بسم الله الرحمن الرحیم Basics of Mechanical Ventilation

بسم الله الرحمن الرحیم

Basics of Mechanical Ventilation

Normal breath inspiration animation, awake

Diaghram contracts

Chest volume

Pleural pressure

Air moves down pressure gradientto fill lungs

-2cm H20

-7cm H20

Alveolarpressure falls

Normal breath

Lung @ FRC= balance

Normal breath expiration animation, awake

Diaghram relaxes

Pleural / Chest volume

Pleural pressure rises

Normal breath

Alveolarpressure rises

Air moves down pressure gradientout of lungs

تغییرات : منحنی

زمان( – 1 فشار

زمان( – 2 حجم

زمان( – 3 جریان

رسم طبیعی تنفسی سیکل یک در را:کنید

0-1-2-5

Expiration

Inspiration

+3+2+1

Normal breath

0-1-2-5

Expiration

Inspiration

+3+2+1

Normal breath

Expiration

Inspiration

Normal breath

0-1-2-5

Expiration

Inspiration

+3+2+1

Expiration

Inspiration

Normal breath

Ventilator breath inspiration animation

Air blown in

lung pressure Air moves down pressure gradientto fill lungs

Pleuralpressure

0 cm H20

+5 to+10 cm H20

Ventilator breath expiration animationSimilar to spontaneous…ie passive

Ventilator stops blowing air in Pressure gradient

Alveolus-trachea

Air moves outDown gradient Lung volume

تغییرات منحنیفشار (1 حجم (2

جریان (3رسم مصنوعی تنفس سیکل یک در را

:کنید

0-1-2-5

+3+2+1

WNormal breath Mechanical breath

Origins of mechanical ventilationOrigins of mechanical ventilation

•Negative-pressure ventilators (“iron lungs”)

•Non-invasive ventilation first used in Boston Children’s Hospital in 1928

•Used extensively during polio outbreaks in 1940s – 1950s

•Positive-pressure ventilators

•Invasive ventilation first used at Massachusetts General Hospital in 1955

•Now the modern standard of mechanical 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 Hospital in 1953.

Several ways to ..connect the machine to Pt

• Oro / Naso - tracheal Intubation

• Tracheostomy

• Non-Invasive

Ventilation

Ventilation = Inspiration + ExpirationInspiration = 1) Start or Triggering 2) inspiratory motive force or control or Mode 3) termination of inspiration or CyclingExpiratory Phase Maneuvers

Classification (the Basic Questions)

A. Trigger mechanism– What causes the breath

to begin?

B. Limit variable– What regulates gas

flow during the breath?

C. Cycle mechanism– What causes the breath

to end?

1 2 3 4

The four phases of each ventilatory cycle

InspirationExpiration

inspira

motive fo

rce or c

ontrol o

r Mode

Cycling

Cycling Vs. Limiting

Cycled

Pressure

Time Time

Limited

Pressure

ببرید نام را مکانیکی تنفس مرحله :چهار1)2)3)4)

Triggering the Ventilator

flow trigger

pressure trigger

volume Trigger

Time Trigger

Other techniques: Neurally Adjusted Ventilatory Assist (NAVA) Chest impedance Abdominal movement

Flow triggering is considered to be more comfortable,

Increasing the trigger sensitivity: decreases the work of breathing accidental triggering and unwanted breaths

Trigger

Which Trigger is correct?

flow trigger

pressure trigger

volume Trigger

Time Trigger Mandatory

all the breaths with mandatory

inspiratory cycling

SpontaneousUnsupported

Mandatory

Trigger

flow trigger

pressure trigger

volume Trigger

Time Trigger

Trigger

flow trigger

pressure trigger

volume Trigger

Time Trigger Mandatory

supported

Trigger

flow trigger

pressure trigger

volume Trigger

Time Trigger MandatorySynchronized

supported

Triggered

Mandatory(VCV)

spontaneous and mandatory

inspiratory cycling

spontaneous and

mandatory

No mandatory inspiratory cycling all the breaths are pressure-targeted and trigger inspiratory-cycled

