2000 ventilator made easy aglan

The maximum pressure is preset; this sealing pressure is not exceeded by any mean.The tidal volume for sure will be determined by the following:- 1 –the compliance 2- the preset pressur

VENTILATOR MADE EASY

BY DR.A AGLAN MD.

CRITICAL CARE DEPARTEMENT ALEXANDRIA UNIVERSITY

CONTRIBUTING AUTHERS

*** CONTENTS

* Introduction - p.

Chapter 1* What is a ventilator? -p.

Chapter 2* The respiratory system -p

Chapter 3* Ventilation -p.

Chapter 4* Patient – ventilator inter action -p.

Chapter 5* Complications of invasive ventilation -p.

Monitoring the patient on a ventilator -P.

*

Chapter 6

Chapter 7* Ventilation of special cases -p.

Chapter 8* Endo tracheal entubation -p.

Chapter 9* Drugs used during ventilation -p.

Chapter 10* Care of ventilated patient -p

Chapter 11* Nutrition of mechanically ventilated patient……… P

Chapter 12* In- hospital transport of mechanically ventilated paient

Chapter 1

WHAT IS A VENTILATOR?

WHAT IS A VENTILATOR

** Definition;

It is a machine designed to alter, transmit, and direct applied energy in a

predetermined manner to augment or replace the patient s muscles in performing the work of breathing

*It is formed of 5 parts:-

1- Power input : - a – Electricity 220 v or 110 v

b – Gases O2 & air 3~ 5 bar

2- Power transmission to down regulate electric and gases load to the control circuit

3-Controle circuits, It may be mechanical, pneumatic, fluid, electric, and or electronic

** All the above three parts are engineering problems

4- Control variables

* The main function of the ventilator is to deliver air to the patient, and the physical characters of air which are changeable are called variables These are the flow, the volume, the time, the pressure, and the oxygen concentration (FiO2)

* These variables are preset by the operator as value and shape

depending on the mode and the type of the ventilator

Inspiratory pause

Cycle offFlow- Volume- Pressure- Time

BaselinePEEP or Atmospheric

Rising time

TriggerFlow- Pressure- Time - Volume

PressureLimit or Target

1- Change from expiration to inspiration = triggering

2- Inspiration = limits or target

3- Change from inspiration to expiration = cycle off

4- Expiration = baseline

* With each phase of the cycle any of the variables can be used

(Time, Volume, Flow, or Pressure.)

**Let us go and sea how the ventilator reacts and responds to the patient efforts 1- The patient starts to take inspiration by making change in the flow, pressure, or volume which is sensed by the demand valve of ventilator which opens whenever it reached the preset value

* Sure each ventilator has its own demand valve system which responds

to flow, pressure or volume

*If the patient is paralyzed the ventilator will start inspiration

automatically by time (60/RR) /min

2- Then after opening the demand valve air flows to the patient , but the machine asks you please how fast you need this flow? This means that you have to preset the flow ( peak flow ) or the rising time

3- Then the ventilator asks again please the flow to the patient developed pressure as a result of the resistance and compliance please would you set a limit to this pressure as an alarm or would put a maximum not to be exceeded this means you have to put the p limit or the p max

4- A good question comes from the ventilator; please this phase should be terminated (cycled) please can you set a time or a flow or a pressure or a volume a- You can inform (set) the ventilator please close the inspiratory limb after

a set VT and keeps this VT in for some time ( inspiratory pause ) and then later open the expiratory valve, or open the expiratory valve immediately after the closure of the inspiratory limb ( no inspiratory pause ) ( volume targeted type as BENNET ) b- Please close the inspiratory limb after certain time (Ti), take a pause or not and then open the expiratory valve ( pressure targeted ,time cycled as ADULT STAR ) A question comes from the ventilator what about the VT ? I should answer that the VT will be adjusted via manipulating the target pressure, the flow ,the rising time ,and the Ti in addition to the parameters of the lung (compliance & resistance ) c- You have a pressure target which should not be exceeded please close the inspiratory limb after delivery of the preset VT, and then open the expiratory valve after the elapse of the Ti (DRAGER) What will happen when if?

1- The Ti is longer than the time for the preset VT? An inspiratory pause will be developed

2 –The Ti is the same as that for the preset VT? No inspiratory pause will appear

3- The Ti is less than that of the preset VT? a volume less than the preset VT will be delivered and an alarm will signal So you have to adjust by either

in creasing the Ti, or increasing the target pressure, or increasing the flow

5- The last question of the ventilator please, shall I allow all the VT to be exhaled totally and reach the atmospheric pressure or shall I keep some air inside (above the FRC) to produce a preset pressure above the atmospheric pressure at the end of expiration (PEEP) So you have to set the value of the PEEP or not

** From the phase variable 2 items have emerged;

A- The types of respiration;

** As we have mentioned before that the phase variable is formed of four phases , the trigger and the cycle phases which could be a patient or a machine function but the

limit and the base phases are only a machine function Accordingly, we have divided the respiratory cycle of the ventilator into two types :-

mismatching with the ventilator

** This type of respiration can be supported by the ventilator as in PSV where the triggering and cycling are of the patient but the limit is aided by the ventilator

