Advanced Modes of Mechanical Ventilation Michael Haines, MPH, RRT-NPS, AE-C Victor Valley Community College

What we will cover… Intro to advanced modes PRVC Automode Volume Support/Variable Pressure Autoflow Adaptive Support Ventilation Volume assured pressure support (VAPS) Automatic Tube compensation Mandatory Minute Ventilation Proportional Assist Ventilation BUT FIRST A LITTLE REVIEW….

Ventilator Formulas

Lung Mechanics resistance = Dpressure / Dflow transairway pressure transrespiratory pressure transthoracic pressure elastance = Dpressure / Dvolume volume The equation of motion says that the pressure necessary to deliver a breath has two components; the pressure to overcome elastic recoil of the lungs and chest wall and the pressure to cause flow through the airways. The left hand side of the equation can be expanded to show that ventilating pressure may be made up of muscle pressure and/or airway pressure generated by the ventilator. The right hand side of the equation can be expanded to show that elastic recoil pressure is the product of elastance times volume while resistive pressure is the product of resistance and flow.

Static Compliance Cs = tidal volume corrected for gas compression Pplat – PEEP total peep Normal 100 - 200 ml / cmH2O (PDQ) Decreased with: Mainstem Intubation Congestive Heart Failure ARDS Atelectasis Consolidation Fibrosis Hyperinflation Tension Pneumothorax Pleural Effusion Abdominal Distension Chest Wall Edema Thoracic Deformity

Principle #1: Ventilation The goal of ventilation is to facilitate CO2 release and maintain a normal PaCO2 Minute Ventilation (Ve) Total amount of gas exhaled per minute Ve = Vt x f Ve comprised of 2 factors VA = alveolar ventilation VD = dead space ventilation Ventilation in the ICU setting Increased CO2 production Fever, sepsis, injury, overfeeding Increased VD Vent circuit, ET tube Adjustments: Vt and f

Fig. 13-1. Factors that affect the partial pressure of arterial carbon dioxide (PaCO2) during mechanical ventilation. V.CO2, carbon dioxide production; V.A, alveolar ventilation; V.E, minute ventilation; V.D, dead space ventilation; VT, tidal volume; TI, inspiratory time; TE, expiratory time; f, respiratory rate. (From Hess DR, MacIntyre NR, Mishoe SC, et al: Respiratory care principles and practice, Philadelphia, 2002, WB Saunders.)

Principle #2: Oxygenation The primary goal of oxygenation is to maximize O2 delivery to the blood (PaO2) Alveolar-arterial O2 gradient Equilibrium between O2 in the blood and O2 in the alveoli A-a gradient measures efficiency of oxygenation PaO2 partially depends on ventilation but more on V/Q matching Oxygenation in the ICU setting PaO2/PAO2 ratio (a/A ratio) Indicator of efficiency of O2 transport CaO2 Adjustments: FiO2 and PEEP

Volume vs. Pressure Control Ventilation Volume Ventilation Volume delivery constant Inspiratory pressure varies Inspiratory flow constant Inspiratory time determined by set flow and Vt Pressure Ventilation Volume delivery varies Inspiratory pressure constant Inspiratory flow varies Inspiratory time set by clinician 23

What’s Wrong with Volume Control Ventilation? The limited flow may not meet the patient’s desired inspiratory flow rate If the patient continues to inspire vigorously -- , added, unnecessary work is done Can lead to fatigue Can cause excessive airway pressure leading to barotrauma, volutrauma, and adverse hemodynamic effects

Pressure Control Ventilation: The Alternative Definition The application of clinician-set inspiratory pressure and inspiratory time. Flow delivery varies according to patient demand The clinician sets the inspiratory pressure, I-time or I:E ratio and RR Tidal volume varies with changes in compliance and resistance Flow delivery is decelerating 24

Pressure Control Ventilation May be used in A/C and SIMV modes In A/C - all breaths (either machine-initiated or patient-initiated) are time-cycled and pressure-limited In SIMV - only machine-initiated breaths are time-cycled and pressure-limited Spontaneous breaths can be pressure-supported 15 25

Pressure Control Ventilation Advantages Limits risk of barotrauma May recruit collapsed and flooded alveoli Improved gas distribution Uses a active exhalation valve which uses servo-control technology that allows gas to be released from the exhalation valve during the inspiratory phase if the patient makes an expiratory effort. Disadvantages Tidal volumes vary when patient compliance changes (i.e., ARDS, pulmonary edema) With increases in I-time, patient may require sedation and/or chemical paralysis Make sure to incorporate discussion on active exhalation valve in notes 27 17

Indications for PCV Enhance patient / ventilatory synchrony Patient determines flow Lung protection strategy Lower inspiratory pressure with decelerating flow may improve V/Q matching Adjusting I-time may improve oxygenation by ↑ MAP Alveolar diseases that produce varying time constants May recruit alveoli by lengthening I-time 28

Rationale of Pressure Modes Ventilator-induced lung injury (VILI) Atelectrauma Pre-existing lung damage and/or inflammation

The Cons of Pressure Control Variable Vt as pulmonary mechanics change Potentially excessive Vt as compliance improves Inconsistent changes in Vt with changes in PIP and PEEP

