may require special equipment so we rely on the measures of oxygenation and gas

exchange that is PF ratio alv to arterial pressure gradient uh and dead space

ventilation that is dead space to tidal volume ratio and most important of all the things is the res rapid shallow

breathing index which is a integrative index so RSB bi is the one which I'm going to discuss now this is a preferred

weaning predictor this is a rapid shallow breathing index which is the ratio of respiratory frequency to the

tidal volume so this is measured by the tidal spirometer or if the patient is connected to the ventilator we can look

for the tidal volume and the respirat rate and calculate the rspi index the spomer measures only the manage

ventilation and the operator counts the actual respiratory rate the tidal volume can be calculated by dividing definite

ventilation by the rate so now how do we interpret the rsba rsba of more than 105 brids per minute

per liter is likely to fail beaning and a negative rsba has a better predictive

value so I have two clinical criteria so which of the patient uh has

an R rsba so if we see in the previous slide rsba more than one5 bricks per minute per liter is a negative rsba and

is likely to fail weening so here the patient the first patient has a spontaneous tidal volume

of4 l and a respirator rate of 10 breaths per minute so it comes to 25 breaths per minute per liter and the

second patient has a spontaneous Tidal volume of uh 025 L and the respiratory rate is 30 breads per minute so if we

calculate rsba for both the patients then the second patient has an RSB of 120 which is more than 105 and is likely

to fail Ving so uh now coming on to the spontaneous breathing trial so this is

the best indicator of ventilation discontinuation potential where we simulate or we take off the patient from

from ventilatory support and observe the patient for a period of 30 to 20 minutes 30 to 120 minutes so we monitor

respiratory rate blood pressure heart rate comfort of the patient oxygenation and spo2 so spontaneous breathing trial

is a short period of time in which the patient is breathing spontaneously either with a minimal support or no

support and uh can be done when the patient is still connected to the ventilator circuit or the patient can be

removed from the circuit to put on a independent source of oxygen that is TPS if the patient is still on ventilator

the patient should have very minimal ventilatory settings like a pressure support of less than uh 5 to 7 around 5

to 7 uh cm of water and wi 1 to 5 cm of water PE the initial trial should last for 30 to 120 Minutes almost 80% of the

patient who can tolerate a 30 minutes SBT can be permanently removed from the ventilator so when do we discontinue an

s B respiratory rate goes up shoots up to more than 38 or 40 SP2 Falls less than 92 a tidal volume generated is less

than 325 ML and heart rate is increasing that is 140 or 25% above the Baseline there is a either hypotension or

hypertension a worsening agitation uh anxiety and discomfort despite reassurances so the patient can fall

into one of these three criteria the patient can be simply weaned who is um EXT on the first attempt without any

difficulty a difficult weaning is the one who patient or the patients who fail an initial weaning trial and can be

weaned within 7 days from the first SBT a prolonged weaning is sp the patient fails three weaning attempts and

requires more than seven days to be weaned off after the first deity there a few uh one uh case report

uh to indicate if the patient is ready to be or if there is a failure of SBT a 76 years old man who has a history of

COPD has been receiving ventilatory support for following day four days following an acute MI so here the

ventilatory settings are tial volume of 500 mandatory ventilation of eight breaths per minute fa2 of5 and P is 5 cm

of water ABG results are pH of 7.37 P of 36 P2 of 78 and spo2 of 93% so the patient current ly meets all the

criteria for beaning and is placed on a TP trial within 10 minutes he develops restlessness tardia rapid shell

breathing and diaphoresis the spo2 drops from 93 to 90 and the pulmonary occlusion pressure raises from 12 to 17

mm of M so this patient has failed the SBT and is not ready to be beaned off the ventilator so now what are the signs

of beaning failure the patient can have teia use of accessory muscles paradoxical abdominal movements disnea

chest pain U asynchronous ventilation and uh if the work of breathing can be measured measured work of breathing can

be more than 1.8 L per kg uh 1.8 lit kg per minute or uh more than 50 15% of the

total oxygen consumption so Vining failure can be due to a respiratory Lo cardiac load or

neuromuscular incompetence critical illness myopathy or neuros pychological factors or other metabolic and endocrine

factors so I have listed few causes of respiratory card respiratory load cardiac Lo neuromuscular neuros

pychological nadas so coming on to the last slide this uh where is the what is the role of

diaphragmatic ultrasound in Ving so we place a instrument which is similar to a rail tube there is an EMG cable attached

to the tip of the uh uh instrument which can measure the

diaphragmatic um contractions and can be uh seen in the ultrasound uh diaphragmatic excursions is dependent on

the diaphragmatic contraction and inspired volume and this can be used as a veining

predictor so measurement of diaphragmatic excursions during a spontaneous unsupported breathing can be

noted and the patient can be veed according to that thank you