physics of mechanical ventilation
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Physics of Mechanical ventilationTRANSCRIPT
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Dr Satish DeopujariM.D., DNB. (Pediatrics)
National Chairperson (Ex)Intensive Care Chapter I A PFounder Chairman.....National conference on pediatric critical careProfessor of pediatrics ( Hon ) JNMC:WardhaNagpur : INDIAPHONE 0091-712-2424588 / 2420075Mobile 00 91 [email protected]@rediffmail.com
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The evolution of Ventilator
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Three problems of ventilation
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Evolution of Ventilators………………
What can we manipulate ? 1) Minute ventilation2) Pressure gradient 3) Surface are 4) Pulmonary vasculature 5) SolubilityHow can we do this ?
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Applied Physics
Compliance Static compliance Dynamic compliance Resistance Work of breathing
Flow Pressure Volume Surface area
What can we manipulate ?
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Compliance
Compliance is a quotient between volume and corresponding pressure change.
C = V
P
Dynamic compliance
Static compliance
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The compliance of any structure is the ease is with which the structure distends ( C= ∆ V / ∆ P)
COMPLIANCE
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C.C.P.
C.O.P.
VOLUME
PRESSURE
c.c.p. = critical closing pressurec.o.p. = critical opening pressure
PEEP
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Pressure
Volume
Optimal Benefit Of PEEP
EX. INS.
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Peak pressure
Plateau pressurePressure
Inspiratory pause
Flow
Time
Cst = Tidal volume.
Cc
Cst : static compliance Cc : circuit compliance end expiratory pressure (Pend-ex)Pend-ex = Peep + P peep
Resistance
Compliance
Static compliance
Static pressure – end expiratory pressure
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Flow …………………….
Flow indicates circulation of an element per unit of time through a given place
Flow…. Linear
Turbulent
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FLOW
Palv
Pmo
FLOW THROUGH A PIPE LIKE STRUCTURE REQUIRES A DRIVING PRESSURE (Palv-Pmo) TO OVERCOME THE FRICTIONAL RESISTANCE
FLOW DEPENDS ON Pressure Difference and Resistance V=P/R
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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
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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
P
O
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And how can we do this ?
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Conditional variables Control variables Phase variables Trigger variables Limit variables Cycle variables Base line
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Conditional variables alone or in combination are
analyzed by Ventilator’s 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.
Conditional variables Pressure Volume Flow Time
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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.
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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
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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
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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
sinusoidalrectangle ramp
ramp exponential
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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 time…Flow……………..
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Peak pressure
Plateau pressureResistance
Compliance
End of inspiration
Volume
Flow
Pressure
Volume control
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End of insp. flow
Volume
Flow
Pressure
Pressure control
What does not change …….1) Volume curve 2) Exp. Flow curve
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End of insp. flow
Volume
Flow
Pressure
Pressure control
Peak p.Plateau p. Resist.
Compliance
End of insp. flow
Volume
Flow
Pressure
Volume control
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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 needs
Variable tidal volume Changes in impedance not easily detected
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Modes of ventilation or moods of ventilation
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PRESSURe
FLOw
VOLUMe
A B C
A normal lung B decreased compliance C increased resistance
Controlled Ventilation…………….
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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.
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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.
A B C
A .Controlled and time triggeredB .Spontaneous C .Synchronized and assisted
Flow
PaW
Volume
Trigger
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Spontaneous breath
Assisted breath
Back up ventilation period
Controlled breath
Spontaneous volume
Trigger Spontaneous breath
Pressure
Volume
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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
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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……
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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.
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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
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Certain other issues
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Fixed insp. TimeTermination sens. off Termination sens. on
Flow
Pressure
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Inspiratory cycle off…………
Proper Inspiratory cycle terminationavoids lung hyperinflation and
Increased work of breathing
40 %
10 %
10 %
5%
1%
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Exp.
Insp
.
PEEP PIP
Vt.
COMPLIANCE LINE
Pressure limited…
Over distension
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Exp.
Insp
.
PEEP PIP
Vt.
COMPLIANCE LINE
Pressure limited…
Exp.
Insp
.
PEEP PIP
Vt.COMPLIANCE LINE
Volume limited…
Pressure – Volume loops
Low compliance
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A
B C
D
Volume
Pressure in CM
B C
Volume
Pressure in CMA
D
Normal resistance
Increased resistance
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volume
Pressure
Elastic work
Resistive work
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Triggering ……………………
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Triggering ……………………Neuro – Ventilatory coupling ………….
Central Nervous System
Phrenic Nerve
Diaphragmatic contraction
Chest Wall and Lung expansion
Air way pressure , flow and volume
NAVA Ventilator
Current Technology
Ideal technology
Neurally Adjusted Ventilatory Assist
EA di Waveform
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Tidal volume ÷ P plat – PEEP Tidal volume ÷ PIP – PEEP PIP – P plat ÷ Flow rate PIP- P2 ÷ Flow rate
Static compliance Dynamic characteristics
Maximum resistance index
Minimum resistance index
Elastic and resistive property of respiratory System
Time constant
×
Resistive property
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Conditional variables
Control variables
Pressure : Volume : Flow
Phase Variables
Trigger : Limit : cycle : Base line
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You can comfortably SLEEP even in difficult situation if you know your physiology well……………
Thanks
SLEEP
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Mechanical Ventilation is a blend science and art ………………….