Basics & principles of mechanical ventilation

Basics & principles of

mechanical ventilationg.k.kumar

Basics & principles of ventilation

-What is ventilator

-How ventilators work

-How to use

?

Ventilator:

The Machine delivers O2 & removes Co2 with out harming the patient.

The Ventilator should have capacity of delivering a consistent tidal volume under all adverse conditions of lung disease.

Mechanical Ventilation:

The process / method by applying

(intermittent) positive airway pressure

& supplementation of Inspired O2 to

achieve desirable oxygenation.

GOALS of Mechanical Ventilation:

Good ventilation (known by pa Co2) Oxygenation (by pa O2). Alveolar recruitment by peep Lowest O2 supplement. Synchrony between patient & Ventilation. & Safe No Negative hemodynamic effect

No Barotraumas No auto PEEP

Classification of Mechanical ventilation:

Positive / Negative pressure ventilation.

Partial / full ventilation.

Invasive / Non invasive ventilation.

Components of ventilator

1. Power source-electrical/pneumatic/both

2. Control systems-circuits, control panel

3. Display systems

compressor

compressor

Insp. limb

Exp.limbPt

blenderoxy

Central unit

V

V

P Fio2T

Hum&neb

PHASES & VARIABLES INITIATION OF INSPIRATION-TRIGGER

INSPIRATION-LIMIT

MAINTENANCE OF INSPIRATION-CONTROL

CHANGING TO EXPIRATION-CYCLE

Triggering variable:

Triggering is a method of starting the inspiration

Types: Pressure Triggering

Flow Triggering - No lag time

Time Triggering -Less effort

Control Variable:

Setting that maintained thro ‘out inspiration

Type : Volume control.

Pressure control.

PCV VCV Vt. Variable set PIP SET & lesser variable & more Plateau pressure Set Variable Inspiratory flow decelerating type fixed flow

type sinusoidal/square Inspiratory time set set Respiratory rate Set Set Barotrauma Less More

Leak compensation +for minor leak nil

Patients acceptance good -

Limit Variable:

Setting that can't be exceeded during inspiration

Type : Pressure limit- [psv]

volume limit

Flow limit

Cycle variable:

Method of termination of inspiration, I.e. changing over from inspiration to expiration.

Types: Volume cycle Pressure cycle Time cycle flow cycle.

Vt PA range

compliance

ClCcw

PAi

PAe

Raw

Compliance-resistance-volume

C=▲V /▲P R=[PIP-Pp] / F

Normal resistance

Un intubated patient ; 0.6 - 2.4 cm H20 / L / Sec, . at 0.5L /sec

Intubated patient; 6cm H20 / L / Sec

Ventilatory controls-inter relation

MV

fVt

T

Ti

I:E

Te

Ventilator Modes Combination of breath type and phase variable.

Conventional modes Recent modes Newer modes

CMV MMV VAPS, PAug

A/C MV APRV VS, PRVC

IMV & SIMV BIPAP AUTOFLOW

CPAP & PEEP IRV AUTOMODE

VCV DLV PAV,PPS

PSV HFJV ASV

Controlled mechanical ventilation:

-CMV All breaths are delivered by ventilator.

No Patient participation.

Set Vt. Delivered at set RR

Requires sedation & neuromuscular blockade.

Time initiated

Volume limited

Volume cycling

CMV Indications Patient with no efforts / complete respiratory failure. When negative inspiratory effort contra indicated. eg.flail chest. During anesthesia. Disadvantages

Patient participation not allowed. Heavy sedation relaxant – need Long term CMV Respiratory muscle

weakness. Varying PIP according to lung compliance &

patient efforts.

Assist / Control Mechanical ventilation:

Patient can trigger ventilation at a rate more than set RR

All breaths are delivered at set volume , set time & set pressure

Triggering pressure / flow (spontaneous)

Time (Mandatory)

Limiting Volume

Cycling Volume Patient can vary RR only but not vt.

Indications: Patient with normal drive but with respiratory weakness

Recovering patient. To preserve patient efforts

Weaning.

Disadvantages Rapid triggering Hyperventilation

Hypotension

Flow rare should be adjusted according to the need.If RR < RR CMV mode.