Which Trigger?

flow trigger

pressure trigger volume Trigger

Time Trigger

Non of the above

Air INAir OUT

InspirationExpiration

A certain amount of time is necessary for pressure equilibration (and therefore completion of delivery of gas) to occur between proximal airway and alveoli. TC, a reflection of time required for pressure equilibratlon, is a product of compliance and resistance. In diseases of decreased lung compliance, less time is needed for pressure equilibration to occur, whereas in diseases of increased airway reslstance, more time is required. Expiratory TC is increased much more than inspiratory TC in obstructive airway diseases, because airway narrowing is exaggerated during expiration.

Time Constant = C X R

3-5 time constant

C = 100 cc/ Cm H2OR = 1 Cm H2O / L / Sec

Time Constant = ? = R.C =100 cc/ Cm H2O X 1 Cm H2O / L / Sec = 0.1 Sec

Time Constant

TC= ? = R.C =50 CC / Cm H2O X 1 Cm H2O / L / Sec = 0.05 Sec

Time Constant = ? = R.C =100 CC/ Cm H2O X 1 Cm H2O / L / Sec = 0.2 Sec

Inspiratory Time = ??

TC = C x R = 0.16

IT = 3 x 0.16 = 0.48

Selection of Appropriate Inspiratory TimeTI too longTI too shortT I = 3-5 time constant Tc = C x R

TI is usually initiated at: 0.5-0.7 sec for neonates, 0.8-1 sec in older children, 1-1.2 sec for adolescents and adultsneed to be adjusted through : individual patient observations and according to the type of lung disease.

T I + T E = Time CycleF ( RR ) = 60/TC I T E T F= 60/ TI +TE

T I = 3-5 time constant Tc = C x R

Many ventilators ask the user to set the I:E ratio and respiratory rate

V T = 100 cc TI = 0.8 sec Inspiratory Flow = ?Inspiratory Flow = 100 / 0.8 = 125 cc/sec (7.5 L/ Min )

• RR = 60 I:E = ½ IT = ? ET = ?F= 60/ TI +TE60 = 60 / TI + 2TI = 60/ 3TI

IT = 0.33 ET = 0.66

• IT= 0.8 ET= 1.2Sec• RR=?

F= 60/ TI +TERR = 60 / 0.8+1.2 = 30

DeceleratingSquareAcceleratingSinusoidal

Inspiratory Flow/Pressure/Volume Pattern

Inspiratory Rise TimeInspiratory Rise Time

Pressure-controlled inflationPm

Inspiratory Rise TimeInspiratory Rise Time

Effect of a pressure-limit on a volume-controlled breath

CyclingTermination of Inspiration (Cycle)

1)Time-cycled 2)Volume-cycled

3) flow-cycled

Cycling at 25% Flow

Pressure Controlled Ventilation

respiratory resistance and compliance are both lower

both the resistance and compliance of the respiratory system are higher

IT>IT<

Cycling at 25% Flow

(high resistance), prolonged inspiration a large tidal volume. the next inspiratory phase starts before expiratory gas flow has reached zero

10%ET ET

Over inflation Improve Over inflation

inspiratory motive force or control or Mode

Critical Opening Pressure

The desired tidal volume is set on the ventilator, and the resulting airway pressure excursion is merely observed. Inspiratory volume is thus the primary, or independent, variable (V) and the change in airway pressure (P) resulting from this is the secondary, or dependent, variable.The value of P is determined by the compliance of the respiratory system, which is given by V/P. If the compliance of the respiratory system falls, V remains constant but P increases

Volume Controlled Ventilator

The desired inflating pressure is set on the ventilator, and the tidal volume that this delivers is merely observed. The change in airway pressure is thus the primary, or independent, variable (P) and the volume change (V) resulting from this is the secondary, or dependent, variable. The value of V is determined by the compliance of the respiratory system, which is givenby (V/P). If the compliance of the respiratory system falls, P remains constant but V falls

