The evolution of Ventilator

Three problems of ventilation

Evolution of VentilatorsWhat can we manipulate ? Minute ventilationPressure gradient Surface are Pulmonary vasculature SolubilityHow can we do this ?

Applied Physics Compliance Static compliance Dynamic compliance Resistance Work of breathing Flow Pressure Volume Surface areaWhat can we manipulate ?

ComplianceCompliance is a quotient between volume and corresponding pressure change.C = VPDynamic compliance

Static compliance

The compliance of any structure is the ease is with which the structure distends ( C= V / P) COMPLIANCE

C.C.P.C.O.P.VOLUMEPRESSUREc.c.p. = critical closing pressurec.o.p. = critical opening pressurePEEP

PressureVolumeOptimal Benefit Of PEEPEX.INS.

Peak pressurePlateau pressurePressure Inspiratory pauseFlow TimeCst = Tidal volume.CcCst : static compliance Cc : circuit compliance end expiratory pressure (Pend-ex)Pend-ex = Peep + P peep Resistance ComplianceStatic complianceStatic pressure end expiratory pressure

Flow .Flow indicates circulation of an element per unit of time through a given placeFlow. Linear

Turbulent

FLOWPalvPmoFLOW THROUGH A PIPE LIKE STRUCTURE REQUIRES A DRIVING PRESSURE (Palv-Pmo) TO OVERCOME THE FRICTIONAL RESISTANCEFLOW DEPENDS ON Pressure Difference and Resistance V=P/R

Pressure .Represents the force that a volume of gas exercises upon a unit area.Kinetic theory states that gas molecules bomb the walls of a container .

If volume remains constant , pressure varies in direct proportion to Temperature.If temperature remains constant , pressure varies in inverse relation to Volume .Increase in pressure decreases volume

Resistance Resistance is defined as the relationship between pressure (p) and flow ( 0 )Therefore important when there is air flow.

R = -----------

Resistance depends upon Diameter of airway Length of airwayViscosity and density of air

Resistance during inspiration Resistance during expiration PO

And how can we do this ?

Conditional variables Control variables Phase variables Trigger variables Limit variables Cycle variables Base line

Conditional variables alone or in combination are analyzed by Ventilators control logic.The state of this variable determines as to which of two types of breath would be delivered.

SIMV is based on timing window and accordingly the ventilator delivers .a pressure triggered ( patient ) or time triggered( machine) breath.

In this situation the patient effort and time are conditional variables for determining triggering.

Control variable manipulates the conditional to cause inspiration.Pressure , volume , flow and time are control variables.

The behavior of control Variable remains constant in spite of changed Ventilatory load.

Control variable manipulates the conditionals to cause inspiration.PRESSURE , VOLUME , FLOW and time are control variables.

The behavior of control Variable remains constant in spite of changed Ventilatory load. Pressure Rectangular Exponential

Control variable manipulates the conditional to cause inspiration.Pressure , VOLUME , FLOW and time are control variables.

The behavior of control Variable remains constant in spite of changed Ventilatory load. Volume Ramp Sinusoidal

Control variable manipulates the conditional to cause inspiration.PRESSURE , VOLUME , FLOW and time are control variables.

The behavior of control Variable remains constant in spite of changed Ventilatory load. Flow sinusoidalrectangleramprampexponential

During pressure support ventilation though one selects a level of support the Inspiration continues till predetermined flow rate or termination criteria is reached.During PSV patient determines the Rate ..Inspiratory timeFlow..

Peak pressurePlateau pressureResistance ComplianceEnd of inspiration Volume Flow Pressure Volume control

End of insp. flowVolume Flow Pressure Pressure control What does not change .Volume curve Exp. Flow curve

End of insp. flowVolume Flow Pressure Pressure control Volume Flow Pressure Volume control

Volume limited and pressure limited ventilation .Volume limited pressure limited Advantages Tidal Volume guaranteed Precise control of Inspiratory flow Easy detection of changed respiratory impedance

Precise control pf pressure Decelerating flow reported to improve distribution of ventilation decrease dead space ventilation decrease PIP match Inspiratory flow Disadvantages PIP vary Inspiratory flow may not match the patients needsVariable tidal volume Changes in impedance not easily detected

Modes of ventilation or moods of ventilation

PRESSUReFLOwVOLUMeABCA normal lung B decreased compliance C increased resistance Controlled Ventilation.

SIMV Patient triggered ventilationSynchronized to patient breathif the threshold is met . Patient controlled variables Respiratory rateInspiratory time Clinician controlled variables PIP if pressure limited Tidal volume if volume cycled Inspiratory time if time cycledFlow SIMV rate Flow cycling .Insp. Terminated at % of peak flow rather than time Synchronizes expiratory and Insp. flow thus total synchrony achieved.

When SIMV is used, the patient receives three different types of breath:The controlled (Mandatory) breath.Assisted (synchronized) breaths.Spontaneous breaths, which can be pressure supported.ABCA .Controlled and time triggeredB .Spontaneous C .Synchronized and assistedFlow PaWVolume

Spontaneous breathAssisted breathBack up ventilation periodControlled breathSpontaneous volumeTrigger Spontaneous breathPressure Volume

Pressure support Pressure support ventilation is a spontaneous mode of ventilation.Inspiratory effort is assisted by the ventilator at an airway pressure that remains constant during the phase of inspiration.Inspiration is terminated when the peak Inspiratory flow reaches a preset level. (usually 25%)

Patient determines Rate Inspiratory time Airflow

PRVCA control mode, which delivers a set tidal volume with each breath at the lowest possible peak pressure. Delivers the breath with a decelerating flow pattern that is thought to be less injurious to the lung

Volume SupportEquivalent to pressure supportset a goal tidal volumethe machine watches the delivered volumes and adjusts the pressure support to meet desired goal within limits set by you.

Airway Pressure Release Ventilation

Can be thought of as giving a patient two different levels of CPAP Set high and low pressures with release time.Length of time at high pressure generally greater than length of time at low pressure.By releasing to lower pressure, lung volume is allowed to decrease to FRC

Certain other issues

Fixed insp. TimeTermination sens. offTermination sens. onFlow Pressure

Inspiratory cycle off

Proper Inspiratory cycle terminationavoids lung hyperinflation and Increased work of breathing 40 %10 %

Pressure Inspiratory rise time ..e.g.. Pressure control ventilationFlow

Exp.Insp.PEEPPIPVt.COMPLIANCE LINEPressure limitedOver distension

Exp.Insp.PEEPPIPVt.COMPLIANCE LINEPressure limitedExp.Insp.PEEPPIPVt.COMPLIANCE LINEVolume limitedPressure Volume loops

BCVolumePressure in CMADNormal resistance Increased resistance

volumePressure Elastic workResistive work

Triggering Neuro Ventilatory coupling .Central Nervous System Phrenic NerveDiaphragmatic contraction Chest Wall and Lung expansion Air way pressure , flow and volume NAVA Ventilator Ideal technologyNeurally Adjusted Ventilatory Assist EA di Waveform

Tidal volume P plat PEEP Tidal volume PIP PEEP PIP P plat Flow rate PIP- P2 Flow rate Static compliance Dynamic characteristics Maximum resistance indexMinimum resistance indexElastic and resistive property of respiratory System Time constant Resistive property

Conditional variables Control variables Pressure : Volume : Flow Phase Variables Trigger : Limit : cycle : Base line

You can comfortably SLEEP even in difficult situation if you know your physiology wellThanks SLEEP

Mechanical Ventilation is a blend science and art .