** Trigger may be by use of pressure or flow sensor valve according to type of the ventilator used

** Termination of inspiration (cycle off) is determined by the device built in the ventilator and these may be: -

1- Increase in expiratory flow 1-2 L/m above the inspiratory flow level 2- Increase in expiratory pressure 1-2 cmH2O above the inspiratory level

** What are the factors which determine the value of the VT.? ?

** Can I make any change in this VT??

* Sure yes, you can adjust VT by adjusting the pressure support in (PSV ) or (PEEP) IN CPAP ,and the difference between the high PEEP and low PEEP in

BiPAP

*

2- MANDATORY CYCLE

** There are two types:

1- Triggering and cycling are done by the ventilator as in paralyzed patient (CMV)

2- The patient triggers but the ventilator terminates (cycle off) the inspiration, so

it is a share between both the patient and the ventilator (ACV)

* How does the ventilator end the cycle?

This is built in device in the machine which may be;

1- Volume, when a preset VT is achieved

2- Flow, when the flow drops to 5L/ m or the flow drops to 25% of the peak flow

3- Time, when the machine Ti (preset Ti) is achieved

* It is clear that the ventilator does not sense the start of the patient

expiration and even is not sensitive to the termination of the patient inspiration

This means that the neural Ti will not match the machine Ti and so mismatch will occur leading to a lot of problems

*What about the respiratory rate?

* Sure it is that of the patient which is affected by the set flow, set

VT, and the ventilator Ti

* What about the VT ?

* In volume targeted pressure limit, it is the preset VT

Ventilator Breaths And Phase Variables

Mandatory Machine Machine Machine

Assisted Patient Machine Machine

Supported Patient Machine Patient

Spontaneous Patient Patient Patient

B- The types of the respiratory cycle (types of ventilator)

** Positive pressure (which supply air with positive pressure through the ETT.), and negative pressure ventilator (which produces negative pressure around the chest wall )

**Ventilators have been divided into two types according

to the target undependable fixed

1- Volume targeted 2- Pressure targeted

** This division has been built on the relation between the VT, PL., and the

compliance which is controlled by the flowing

C = VT / PL

* It is clear from this equation that you will adjust the variables where the parameter

C is fixed, so in one ventilator you will set and change the VT and accordingly the P will change according to the C (volume targeted), and I the other one you set or change the P( P max) and accordingly the VT will be determined by the C( pressure targeted)

So in cases of bade (low) C when the preset VT is delivered the PL will increase too much and this may expose the alveoli to over distension and volutrauma.

Also, if the patient developed Pneumothorax, the VT will be delivered totally

leading to more increase in the pleural pressure pressing on the cardiac fossa to

produce cardiac tamponade The patient will die from C.V collapse

The monitor in such type will be the PL and the homodynamic

Such ventilators are harmful to infants and children

*

The maximum pressure is preset; this sealing pressure is not exceeded by any mean.The tidal volume for sure will be determined by the following:-

1 –the compliance 2- the preset pressure 3- the flow 4 – the inspiratory time

So increase or decrease of any of the above will be associated with increase or

decrease of the VT as is demonstrated by the following diagram

3- The Ti is less than the time required to deliver the preset VT So a part of the preset VT is delivered and the expiratory limb will open to end the cycle (inspiration).

** THE CONTROL PANEL

* The value of the VT is usually 10 -15 ml/kg for normal lung, but it is 5 -6 ml/kg for COPD, bronchial asthma, and ARDS

** F.R

* Should be adjusted to be the same as the patient drive

* The set value is usually 40 – 60 L/m for adult

*It determines the value of the Ti in volume target and pressure target volume controlled, and VT in pressure target time controlled

* An increase in the flow rate is associated with an increase in the patient R.R and vice versa

* It is the variable for changes in the pressure resistance

* It is used to define the rising time

* Flow triggering and flow by system are important advances to decrease the work of breathing and to over come the tube resistance

*Decelerating wave form is associated with an improved gas exchange and a lower peak airway pressure

** FiO2

* Certain important points should be considered and these are;

* When you start ventilation you should start with 100% O2 for 20 -30 min then decrease gradually every 20 min to be below the toxic threshold 60% with SaO2 90% or to reach to the least FiO2 with SaO2> 90%

* FiO2 of 100% should be given 3 min before and after suctioning to increase the O2 reserve capacity and avoid desaturation and hypoxia

*Avoid FiO2 of > 60 % to avoid O2 toxicity

* You can calculate the oxygenation indices from the FiO2 and these are; the A- a gradient, shunt, PaO2 / FiO2, and PaO2 / PAO2

** Ti

*It is determined by the preset VT and FR in the volume target ventilator

* It is preset in the pressure target ventilator

* The total Ti = Ti + inspiratory pause

* You should consider the back up Ti (constant Ti) when you change from CMV

to A / C when the patient takes higher rate to avoid the decrease in the Te

complications and fighting the ventilator

** I: E

*It is the inspiratory and expiratory time ratio

* I: E of about 1: 2 is optimal because it limits gas trapping and mean intra thoracic pressure

*In the volume target ventilator it is determined by the preset VT and FR ( Ti) and the RR ( Te)