Pressure Controlled Ventilator

A: Volume/time curve for a volume-controlled inspiration witha tidal volume of VT1 litres and an inspiratory time of TIaseconds. The inspiratory flow ( ˙VI ) is the slope of the volume/time : ˙VI = VT 1 / TI a

volume-controlled inspiration

I time instant

Low VT

High VT

Low Flow

High Flow

volume-controlled inspiration

جاری حجم در تغییر

کنید رسم مختلف های حجم در را فشار تغییرات :منحنی

جاری افزایش (1 حجم

جاری ( 2 حجم کاهش

VT Constant

I time variable

Low Flow

High Flow

دم زمان در تغییر

کنید رسم دم مختلف زمانهای در را فشار تغییرات :منحنی

دم (1 زمان افزایشدم (2 زمان کاهش

Inspiration sometimes have two phases, 1)an active ‘flow’ (TI f low) phase during which gas is being delivered to the patient, 2) end-inspiratory pause (TI pause )

TI = TI f low + TI pause

end-inspiratory pause

Changes inEnd-inspiratory

Pressure profile of a volume-controlled breath with an end-inspiratory pause

در دم مختلف های وقفه در را فشار تغییرات :vcvمنحنی کنید رسم

دم (1 وقفه زمان افزایشدم (2 وقفه زمان کاهش

تغییرات در جریانمنحنی دم مختلف های وقفه در :vcvرا کنید رسم

تغییرات در حجممنحنی دم مختلف های وقفه در :vcvرا کنید رسم

Volume-controlled inflation

. A good indicator of adequate tidal volume is:

. . . . . a. good chest rise

. . . . . b. adequate breath sounds

. . . . . c. oxygen saturation = 100%

. . . . . d. a and b

As compliance worsens in a child receiving volume controlled mechanical ventilation, the TV delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change

As resistance increases in a child receiving volume controlled mechanical ventilation, the TV delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change

As resistance decreases in a child receiving volume controlled mechanical ventilation, the TV delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change

As compliance worsens in a child receiving volume controlled mechanical ventilation, the Pressure delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change

As resistance decreases in a child receiving volume controlled mechanical ventilation, the Pressure delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change

As resistance increases in a child receiving volume controlled mechanical ventilation, the Pressure delivered to the patient will: . . . . . a. increase . . . . . b. decrease. . . . . c . No change

Comparison of ‘volume-controlled’and ‘pressure-controlled’ breaths

Trigger Inspiratory cycling Inspiratory support Breath type Example

Time Time Yes Mandatory IPPV

Patient Patient Yes Triggered Pressure support

Patient Patient No Spontaneous CPAP

IPPV PSV CPAP

CONVENTIONAL VENTILATOR SETTINGSFI02Is the patient adequately oxygenated?2 Question

1: ‘how well are this patient’s lungs able to take up the oxygen I am supplying?’2: ‘is enough oxygen being supplied to the patient’s vital organs?’

The clinical assessment of the adequacy of oxygenation is deceptively difficult

Measurement of PaO2 or (SaO2), or both

The PaO2 and SaO2 are not equivalent and provide different information

PaO2/ FiO2A-a Gradient

CaO2 = ( Hb × 1.34 × SaO2/100 ) + (0.0225 × PaO2 )

A-a Gradient = PAO2 − PaO2

PAO2 = FIO2 × (Pb − 47) − PaCO2/0.8

PAO2=F IO2 × (Pb + { PEEP/75} − 47) − PaCO2/0.8

oxygenation index OI = 100 × FIO2 × Paw/ PaO2

PAO2/ PaO2 more indicative of V/ Q mismatch and alveolar capillary integrity.VI = )PIP x ventilator rate/min x Paco2) / 1000==================================================================

extra-pulmonary

CaO2 = ( Hb × 1.34 × SaO2/100 ) + (0.0225 × PaO2 )

oxygen delivery D ˙ O2 = ˙Qt × CaO2/ 100

oxygen consumption

FiO2Pa O2 SaO2 = 95

Pa02 value of 70-75 torr is a reasonable goal

Fi O2 values should be decreased to a level ~0.4 as long as SaO2 remains 95% or above

Rate of diffusion = Area × K × PAO2− PaO2 / d

RR by ETCPAP

IT / Plateau

Positive end-expiratory pressure (PEEP)

What is PEEP?Positive pressure measured at the end of expiration.