Most Commonly used Waveforms Pressure vs. Time Flow vs. Time Volume vs. Time

Pressure-Time Curve Paw Volume Ventilation Pressure Ventilation 20 Volume Ventilation Pressure Ventilation Paw Expiration cmH2O Sec 1 2 3 4 5 6

Pressure vs. Time Curve Paw cmH2O 1 2 3 4 5 6 30 A B C PIP Baseline Sec Paw cmH2O A B C PIP Baseline Mean Airway Pressure -10

Volume Control Breath Types 60 P aw cmH 2 SEC 1 2 3 4 5 6 -20 120 INSP Flow SEC How do you know the problem is with the patient? Look at your flow curve. 1 2 3 L/min 4 5 6 120 EXH If compliance decreases the pressure increases to maintain the same Vt 45

Volume/Flow Control Pressure Control Inspiration Expiration Inspiration Expiration 20 20 Paw Pressure Paw 1 2 1 2 20 20 Volume 1 2 1 2 3 3 If follows from the equation of motion that the ventilator can control either the left side of the equation (ie, airway pressure) or the right side (ie, volume and flow). These curves illustrate the two basic approaches to ventilator control. If the ventilator controls flow, it controls volume indirectly (by definition) and vice versa. Usually, inspiratory flow is held constant during inspiration, causing volume and pressure to rise linearly. Inspiration ends (cycles off) when a preset tidal volume is met. In contrast, with pressure control ventilation, airway pressure may be held constant during inspiration. This causes inspiratory flow to decay exponentially from its peak value towards zero as volume rises exponentially. Inspiration usually ends after a preset inspiratory time or (in the case of pressure support) after a preset inspiratory flow threshold has been crossed. If inspiratory time is long enough (usually about 5 time constants) lung pressure will equilibrate with airway pressure and inspiratory flow will cease. You will note that for passive exhalation is exponential. That mean expiratory time must be at least 5 time constants long to exhale more that 99% of the tidal volume. As expiratory time becomes shorter than 5 time constants, gas trapping (ie, autoPEEP) occurs. Flow Time (s) Time (s) -3 -3

These curves illustrate the two basic approaches to ventilator control These curves illustrate the two basic approaches to ventilator control. If the ventilator controls flow, it controls volume indirectly (by definition) and vice versa. Usually, inspiratory flow is held constant during inspiration, causing volume and pressure to rise linearly. Inspiration ends (cycles off) when a preset tidal volume is met. In contrast, with pressure control ventilation, airway pressure may be held constant during inspiration. This causes inspiratory flow to decay exponentially from its peak value towards zero as volume rises exponentially. Inspiration usually ends after a preset inspiratory time or (in the case of pressure support) after a preset inspiratory flow threshold has been crossed. If inspiratory time is long enough (usually about 5 time constants) lung pressure will equilibrate with airway pressure and inspiratory flow will cease. You will note that for passive exhalation is exponential. That mean expiratory time must be at least 5 time constants long to exhale more that 99% of the tidal volume. As expiratory time becomes shorter than 5 time constants, gas trapping (ie, autoPEEP) occurs.

Work to Trigger 30 Paw cmH2O Sec 1 2 3 4 5 6 -10

Assisted Breath

Lung Overdistension

Analysis of Compliance Waveforms Compliance waveforms simultaneously display volumes and the amount of pressure necessary to deliver these volumes. Volume normally is plotted on the “Y” axis and pressure on the “X” axis. The curve to the right depicts a compliance curve from a patient with normal compliance and airway resistance. The arrow pointing down and to the left is on the expiratory side of the curve.

Analysis of Compliance Waveforms One of the clinical indications for the addition of positive-end expiratory pressure (PEEP) is low lung compliance. If PEEP is added, the baseline pressure would then be elevated and the curve would shift to the right.

Altering Compliance with PEEP The curve drawn in a heavy, non-dashed line represents an improved lung compliance due to the addition of PEEP. Notice that the tidal volume is the same (note the “Y” axis) while the PIP has fallen (note the “X” axis). Since the same volume is delivered with less of a pressure difference (PIP-PEEP), compliance has increased.

Compliance Curves The following series of compliance curves reflect a steady fall in lung compliance, as would occur with the development of cardiogenic or noncardiogenic pulmonary edema. The first curve (1) reflects the patient’s baseline condition. As his compliance falls, higher pressures are needed to deliver the same tidal volume (2) (second set of curves with the initial curve indicated in gray). As the patient’s condition deteriorates further, the final compliance curve is obtained (3).

Assist/Control Mechanical Ventilation Notice that the third mechanical breath was preceded by a drop in airway pressure (indicating a spontaneous inspiratory effort). In addition, note that the TCT had not elapsed prior to the initiation of this breath. Although only one of the breaths was initiated spontaneously, all breaths had the same tidal volume.

Synchronized Intermittent Mandatory Ventilation (SIMV) Notice that the fifth breath was a mechanical breath that was initiated by a spontaneous inspiratory effort. If this effort had occurred before the sensitivity window began, the patient would have only had a spontaneous, unassisted breath (circled). In addition, notice that the therapist selected a constant flow pattern for this patient.