* In the pressure target it is determined by the preset Ti and RR

* Inversed ratio I: E (2: 1 or more) sometimes used to improve oxygenation by improving gas distribution and opening atelectatic alveoli, and this can be done through increase Ti, decrease FR or adding inspiratory pause

** R.R

* It should be around 20 b/min in adult to decrease the shear force

* It should not exceed 35 b/ min to avoid, CO2 wash out, shallow breathing, or respiratory fatigue

* Low RR in both COPD and bronchial asthma is important to increase the Te

* The mandatory rate in SIMV is decreased gradually while weaning the patient

** Pmax

*It is set in the pressure target ventilator

* It should not exceed the value of 45 cmH2O

* You should keep in mind that our target pressure is the PLP which should not exceed 35 cmH2O to avoid volutrauma

* It has a good share in determining the VT in the pressure target ventilator

2- Phase variables where you set:

** Trigger value

* The usual value is 2 – 3 cmH2O for the pressure triggering

* In flow triggering its value should be less than the basal flow

* Try to avoid low value of triggering to avoid the outotriggering problems

* High value of triggering will lead to increased working of breathing and non triggering

** Rising time

* It is the time taken to reach to the target pressure

* Decrease in this time means increase in the flow and vice versa

* It determines the value of the starting flow which should match the patient drive, and this can adjusted from the P – T curve

* It affects the total Ti

* The starting value is 0.2 sec

** It is the response of the ventilator to certain change in the control variable in a conditioned way.

** If some changes happened the ventilator responds in a preset way

** Example, 1- apnic ventilation, you preset the condition that if the patient respiratory rate decreased to 8 b/ m or the expiratory time exceeded 10 sec the ventilator should shift to the controlled(apnic) mode of ventilation You set the triggering values and the back up data for CMV

2- Sigh, you preset the condition that after each 15 sec the VT should of the value 800 ml You set the rate (single or multiple) and the value of the sigh volume

4- Flow wave forms where you select one of them

P -

B

* High and low values for the pressure, VT, MV, and R.R

* Failure of the device, the O2 supply, and the compressed air supply

*

*

*

C

* Resistance * Compliance * Dead space

*Shunt * Oxygenation indices

* Respiratory drive * Muscle power * Triggering

* Muscle endurance

** 1- VARIABLES

** Expiratory VT changes;

* VT should be the same as the set one or may be less due to the minimal leak

* VT may be larger than the set value, by the value of the volume loss in the

expansion of the patient circuit as in Adult star where the delivered volume equals the set VT + the volume loss in the expansion of the patient circuit( PL.P X C of the tube)

* VT may be less than the set value due to;

* Leak or disconnection of the patient circuit, ETT and its cuff, and or the I.C tube

* Increase in resistance, decrease in the compliance, and closed

pneumothorax in pressure target types of ventilators

* VT in spontaneous and supported breathing is;

* Decrease in respiratory muscle pump

** PIP (peak inspiratory pressure& plateau pressure)

*

* * A change in the PIP by increase or decrease should direct us to screen the

following four points;

1- The patient circuit, for kink, obstruction, leak, or disconnection

2- The ETT, for disconnection, kink, being bitten by the patient, obstruction by secretion, cuff leak, cuff herniation, or the tube in the right bronchus

3- The conducting tube for the proximal airway pressure for disconnection, kink, mal function of the diaphragm, or presence of water in its lumen

4- The patient for, bronchospasm, decrease in compliance, closed

pneumothorax, or I.C.T leak

* When we keep in mind that P res = FX R, we can define the causes of its increase

as kink, obstruction, or spasm, and at the same time when know that Pel =VT/ C, we can define the causes of its increase as decrease in compliance, hyperinflation, or PEEPi

** Mean airway pressure (MAP)

* MAP is a formula which is formed from the following equation;

MAP = PIP X Ti / T total + PEEP X Te / T total

* It is a good guide for the adjustment of ventilator setting

* Increase in MAP is associated with an increase in oxygenation not related to I: E ratio or PEEP

* MAP is increased due to;

* Increase in VT (which causes increase in PLP and accordingly PIP)

* Increase in RR (with decrease in Te leading to air trapping and PEEPi)

* Decrease in FR (with increase in Ti)

* Addition of inspiratory pause (with increase in Ti)

* Employment of decelerating flow (with high starting flow leading to high PIP)

* Addition of PEEP

** PEEP

* It is meant to keep alveoli open

* Its value should be 1 – 2 cmH2O above the lower inflection point or the super imposed pressure (> 7.5 cmH2O)

* Take care of its effect on the hemodynamic state

* It should be 85% of the PEEPi to decrease the inspiratory load

* It is an important item to improve oxygenation, so it should be handled carefully with FiO2

**Respiratory rate (R.R.)

* It is set in the CMV, but changes with the assisted and spontaneous ventilation

**** High R.R may be due to;

* Central stimulation (chemical) as acidosis, hypoxia, hypercarbia, or C.N.S lesion

* Mechanical stimulation as

* Increase in spasm

* Obstruction

* Increase in flow

* Increase in sensitivity with auto triggering

* Lung parenchymatus lesion as consolidation

*Non synchronization

**** Low R.R may be due to;

* Central inhibition as brain lesion, drugs, or CO2 washout to be below the apnic threshold