PHYSIOLOGICAL PEEPPEEP (3 to 5 cm H2O) to overcome the decrease in FRC that results from the bypassing of the glottic apparatus by the ETT

Positive End-expiratory Pressure (PEEP)

PEEP FOR HYPOXAEMIA• ‘to open the lungs and keep them open’• To improve respiratory mechanics,• To reduce intrapulmonary shunt, • To stabilize unstable lung units • To reduce the risks of ventilator-induced lung injury (VILI• Recruit lung in ARDS• Prevent collapse of alveoli• Diminish the work of breathing

What is the goal of PEEP?

Critical Opening Pressure

Collapse/ atelectosis/ ARDS

Increases Surface area for gas exchangeOpens the collapsed lung

Collapsed alveoli

After PEEP

PEEP- Indications. • If a PaO2 of 60 mmHg cannot be achieved

with a FiO2 of 60% • If the initial shunt estimation is greater than

25% • Pulmonary edema• ARDS/ALI• Atelectosis

Complications of positive end-expiratory pressure (PEEP) Pulmonary over-distension Barotrauma Ventilator-induced lung injury (VILI) Increased dead space Impaired carbon dioxide elimination Reduced diaphragmatic force-generating capacity Reduced cardiac output and oxygen delivery Impaired renal perfusion Reduced splanchnic blood flow Hepatic congestion Reduced lymphatic drainageDiminish cardiac outputRegional hypoperfusionAugmentation of I.C.P.?Paradoxal hypoxemiaHypercapnoea and respiratory acidosis

Prolongation of inspiratory time

INVERSE RATIO VENTILATION

first described in the early 1970s in infants with ARDS

the inspiratory period extends beyond 50% of the total cycle time

IRV can be applied in either volume- (VC) or pressure-controlled (PC) mod.

To maintaining an open lung in ALI/ARDS

requires profound sedation and frequently the use of neuromuscular blockade.

adverse consequences to cardiac output; any perceived benefits to oxygenation maywell be offset by consequent reductions in oxygen delivery.

AIRWAY PRESSURE RELEASE VENTILATION (APRV)first described in 1987. is a form of bi-level assisted ventilation utilizing continuous positive airway pressure (CPAP) with periodic pressure releases, either to a lower CPAP pressure or to atmospheric pressure The ventilator settings for APRV do not usually include the respiratory frequency but instead :the duration of Phigh, Thigh in seconds;the duration of Plow, Tlow in seconds; absolute value of Phigh and Plow.the patient is able to breathe spontaneously during both of these phases.

Bi-level ventilation

Bi-level ventilation. the airway pressure cycles between two levels of CPAP. The patient can breath spontaneously during both Phigh and Plow phases, and only receives inspiratory assistance during the low–high transition.

High-frequency oscillatory ventilation. (HFOV) A system of ventilation which uses respiratory rates between 300 and 900 breaths per minute

Oscillator

ET tube

Carina

Segmental bronchi

Alveoli

Recruitment maneuvers

PRONE POSITION

Ventilation

at rest 200 mL.min−1

1) volume of dead space,2) tidal volume, 3) respiratory frequency 4) Positive end-expiratory pressure (PEEP

Influences on the production of carbon dioxide• Factors associated with increased carbon dioxide production

– Systemic inflammation– Sepsis– Burnt patients– Hyperpyrexia– Thyrotoxic crisis– Muscular activity (seizures, excessive respiratory work)– Predominance of glucose as metabolic substrate– Administration of exogenous bicarbonate

• Factors associated with reduced carbon dioxide production– Hypothermia– Hypothyroidism– Sedation and neuromuscular blockade– Predominance of fatty acids as metabolic substrate

P CO2 = K X ( V CO2 / MV)

