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Postoperative Ventilation Postoperative Ventilation in in
CV ProblemsCV Problems Non-uniform inflation occuring in non-Non-uniform inflation occuring in non-
homogenous lungshomogenous lungs CMV’s with high PIPs CMV’s with high PIPs Those pressures are also transmitted to Those pressures are also transmitted to
the healthiest regions of lungsthe healthiest regions of lungs Over-distention and over-pressurization Over-distention and over-pressurization
produces volutrauma and barotraumaproduces volutrauma and barotrauma Inflammatory Cascade is triggeredInflammatory Cascade is triggered
HFOV can be used as a HFOV can be used as a bridgebridge to to ECMO in pts with intractable ECMO in pts with intractable cardiorespiratory conditionscardiorespiratory conditions
So, why consider HFV?So, why consider HFV? 3 Words: 3 Words: Small Tidal VolumesSmall Tidal Volumes Small Tidal Volumes allow gas exchange to Small Tidal Volumes allow gas exchange to
occur using extremely small volume occur using extremely small volume displacements of ventilatory gases displacements of ventilatory gases
Small Tidal Volumes < Anatomical Dead Small Tidal Volumes < Anatomical Dead SpaceSpace
Small Tidal Volumes allow safer use of Small Tidal Volumes allow safer use of Optimal PEEP minimizing the risk of Optimal PEEP minimizing the risk of atelectasis and oxygen toxicityatelectasis and oxygen toxicity
Often referred to as Lung Protective Often referred to as Lung Protective Ventilation/StrategyVentilation/Strategy
Evolved from studies of pulmonary Evolved from studies of pulmonary physiology using mathematics, fluid physiology using mathematics, fluid mechanics, and other engineering mechanics, and other engineering principles.principles.Facilitates gas exchange by sending a Facilitates gas exchange by sending a steady stream of very small tidal volumes steady stream of very small tidal volumes into the airways using relatively low PIPs into the airways using relatively low PIPs The further the gas goes into the airways, The further the gas goes into the airways, the lower those airway pressures are.the lower those airway pressures are.
How does HFV work?How does HFV work?Conventional studies indicate that smaller Conventional studies indicate that smaller tidal volumes are safer than larger tidal tidal volumes are safer than larger tidal volumes *volumes *As Tidal Volumes are pushed smaller and As Tidal Volumes are pushed smaller and smaller, two things must be raisedsmaller, two things must be raised
PEEP/MAP - to keep the lungs open PEEP/MAP - to keep the lungs open Rate - to maintain normal PaCO2Rate - to maintain normal PaCO2
*Kacmaerk RM, Chiche J-D. Resp. Care 1998;43:724-727 & Lee PC, Helemoortel CM,Cohn Sm, Fink MP. Chest 1990;97:430-434www.cardiacanaesthesia.in|Dr Amarjawww.cardiacanaesthesia.in|Dr Amarja
Airway Pressure PhobiasAirway Pressure Phobias
Monitoring and controlling HFV with Monitoring and controlling HFV with airway pressure instead of tidal airway pressure instead of tidal volumes creates problems for many volumes creates problems for many clinicianscliniciansPressure is a Pressure is a DependentDependent variable variableIt depends on gas flow, tidal volume, It depends on gas flow, tidal volume, airways resistance, and lung airways resistance, and lung compliancecompliance
Benefits of HFVBenefits of HFV ‘‘Low stretch ‘ ventilation with continous Low stretch ‘ ventilation with continous
alveolar recruitment alveolar recruitment Adequate gas flow with small TVAdequate gas flow with small TV Preserves end exp lung volumePreserves end exp lung volume Keeps the lung openKeeps the lung open Minimizes cyclic stretchMinimizes cyclic stretch Avoids overdistension at end inspiration Avoids overdistension at end inspiration
by limiting TV & transpulm pressureby limiting TV & transpulm pressurewww.cardiacanaesthesia.in|Dr Amarjawww.cardiacanaesthesia.in|Dr Amarja
In HFPPV : RR is increased to achieve In HFPPV : RR is increased to achieve MV , so the peak pressure remains lowMV , so the peak pressure remains low
As rate increases insp time decreases to As rate increases insp time decreases to allow adequate exhalation & prevent air allow adequate exhalation & prevent air trappingtrapping
MAP – may increase – barotraumaMAP – may increase – barotrauma IC bleedIC bleed cardiac compromisecardiac compromise
HFJVHFJV Rate – 240 to 660/minRate – 240 to 660/min Special adaptor is attached to ETT Special adaptor is attached to ETT Specially designed ETT – allows Specially designed ETT – allows
pulsed gas to exit inside the ETTpulsed gas to exit inside the ETT
conventional ventilation : conventional ventilation : 1) occasional sighs – surfactant ,1) occasional sighs – surfactant , prevent atelectasisprevent atelectasis 2) PEEP2) PEEP 3) continous gas is available at ETT3) continous gas is available at ETT for entrainment by Jetfor entrainment by Jet
HFJV Contd. . . HFJV Contd. . . Adv – equivalent ventilation at lowerAdv – equivalent ventilation at lower MAP MAP - limits effects of PPV on CV - limits effects of PPV on CV systemsystem - beneficial in pts with RV - beneficial in pts with RV dysfunction & after Fontandysfunction & after Fontan operationoperation
HFV reduces physiologic dead space HFV reduces physiologic dead space volume by pulsing fresh gas through volume by pulsing fresh gas through the core or center of the airways & the core or center of the airways & dead space instead of pushing all the dead space instead of pushing all the dead space gas ahead of the fresh gasdead space gas ahead of the fresh gas
Flow StreamingFlow Streaming Allows HFV to use TV < anatomic dead space Allows HFV to use TV < anatomic dead space
volume because gas in the terminal airways volume because gas in the terminal airways gets replenished so rapidly that a substantial gets replenished so rapidly that a substantial Partial PressurePartial Pressure difference is established with difference is established with alveolar gas.alveolar gas.