* Mechanical causes as;

*High VT

* None triggering due to;

* Decrease patient drive

* Decrease respiratory muscle power

* Hyper inflation

* PEEPi

* High sensitivity of the ventilator trigger

*** R.R > 35 b / min is a good criteria for weaning failure

ventilators by the difference between the set Ti and the time spent for the delivery of the set VT

* It should be noted that it is added to the Ti and so can change the I: E ratio

* It can have some share in the development of PEEPi through incomplete exhalation recoil (expiration) due to loss of inspiration energy as heat during that time

* It is used to study the compliance by measuring the plateau pressure

* Its time should be short (0.2 sec) if not used for I: E changes

** 2- PARAMETERS

* Resistance

*We have two types of resistance, one inspiratory and the second is the expiratory

* The inspiratory resistance measured is the total one which is due to the resistance of air flow in the tube circuit, the ETT, and the large bronchial tree This resistance can

be measured from the difference between the PIP and PLP and this is the Pres and according to the equation P = F X R you can calculate the inspiratory resistance This Pres changes will affect the PIP in the volume target ventilator where its increase will increase PIP and the reverse is correct, but in the pressure target ventilator its increase will encroach on the PLP and not the Pmax (which is fixed) and accordingly the VT will be the one to decrease and also the reverse is correct The increase in such

resistance is usually due to kink, secretions, obstruction, or spasm

* The expiratory resistance is usually due to spasm of the small bronchioles as in wheezy chest (bronchial asthma) Since P = F X R , the pressure will be the starting pressure at the beginning of expiration which is the PLP, and the flow will be that flow measured at the flow time curve recording the starting highest flow, so you can calculate the expiratory resistance So the increase in expiratory resistance will not make change in the Pres but through its hyperinflation effect it will increase PLP with increase in the PIP in the volume target ventilator but it will decrease the VT in the pressure target ventilator

* Compliance

* It is a change in volume per unit change in pressure

* It is measured from the equation; C = VT (ml) / (PLP – PEEP) cmH2O

* The normal compliance is;

* Alveolo arterial oxygen gradient (A – a), with normal value of FiO2 X age + 2.5

* Arterial – inspired FiO2 ratio (PaO2 / FiO2) which exceeds 400, whatever the FiO2, but it is < 300 in ALI, and <200 in ARDS and its weaning threshold should be > 350

* Arterial – alveolar O2 tension ratio (PaO2 /PAO2) which is >0 8 but the weaning threshold should be > 0.35

* Respiratory index (PAO2 – PaO2 / PAO2)

* Dead space is between 33% and 45% of the VT and the weaning value should < 60% It is increased mainly with pulmonary embolism

* Shunt fraction can be measured from the equation = O2 content of

capillary blood – O2 content of arterial blood / O2 content of capillary blood – O2 content of mixed venous blood or can be calculated from the equation of A – a / 20 at FiO2 100% The normal value is < 10% and the weaning value should be < 20%

* Neuro- muscular functions

* Respiratory drive can be measured in both conscious and unconscious patients but not in paralyzed one, by airway occlusion pressure at 100msc (p0.1) Its normal value = 0.95 cmH2O, and an increase in this value is an indication of the respiratory distress with encroachment on the reserve capacity which might not be doubled by inhalation of CO2 of 3% to give failure of weaning at >4 cmH2O

* Muscle power, which can be defined by measuring NIP which should be >

30 cmH2O to wean the patient

* Triggering, can be a good monitor as a parameter when you watch the non triggering with low sensitivity (equals weak respiratory muscles), in addition to measuring the P0.1 sec for assessment of the patient drive

* Muscle endurance, is a good monitor for the sustainability of the

respiratory work indefinitely, and this can be measured from the equation PTI which should be less than 0.15 for weaning (normal value = 0.02)

** It is defined as a particular set

1- Control variable 2- Phase variable 3- Conditioned variable 4- Respiratory cycle type 5- Type of respiration

** There are different modes of ventilation which increases with time due to the advance in technology and the more understanding of the respiratory physiology.

** Some modes are common and present in the majority of ventilators and these will

be dealt with in more details

** These modes

* CMV (Controlled Mandatory Ventilation)

* A/ C (Assisted Controlled)

* PSV (Pressure Support Ventilation)

*CPAP (Continuous Positive Airway Pressure)

*BiPAP (Bi-level Positive Airway Pressure)

*SIMV (Synchronized Intermittent Mandatory Ventilation)

*PAV (Proportional Assist Ventilation)

*The data of each mode is selected from each of the above 5 items

**** CMV volume target

*

* Type of the ventilator (respiratory cycle)

Pressure T Time CY Pressure T Volume CON

Volume T

Mandatory

aneous

Spont

*It is used when the patient is apnic or on muscle relaxant

*The job is totally of the ventilator

* Control variables

FiO2 RRTARGET

PR

PR LIMIT

Ti

+ Time

V

PR

Time

PR F

Preset flow

PIP is determined by R., C, and preset VT Pressure limit

is an alarm

VT is constant and preset and is delivered whatever R

or C isTime triggering

* The trigger will be by time determined by the respiratory rate and you will set the pressure limit as an alarm, the VT, and you may add inspiratory pause or not, PEEP or not.