MV = RR X VT

VT = Alveolar Space + Dead Space

Dead Space Physiological dead space (VD) = Alveolar (VDA) + Anatomical (VDanat)

VD = Alveolar (VDA) + Anatomical (VDanat) +Equipment (VDequip)

Vd/Vt = 0.3

VD / VT = PaCO2 − PE TCO2 / PaCO2

Tidal Volume and Rate

VT and rate depends on the time constant. In normal lungs :

age-appropriate ventilator rate tidal volume of 7-10 mL/kg

Diseases associated with decreased time constants (decreased static compliance, are best treated with :

small (6 mLlkg) tidal volume and relatively rapid rates

Diseases associated with prolonged time constants (increased airway resistance, e.g., asthma, bronchiolitis)are best treated with:

relatively slow rates and higher (10-12 mLlkg) tidal volume

Positive end-expiratory pressure (PEEP)effects on CO2

Low levels of PEEP (3 to 5 cmH2O) have little effect Higher levels of PEEP (8 to 15 cmH2O) may increase the Vd/Vt ( mostly with low VT) CO2

in recruitable lung CO2intrinsic PEEP

General techniques to lower carbondioxide production

Avoidance of pyrexia induced hypothermiaLowering the respiratory quotient (use of fatty acids)Sedation and neuromuscular blockade reduce metabolic rate by around 9%

Conventional mechanical ventilation alveolar ventilation

Adjunctive pulmonary therapiesBronchodilatorsPhysiotherapy

Tracheal gas insufflation

Permissive hypercapniapotential advantage of permissive hypercapnia: deliberate hypoventilation

reduction in tidal volumes reduction transpulmonary pressures

limit pulmonary injury. In vitro, hypercapnia reduces the activation of: NF-kB, intercellular adhesion molecule-1 (ICAM-1) interleukin-8 (IL-8)in human pulmonary endothelial cells

NF-kB is a key regulatory molecule in the activation of many pro-inflammatory genes, including those that produce ICAM-1 and IL-8, molecules that trigger the movement of leukocytes into the inflamed lung.

In vivo, Hypercapnia may reduce inflammation in experimental lung injury.

Finally, hypercapnia may improve ventilation perfusion matching and intestinal andsubcutaneous tissue oxygenation

Increase in: pCO2 pO2 MAP

FiO2 no change increase no change

Rate decreaseusually no

changeincrease

PIP/TV decrease increase increase

Inspiratory time

usually no change

increase increase

PEEPusually no

changeincrease increase

MONITORING RESPIRATORY MECHANICSExhaled Tidal Volumeleak outdecrease in VTE ( PCV) : decrease in compliance or increase in resistance

increase in VTE is indicative of improvement and may require weaning of inflation pressures to adjust the VTE.Peak Inspiratory PressureIn VCV and PRVC, the PIP is determined by compliance and resistance.

increase in PIP decreased compliance (atelectasis, pulmonary edema, pneumothorax) or increased resistance (bronchospasm, obstructed ET).

decreasing the respiratory rate lower PIP in patients with prolonged TC or prolonging the TI

In such patients, a decrease in PIP suggests increased complianceor decreased resistance of the respiratory system.

CDYN= VTE / ( PIP - PEEP)

VCV and PRVC

CDYN= VTE / ( PIP - PEEP)

CSTAT= VTE/ (Pplat - PEEP)

Respiratory System Dynamic Complianceand Static Compliance

Assessment of Auto-PEEP

Auto-PEEP is assessed with the use of an expiratory pause maneuver

-have adverse effects on ventilation and hemodynamic status. Management : decreasing RR or decreasing inspiratory time increasing the set PEEP ("extrinsic" PEEP),

Ventilator settings1. Ventilator mode2. Respiratory rate3. Tidal volume or pressure settings4. Inspiratory flow5. I:E ratio6. PEEP7. FiO28. Inspiratory trigger