Support Ventilation (PSV) Salient features of the flow graph: The amount of inspiratory flow may vary from breath to breath based on patient inspiratory effort (V1<V2). Duration of each breath may vary. http://www.youtube.com/watch?v=Rwr5ZjJI1ZQ

Support Ventilation (PSV) Salient features of the volume graph: The tidal volume may vary from breath to breath based on patient inspiratory effort (V1<V2). Duration of each breath may vary.

Pressure, Flow, and Volume Curves A clearer picture of the dynamics of plateau pressures and inflation holds is obtained when pressure curves are viewed along with their corresponding flow and volume curves. Notice that flowrate drops to zero during the plateau interval, separating expiratory flow from inspiratory flow. In addition, even though flow is not occurring during the inflation hold, the inflation hold is still considered to be part of inspiratory time or Ti. Since no flow is occurring the volume does not change during the pause.

Pressure vs. Volume Ventilation (From Branson, R Pressure vs. Volume Ventilation (From Branson, R., Bird product literature)

New Modes: Dual Modes Within-breath Adjustment Automatic Tube Compensation (ATC) Volume-Assured Pressure Support Between-Breath Adjustment Volume Support (VS) Pressure-Regulated Volume Control

Why use newer modes of ventilation? Newer ventilators can be set to modes other than the pressure-control and volume-control modes of older machines The alternative modes of ventilation were developed to prevent lung injury and asynchrony through patient adaptation, promote better oxygenation and faster weaning, and be easier to use. However, evidence of their benefit is scant. Remember: weaning is a dynamic process requiring frequent intervention and adjustments, best performed by the RT!

Why use newer modes of ventilation? Technologic advances and computerized control of mechanical ventilators have made it possible to deliver ventilatory assistance in new modes. Driving these innovations is the desire to prevent ventilator induced lung injury, improve patient comfort, and liberate the patient from mechanical ventilation as soon as possible We call these innovations “alternative” modes to differentiate them from the plain volume-control and pressure-control modes

Terminology APC—adaptive pressure control APRV—airway pressure-release ventilation ASV—adaptive support ventilation HFOV—high-frequency oscillatory ventilation MMV- Mandatory Minute Ventilation PAV—proportional assist ventilation PRVC – Pressure Release Volume Control PSV—pressure support ventilation VC+ - Volume control plus VS- Volume Support APV- adaptive pressure ventilation ATC – Automatic tubing compensation VP- variable pressure VTPC- Volume targeted pressure control

Patient-ventilator Asynchrony 24% of mechanically ventilated patients exhibit patient-ventilator asynchrony in > 10% of their respiratory efforts during AVC and PS ventilation (ineffective triggering and double triggering). Patient-ventilator asynchrony during assisted mechanical ventilation Intensive Care Med. 2006;32:1512 Here we see data from the Thille study. The main emphasis here is that those patients who experience asynchrony in greater that 10% of their breaths stay on the ventilator for an average of 25 days. Those who do not experience the asynchrony are on the ventilator for an average of only 7 days. This is a difference of 18 extra days and represents 24%, almost a quarter, of ventilator patients. Arnold W. Thille, Pablo Rodriguez, Belen Cabello Francois Lellouche, Laurent Brochard

Prolonged ventilation time1 Possible muscle atrophy2 and VAP3 Length of Stay Asynchrony Sedation Prolonged ventilation time1 Possible muscle atrophy2 and VAP3 Weaning is delayed Ventilator asynchrony is manifested in several forms. Common asynchrony patterns include missed efforts, double triggering and auto-cycling. These problems typically occur when the breath parameters set on the ventilator do not match the signals from the patient’s respiratory center in the brain. The upper graphic shows multiple missed efforts in the pressure support mode. The lower graphic shows an asynchronous pattern called “double trigger” in the assist control mode. Because patient conditions are constantly changing, frequent manipulation of the ventilator settings are required to manage the asynchrony. It is not uncommon for patients to be sedated as a result of asynchrony and this has been shown to prolong ventilation time.1 Furthermore, prolonged ventilation time can result in rapid disuse atrophy of the diaphragm2 and ventilator-associated pneumonia.3 1. Kollef M et al. The use of continuous intravenous sedation is associated with prolongation of mechanical ventilation. Chest. 1998;114:541–548. 2. Levine S et al. Rapid Disuse Atrophy of Diaphragm Fibers in Mechanically Ventilated Humans. NEJM. 2008;358:1327-1335. 3. Rello J et al. Epidemiology and outcomes of ventilator-associated pneumonia in a large US database. Chest. 2002;122:2115-2121. 1. Kollef M et al. Chest. 1998;114:541–548. 2. Levine S et al. NEJM .2008;358:1327-1335. 3. Rello J et al. Chest .2002;122:2115-2121.

