Terrence Shenfield BS, RRT- RPFT, NPS, AE-C

Clinical Educator

Objectives What is AVAPS

What kind of patients does it benefit

How do you set it up?

Underlining principles in respiratory mechanics

How to monitor a patient for improvement

Hybrid mode average volume-assured pressure support (AVAPS) developed by Philips/Respironics

Blends both pressure support ventilation with volume targeted breaths ( PRVC?)

Pressure limited and volume limited

Volume targeted with pressure ramping

Increase IPAP level incrementally to achieve set tidal volume to a maximum IPAP setting

AVAPS ™ Technology

AVAPS ™ Technology

Respironics Digital Auto-Trak™ Sensitivity algorithm Leak compensation Triggering Termination sensitivity criteria

AVAPS™ estimates the patient's tidal volume with each breath and compares it with the target tidal volume

Algorithm slowly increases or decreases inspiratory pressure for each breath (0.5 to 1 cm H2O/min) in order to achieve the preset tidal volume

Pressure changes smoothly patient comfort or safety leaks are taken into account so that AVAPS™ ensures a true averaged

patient tidal volume

Auto- trak Leak compensation

• Recognize and compensate for leaks• Intentional

• Mask face interface• Unintentional

• Changes in patients breathing pattern

• Adjust intentional leaks by setting the correct “ Mask & Circuit” interface settings

• V60 recalculates at the end of exhalation the base line flow needed to adjust for leakage by using two mechanisms to update base line flow

Expiratory flow adjustment Every breath, at end-exhalation, the ventilator updates its flow baseline. At end-exhalation

patient flow is assumed to be zero ,so any difference between actual patient flow and the original baseline flow indicates a change in leakage.

Tidal volume adjustment Every breath, the ventilator compares the inspiratory and expiratory tidal volumes. Any

difference is assumed to be due to an unintentional circuit leak. The ventilator adjusts the baseline to reduce this tidal volume difference for the next breath.

Auto-Trak Triggering Triggering

Volume method

Breaths are patient (flow) triggered in all modes, typically when patient effort causes a certain volume of gas to accumulate above baseline flow

Shape signal method

Inspiration is also triggered when the patient inspiratory effort distorts the expiratory flow waveform sufficiently

Auto-Trak Expiratory Cycling Algorithms

Cycling to exhalation occurs in these cases Patient expiratory effort distorts the inspiratory flow waveform

sufficiently (shape signal method or shadow trigger) When a flow reversal occurs, typically due to a mask or mouth leak a

new flow signal (shape signal) is generated from the actual flow and delays a second signal ( very technical)

Delay causes the flow shape signal to be slightly behind the patient’s flow signal

Decrease in expiratory flow from an inspiratory effort will cross the shape signal and create a signal for ventilator triggering.

Patient flow reaches the spontaneous exhalation threshold (SET) approx 25%

After 3 seconds at the IPAP level (timed backup safety mechanism)

When a flow reversal occurs, typically due to a mask or mouth leak

Patient’s Who Benefit with AVAPS Obesity Hypoventilation Syndrome

Congenital Central Hypoventilation Syndrome

OSA patients non respondent to CPAP for BIPAP

COPD

Respiratory Physiology Total Lung Compliance

Chest wall ( thorax) compliance

Lung compliance

Lung Compliance

Static compliance

Dynamic compliance

Airway Resistance

Lung Compliance Measure of how easy of expansion of lung and thorax

Compliance in the lungs is defined as a change in volume divided by a change in transpulmonary pressure

(CL = ∆V / ∆PL). A typical value of compliance is 200 ml/cm H20

Chest Wall Compliance Chest wall compliance in obese individuals

Thorax compliance is typically equal to lung compliance in NORMAL PATIENTS

In supine position lung compliance is normal

In supine position thorax compliance (chest wall) may be lower due to the weight of the abdomen pushing against thorax

Increased pressure needed to expand the lungs and get better tidal volume

Increased WOB

Sleep sitting up

Static Lung ComplianceStatic Compliance (Cstat)

The static compliance of the lung is the change in volume for a given change in transpulmonary pressure with zero gas flow.

Dynamic Lung ComplianceDynamic Compliance (Cdyn)Dynamic

compliance measurements are made by monitoring the tidal volume used, while intra thoracic pressure measurements are taken during the instance of zero air flow that occur at the end inspiratory and expiratory levels with each breath.

