Physics of mechanical ventilationPresentation Transcript
Physics of Ventilation Dr Satish Deopujari M.D., DNB. (Pediatrics) National Chairperson (Ex) Intensive Care Chapter I A P Founder Chairman..... National conference on pediatric critical care Professor of pediatrics ( Hon ) JNMC:Wardha Nagpur : INDIA PHONE 0091-712-2424588 / 2420075 Mobile 00 91 9823024588 [email_address] [email_address]
Compliance Compliance is a quotient between volume and corresponding pressure change. C = V P Dynamic compliance Static compliance
The compliance of any structure is the ease is with which the structure distends ( C= ∆ V / ∆ P) C O M P L I A N C E
C.C.P. C.O.P. V O L U M E PRESSURE c.c.p. = critical closing pressure c.o.p. = critical opening pressure PEEP
Pressure Volume Optimal Benefit Of PEEP EX. I NS.
Peak pressure Plateau pressure Pressure 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
Flow ……………………. Flow indicates circulation of an element per unit of time through a given place Flow…. Linear Turbulent
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
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 airway Viscosity and density of air Resistance during inspiration Resistance during expiration P O
And how can we do this ?
T rigger variables
L imit variables
C ycle variables
Mechanical Ventilation Concept
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 VARIABLE
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. CONRTOL VARIALBE
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. CONRTOL VARIALBE 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. CONRTOL VARIALBE 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. CONRTOL VARIALBE Flow sinusoidal rectangle ramp ramp exponential
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…………….. LIMIT VARIBALE
Peak pressure Plateau pressure Resistance Compliance End of inspiration Volume Flow Pressure Volume control
End of insp. flow Volume Flow Pressure Pressure control
What does not change …….
Exp. Flow curve
End of insp. flow Volume Flow Pressure Pressure control Volume Flow Pressure Volume control Peak p. Plateau p. Resist. Compliance End of insp. flow
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
Modes of ventilation or moods of ventilation
P R E S S U R e F L O w V O L U M e A B C A normal lung B decreased compliance C increased resistance Controlled Ventilation…………….
SIMV Patient triggered ventilation Synchronized to patient breath if the threshold is met . Patient controlled variables Respiratory rate Inspiratory time Clinician controlled variables PIP if pressure limited Tidal volume if volume cycled Inspiratory time if time cycled Flow 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. A B C A .Controlled and time triggered B .Spontaneous C .Synchronized and assisted Flow PaW Volume Trigger
Spontaneous breath Assisted breath Back up ventilation period Controlled breath Spontaneous volume Trigger Spontaneous breath Pressure Volume
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%)
PRVC A 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……
Equivalent to pressure support
set a “goal” tidal volume
the 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. Time Termination sens. off Termination sens. on Flow Pressure
Inspiratory cycle off………… Proper Inspiratory cycle termination avoids lung hyperinflation and Increased work of breathing 40 % 10 % 10 % 5% 1%
Pressure Inspiratory rise time ….. e.g.. Pressure control ventilation Flow
Exp. Insp. PEEP PIP Vt. COMPLIANCE LINE Pressure limited… Over distension
Exp. Insp. PEEP PIP Vt. COMPLIANCE LINE Pressure limited… Exp. Insp. PEEP PIP Vt. COMPLIANCE LINE Volume limited… Pressure – Volume loops Low compliance
B C Volume Pressure in CM A D Normal resistance Increased resistance A B C D Volume Pressure in CM
volume Pressure Elastic work Resistive work
Triggering …………………… Neuro – Ventilatory coupling …………. Central Nervous System Phrenic Nerve Diaphragmatic contraction Chest Wall and Lung expansion Air way pressure , flow and volume NAVA Ventilator Ideal technology Neurally Adjusted Ventilatory Assist EA di Waveform Current Technology
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
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 well…………… Thanks SLEEP
Mechanical Ventilation is a blend science and art …………………. THANKS