* Conditioned variables

Apnea data Sigh

Rate/min Single/Multiple VT

CMV

* Type of the ventilator (respiratory cycle)

Pressure T Time CY

Pressure T Volume CON

Mandatory

Spontaneous

** Control variables

FiO2 RR

PR TARGET

PR LIMIT

Ti FLOW

VT

*You set the, VT, flow, Ti, PR target, RR, and FiO2

*VT will be determined by the flow, target pressure, and patient compliance

* Ti you set may be the same time for the set VT, or larger to give an inspiratory pause, or less than it and in this case the set VT will not be delivered totally

* * Phase variables

Trigger Limit Cycle Insp.Pause PEEP

+

+

Time V

PR

Time

PR F

* The limit will be a target

* In the cycle the inspiratory limb will closed after delivery of the set VT, but the expiratory limb will open after the lapse of the Ti

*Inspiratory pause will appear when the Ti is larger than the time consumed for the delivery of the set VT

CMV

*

* Increase in the VT is associated with increase in its delivery time to decrease the inspiratory pause and increase the PLP and accordingly the PIP so long as it is below the Pmax

*

*Increase in the Ti will be associated with increase in the inspiratory pause

Pmax

* Increase in the flow is associated with decrease in the delivery time of the VT with

an increase in the inspiratory pause, and increase in the Pres and accordingly PIP

*

* When the Pmax -1 is above the PIP the set VT is delivered totally, but when the Pmax-2 becomes just above the PIP, delivery of the VT will take longer time which might encroach on the inspiratory pause, and finally when the Pmax 3 is lower than the PIP the set Ti will not be sufficient to deliver the set VT with loss of the

Pressure T Volume CON

Mandatory

Spontaneous

*It is used when the patient is apnic or on muscle relaxant

*The job is totally of the ventilator

*** Control variables

Pmax3Pmax 1

2

FiO2 RR

PR TARGET

PR LIMIT

Ti FLOW

+

Time V

PR

Time

PR F

* The pressure is a target

* The inspiratory limb closes and the expiratory limb opens simultaneously at the end

of the set Ti

*Conditioned variables

Apnea data Sigh

min Single/Multiple VTRate/

CMV

Trigger

•The same as before

•

*

* The set Pmax is reached according to the set rising time or flow rate

* The VT is determined by the set Ti, FR, Pmax, and C of the lung

* Increase in the Pmax is associated with increase in the VT as seen in the curve

*** A/C (ASSIST/ CONTROL)

** To solve this problem we have to increase the back up rate of the ventilator to be close to that of the patient, or increase the flow rate to shorten the Ti

** An other problem is that increase in the RR will be associated with wash out of CO2, so it is important to adjust it by, sedation, analgesia, increasing the flow,

increasing the VT, or back to muscle relaxant

** An example of this problem is as follow;

*If the VT=O.5L and RR= 10/m with F.R =0.25L /s

T total =60/10 = 6 s , Ti =0.5/0.25 = 2 s , Te = 6 – 2 = 4 s, I/E =2/4 =1 : 2 *If the RR became 20/m , the T total =60/20 = 3 s since the Ti = 2 s (back up) the Te= 3 – 2 = 1 s and so the I/E = 2/1 = 2:1

* If the RR became 30 /m, the T total = 60/30 =2 s and since the Ti = 2 s(back up) the Te =3- 3 = 0and this means no time for expiration and the patient will fight the machine

*A third important point is that, the increase in the flow rate will be associated with a decrease in the ventilator Ti, and this increases the RR by the patient as feedback and interaction to this change So you have to watch such increase to match the patient Ti

*** SIMV (SYNCHRONIZED INTERMITTENT

MANDATORY VENTILATION)

* It is formed of two respiratory cycles one is mandatory (A) and the second is

spontaneous (B)

* With each trigger the patient gains either a mandatory or a spontaneous

* You set the mandatory rate and other character as in CMV and according to the type

of the ventilator, volume target, pressure target time cycled, or pressure target volume controlled as mentioned above

* In the interval between the set mandatory cycles when the patient triggers he

initiates a spontaneous breath but not a repetition of the set mandatory as A/C

*The spontaneous breath will have the following character;

* The rate will be determined by the patient

* The type of triggering will be that of the ventilator (pressure or flow)

* The sensitivity of triggering will be that already set for the mandatory

* You either set a value for pressure support or not

* The cycle off will be that of the device built in the ventilator

* The VT will be determined by the pressure support, the patient drive, and the lung compliance

* So, change in the pressure support will change the VT

* The back up mandatory rate will be the apnic rate

* Unloading the patient will depend on the balance between the rate of mandatory and spontaneous Early you increase the mandatory, but while weaning you decrease it to give spontaneous breathing the major share

*** PSV (PRESSURE SUPPORT VENTILATION)

* You watch the variability of the VT which depends on the patient drive or effort i.e the difference between the set pressure and the negative pressure produced by the patient and the C of the lung

* * Type of the ventilator (respiratory cycle)