Ventilator asynchrony is manifested in several forms Common asynchrony patterns include missed efforts, double triggering and auto-cycling. These problems typically occur when the breath parameters set on the ventilator do not match the signals from the patient’s respiratory center in the brain. The upper graphic shows multiple missed efforts in the pressure support mode. The lower graphic shows an asynchronous pattern called “double trigger” in the assist control mode. Because patient conditions are constantly changing, frequent manipulation of the ventilator settings are required to manage the asynchrony. It is not uncommon for patients to be sedated as a result of asynchrony and this has been shown to prolong ventilation time.1 Furthermore, prolonged ventilation time can result in rapid disuse atrophy of the diaphragm2 and ventilator-associated pneumonia.3

Mechanical breath terminology Control variable—the mechanical breath goal, ie, a set pressure or a set volume Trigger variable—that which starts inspiration, ie, the patient (generating changes in pressure or flow) or a set rate (time between breaths) Limit variable—the maximum value during inspiration Cycle variable—that which ends inspiration

Mechanical breath terminology Continuous mandatory ventilation—all breaths are controlled by the ventilator, so usually they have the same characteristics regardless of the trigger (patient or set rate); no spontaneous breaths are allowed Intermittent mandatory ventilation—a set number of mechanical breaths is delivered regardless of the trigger (patient initiation or set rate); spontaneous breaths are allowed between or during mandatory breaths Continuous spontaneous ventilation—all breaths are spontaneous with or without assistance

Mechanical breath terminology Set point—the ventilator delivers and maintains a set goal, and this goal is constant (eg, in pressure control, the set point is pressure, which will remain constant throughout the breath) Servo—the ventilator adjusts its output to a given patient variable (ie, in proportional assist ventilation, the inspiratory flow follows and amplifies the patient’s own flow pattern) Adaptive—the ventilator adjusts a set point to maintain a different operator-selected set point (ie, in pressure-regulated volume control, the inspiratory pressure is adjusted breath to breath to achieve a target tidal volume) Optimal—the ventilator uses a mathematical model to calculate the set points to achieve a goal (ie, in adaptive support ventilation, the pressure, respiratory rate, and tidal volume are adjusted to achieve a goal minute ventilation)

Examples of the first dual modes Volume Assured Pressure Support (VAPS) & Pressure Augmentation Pressure Regulated Volume Control (PRVC) & similar modes Volume Support Ventilation (VS or VSV) & similar modes

NEW MODES OF VENTILATION DUAL-CONTROLLED MODES Type Manufacturer; ventilator Name Dual control within a breath VIASYS Healthcare; Bird 8400Sti and Tbird VIASYS Healthcare; Bear 1000 Volume-assured pressure support Pressure augmentation Dual control breath to breath: Pressure-limited flow-cycled ventilation Siemens; servo 300 Cardiopulmonary corporation; Venturi Volume support Variable pressure support Pressure-limited time-cycled ventilation Hamilton; Galileo Drager; Evita4 Pressure-regulated volume control Adaptive pressure ventilation Autoflow Variable pressure control SIMV Adaptive support ventilation

Dual Control Breath-to-Breath pressure-limited time-cycled ventilation Pressure Regulated Volume Control Servo 300 Maquet Servo-i

Other Names for PRVC… AutoFlow (Drager • Medical AG, Lubeck, Germany) Adaptive Pressure Ventilation (Hamilton Galileo, Hamilton Medical AG, Bonaduz, Switzerland) Volume Control+ (Puritan Bennett, Tyco Healthcare; Mansfield, MA) Volume Targeted Pressure Control, Pressure Controlled Volume Guaranteed (Engstrom, General Electric, Madison, WI).

Pressure Regulated Volume Control (PRVC) One of the concerns with pressure-control ventilation is that it cannot guarantee a minimum minute ventilation in the face of changing lung mechanics or patient effort, or both. To solve this problem, in 1991 the Siemens Servo 300 ventilator introduced Pressure Regulated Volume Control, a mode that delivers pressure-controlled breaths with a target tidal volume and that is otherwise known as adaptive pressure control (APC) On the Servo it was initially only available on AC mode

Pressure Regulated Volume Control (PRVC) PRVC is not a volume-control mode (Despite the name!). In volume control, the tidal volume does not change; in APC the tidal volume can increase or decrease, and the ventilator will adjust the inflation pressure to achieve the target volume. Thus, APC guarantees an average minimum tidal volume but not a maximum tidal volume

Pressure Regulated Volume Control (PRVC) Combines volume ventilation & pressure control (for mech., time-cycl. breaths only) Set TV is “targeted” Ventilator estimates vol./press. relationship each breath Ventilator adjusts level of pressure control breath by breath

Pressure Regulated Volume Control (PRVC) Delivers patient or timed triggered, pressure-targeted (controlled) and time-cycled breaths Ventilator measures VT delivered with VT set on the controls. If delivered VT is less or more, ventilator increases or decreases pressure delivered until set VT and delivered VT are equal

Pressure Regulated Volume Control (PRVC) This mode differs from pressure AC by adjusting rhe pressure level on a breath-by-breath basis to ensure a targeted Vt The respiratory therapist must set: Pressure Target Vt, Inspiratory time Backup rate Rise time FiO2 PEEP Sensitivity

Pressure Regulated Volume Control (PRVC) For each breath, the ventilator assesses each breath and adjusts pressure 1-3 cm H2O and assesses the Vt This mode works best for pts who are apneic or have a weak ventilatory drive, used on AC mode and also SIMV (only on Servo I)

Pressure Regulated Volume Control (PRVC) First breath = 5-10 cm H2O above PEEP First breath is a “test breath”, an inspiratory hold is also applied to obtain a plateau pressure to be applied on the next breath V/P relationship measured Next 3 breaths, pressure increased to 75% needed for set TV Then up to +/- 3 cm H2O changes per breath Time ends inspiration

2nd 1st breath The pressure is constant after the first test breath (square pattern) and flow becomes variable with a decelerating ramp pattern just as in pressure control mode.

