Mechanical Ventilation 16-3

8/6/2019 Mechanical Ventilation 16-3

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Mechanical VentilationMechanical Ventilation

Dr. Ekramy Essa Abdel Rahman

Lecturer of geriatric medicine

Ain Shams university

16/3/2011


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J. Rasanen


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MV

Non-invasive

Negative pressure(NIPPV) Positive pressure

Invasive

Positive ressure

Extracorporeal

Novel modes of improving gas exchange

ECMO - ExtraCorporeal Membrane Oxygenation - ECCO2R - ExtraCorporeal CO2 Removal are intended to "keep the lung rest" to avoid further

damage


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Origins of mechanical ventilationOrigins of mechanical ventilation

Negative-pressure ventilators(iron lungs)

Non-invasive ventilation firstused in Boston ChildrensHospital in 1928

Used extensively during polio

The era of intensive care medicine began with positive-pressure ventilation

outbreaks in 1940s 1950sPositive-pressure ventilators

Invasive ventilation first used atMassachusetts General Hospitalin 1955

Now the modern standard ofmechanical ventilation

The iron lung created negative pressure in abdomen

as well as the chest, decreasing cardiac output.

Iron lung polio ward at Rancho Los Amigos Hospitalin 1953.


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5


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Indications For Mechanical

Ventilation

Rule 1. The indication for intubation andmechanical ventilation is thinking of it.

elective intubation carries fewer dangers than

emergen n u a on. Rule 2. Intubation is not an act of weakness.

Rule 3. Endotracheal tubes are not a disease,

and ventilators are not an addiction.


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Indications for MV

Acute Respiratory Failure(Hypoxic, hypercapnic)

Post arrest

. . ,

Very rare specific indications (flail chest ,hyperventilation for ICP )

Acute reduction of ICP (PCO2 30-35 -short term)


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What is a Mode? In simple terms mode can be defined as a set of operating

characteristics that control how the ventilator functions.

3 components Control variable

Pressure or volume

Breath sequenceContinuous mandatory

Intermittent mandatory

Continuous spontaneous Targeting scheme (settings)

TV (insp.press.), inspiratory time (insp.flow), frequency, FiO2,PEEP, trigger


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Basics Phase Variables

A. Trigger (start)- begins inspiratory flow

B. Cycling (end)- ends inspiratory flow

C. Limiting (continue)- places a maximum value on a

control variable

A. pressure

B. volumeC. Flow

D. Baseline Variable- (PEEP)A

B C


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Trigger Variable

Start of a Breath

Pressure (patient assisted) -inspiration beginswhen a pre-set pressure change is detected

when a pre-set flow is detected

Time(control ventilation) -inspiration begins

when a pre-set time change is detected Manual - operator control


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Inspiratory - delivery limits

(continue)

Maximum value that can be reached of a

variable during inspiration.

Continue =(i.e., it does not end inspiration).

Pressure, flow, or volume can be limitvariables


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Cycle(End of Insp.)

The phase variable used to terminate inspiration-

Pressure -inspiration ends when a pre-set

Time -inspiration ends when a pre-set timechange is detected

Volume-inspiration ends when a pre-setvolume change is detected (VCV)

Flow-inspiration ends when a pre-set flow is

detected


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Breath Type

Mandatory (trigger off or no trigger)

Ventilator does the work

Ventilator controls start and stop breath

ss ss e r gger on-Ventilator does the work

-Patient initiate breath

Spontaneous +/- suuportPatient takes on work

Patient controls start and stop


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The Control Variable-

Flow (volume) controlled

Flow (volume) waveform unchanged

pressure may vary with compliance/resistance

Pressure controlled

pressure waveform unchanged

flow and volume may vary with compliance/resistance

Time controlled (HFOV)pressure, flow, volume may vary with compliance


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Pressure Ventilation vs. Volume

Ventilation modes of Mechanical ventilation are Pressure cycled and

Volume cycled modes (or dual).

Volume-cycled modes sets insp. flow and TV delivers that

tidal volume at variable pressure depending on the patient's

.

Control

Assist/Control

Synchronous Intermittent Mandatory Ventilation (SIMV)


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Pressure Ventilation vs. Volume

Ventilation

Pressure-cycled modes : sets a maximum inspiratorypressure so that the ventilator delivers a fixed pressure at

variable volume depending on the patient's compliance

.

