Approaches for Asthma

8/14/2019 Approaches for Asthma

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Approaches for Asthma

Jon N. Meliones, MD, MS, FCCMProfessor of Pediatrics and Anesthesia

Duke University


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Outline

What is the question?

Pressure Control vs Volume Control

Decelerating Flow vs Constant Flow Ventilation Physiology

Asthma Pathology

Data on Decelerating Flow

If you have to ventilatethe preferred approach


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Modes of Ventilation

PressureControl

Pressure

Control VolumeControl

PRVC

Pressure

Flow

Decelerating

Constant

Limit

Volume


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Outline

What is the question? Ventilation Physiology

Asthma Pathology Data on Decelerating Flow

If you have to ventilatethe preferredapproach


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Ventilation Myths Increasingly Complex (Marketing directors) Host of New Toys

New Modes: Do Not Describe Functionality

Different Ventilator Manufacturers Similar modes = different functions

Cute names that mean nothing

Dont say what they do Measures are inaccurate


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Key Functionality of Ventilators

Flow Pattern Gas Flow Delivered & Distribution During Inspiration Decelerating or Constant

Limit Safety: Prevents the Ventilator from Exceeding Preset limit Volume or Pressure

Cycle When Inspiration Ends

Trigger How the Breath is Initiated

Breath Type Single or Mixed


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Effects of Flow Pattern on Airway

Pressures

Decelerating Square

Flow

(l/sec)

AirwayPressure(cmH20)

MAP = Area Under Curve

PIPPIP

MAP


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Square Wave Flow v. Decel

Flow Randomized Cross Over Controlled

Study of VCV v PCV

Saline Lavage

Decel Square Wave pValue

PIP 38.2 + 5.5 46.0 + 4.4


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Peak Inspiratory Pressure

PIP(cm H2O)

Cheifetz: CCM 1995

P


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Dynamic Compliance

P


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Benefits of Limiting Peak Plateau

Pressure There are no prospective randomized controlled

studies demonstrate ANY significant benefit basedon the method of ventilation except for limitingPplat:

Benefits of Limiting Pplat: Amato; ARDS networketc. Pplat


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Pediatric Asthma Data

Heliox: Pediatrics 2005 Nov Kim IK

Reduces the risk of admission for greater than 12

hours by 60% Iipratropium bromide

No Data to support

Magnesium No good data

NIBP

Transient improvements


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Limit

Safety Check Prevents The Ventilator From

Exceeding a Set Variable Pressure Limit

Controlled or Support Modes

Volume LimitControlled Modes

Minute Volume - Support Modes


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Limits Pressure Limits Dependent Variable = VT:(compliance/resistance)

Theoretical Advantage: Limit PIP (barotrauma) Theoretical Disadvantage: Hypo/Hyper Ventilation

Volume Limits Dependent Variable = Pressure

:(compliance/resistance) Theoretical Advantage: Stable Min Vent (PaCO2)

Theoretical Disadvantage: PIP (barotrauma) Minute Volume

Advantage: Auto weaning Disadvantage: Fast / slow breathing rates


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Modes of Ventilation

PressureControl

Pressure

Control VolumeControl

PRVC

Pressure

Flow

Decelerating

Constant

Limit

Volume


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Outline

What is the question? Ventilation Physiology

Asthma Pathopsiology Data on Decelerating Flow

If you have to ventilatethe preferredapproach


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Pathophysiology of Asthma Marked increased airways resistance

Prolonged Time Constant

TC = Resistance x Compliance

Degree of obstruction non-uniformresulting in varying TC

Expiratory TC worse:

Narrowing of airway during expiration.

Upstream displacement of equal pressure point,

Usually, minimal alveolar disease


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Pathophysiology ofAsthma

I t i i PEEP D i


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Intrinsic PEEP: Dynamic

Hyperinflation

Terminationof

Exhalation

Beginningof

ExhalationPremature

Termination ofExhalation

Retained GasResults in PEEPi

Beginningof

InspirationEndof

Inspiration

Premature initiation

of Inspiration


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Intrinsic PEEP/Dynamic Hyperinflation

Expiratory gas flow continues at theend of the time allotted for exhalation.