Pressure Regulated Volume Control (PRVC) PRVC. (1), Test breath (5 cm H2O); (2) pressure is increased to deliver set volume; (3), maximum available pressure; (4), breath delivered at preset E, at preset f, and during preset TI; (5), when VT corresponds to set value, pressure remains constant; (6), if preset volume increases, pressure decreases; the ventilator continually monitors and adapts to the patient’s needs

Press increase +3 The vent then regulates the amount of pressure needed to obtain the desired set VT. It will increase or decrease the amount of pressure on a “breath by breath” basis, (+/- 3 cmH2O per breath)

PRVC flowchart Test Breath Measure tidal Volume Compare to set Tidal Volume More Less Increase Insp Pressure Decrease Insp Pressure Equal Give Same Insp Pressure

Pressure Regulated Volume Control (PRVC)- Considerations Assist-control mode Like PC, flow varies automatically to varying patient demands Constant press. during each breath - variable press. from breath to breath Time is cycling method; delivered TV can vary from set

Pressure Regulated Volume Control (PRVC)- Considerations The ventilator will not allow delivered pressure to rise higher than 5 cm H2O below set upper pressure limit Example: If upper pressure limit is set to 35 cm H2O and the ventilator requires more than 30 cm H2O to deliver a targeted VT of 500 mL, an alarm will sound alerting the clinician that too much pressure is being required to deliver set volume (may be due to bronchospasm, secretions, changes in CL, etc.)

Pressure Regulated Volume Control (PRVC) Indications Patient who require the lowest possible pressure and a guaranteed consistent VT ALI/ARDS—Questionable, ideally change to PC, VC with low VT/high rate or APRV or HFOV Patients requiring high and/or variable I Patient with the possibility of CL or Raw changes

Pressure Regulated Volume Control (PRVC) Disadvantages and Risks Varying mean airway pressure May cause or worsen auto-PEEP When patient demand is increased, pressure level may diminish when support is needed May be tolerated poorly in awake non-sedated patients A sudden increase in respiratory rate and demand may result in a decrease in ventilator support Pressure delivered is dependent on VT from previous breath. If patient intermittently makes a significant inspiratory effort, it can result in variable volumes that can be higher or lower than the setting

In this example, the first breath is a control breath with the patient making no respiratory effort this time. The desired tidal volume of 500 is delivered here.

Pressure unchanged The second breath is triggered by the patient who made a significant inspiratory effort. Although, PIP has remained the same as the first breath, a higher tidal volume results because of higher transpulmonary pressure

The ventilator will then reduce the amount of pressure needed for the next breath. The patient doesn’t make any inspiratory effort with this breath, the result is a tidal volume that is lower than the set tidal volume

Pressure Regulated Volume Control (PRVC) Advantages Maintains a minimum PIP Targeted VT and E Patient has very little WOB requirement Allows patient control of respiratory rate and E Variable E to meet patient demand Decelerating flow waveform for improved gas distribution Breath by breath analysis??

Understanding PRVC part 1

Auto-mode/Volume Support on PRVC For patients that are making intermittent inspiratory efforts, or breathing spontaneously, switching to Automode may be better (on Servo, called adaptive support ventilation on Galelio) In Automode, the ventilator will automatically switch between PRVC and Volume Support mode. PRVC breaths when there is no patient effort and VS breaths with patient effort

Auto-mode/Volume Support on PRVC Volume Support works the same way as PRVC VS automatically adjusts the level of pressure support needed to achieve a targeted tidal volume, based on the amount of inspiratory effort given by the patient Volume Support is basically, Pressure Support that guarantees a set tidal volume

VS (Volume Support) Entirely a spontaneous mode Delivers a patient triggered (pressure or flow), pressure targeted, flow cycled breath Can also be timed cycled (if TI is extended for some reason) or pressure cycled (if pressure rises too high). Similar to pressure support except VS also targets set VT. It adjusts pressure (up or down) to achieve the set volume (the maximum pressure change is < 3 cm H2O and ranges from 0 cm H2O to 5 cm H2O below the high pressure alarm setting Used for patients ready to be “weaned” from the ventilator and for patients who cannot do all the WOB but who are breathing spontaneously

VS (Volume Support) (1), VS test breath (5 cm H2O); (2), pressure is increased slowly until target volume is achieved; (3), maximum available pressure is 5 cm H2O below upper pressure limit; (4), VT higher than set VT delivered results in lower pressure; (5), patient can trigger breath; (6) if apnea alarm is detected, ventilator switches to PRVC

Volume Support (VS) Pressure limited Flow cycled Automatic weaning of pressure support as long as tidal volume matches the minimum required to Vt.