Pressure Control Ventilation (PCV)

Pressure Support Ventilation (PSV)

CPAP BiPAP


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Inspiration Expiration

0 1

20

20

021

20

20

02

Inspiration Expiration

Volume/Flow Control Pressure ControlVolume/Flow Control Pressure Control

PawPaw

Pressure

00 1 2

3

-3

0

00 1 2

3

-3

0 Time (s) Time (s)Flow


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Volume ControlAdvantages

Guaranteed tidal volume& Minimum min. vent.

VT is constant with variable compliance and resistance.

Less atelectasis compared to PC.

VT increase is associated with a linear increase in minute ventilation.

Disadvantages

The limited flow (high flow rate demands pt) .

Variable effort = variable work/breath

If patient continues to inspire vigorously, unnecessary work & fatigue.

Variable pressures-- risk for barotrauma and adverse hemodynamic effects.

Leaks = vol. loss


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Pressure ControlAdvantages : limits excessive airway pressure

Lower peak inspiratory pressures (Peak pressures are limited).

Adjustable inspiratory time.

Improved gas distribution, V/Q matching, and oxygenation( increased mean airway

pressure)

Reduced WOB

etter w t ea s

Variable flow --usually better tolerated, less need for sedation

Disadvantages :

Variable VT as pulmonary mechanics change(Too large(volutrauma)- ortoo small

(hypovent).

Potentially excessive VT as compliance improves

Inconsistent changes in VT with changes in PIP and PEEP

Minimal VE is not ensured

Some variability in max pressures (PC, expir. effort)


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Assist control mode(AC)breaths may be assisted (trigger on) or mandatory

Should be initial mode in most patients , especially unstable patients who areawake and controlling their own

Advantages:ensures a minimum MIN V;

better patient synchrony if higher MIN V is desired.

.

disadvantages:

Not a weaning mode

often results in patient-ventilator dissynchrony and respiratory muscle

(setting mismatch) high respiratory drive (i.e., liver failure , central)>>overventilation &

respiratory alkalosis>> Hyperinflation and Auto-PEEP

I:E ratio can vary because the variable RR can alter the expiratory phase


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CMV (trigger off)


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Assist-control

Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB, Scmidt GA, & WoodLDH(eds.): Principles of Critical Care


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Synchronised Intermittent Mandatory

Ventilation Breaths may be spontaneous, assisted, and mandatory

Advantages

Synchronised mandatory breath

More comfortable for some patients

Less hemod namic effects

ensures a minimum minute ventilation

Pressure support for sponteous breath.

Disadvantages

-Increased work of breathing(the least beneficial weaning mode)

. -Cannot fully control the I:E ratio (variable in RR and spontaneous

breaths).

-Sometimes complicated to set


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ACV vs. SIMV

Switch to ACV for:Patients with respiratory muscle weakness or

Switch to SIMV for:

evidence of overventilation (respiratory alkalosis) orhyperinflation (auto-PEEP)


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Patient determines RR, VE, inspiratory timea purely spontaneous mode. Theclinician sets only the inspiratory pressure above the PEEP.

Parameters

Triggered by Patient only

Limited by pressure

Flow-cycled: inspiration ended by reaching (25%) of PIF

Flow: decelerating rate; patient can increase

ects nsp rat on on y

Volume: varies with pressure, effort, and compliance of lung and chest wall

Uses

Complement volume-cycled modes (i.e., SIMV)

not for augment TV but overcomes resistance.

PSV alone for recovering intubated pts who are not quite ready for extubation.

Augments inflation volumes during spontaneous breaths

BiPAP (CPAP plus PS)


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Pressure Support Ventilation (PSV)What is the right amount of pressure support?

overcome WOB imposed by ETT (varies with flow rates, impedance )(about 5-10)

Estimated PS level = PIP Ppt - (ATC mode) When the intent is to assume most of the work of breathing .No

formula to calculate the right amount, the right level of PS is at which.