Pressure T Time CY

Pressure T Volume CON

Volume T

* * Type of respiration

Assisted mandatory

Mandatory

Spontaneous

*It is totally spontaneous

* * Control variables

FiO2 RR

PR TARGET

PR LIMIT

Ti

FLOW

VT

*You set the flow or the rising time, the pressure target, and FiO2

* The RR, Ti, and the VT will be that of the patient

* * Phase variables

Trigger Limit Cycle Insp.Pause PEEP

+

+ Time

#V

PR

Time

* You set a target pressure (it is not a limit)

* Rising to the preset pressure is either a machine fixed or variable via manipulating the rising time

#The termination of the cycle will depend on the system or device used which may be;

* Fixed value of the peak flow

* A percent of the peak flow

* An increase in the expiratory pressure 1 -3 cm H20 than that of the inspiratory

* An increase in the expiratory flow 1 – 3 L/ m than that of the inspiratory

* Increase in the inspiratory time > 80% of the T total

* Increase in the inspiratory time > 3 s

* You can use PEEP

* Conditioned variables

Apnea data Sigh

Rate/min Single/Multiple VT

CMV

* You can not set the sigh because this is spontaneous

* PSV & breathing pattern;

* Increase in the PSV will lead to;

* Increase in the VT, decrease in the RR, decrease in the O2 consumption, decrease in the work of breathing, and increase in the patient comfort

* Stretch of the mechano receptors leading to decrease in the RR and may be apnic ventilation

* Increase in the minute volume with wash out of CO2 and apnic ventilation

* PSV is associated with decrease in the RR, and the inspiratory duty cycle (Ti/T total), so PSV was found to decrease PEEPi in COPD patient

** Tube compensation and PSV;

* Resistance during inspiration is mainly due to the resistance imposed by the demand valve, patient circuit, and the ETT

* This resistance can be detected through the study of the post trigger phase in the rapid drop in pressure, where there is a linear relation between pressure and flow changes

* PSV of 5 – 10 cmH2O can unload a flow of o.05 – 1 L/s

* It is agreed to give PSV of 5 – 10 cmH2O with SIMV

* PSV of 5 cmH2O in spontaneous breathing equal use of flow by system in unloading inspiration

** How much is the level of PSV?

* The minimal level is 5 – 8 cmH2O to unload the ETT

* We adjust the level to;

* Stop work of sternocleidomastoid

* Get VT 8 – 12 ml/Kg

* Get RR around 25/m

** Advantages of PSV;

* Increases patient comfort

* Reduces need for sedation

* Good synchrony with the ventilator, because it is designed to

recognizes the beginning and end of each spontaneous breath together with

adjustment of to patient drive

* No particular hemodynamic consequences have been described with it

* It is a good mode of weaning

* Non invasive PSV was found to be good in avoiding the intubations, improving the out come, and decreasing the stay of COPD in the ICU

** Disadvantages and risks of PSV;

* It varies among ventilators which make it difficult in defining

guidelines

* It is difficult to compute and monitor the respiratory mechanics

* Circuit leak may lead to persistent inspiratory pressure

* May lead to high VT and apnic ventilation

* Variation in the patient drive may lead to fighting the ventilator

*** CPAP (CONTINEOUS POSITIVE AIRWAY PRESSURE)

* CPAP represents the application of a constant level of positive pressure at the airway opening during spontaneous ventilation throughout intact upper airway or ETT

* It is delivered throughout the respiratory cycle, either by a portable compressor or from generator in conjunction with a nigh pressure gas source

* It can not provide ventilation to apnic patient

* It is a spontaneous breathing mode

* You set only CPAP level and the sensitivity for triggering

* Trigger is usually via flow by system

* It is used to;

= Increase the FRC

= Recruit collapsed alveoli

= Improve oxygenation

*CPAP results in a lower intrathoracic pressure compared to PEEP

* PEEP and CPAP are different;

= CPAP is a mode of ventilation

= PEEP is only an elevation of the base line

= CPAP can be used without an elevation of the baseline

*

* As we know that the equation of motion stats that;

Pressure = Flow x Resistance

Peak Inspiratory Pressure (PIP) = F X R + VT/ Compliance

PIP is usually the some effect of both ventilatory work and inspiratory work

So PIP = VENT Pr + MUSC Pr

Muscle pressure is the imaginary Tran respiratory pressure (i.e airway pressure – body surface pressure) generated by respiratory pump to expand the thoracic cage and lung It is imaginary because it is not directly measured

Ventilator pressure = the trans respiratory pressure generated by the ventilator

So vent Pr + muscle Pr = F X R + VT/C

C and R as parameters are considered the load experienced by the ventilator and the inspiratory muscle (pump)

It is important to know that flow, volume, and pressure are all measured relative to their base lines This means that the pressure to cause inspiration is measured as the change in pressure above PEEP

Whenever airway pressure rises above the base line during inspiration, the ventilator does work for the patient

So with CPAP no change in pressure above PEEP, so ventilatory work = PIP (PEEP) – PEEP = 0 This means that there is no direct ventilatory share in work unloading

* Depression of QT is less with CPAP than PEEP

*With CPAP, FRC increases and this will lead to;

