Basics & principles of mechanical ventilation

g.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:     

G

ood ventilation (known by pa Co2)

O

xygenation (by pa O2).

A

lveolar recruitment by peep

L

owest O2 supplement.

S

ynchrony between patient & Ventilation.

&

S

afe  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.

2.

3.

Power source-electrical/pneumatic/both Control systems-circuits, control panel Display systems

oxy Central unit blender Hum& neb

V

Exp.limb

Insp. limb

V T Pt P Fio2

compr essor

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 PIP SET & lesser set variable & more    Plateau pressure Set Inspiratory time set Variable Inspiratory flow decelerating type fixed flow type sinusoidal/square set  Respiratory rate Set  Barotrauma Less Leak compensation +for minor leak Patients acceptance good Set More nil

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 .

Compliance-resistance-volume C= ▲V /▲P Vt Ccw compliance R=[PIP-Pp] / F Cl PA range PAi Raw PAe

Normal resistance

Un intubated patient ; 0.6 - 2.4 cm H 2 0 / L / Sec, . at 0.5L /sec Intubated patient; 6cm H20 / L / Sec

Ventilatory controls-inter relation

MV Ti T I:E Te Vt f

Ventilator Modes

Combination of breath type and phase variable.

Conventional modes Recent modes Newer modes CMV A/C MV IMV & SIMV CPAP & PEEP VCV PSV MMV APRV VAPS, PAug VS, PRVC BIPAP AUTOFLOW IRV AUTOMODE DLV PAV,PPS 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  weakness.

Respiratory muscle  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.

Assist / Control Mechanical Ventilation

   

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.

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 PEEP

Pr 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 PIP SET & lesser set variable & more    Plateau pressure Set Inspiratory time set Variable Inspiratory flow decelerating type fixed flow type sinusoidal/square set  Respiratory rate Set  Barotrauma Less Leak compensation +for minor leak Patients acceptance good Set More nil

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 H 2 O & EAP is 3 cm H 2 O •

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

BREATH CHANGES WITH IN •

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

BREATH CHANGES WITH IN •Trigger – •Limit - •Cycle - patient patient pressure variable pr flow volume

PSV Paug VAPS

DUAL MODES BREATHS

-

CHANGES OVER SEVERAL

•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 BREATHS

-

CHANGES OVER SEVERAL 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



W

earing off primary pathology 

E

limination of effects of sedation & relaxants 

A

bsence of sepsis 

N

o metabolic / electrolyte abnormality 

I

nvolvement of patient 

N

utritionally stable 

G

ood & stable CVS