Volume Support (VS) What happens in VS if impedance changes (higher resistance or less compliance )? – TV will decrease, subsequent pressure will be increased to bring TV back toward the goal. Little data to show it actually works. • If pressure support level increases to maintain TV in pt with increased airways resistance, PEEPi may increase. • If minimum TV set too high, weaning may be delayed

VS (Volume Support) Advantages Guaranteed VT and E Pressure supported breaths using the lowest required pressure Decreases the patient’s spontaneous respiratory rate Decreases patient WOB Allows patient control of I:E time Breath by breath analysis Variable I to meet the patient’s demand

VS (Volume Support) Disadvantages Spontaneous ventilation required VT selected may be too large or small for patient Varying mean airway pressure Auto-PEEP may affect proper functioning A sudden increase in respiratory rate and demand may result in a decrease in ventilator support

Auto Flow-on Drager Essentially the same as PRVC: Autoflow is not a specific mode, it can be used with all volume modes, and is effective during the inspiratory phase. Autoflow converts a volume mode to a volume targeted, pressure limited mode. The goal is to deliver the set tidal at the lowest possible pressure (plateau pressure) utilizing a decelerating gas flow pattern. Autoflow allows the exhalation valve to behave as a CPAP valve (threshold resistor) allowing the patient to alter their flow patterns, enhancing the ability to breathe spontaneously. During the inspiratory period the patient is able to exhale, cough or sigh.

Auto Flow-on Drager When autoflow is activated, a test breath is delivered at a pressure of 5 cmH20 above PEEP. The second breath is delivered at 75% of the set tidal volume. The third breath will be the set tidal volume, provided the pressure is 3 to 5 cmH20 below the pressure limit. The microprocessor algorithm then calculates the minimal pressure capable of achieving the targeted tidal volume. Autoflow recalculates compliance with each breath, and the next breath reflects any change in compliance. As the patients lung compliance changes, the pressure will adjust up or down in increments of no more than 3 cmH20 per breath.

Adaptive Support Ventilation- Adaptive support ventilation (ASV) evolved as a form of mandatory minute ventilation implemented with a daptive pressure control. ASV delivers pressure-controlled breaths using an adaptive (optimal) scheme “Optimal,” in this context, means minimizing the mechanical work of breathing: the machine selects a tidal volume and frequency that the patient’s brain would presumably select if the patient were not connected to a ventilator.

Adaptive Support Ventilation- Galileo vent A dual control mode that uses pressure ventilation (both PC and PSV) to maintain a set minimum Ve (volume target) using the least required settings for minimal WOB depending on the patient’s condition and effort. It automatically adapts to patient demand by increasing or decreasing support, depending on the patient’s elastic and resistive loads

Adaptive Support Ventilation- Galileo vent The clinician enters the patient’s IBW, which allows the ventilator’s algorithm to choose a required Ve. The ventilator then delivers 100 mL/min/kg. A series of test breaths measures the system C, resistance and auto-PEEP If no spontaneous effort occurs, the ventilator determines the appropriate respiratory rate, VT, and pressure limit delivered for the mandatory breaths

Adaptive Support Ventilation- Galileo vent The ventilator initially delivers test breaths, in which it measures the expiratory time constant for the respiratory system and then uses this along with the estimated dead space and normal minute ventilation to calculate an optimal breathing frequency in terms of mechanical work. The optimal or target tidal volume is calculated as the normal minute ventilation divided by the optimal frequency.

Adaptive Support Ventilation- Galileo vent I:E ratio and TI of the mandatory breaths are continually being “optimized” by the ventilator to prevent auto-PEEP If the patient begins having spontaneous breaths, the number of mandatory breaths decrease and the ventilator switches to PS at the same pressure level Pressure limits for both mandatory and spontaneous breaths are always being automatically adjusted to meet the Ve target

ASV: Principle mode of ventilation + + Flow I Flow E * * Pinsp PEEP no patient activity: * machine triggered + time cycled patient is active: * patient triggered + flow cycled From Hamilton Medical 7

Adaptive Support Ventilation- Galileo vent The target tidal volume is achieved by the use of APC This means that the pressure limit is automatically adjusted to achieve an average delivered tidal volume equal to the target. The ventilator continuously monitors the respiratory system mechanics and adjusts its settings accordingly. The ventilator adjusts its breaths to avoid air trapping by allowing enough time to exhale, to avoid hypoventilation by delivering tidal volume greater than the dead space, and to avoid volutrauma by avoiding large tidal volume

: Hamilton Galileo’s ASV - Considerations Mandatory breaths = PC, pt. triggered = PS both at same targeted TV and calculated press. If pt.’s f > “set” by vent., mode is PS If pt.’s f < “set” by vent., mode is PC-SIMV/PS If patient is apneic, all breaths are PC

Ventilator settings in adaptive support ventilation Ventilator settings in ASV are: Patient height (to calculate • the IBW), Sex Percent of normal predicted minute ventilation goal Fio2 PEEP Clinical applications of adaptive support ventilation ASV is intended as a sole mode of ventilation, from initial support to weaning.