* Decrease in the inspiratory muscle length leading to decrease in the inspiratory muscle power and work

* Increase in the expiratory length leading to active expiration with unloading the inspiratory muscle via increasing its length

* Shift of the P – V curve from the lower zone to the middle zone and this will improve both the lung mechanics and the work of breathing

* In COPD patients, CPAP decreases patients effort and does not change end

expiratory lung volume so long as PEEP is less than PEEPi

* High CPAP will be associated with increase in the FRC with shift of the P – V curve to the upper flat zone with increase liability for volutrauma, VQ mismatch, decrease in QT, and decrease in the inspiratory power

** Type of the ventilator (respiratory cycle)

Volume CON Pressure T Time CY Pressure T

Mandatory

Spontaneous

** Control variables

FiO2 RR

PR TARGET

PR LIMIT

Ti

FLOW

+ Time

# V

PR

Time

F

PR

*Trigger is usually by flow in a flow by system and may be by pressure

*The limit is pressure and the cycle is either flow or pressure

* Conditioned variables

Apnea data Sigh Trigger CMV Rate/min Single/Multiple VT

* No apnea or sigh data

*** Bi PAP (BILEVEL POSITIVE AIRWAY PRESSURE)

** It is a bi-level CPAP

** It is a CPAP flow generator

** It is a pressure controlled (target) valve which maintains pressure at one of two levels, inspiratory and expiratory

** In CPAP, the pressure is maintained at preset level all through inspiration and expiration, but in BiPAP the pressure is maintained at certain level at expiration and

at another level at inspiration

** The high pressure level is called P high and the low level is called P low

** The time of the P high is preset and is considered as an inspiratory time but the expiratory time is calculated from setting the RR

** In order to adapt easily to the patient spontaneous breath, the change- over from expiration to inspiration pressure level and also from inspiration to expiration pressure level, it is synchronized with the patient spontaneous breath

** Change from expiration to inspiration occurs when the patient develops an

inspiratory flow 2.8 L/m (40ml/s) for > 30 s or a drop in the expiratory valve by the same value than the inspiratory valve

** Change from inspiration to expiration when;

* Inspiration stays > 3.5 s

* Decrease in the inspiratory flow to either 5L/ m, or 25 % of the peak flow

* Increase in the expiratory flow 2L /m more than the inspiratory flow

* Increase in the expiratory pressure 2cmH2O than the inspiratory pressure

Volume CON

Pressure T

Volume T

*** Type of respiration

Assisted mandatory

Mandatory

Spontaneous

*** Control variables

FiO2 RR

PR TARGET

PR LIMIT

Ti FLOW

VT

* You set the flow, rising time and FiO2

*You set the Ti and RR and the Te comes as a result of them

* The RR of the patient is added to the set machine rate

* You set the two pressures high and low

** Phase variables

Trigger Limit Cycle Insp.Pause PEEP

+

+

Time

# V

PR

Time

* The limit will be the P high (target) and PEEP will be the P low

* Cycling from high to low and from low to high is controlled as we mentioned before

* * Conditioned variables

Apnea data Sigh Trigger CMV Rate/min Single/Multiple VT

* No apnea or sigh data

APRV (AIRWAY PRESSURE RELEASED VENTILATION)

** Conventional ventilation begins the ventilatory cycle at a base line pressure and elevates airway pressure to get the desired VT, but in APRV it starts at an elevated baseline pressure (the same as plateau pressure) and follows with a deflation to get the desired VT

** Spontaneous breathing may occur at any level

**It is a CPAP with regular, brief, intermittent release in airway pressure

** It is a pressure target; time cycled, and time triggered ventilation

* BiPAP differs only from APRV in the Ti and Te In BiPAP Ti (high) is usually

shorter than Te (low), but in APRV is the reverse

* Ti is increased o.5 – 2.0 s increments to reach 12 – 15 s

* The goal is to arrive to CPAP at 12 cm H2O then wean at

that level

* ADVANTAGES;

* Decreases the PIP and so decreases the volutrauma

* Decreases the dead space

* Since it is a pressure target the VT may be difficult to adjust

especially with bad compliance

* Limited research

*** PAV (PROPORTIONAL ASSIST VENTILATION)

* It is a form of synchronized partial ventilatory support in which the ventilator generates pressure in proportion to patient effort, the more the patient pulls, the more the machine generates

* The ventilator amplifies patient effort without imposing any ventilatory or pressure target

* Determination of the level and pattern of breathing is entirely to the patient

* In conventional ventilation the variables are determined by the machine setting, but with PAV non of these variables are preset

*With PAV the flow of air to the patient is monitored, and this signal is integrated to provide instantaneous volume Each signal is subjected to amplification through gain control These two signals are then summed to determine the current flow to the patient The flow gain measures the pressure per unit flow i.e the resistance (P = FX R and R

= 1 so, P = 1X R= R) So when you set the gain to 50% this means that 50% of the R will be multiplied by the actual flow (1/2L/s, 1L/s, 1.5L/s…) This means that the amplification will be according the patient drive