Airway Resistance Mechanical factors which limit the access of inspired

air to the pulmonary alveoli

Dictated by

diameter of the airways ( very important)

density of the inspired gas

Airflow = driving force/distance

Driving force in the lungs is the difference

Alveolar pressure and pressure at the mouth

Pmouth- PA

Airway Resistance

How to Set Up AVAPS Settings and Terminology

Min P - this is the set value of IPAP that it takes to return 8cc/kg on ST mode

Max P – this is typically set to 4-5 above IPAP min

Rise time- rise to pressure ( 1 fastest -5 slowest)

Settings Put the patient on ST mode

Set IPAP level to a pressure setting that the returned tidal volume is 8 CC/kg of ideal body weight ( ex. 50kg patient = 400cc tidal volume @ 18 cmH2O)

Switch the patient to AVAPS

Set the Min P to the IPAP level on ST

Set the Max P to 4-5 above the IPAP min

Set the tidal volume ( 8cc/kg), rate, FI02, I-time, rise time, EPAP from the ST mode

Alarms Low and High Tidal Volume

Compliance changes can impact the delivered tidal volume

Adjust high and low tidal volume with 10%

Very Important with AVAPS

Supporting Evidence Average Volume Assured Pressure Support in Obesity Hypoventilation:

a Randomized Cross-Over Trial , Jan Hendrik Storre, Chest, 2006;130;815-821.

Average volume-assured pressure support in a 16-year-old girl with congenital central hypoventilation syndrome. Vagiakis E, Koutsourelakis , J Clin Sleep Med. 2010 Dec 15;6(6):609-12.

Subjective sleep quality during average volume assured pressure support (AVAPS) ventilation in patients with hypercapnic COPD: a physiological pilot study. Crisafulli E, Manni G, Lung. 2009 Sep-Oct;187(5):299-305.

Obesity Hypoventilation SyndromePickwickian Syndrome

•Weight of chest wall and obstructing fat

•Increased WOB

•Lung compliance is less with OHS patients than equally obese patients

•Hypercapnia has a known deleterious effect on diaphragmatic function

•Chest wall restriction

•Diaphragmatic movement is impeded due to abdominal contents

•AVAPS has “floating” IPAP setting to target set tidal volume resulting in the normalization of PCO2

Obesity Hypoventilation SyndromePickwickian Syndrome Study by Jan Hendrick Storre MD et al. Chest 2006

Randomized Cross Over Trial

BIPAP ST OR AVAPS versus straight CPAP

ST patients

Improved gas exchange

Improved sleep quality

NREM ( non rapid eye movement) stage 3 and 4 increased

PCO2-did not normalize

AVAPS patients Same findings as above with the addition of normalization of PCO2

Congenital Central Hypoventilation Syndrome

Research by Emmanouil Vagiakis MD et al. Journal of Sleep Medicine 2010

Congenital disease Absence of autonomic control of respirations Alveolar hypoventilation Decreased sensitivity to hypercapnia and hypoxemia During sleep this is greatly pronounced Life time ventilatory support

Treatment options are mechanical ventilation at night via tracheostomy or NIV

Patient was decannulated and put on BIPAP with AVAPS at night Findings

PCO2 is more stable than BIPAP More stable minute ventilation Better tolerated

Subjective Sleep Quality Using AVAPS Pilot study done by Ernesto Crisafulli et al. Lung 2009

Short term night time efficacy of compliance and physiological responses of AVAPS versus PS ventilation on nine patients

Parameters monitored

Subjective sleep quality ( 10 item questionnaire) Diurnal hypersomnia ( daily day time sleepiness)

Sleep quality

Subjective perception of comfort ( VAS score-Visual Analog Scale)

Physiologic responses ( PCO2, Ph, and PO2)

Findings Vt and VE higher with AVAPS with decreased PCO2

Improved sleep quality ( validated to specific to OSA patients)

VAS score was similar

New Research Average Volume Assured Pressure Support (AVAPS) in ALS Patients

with Nocturnal Hypoventilation: A Randomized Crossover Trial

Jonathan Katz, MD - Forbes Norris ALS Research Center Aim:

To compare adherence to traditional pressure-limited versus volume-assured pressure support ventilation options.

To determine if symptoms of perceived sleep quality, dyspnea, orthopnea and quality of life are affected by either of the two types of NPPV.

To define and determine if a specific subset of patients with “pure” diaphragmatic failure adhere to and benefit from one or both therapies.

To develop a novel assessment measure to identify symptoms of orthopnea.

New Research

Efficacy of Average Volume Assured Pressure Support With Bi-Level Pressure Support Nocturnal Ventilation This study aims to compare, in a randomized order, two consecutive nights with a bi-

level positive pressure ventilator (Synchrony, Respironics, USA), with and without average volume assured pressure support (AVAPS), in patients with chronic respiratory failure, treated on a long term basis by home nocturnal non-invasive ventilation.

Endpoints

Quality of sleep assessed by polysomnography scored by an independent investigator(sleep efficiency, distribution of sleep stages, arousals and sleep stage changes) and subjective scores

Perception of comfort of ventilation (clinical score)

Efficacy of ventilation (pulsoximetry, transcutaneous capnography , effective ventilation and tidal volumes, leaks as measured by ventilator, Respironics).