Assist – Control AC

Trigger windowCan be set

Vent breath Vent breath Synch Vent breath Vent breath

Spont breath sensedSensitivity can be set

• Patient only gets ventilator breaths• These are just delivered at different times to

coincide with patient spontaneous effort• Can help keep lungs recruited

Trigger window 1 for Vent breath

Vent breath Vent breath Synch Vent Supported Vent breath breath breath

Spont breath sensedTrigger window 2 for supported breath

Pressure Support

• Because it is difficult to breathe through a ventilator, the vent can help

• It supports spontaneous effort• Pressure support

– No background rate– Patient determines resp rate & I:E– Usually apnoea backup

Pressure Support

Spontaneous breath sensed by ventilator

Pressure is applied throughout inspiratory effort

CPAP & PEEP

The constant bit

CPAP and PEEP

• What do they do for your lungs?

• What about your cardiovascular system?

• Bi-Level Positive Airway Pressure• 2 PEEPs basically• Patient can breathe at any point

– Easier for patient to tolerate– Less sedation?

• Pressure support can be added if required

Origins of mechanical ventilationOrigins of mechanical ventilation

•Negative-pressure ventilators (“iron lungs”)

•first used in Boston Children’s Hospital in 1928

•Used extensively during polio outbreaks in 1940s – 1950s

The iron lung created negative pressure in abdomen as well as the chest, decreasing cardiac output.

Iron lung polio ward at Rancho Los Amigos Hospital in 1953.

Era of intensive care begun with this

• Positive-pressure ventilators– Invasive ventilation first used at Massachusetts

General Hospital in 1955– Now the modern standard of mechanical

ventilation

CMV-Volume

Volume

Tidal Volume

Pressure Support Ventilation (PSV)Pressure Support Ventilation (PSV)Patient determines RR, VE, inspiratory time – a purely spontaneous mode

CPAP and BiPAPCPAP and BiPAPCPAP is essentially constant PEEP; BiPAP is CPAP plus PS

•ParametersCPAP – PEEP set at 5-10 cm H2OBiPAP – CPAP with Pressure Support (5-20 cm H2O)

Shown to reduce need for intubation and mortality

Respiratory Rate• 10-12/Min – Adult

• 20+_ 3 - Child

• 30- 40 - New born

Respiratory Rate

• Increase – HypoxiaHypercapnoea / Resp.Acidosis

• DecreaseHypocapnoeaResp.AlkalosisAsthma / COPD

DHIDHI

Hey not always

the same buddy

Tidal Volume or Pressure setting

• Optimum volume/pressure to achieve good ventilation and oxygenation without producing alveolar overdistention

• Max = 6-8 cc/kg

Inspiratory Trigger• Normally set automatically

• 2 modes:

– Airway pressure– Flow triggering

I:E Ratio

• Normaly 1:2

• Asthma/COPD 1:3, 1:4, …

• Severe hypoxia ARDS/ALI

Pul.Edema 1:1 , 2:1

FIO2• Goal – to achive PaO2 > 60mmHg or a sat

• Start at 100% aim 40%

Vent settings to improve <oxygenation>Vent settings to improve <oxygenation>

•FIO2

•Simplest maneuver to quickly increase PaO2

•Long-term toxicity at >60%• Free radical damage

•Inadequate oxygenation despite 100% FiO2 usually due to pulmonary shunting•Collapse – Atelectasis•Pus-filled alveoli – Pneumonia•Water/Protein – ARDS•Water – CHF•Blood - Hemorrhage

PEEP and FiO2 are adjusted in tandem

Pulmonary edema

Translocation of fluid to peribroncheal region – helps in oxygenation

DOPE• D- Disposition of ETT• O- Obstruction / kinking• P- Pneumothorax• E- Equipment failure

Prerequisites to extubation include:

•1) A good cough/gag (to allow the child to protect their airway).

2) NPO about 4 hours prior to extubation (in case the trial of extubation fails and reintubation is required). 3) Minimize sedation. 4) Adequate oxygenation on 40% FiO2 with CPAP (or PEEP) = 4. 5) The availability of someone who can reintubate the patient, if necessary. 6) Equipment available to reintubate the patient, if necessary.

بسم الله الرحمن الرحیم Basics of Mechanical Ventilation

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