* When you measure the R it is the total resistance (R of the ETT + R of the bronchial tree), so you have to deal with the bronchial tree R after subtracting the ETT

resistance

* The volume gain measures the pressure per unit volume (since C=VT/P, I/EL=VT/P

so P =EL X VT and since VT = 1L so P = EL) When you set the volume gain to 50%, this means that 50% of the elastance will be multiplied by the actual flow time value

* These two gains are summed together instantaneously to give the delivered flow from the ventilator to the patient according to the ratio set by the operator

* The relation between the maximum inspiratory force and the VT can be represented

by the slope N for a normal person (MIP =100 cmH2O, R =4 cmH2O/L/s, &

C=100ml/cmH2O), you will see that a minimal change (effort =MIP) will be

associated with a large change in the VT In patient with (MIP =30cmH20, R

=12cmH2O /L/s, & C= 40 ml/cmH2O), the slope will be O which is usually one ninth

P

V

of the normal slope and you will see that a large effort (MIP) is needed to make a change in the VT and sometimes the needed VT is not gained and the patient reaches

to fatigue early With PAV 80% you can get a slope close to the normal which means less effort of the patient to get the desired VT

* * Type of the ventilator (respiratory cycle)

Volume T Pressure T Volume CON Pressure T Time CY

* It is a proportional pressure support so, it is a pressure limit

**** Type of respiration

Assisted mandatory

Mandatory

ntaneous

PR TARGET

PR LIMIT

Ti FLOW

+

eTim

# V

PR

Time

* You set the triggering level which is usually flow

*You set the pressure limit as an alarm

*Cycle off will be by flow or pressure

* You set or not PEEP

** * Conditioned variables

Sigh

Apnea data

Rate/min Single/Multiple VT

Trigger CMV

*You set the back up the apnea data as CMV of pressure target ventilator

Chapter 2

THE RESPIRATORY SYSTEM

*

THE RESPIRATORY SYSTEM

** This system is meant to keep PaO2 and PCO2 constant at different levels of

increase in PCO2 >50mmHg or both

** This system is composed of two important parts:

1- The broncho- pulmonary part which is meant for gas exchange 2- The neuromuscular part which is meant for air in and out (ventilation)

** The substrate or the tool of this system is air which changes in volume to satisfy the body needs and since its physical characters are changeable it is called variables

** The items of this system which deals with this air does not change except with pathology that is why they are called parameters

** We will discuss these variables and parameters from the ventilation point of view, regarding the function, the pathological problems, how to monitor, what are the normal values, what is their threshold failure, what are the weaning values, what is the ventilator strategies adopted, and how to treat these problems

1- BRONCHO – PULMONARY SYSTEM

** It is formed of two parts:

A- Bronchial tree B- Pulmonary part

** Passage of air through this tree produces pressure according to the equation:

Pressure = Flow x Resistance (1)

** We should know that we have two bronchial pressures, one is produced during inspiration and the second is produced during expiration

* This inspiratory pressure is the sum of pressure resulting from flow

of air through both ETT and bronchial tree, and accordingly the resistance calculated will be the total resistance (ETT resistance + bronchial tree resistance)

* ETT resistance and pressure can be known from the post trigger phase ( ) or from the table ( )

* The resistance developed by the ETT depends on its size, and the presence of kink, and or secretion

* The resistance of the bronchial tree can then be calculated and we should know that this resistance is affected by;

- Bronchial secretion - Bronchial edema

- Bronchial hyper vascularity - Bronchial smooth muscle spasm and

*Inspiratory resistance is an important element in determining the inspiratory work load

* Using large size ETT, utilizing the tube compensation facility, clearing the secretion, treating the edema, and releasing the spasm are important to decrease the inspiratory work load

* When you disconnect your patient from the ventilator but still on the tube, you should know that he has a higher inspiratory load due to ETT which is corrected by extubation

** Expiratory pressure;

*It is the platue pressure

* From equation (1), the flow can be measured from the flow time curve as the peak flow, and you already measured the platue pressure so you can calculate the expiratory resistance

* Increase in the expiratory resistance will lead to;

1- Increase in the expiratory time constant

2- Incomplete empting of the VT

3- Air trapping and increase in the FRC

4- Development of PEEPi due to static and dynamic hyper inflation

5- PEEPi will lead to;

*- Increase inspiratory work load due to, increase in resistance,

decrease in lung compliance, decrease in chest cage compliance

(out ward movement during inspiration), and the work to counteract the PEEPi

*- Shortening of the diaphragm and intercostals leading to decrease

in its power

*- Increase in dead space

*-Cardio vascular compromisation in the form of, decrease in venous return, decrease diastolic function, increase after load, and finally decrease in cardiac out put

** How to monitor the bronchial tree?

*= Measure the total inspiratory resistance as follow;

T = Compliance x Expiratory resistance

*= Tray to adjust the actual expiratory time to be more than 5 x T

* It is the inherent capacity of the air – conducting system (ETT and air ways)

to resist air flow and is expressed as the change in pressure per change in flow RESISTANCE = PRESSURE/ FLOW

*Resistance has a good share in the time constant whether inspiratory or expiratory

* Resistance is the opposition to the flow of gases due to frictional forces within the respiratory system The energy required to overcome resistance is dissipated as heat within the respiratory system

* The customary units of resistance are cm H2O/L /s