Theoretical benefits of adaptive support ventilation In theory, ASV offers automatic selection of ventilator settings, automatic adaptation to changing patient lung mechanics, less need for human manipulation of the machine, improved synchrony, and automatic weaning Physiologic benefits. Ventilator settings are adjusted automatically. ASV selects different tidal volume-respiratory rate combinations based on respiratory mechanics in passive and paralyzed patients

Clinical Evidence for ASV In actively breathing patients, there was no difference in the ventilator settings chosen by ASV for different clinical scenarios (and lung physiology).10 Compared with pressure-controlled intermittent mandatory ventilation, with ASV, the inspiratory load is less and patient-ventilator interaction is better Two trials suggest that ASV may decrease time on mechanical ventilation. However, in another trial,16 compared with a standard protocol, ASV led to fewer ventilator adjustments but achieved similar postsurgical weaning outcomes.

Disadvantages ASV Inability to recognize and adjust to changes in alveolar VD Possible respiratory muscle atrophy Varying mean airway pressure In patients with COPD, a longer TE may be required A sudden increase in respiratory rate and demand may result in a decrease in ventilator support

Clinical Evidence for ASV Adaptive support ventilation: Bottom line ASV is the first commercially available mode that automatically selects all the ventilator settings except PEEP and Fio2. These seem appropriate for different clinical scenarios in patients with poor respiratory effort or in paralyzed patients. Evidence of the effect in actively breathing patients and on outcomes such as length of stay or death is still lacking

Initializing ASV ASV in Obese patient

Volume Assured Pressure Support (VAPS) Designed to reduce work of breathing while maintaining a minimum minute volume and a minimum Vt Combines a high initial flow as in PC and a constant volume delivery as in VC This mode allows a feedback loop based on tidal volume Switches even within a single breath from pressure control to volume control if minimum tidal volume has not been achieved

Volume Assured Pressure Support (VAPS) The respiratory therapist sets: Pressure limit = plateau seen during VC RR Peak flow rate PEEP FiO2 Trigger sensitivity Minimum tidal volume Also called AVAPS used in NPPV on Respironics Bipap

Switch from Pressure control to Pressure limit overridden Switch from Pressure control to Volume/flow control 40 Set pressure limit P aw cmH 2 -20 0.6 Set tidal volume cycle threshold Tidal volume met Tidal volume not met Volume L Inspiratory flow greater than set flow 60 Inspiratory flow equals set flow Flow cycle Set flow limit Flow L/min 60

Volume Assured Pressure Support (VAPS) Limitations If pressure too high, all breaths are pressure limited If peak flow is set too low, the switch from pressure to volume is late in the breath, inspiratory time is too long. Once a breath is triggered, rapid, variable flow pushes pressure to reach set pressure support level. Tidal volume delivered from the machine is monitored.

Volume Assured Pressure Support (VAPS) Combines volume ventilation & pressure support (for mech., vol. limited breaths only) Uses TV, peak flow, and pressure sup./control settings Targets PS level with at least set peak flow first Continues until flow decreases to set peak flow, then: If TV not delivered, peak flow maintained until vol. limit If TV or more delivered, breath ends

VAPS: Volume Assured Pressure Support (From Branson, R., Bird product literature)

VAPS: (and Pressure Augmentation) - Considerations The set TV is the minimum TV the patient will receive The set pressure support is the minimum the patient will receive The set peak flow is the minimum the patient will receive No ventilatory mechanics measured

VAPS vs. VS How does volume support differ from VAPS ? – In volume support, we are trying to adjust pressure so that, within a few breaths, desired TV is reached. – In VAPS, we are aiming for desired TV tacked on to the end of a breath if a pressure-limited breath is going to fail to achieve TV

Automatic Tube Compensation (ATC) Additional Work of Breathing Tube resistance causes the highest workload for patients with normal lung mechanics Tube resistance is proportional to the flow Tube resistance increases with smaller tubes New Modes of Ventilatory Support in Spontaneously Breathing Intubated Patients by Stocker et al, Yearbook of Intensive Care and Emergency Medicine 1997: 514-533

Automatic Tube Compensation (ATC) How Does It Work? The spontaneously breathing intubated patient has to perform work of breathing to overcome the tube resistance ATC takes over the work of breathing induced by the tube resistance The patient breathes like without any tube Respiratory comfort of automatic tube compensation and inspiratory pressure support in conscious humans by Guttman, J. et al, Intensive Care Medicine 1997, Vol. 23, No. 11, 1119-1124

Automatic Tube Compensation (ATC) Benefits Patient comfort ATC adjusts on-line the pressure to compensate the pressure drop over the tube caused by the current inhaled gas flow of the patient Stocker et al have suggested that a patient’s breathing during ATC looks like it would if the patient was extubated – “electronic extubation” Cannot predict airway patency, after extubation

With ATC switched ON, if patient inhales with a higher flow rate, Evita increases the support pressure within the breath and vice versa. The pressure is automatically adjusted in real time about 200 times within an inspiration. Thus ATC compensates for the resistive work load of the endotracheal tube. Patient experiences "Virtual Extubation".