PEEPi may lead to excessive MAP.

Pulmonary effects:

Barotrauma

Cardiac effects: Impedance of venous return

Decreased cardiac output


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Systemic Venous Return(RV Preload)

PSV RAP = mean systemic venous pressure

00

Right Atrial

Pressure

PPV increases

right atrial pressure

spontaneousbreathing

Max

Systemic Venous Return


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Lung VolumeLung Volume

PVRPVRTotal PVRTotal PVR

Large VesselsLarge VesselsSmall VesselsSmall Vessels

AtelectasisAtelectasis

OverexpansionOverexpansionDHI

Effect of Lung Volume on PVR

FRCFRC


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500

550

600

650

700

750

800

850

900950

1000

10 15 20

PEEP 5 PEEP 10

Overdistention and C.O.Overdistention and C.O.

CardiacOutput

(mL/min)

CardiacOutput

(mL/min)

Tidal Volume (mL/kg)Tidal Volume (mL/kg)Cheifetz: CCM 1998


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Outline What is the question?

Ventilation Physiology


If you have to ventilatethepreferred approach


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Decelerating Flow in Asthma Pressure controlled ventilation in severe asthma.

Lopez Pediatr Pulmonol 1996;21:401

Pressure-support ventilation in children with severe

asthma. Wetzel Crit Care Med 1996;24:1603-1605.

Refractory asthma, part 2: airway interventions and

management. Jagoda A. Ann Emerg Med. 1997;29:275-

281

Mechanical ventilation for children with status

asthmaticus. Sabato K, Hanson JH. Respir Care Clin

North Am. 2000;6:171-188.

Decelerating Flow in 51 Pediatric Asthma Patients


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Decelerating Flow in Asthma Hypothesis:

VCV with constant flow distributes more

volume to the less obstructed airways with

shorter TC and less volume to longer TC.

Uneven Ventilation, Hyperexpansion of normallung under-ventilation of obstructed units

Elevated PIP and higher airways resistance

Decreased Compliance

High resistance, short IT = Premature

termination of breath and set VT not achieved


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Decelerating Flow in Asthma Decelerating flow

Flow varies;

High at first (overcomes high resistance) to

achieve set pressure early in inspiration

Lower later in inspiration to maintain this

pressure through the inspiratory time.


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Decelerating Flow in Asthma Decelerating flow

Provides a relatively constant inflation pressure:

Large airways fill with peak flow, smaller airways

with slower flow Lung units with short TC attain final volume early

Lung units with long TC continue to receive

volume later in inspiration Pressure equilibrium more even ventilation

Lower Pplat or better ventilation for same PIP

Increased Compliance


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Decelerating Flow in 51Pediatric Asthma Patients

Sarnaik, PCCM 2004

pH

Mode of VentilationVCV PCV


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PaCO2

Mode of VentilationVCV PCV


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In Pts with PCO2>45, median time toreversal was 5 hrs

SaO2 >95% in all patients

2 pts with Pneumos pre PCV 1 pts developed pneumothorax, 1 pt subq

emphesema; all well tolerated and resolved

100% survival 100% neuro intact

Median ventilation 4-107 hrs.


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Adults Agree!Decelerating flow not just for kids! Measurement of air trapping, PEEPI and DHI in

mechanically ventilated patients. Blanch Respir Care.

2005;50:110-124.

Clinical Review: Severe Asthma Papiris Critical Care

2002;6:30-44.

Lung Protective Strategies for Acute Severe Asthma.

Brown. J of Resp Care Pract. 2002;2 Refractory asthma, part 2: airway interventions and

management. Jagoda Ann Emerg Med. 1997;29:275-281.

Mechanical ventilation for children with status


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Outline What is the question?

Ventilation Physiology


If you have to ventilatethepreferred approach


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Ventilation Approach Get the gas outLimit lung injury!

Avoid DHI / Auto PEEP:

Prolong exhalation times & Low rates

Graphics to ensure complete exhalation

MinimizePplat

: Assure adequateoxygenation & ventilation but allow

hypercapnea if Pplat elevated


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Ventilation Approach PEEP controversial; low but not zero,

usual

Documents

Approaches for Asthma