modes of ventilation

“…an opening must be attempted in the trunk of the trachea, into which a tube of reed or cane should be put; you will blow

into this, so that the lung may rise again… and the heart becomes strong…”

Andreas Vesalius (1555)

MODES OF MECHANICAL VENTILATION

Dr. Nikhil Yadav

Mechanical ventilation forms a mainstay of critical care

in patients with respiratory insufficiency.

Ventilator must generate inspiratory flow to deliver tidal

volume.

Transairway pressure (PTA) = PAO – PALV

PTA = 0, at the end of expiration and beginning of

inspiration.

Mechanical ventilator produce either negative or

positive pressure gradient.

Introduction

PTA gradient is created by decreasing PALV to below PAO

e.g.- Iron lungsDisadvantages- poor patient access,bulky size, cost, dec. cardiac output(Tank shock). Chest cuirass or chest shell

Negative pressure ventilation

Achieved by applying positive pressure at airway opening which produces PTA gradient that generates inspiratory flow.

Inspiratory flow results in the delivery of tidal volume.

Positive pressure ventilation

Ventilator mode is a set of operating characteristics that controls how the ventilator functions.

An operating mode describes the way a ventilator is-• triggered into inspiration• cycled into exhalation• what variables are limited during inspiration• allowing mandatory or spontaneous breaths or both

Modes of ventilation

The ventilator delivers a preset TV at a specific R/R and inspiratory flow rate.

It is irrespective of patients’ respiratory efforts. In between the ventilator delivered breaths the

inspiratory valve is closed so patient doesn’t take additional breaths.

PIP developed depends on lung compliance and respiratory passage resistance.

Controlled Mode VentilationVolume control

Controlled Mode Ventilation

Indications-• In initial stage when patients “fighting” or “bucking”

with the ventilator• Tetanus or other seizure activity• Crushed chest injury Disadvantages- • Asynchrony• Barotrauma d/t high PAW & dec. lung compliance• Haemodynamic disturbances• V/Q mismatch• Total dependence on ventilator

Volume controlled CMV

Ventilator gives pressure limited, time cycled breaths thus preset inspiratory pressure is maintained.

Decelerating flow pattern. Peak airway/alveolar pressure is controlled but TV,

minute volume & alveolar volume depends on lung compliance, airway resistance, R/R & I:E ratio.

Pressure Controlled CMV

PC- CMV

Advantages- Less PAW, thus chances of barotrauma and

hemodynamic disturbances are less. Even distribution of gases in alveoli In case of leakage, compensation for loss of ventilation

is better as gaseous flow increases to maintain preset pressure.

Disadvantages- Asynchrony TV dec. if there is dec. lung compliance or inc. airway

resistance, thus causes hypoventilation and alveolar collapse.

V/Q mismatch.

PC-CMV

Ventilator assists patient’s initiated breath, but if not triggered, it will deliver preset TV at a preset respiratory rate (control).

Mandatory mechanical breaths may be either patient triggered (assist) or time triggered (control)

If R/R > preset rate, ventilator will assist, otherwise it will control the ventilation.

ASSIST-CONTROL MODE Ventilation (A-C Mode)

A-C Mode Ventilation

Advantages- Dec. patients work of breathing. Better patient ventilator synchrony. Less V/Q mismatch. Prevents disuse atrophy of diaphragmatic muscle.Disadvantages- Alveolar hyperventilation Development of high intrinsic PEEP in obstructed pts. Inc. mean airway pressure causes hemodynamic

disturbances.

A-C Mode Ventilation

Ventilator delivers preset number of time cycled mandatory breaths & allows patient to breath spontaneously at any tidal volume in between.

Advantages- Lesser sedation Lesser V/Q mismatch Lesser hemodynamic disturbancesDisadvantage- Breath stacking- lung volume and pressure could

increase significantly, causing barotrauma.