This partial pressure difference facilitates This partial pressure difference facilitates DiffusionDiffusion, and good gas exchange results, and good gas exchange results
HFJV is especially good at creating flow HFJV is especially good at creating flow streaming because it squirts gas into the lungs streaming because it squirts gas into the lungs with a great deal of with a great deal of Velocity.Velocity.
Uses an electrically powered piston Uses an electrically powered piston oscillator to alternate positive and oscillator to alternate positive and negative pressures in the airway negative pressures in the airway which assists both inspiration & which assists both inspiration & expirationexpiration
HFOVHFOVAdvantages :Advantages :1)1)MAP is MAP is maintained at maintained at low peak low peak pressurespressures2)2)Prevents Prevents release of release of inflammatory inflammatory chemical chemical mediatorsmediators
Contd . . .Contd . . . Recruitment : MAP – 40cmH2O -40sRecruitment : MAP – 40cmH2O -40s MAP – 5 cmH2O above that in CV , MAP – 5 cmH2O above that in CV ,
maximum upto 45-55 cmH2Omaximum upto 45-55 cmH2O FiO2 – 1 then taperedFiO2 – 1 then tapered If SpO2 not raised , MAP is increased If SpO2 not raised , MAP is increased
by 2-3 cmH2O over 30-60-minby 2-3 cmH2O over 30-60-min
Weaning of HFOVWeaning of HFOV Decrease FiO2 before reducing MAPDecrease FiO2 before reducing MAP FiO2 < 40 % - SpO2 of 90 %FiO2 < 40 % - SpO2 of 90 % then reduce MAP – 1-2 cmH2O every 30 then reduce MAP – 1-2 cmH2O every 30
minmin With MAP – 20-24 cmH2O &With MAP – 20-24 cmH2O & FiO2 – 40 % = ConventionalFiO2 – 40 % = Conventional ventilation can be startedventilation can be started
HFJVHFJV Jet squirt gas into the Jet squirt gas into the
lungs faster than lungs faster than OscillatorsOscillators
Expiration during Expiration during HFJV is passive, HFJV is passive, accomplished by the accomplished by the natural recoil of the natural recoil of the lungs. lungs.
HFOVHFOV Oscillators get the gas Oscillators get the gas
back out faster than back out faster than Jets by actively Jets by actively sucking it out sucking it out
Expiration is active, Expiration is active, driven by the active driven by the active retraction of the retraction of the oscillating diaphragm oscillating diaphragm or pistonor piston
Study : Critical care 2011, Study : Critical care 2011, 15:R259 , 28 oct 201115:R259 , 28 oct 2011
HFOV with short term outcome in HFOV with short term outcome in neonates & infants undergoing neonates & infants undergoing cardiac surgerycardiac surgery
In this study , author concludes that In this study , author concludes that when commenced on the day of when commenced on the day of surgery HFOV leads to shorter length surgery HFOV leads to shorter length of mech ventilation & ICU stay than of mech ventilation & ICU stay than conventional ventilationconventional ventilation
High Frequency Ventilation in High Frequency Ventilation in PPHTNPPHTN
V/Q matching to improve V/Q matching to improve oxygenationoxygenation
Respiratory alkalosis to reduce PVRRespiratory alkalosis to reduce PVR Improved response to inhaled NOImproved response to inhaled NO ““Rescue” for air leak syndromesRescue” for air leak syndromes
HFV ChallengesHFV Challenges HFV ventilates so effectively that hypocarbia HFV ventilates so effectively that hypocarbia
can easily be induced, especially when PEEP in can easily be induced, especially when PEEP in low.low.
Inadvertent PEEP can develop when HFV rate is Inadvertent PEEP can develop when HFV rate is inappropriately high , can interfere with CO.inappropriately high , can interfere with CO.
Gas trapping can also occur when MAP is too Gas trapping can also occur when MAP is too low and airways become smaller thereby low and airways become smaller thereby increasing resistance.increasing resistance.
ECMOECMO ECMO is a temporary support of ECMO is a temporary support of
heart & lung function by partial CP heart & lung function by partial CP bypassbypass
Used for pts – reversible Used for pts – reversible cardiopulmonary failure from cardiac, cardiopulmonary failure from cardiac, pulmonary or other diseases pulmonary or other diseases
VenoarterialVenoarterial Blood is drained from Blood is drained from
RA via IJV and RA via IJV and returned to aorta via returned to aorta via carotid artery carotid artery
It provides cardiac as It provides cardiac as well as pulmonary well as pulmonary supportsupport
It requires arterial It requires arterial cannulationcannulation
VenovenousVenovenous Blood is drained from Blood is drained from
RA via sideholes of a RA via sideholes of a double lumen catheter double lumen catheter & returned to RA via & returned to RA via the endhole of same the endhole of same catheter catheter
It aids mainly in It aids mainly in recovey of lungsrecovey of lungs
It requires only venous It requires only venous cannulationcannulation
Timing of initiation of ECMO is very Timing of initiation of ECMO is very crucial in determining the patient crucial in determining the patient outcomeoutcome