MMV (Mandatory Minute Ventilation) AKA: Minimum Minute Ventilation or Augmented minute ventilation Operator sets a minimum E which usually is 70% - 90% of patient’s current E. The ventilator provides whatever part of the E that the patient is unable to accomplish. This accomplished by increasing the breath rate or the preset pressure. It is a form of PSV where the PS level is not set, but rather variable according to the patient’s need

MMV (Mandatory Minute Ventilation) Indications Any patient who is spontaneously and is deemed ready to wean Patients with unstable ventilatory drive Advantages Full to partial ventilatory support Allows spontaneous ventilation with safety net Patient’s E remains stable Prevents hypoventilation

MMV (Mandatory Minute Ventilation) Disadvantages An adequate E may not equal sufficient A (e.g., rapid shallow breathing) The high rate alarm must be set low enough to alert clinician of rapid shallow breathing Variable mean airway pressure An inadequate set E (>spontaneous E) can lead to inadequate support and patient fatigue An excessive set E (>spontaneous E) with no spontaneous breathing can lead to total support

PAV (Proportional Assist Ventilation) Patients who have normal respiratory drive but who have difficulty sustaining adequate spontaneous ventilation are often subjected to pressure support ventilation (PSV), in which the ventilator generates a constant pressure throughout inspiration regardless of the intensity of the patient’s effort. In 1992, Younes and colleagues19,20 developed proportional assist ventilation (PAV) as an alternative in which the ventilator generates pressure in proportion to the patient’s effort. PAV became commercially available in Europe in 1999 and was approved in the United States in 2006, available on the Puritan Bennett 840 ventilator

PAV (Proportional Assist Ventilation) Provides pressure, flow assist, and volume assist in proportion to the patient’s spontaneous effort, the greater the patient’s effort, the higher the flow, volume, and pressure The operator sets the ventilator’s volume and flow assist at approximately 80% of patient’s elastance and resistance. The ventilator then generates proportional flow and volume assist to augment the patient’s own effort PAV, the pressure applied is a function of patient effort: the greater the inspiratory effort, the greater the increase in applied pressure (servo targeting scheme) The operator sets the percentage of support to be delivered by the ventilator. The ventilator intermittently measures the compliance and resistance of the patient’s respiratory system and the instantaneous patient-generated flow and volume, and on the basis of these it delivers a proportional amount of inspiratory pressure. In PAV, as in PSV, all breaths are spontaneous

Ventilator settings in proportional assist ventilation Ventilator settings in PAV are: Airway type (endotracheal tube, tracheostomy) Airway size (inner diameter) Percentage of work supported (assist range 5%–95%) Tidal volume limit Pressure limit Expiratory sensitivity (normally, as inspiration ends, flow should stop; this parameter tells the ventilator at what flow to end inspiration).

PAV (Proportional Assist Ventilation) Indications Patients who have WOB problems associated with worsening lung characteristics Asynchronous patients who are stable and have an inspiratory effort Ventilator-dependent patients with COPD

How does the clinician know where to set the “%Support”? Sound clinical assessment Work of Breathing (WOB) bar The PB 840 has the option of measuring WOB

Sound Clinical Assessment. Respiratory rate > 40 breaths/minute PLUS… Marked use of accessory muscles Diaphoresis Abdominal paradox Marked complaint of dyspnea Etc… Vital signs ABG Signs of respiratory distress

PAV (Proportional Assist Ventilation) Advantages The patient controls the ventilatory variables ( I, PIP, TI, TE, VT) Trends the changes of ventilatory effort over time When used with CPAP, inspiratory muscle work is near that of a normal subject and may decrease or prevent muscle atrophy Lowers airway pressure

Or Ventilatory Demand Sedate Increase Support The practitioner’s typical response to an increase in demand is what? Increase Support Sedate Or These can lead to disuse atrophy of the respiratory muscles or lowering of the CO2 set point.

PAV™+ Software Option Clinical Description Management tips from Dr. Magdy Younes, inventor Start patients at 70% and wean back to stabilize When disease process has sufficiently reversed, decrease %Support over 2 hr intervals On average, patients will breathe at 7 mL/kg; some may want less while others may want more Some patients have a high rate normally, so a high rate on PAV+ may or may not reflect distress; check other signs; try increasing assist to see if rate goes down Don’t be surprised if respiratory rate climbs when switching from other modes Dr. Younes is the inventor of Proportional Assist/PAV. The tips in this presentation are his suggestions and are not necessarily those of Tyco Healthcare/Puritan Bennett. Proportional Assist and PAV are trademarks of The University of Manitoba and are used under license by Puritan Bennett.

PAV (Proportional Assist Ventilation) Disadvantages Patient must have an adequate spontaneous respiratory drive Variable VT and/or PIP Correct determination of CL and Raw is essential (difficult). Both under and over estimates of CL and Raw during ventilator setup may significantly impair proper patient-ventilator interaction, which may cause excessive assist (“Runaway”) – the pressure output from the ventilator can exceed the pressure needed to overcome the system impedance (CL and Raw) Air leak could cause excessive assist or automatic cycling Trigger effort may increase with auto-PEEP

PAV+ is NOT recommended for… Low drive due to meds. Abnormal breathing pattern. Extreme air trapping. Large mechanical leaks (TEF).

Paw PDI VT Flow 0.2 sec/div PSV PAV

Review What is it, why do we use it, what do we set and who does it benefit? -APRV -PRVC -Autoflow Volume support Adaptive Support Ventilation Volume Assured Pressure Support MMV PAV ATC