Intermittent Mandatory Ventilation (IMV)

Ventilator delivers either assisted breaths to the patient at the beginning of a spontaneous breath or time triggered mandatory breaths.

Synchronization window- time interval just prior to time triggering.

Breath stacking is avoided as mandatory breaths are synchronized with spontaneous breaths.

In between mandatory breaths patient is allowed to take spontaneous breath at any TV.

Synchronized Intermittent Mandatory Ventilation (SIMV)

It provides partial ventilatory support

Advantages- Maintain respiratory muscle strength and avoid

atrophy. Reduce V/Q mismatch d/t spontaneous ventilation. Decreases mean airway pressure d/t lower PIP &

inspiratory time Facilitates weaning.

SIMV

Disadvantages- Desire to wean too rapidly results in high work of

spontaneous breathing & muscle fatigue & thus weaning failure.

SIMV

An airway pressure strategy in ventilation that increases the end expiratory or baseline airway pressure greater than atmospheric pressure.

Used to treat refractory hypoxemia caused by intrapulmonary shunting.

Not a stand-alone mode, used in conjugation with other modes.

Indications- Refractory hypoxemia d/t intrapulmonary shunting. Decreased FRC and lung compliance

Positive End Expiratory Pressure (PEEP)

PEEP reinflates collapsed alveoli & maintain alveolar inflation during

exhalation.

PEEP

Increases alveolar distending pressure

Increases FRC by alveolar recruitment

Improves ventilation

Increases V/Q

Improves oxygenation

Decreases work of breathing

Physiology of PEEP

Complications Dec. venous return and cardiac output. Barotrauma Inc. ICP d/t impedance of venous return from

head. Alteration of renal function & water

imbalance.

PEEP

PEEP applied to airway of patient breathing spontaneously

Indications are similar to PEEP, to ensure patient must have adequate lung functions that can sustain eucapnic ventilation.

Continuous Positive Airway Pressure (CPAP)

Similar to IMV mode except that minimum minute volume is set rather than R/R.

Ventilator measures spontaneous minute volume, if found less than preset mandatory minute volume, the difference b/w two is delivered as mandatory breaths by ventilator at preset flow & TV.

Suited for patients with variable respiratory driveDisadvantage- Hypoventilation as either minute volume recorded is

not necessary alveolar ventilation.

Mandatory Minute Ventilation (MMV)

Supports spontaneous breathing of the patients. Each inspiratory effort is augmented by ventilator at a

preset level of inspiratory pressure. Patient triggered, flow cycled and pressure controlled

mode. Decelerating flow pattern. Applies pressure plateau to patient airway during

spontaneus br. Can be used in conjugation with spontaneous

breathing in any ventilator mode.

Pressure Support Ventilation (PSV)

Commonly applied to SIMV mode during spontaneous ventilation to facilitate weaning

With SIMV, PS- Inc. patient’s spontaneous tidal volume. Dec. spontaneous respiratory rate. Decreases work of breathing. Addition of extrinsic PEEP to PS increases its efficacy.

PSV

SIMV (VC) -PS

Disadvantages- Not suitable for patients with central apnea.

(hypoventilation) Development of high airway pressure. (hemodynamic

distubances) Hypoventilation, if inspiratory time is short.

PSV

Available on Galileo ventilator. Patient body weight (deadspace) & percent minute

volume are feed in ventilator. Ventilator has pre determined setting of

100ml/kg/min. Test breath measures compliance, airway resistance

& i. PEEP. Ventilator selects and provide the frequency,

inspiratory time, I:E & sets high pressure limit for mandatory and spontaneous breaths.

May be either time triggered or patient triggered.

Adaptive Support Ventilation (ASV)

PAV is a spontaneous breathing mode that offers assistance to the patient in proportion to the patient’s effort.

Inspiratory flow, volume & pressure are variable & pressure support changes according to elastance & airflow resistance & patients demand (volume or flow).

PAV is set to overcome 80% of elastance & airflow resistance.