Assist / Control Mechanical Ventilation

IMV / SIMV

The patient receives the Mandatory set Vt at set RR. The set Mandatory breaths are synchronized with patient

efforts. Between the mandatory breaths the patient can breath

spontaneously Spontaneous breath vt depends on Patients respiratory effort PS Triggering - Pressure Limiting - Volume Cycling - Time

IMV / SIMV

Advantages: The mandatory breaths are synchronized with

patient’s Spontaneous efforts. Hyperventilation is less More active participation of patient

Disadvantages: More WOB

A/CMV SIMV

Patient decides only RR < -- > patient effort decides RR &vt.

Less WOB as only < -- >more WOB as Initiation by patient patient has to . operate demand

. flow system

Possibility of hyper ventilation < -- > No

CPAP:

A mode is which positive pressure is applied tho’ out the respiratory cycle using during spontaneous ventilation.

(Pr applied in mechanical ventilation :PEEP) No Ventilatory assistance Positive Pressure causes: Prevention of alveolar collapse & alveolar recruitment

Î FRC & Atelecasis

FlO2 requirement

CPAP PEEPPr applied and base line Pr. Applied with

Pr elevated when ventilatory some ventilatory Assistance is nil. Assistance present.

PEEP

Applied when Fio2 requirement is 50% - 60%.

Best Peep: PEEP titrated to achieve optimal respiratory system compliance.

Optimal Peep :Titration of PEEP until Qs /Qt is < 15 %

Volume Control Ventilation:

Vt. Delivery is constant according to pressure regardless of changes in airway resistance or respiratory system compliance.

VCV is given when constant MV is needed (eg, : patient with Î ICT)

Pressure control ventilation: The pressure applied to the airways is constant

regardless of airway resistance and compliance. Constant pressure is delivered throughout inspiration at

set RR Time initiated pressure limiting time cycling. Vt may vary according to patient lung conditions. PCV avoids over distention in patient with ALI, because

PIP can be set.

Settings Preset pressure is equal to half of present PIP. PEEP half of present PEEP (if > 8cm H2 O) I: E is 1:2

PCV VCV Vt. Variable set PIP SET & lesser variable & more Plateau pressure Set Variable Inspiratory flow decelerating type fixed flow

type sinusoidal/square Inspiratory time set set Respiratory rate Set Set Barotrauma Less More

Leak compensation +for minor leak nil

Patients acceptance good -

Pressure – Support Ventilation (Psv)

Patients spontaneous activity is assisted by delivery of a preset amount of inspiratory positive pressure.

Patient triggers set pressure is maintained throughout inspiration.

Pressure initiated. Pressure limiting . Flow Cycling As flow reaches 25% of peak inspiratory flow /5

litres / min

Pressure – Support Ventilation (Psv)

Low PSV – to overcome the patients WOB associated with ETT and circuits.

PSV max – to achieve Vt of 10 -12 ml / Kg - may require upto 40 -50 cm H2O Can be used alone as full ventilatory support or with

SIMV. Can be used as non invasive ventilatory support up to

20cm H2O2 for – transient Ventilatory support ( Narcotic overdose, asthma, acute exacerbation of COPD).

Mandatory Minute Ventilation (MMV):

Preset MV is selected. The Ventilator calculates the patients spontaneous MV. It patients spontaneous MV < set MV, ventilator assists to achieve

set MV

Ventilatory assisstance may be

- Volume controlled SIMV breaths Î RR /Vt

- Î PSV

Mandatory Minute Ventilation (MMV):ADVANTAGES:

•MV guaranteed

•Useful as weaning mode

DISADVANTAGES:

• RR may cause dead space ventilation even with acceptable MV.

•Respiratory muscle fatigue may develop (so high RR alarm should be activated.

Mandatory Minute Ventilation (MMV):

INDICATIONS:

•During weaning period

•To aspiratory flow and WOB

•To overcome ETT/circuit resistance

BILEVEL POSITIVE AIRWAY PRESSURE VENTILATION(BIPAP)

•A pressure controlled ventilation

•Allows unrestricted spontaneous breathing at any point of ventilatory cycle

•Time cycled changes of pressure application.

•Independent positive airway pressure to inspiration & expiration

•Inspiratory set pressure is called IAP/T high& Expiratory set pressure is called EAP/T low

•Usual IAP is 8 cm H2O & EAP is 3 cm H2O

•Trigger:flow, Limit:pressure; Cycle:time

BILEVEL POSITIVE AIRWAY PRESSURE VENTILATION(BIPAP)

•IAP causes better ventilation Paco2

•EAP causes better oxygenation Pao2

•Types

--CPAP+PS

--Two alternating CPAP level

--APRV

BILEVEL POSITIVE AIRWAY PRESSURE VENTILATION(BIPAP)

ADVANTAGES:

•Non invasive ventilation

•Useful in—end stage COPD

---restricted chest wall diseases

---neuromuscular diseases

---nocturnal hypo ventilation

•A weaning mode.