Comfort can be assessed from the RR (


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A vantagesSimple, avoids high inspiratory pressure, less sedation,better haemodynamics. mode of weaning ,decreasesWOB

Patient comfort

May enhance patient-ventilator synchrony


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Disadvantages:

If sole mode of ventilation--apnea alarm mode backup

Inadequate volumes could be delivered if the ETT is

blocked or decreased lung compliance/ increase

res s ance

Inspiratory off-switch failure, that is, application of

inspiratory pressure after cessation of inspiratory muscle

activity, is common during PSV. High inspiratory pressure

settings, a low respiratory drive, airflow obstruction with

dynamic hyperinflation, and air leaks predispose patients

to this form of patient-ventilator asynchrony.

C i P i i Ai P


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Continuous Positive Airway Pressure

CPAP Constant PEEP applied to spontaneously breathing patient

Orders: FIO2 and PEEP

Initiate: patient

Termination: patient

Pressure: oscillates around the PEEP

Volume: varies with pressure, effort and compliance

Allows spontaneous breathing at elevated baseline pressure

Patient controls rate and tidal volume (

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( )


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(CPAP)

- Used for oxygenation support not for ventilation(no inspiratory flowis delivered).

-Does not directly decrease the WOBWOB is reduced compared (T-piece). CPAP stents the airways open and allows for beer

exhaled Vt. &Patient does not need to generate negative pressure to receive inhaled gas

Indications: MV or facemask (CPAP improve oxygenation without

harmful effects of MV)

Weaning protocols.

Obstructive Sleep Apnea.

Restrictive lung diseases.

Neuromuscular lung diseases.

Post op respiratory failure

Risks--Barotrauma & Pneumothorax


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Basic Ventilator Modes

MODE

Orders

(FIO2,PEEP)

Initiate Terminate(cycled)

Flow Pressure VT

VC VT, RR(I:E)

(P)atient

(C)ontrolled

VT or time constant

(usually)

rising fixed

PC Pinsp, RR(I time)

P, C I time decelerate constant varieswith

com liance

SIMV PC or VC;PS, CPAP

P, C (synchwith patient)

PS/bilevel Pinsp P only 25% of

peak flow

decelerate constant complianc

e, effort

CPAP PEEP P only Patientdetermines

Patientdetermines

aroundPEEP

compliance, effort

T-tube FIO2 P only Patient

determines

Patient

determines

around

atm

complianc

e, effort


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Vent. Orders

Your orders

Mode, Flow rate, FIO2,

set RR, set VT/ PS/PClevel, PEEP

Total RR

PIP= Peak inspiratorypressure

Plateau pressure Total PEEP

VT VE= minute ventilation

Ventilator bundle

aw

pressure I:E; % I time

ABG

Weaning parameters


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Volume control

Fixed settings

RR, VT, I:EPEEP, FIO2

Pressure Control

Fixed settings

RR, Pinsp, I timePEEP, FIO2

PIP, Plat

VE, total RR; ABG

Total PEEP

epen ent actorsV

T

VE, total RR; ABG

Total PEEP


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Pressure support

Fixed settings

PinspPEEP, FIO2

SIMV

Fixed andDependent factors

Combination ofthe two different

VTVE, total RR

modesDependent factors

Compliance,resistance, and

patienteffort


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Inspiratory flow rate(inverse correlation with Ti)

Set to target I:E ratio (about 4 X min. volume)(TV/Ti) 40-60l/min(up to 90 in COPD)(decrease in hypoxia) Monitor: patient response, airway pressure/flow graphics

decelerating flow pattern( preferred) SE: high flow increase PIP - low flow ---autoPEEP

Inspiratory timeI:E normally 1:2, simulates normal breathing synchrony

1:3or4 in COPD patient

Inverse ratio(ARDS)

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Monitoring Lung Mechanics

Proximal Airway Pressures (end-inspiratory)

1. Peak Pressure

Function of: Inflation volume, recoil force of lungs and

chest wall, airway resistance

. ateau ressure

Occlude expiratory tubing at end-inspiration Function of

elastance alone

Mean Airway Pressure:Area under curve

Main factor in oxygenation and recruitment(Increased

surface area for O2 diffusion)

Alveolar pressure = (Volume/Compliance) + PEEP


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Alveolar pressure = (Volume/Compliance) + PEEP

Airway pressure = (Flow x Resistance) + (V/C) + PEEP


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Mechanical Ventilation 16-3