PAV instantaneously measures the flow and volume being pulled in by the patient, and automatically calculates the compliance and resistance of the respiratory system to determine how much pressure to provide for each breath.

Proportional Assist Ventilation (PAV)

Flow Assist (FA)- Pressure is provided to meet patient’s inspiratory flow demand. Dec. inspiratory effort to overcome airflow resistance.Volume Assist (VA)- Pressure is provided meet patient’s volume requirement. Dec. inspiratory efforts to overcome systemic elastance.

Indications- Spontaneously breathing patient Intact respiratory drive Intact neuromuscular function Generally, a patient considered suitable for pressure support

ventilation could be considered for PAV.

PAV

Advantage- The patient ‘drives’ the ventilator Better patient ventilator synchrony as pressure vary to

augment flow & demand.

Disadvantage- Barotrauma- if elastance & resistance show sudden

improvement.

PAV

Incorporates inspiratory pressure support ventilation & conventional volume assisted cycles to provide optimal inspiratory flow during assisted/controlled ventilation.

Desired TV & pressure support level are preset. Once triggered desired PS level reaches asap &

delivered volume is compared with preset TV. If volume delivered = 0r > preset volume, it is PS

breath. If volume < preset volume, ventilator switches to

volume limited, resulting in longer inspiratory time until preset TV is delivered

Volume Assured Pressure Support (VAPS)

Used to achieve volume support while keeping PIP to lowest

level.

Achieved by altering the peak flow & inspiratory time in

response to changing airway or compliance characteristics.

At constant flow PIP increases d/t inc. airflow resistance, so

decreasing flow reduces the airflow resistance.

To compensate for lower flow, inspiratory time is prolonged.

Pressure Regulated Volume Control (PRVC)

Similar to CPAP as patient breathes spontaneously.

Airway pressure is maintained at moderately high level (15-20

cmH2O) throughout most of respiratory cycle with brief periods of

lower pressure to allow deflation of lungs.

Inc. pressure ensures alveolar recruitment & oxygenation & brief

deflation allows CO2 elimination without alveolar collapse.

Indicated as an alternative to conventional volume cycled ventilation

for patients with decreased lung compliance (ARDS), as chances of

barotrauma is less d/t less PAW.

Airway Pressure Release Ventilation (APRV)

Used to promote oxygenation esp. in ARDS. Normal I:E ratio is 1:1.5 – 1:3, in IRV I:E is 2:1 – 4:1 Improves oxygenation by• Reducing intrapulmonary shunting.• Improving V/Q mismatch.• Decreasing deadspace ventilation.• Increasing mean airway pressure.• Presence of auto PEEP.Disadvantages- Barotrauma d/t inc. mPaw & auto PEEP. High rate of transvascular fluid flow. May worsen pulm.

oedema

Inverse Ratio Ventilation (IRV)

Adjuvant to mechanical ventilation in which O2

enriched gas is insufflated into trachea to ventilate

anatomical dead space during expiration.

Decreases PaCO2 at any level of inspiratory minute

ventilation.

Extra flow may cause inc. airway pressure and

hyperinflation.

Tracheal Gas Insufflation (TGI)

It is simultaneous separate ventilation of individual lung.

Separation achieved by double lumen tube and two ventilators- synchronized or asynchronized.

Indication- Severely diseased one lung which can not be treated

with conventional ventilation.e.g.- unilateral pulmonary contusion, aspiration pneumonia, bronchopleural fistula, massive unilateral pulmonary embolism etc.

Independent Lung Ventilation (ILV)

For all high frequency techniques during which tidal volume equals or less than anatomical dead space volume and respiratory frequency between 60 to 3000 breaths / minutes.

They are 3 types: HFPPV …..60 to 110 breaths/min HFJV…….110 to 600 breaths/min HFO……..600 to 3000 breaths/min

Advantages-Low PAW, less V/Q mismatch, less barotrauma

High frequency ventilation (HFV)

THANK YOU

modes of ventilation

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