AIRWAY PRESSURE RELEASE VENTILATION(APRV)

A CPAP circuit with release valve at expiratory limb –driven by time device

APRV is a CPAP system causing . alveolar ventilation by briefly interrupting CPAP.

APRV…….,

Release valve opens for 1-2sec.

Pr drops to lower level-low CPAP(0to-2cmH2O)

Lung volume less than FRC in expiration

alveolar ventilation & CO2 elimination

Reapplication of CPAP by closing valve- Higher CPAP(10to 12 cm H2O)

FRC & oxygenation.

APRV…….,

ADVANTAGES:

•Lesser PIP ,so less hemo dynamic changes.

•To alveolar ventilation in ALI of mild to moderate.

•A weaning mode.

INVERSE RATIO VENTILATION(IRV)

•I:E >1

•PC-IRV / VC-IRV

• Ti with set pr opening of stiff alveoli units improved oxygenation

• Te not allowing alveoli to collapse

development of intrinsic PEEP

reduction of shunting

IRV……,Improve oxygenation by

•Reducing intra pulmonary shunting

•Improvement of V/Q matching

•Decreased dead space ventilation

•Increased MAP & intrinsic PEEP

Useful when high FiO2 & high PEEP to be avoided

NEWER MODES

1.Dual modes: VAPS, Paug, - VS, PRVC, Autoflow, VPC

2.Switching modes: Automode

3.Proportional modes: PAV,PPS.

4.Adaptive modes: ASV

DUAL MODES Combination of 2modes of ventilation(PCV&VCV) to

deliver guaranteed Vt/MV

Volume guaranteed pr targeted ventilation

Mode changes occur

with in a breath-VAPS,Paug

over several breaths-VS,PRVC,Auto flow,VPC

DUAL MODES - CHANGES WITH IN BREATH•VAPS:volume assured pr support-T bird,bird8400st

•Paug :pr augmented ventilation-bear 1000

•Vt guaranteed variable pr limited modes

•During inspiration,the ventilator monitors Vt

if desired Vt delivered before flow drops---PSV

if desired Vt not delivered before flow drops—

flow continued at set pr support level till adequate

Vt delivered.

DUAL MODES - CHANGES WITH IN BREATH

•Trigger – patient patient

•Limit -- pressure variable pr

•Cycle -- flow volume

PSV Paug

VAPS

DUAL MODES - CHANGES OVER SEVERAL BREATHS

•PRVC:Pr regulated VC-siemen300

VS:volume support:servo 300

Auto flow;DragerE4

•VS-volume assured PSV

•PRVC-volume assured PCV

•Vt measured over several breaths&adequate MV achieved by changing PS/PC mode for remaining breaths.

DUAL MODES - CHANGES OVER SEVERAL BREATHS

AUTOFLOW:

•Autoflow alters the function of inspiratory and expiratory valves

Allowing patient to receive inspiratory flow demand

•Auto flow provides better ventilatory tolerance

•A weaning mode

Switching modes•Ventilator can switch modes according to monitored information

•Automode:servo300

Switching between control /support mode depending on patient’s respiratory pattern

•Monitoring of patient’s respiration over fixed time period – if 2consecutive effort + PSV . -- if no efforts - PCV

Proportional modes•PAV:proportional assist ventilation-PB840

PPS: proportional PS-Evita-E4

•Proportional modes are assisting spontaneous ventilation

•PPV:a support mode in which pr, flow,volume are set proportional to patient’s inspiratory efforts

Proportional modes

•The more effort pt exerts-the more support the machine provides

•PAV allows patients to comfortably reach whatever the ventilatory pattern that suit their need.

Adaptive modes•ASV-Adaptive support ventilation

•Uses pr targeted breaths to assure a target MV with decreased WOB

•ASV adapts to the changing capabilities of patient’s lung conditions.

•More efforts the patient does less - support the machine provides.

Adaptive modes

•ASV calculate the over all MV combination of volume guaranteed PSV(VS) & volume guaranteed PCV(PAVC)

•ASV can ventilate the patient from acute stage to a weaning stage.

Weaning

Wearing off primary pathology Elimination of effects of sedation & relaxants Absence of sepsis No metabolic / electrolyte abnormality Involvement of patient Nutritionally stable Good & stable CVS