Advanced Modes of Ventilation

PRVC, MMV, VS, and ASVBy Joshua and Marissa

Lets review!!!

What are the 3 modes?

Review continued…

What are the 3 different breath types?

REVIEW!! What is PEEP? Why is it used? What do you need to be careful of when

using PEEP? What is “optimal PEEP”? How do you assess for auto-PEEP? How is it

treated?

Ventilator GraphicsWhich breath type is this??

VOLUME CONTROL PRESSURE CONTROL

Understanding Ventilator Mechanics and Physics

Various pressures involved in inspiration/expiration. The same are either provided or overcome by the ventilator

Often they fail to match the patient based requirements

A ventilator setting appropriate for one point of time may not be optimal with patient deterioration or improvement (These ventilators only deliver the set parameters and take no feedback from patient variables).

Problems With Conventional Modes of Ventilation

All the classical volume/pressure control modes are “Open Loop” (the feedback loop is absent). The newer modes target to make alterations with the changing lung and take feedback from patient parameters, thus completing the feedback loop and are “Closed loop” type.

The control, cycle, or the limit variables undergo self adjustment and these variables are no longer limited to single parameter determinant but if the threshold of one component is reached they shift to the other alternate set parameter.

“Open-loop” vs. “Closed-loop” Systems

Adaptable to a wide variety of patients. Able to adapt to changing lung mechanics on

a breath to breath basis. Utilizes lung protective strategies Shortens the weaning time Shortens time of mechanical ventilation

Benefits of Advanced Modes of Ventilation

Many do not give an “exact” pressure or tidal volume but instead pressure and Vt are “targeted”.

Some modes may favor a faster RR and sacrifice a lower Vt

Mean Airway Pressure is variable If auto-PEEP is present, the ventilator may

not be able to recognize to correct, and/or it may not operate properly

Drawbacks/Limitations of Advanced Modes of Ventilation

Limit the duration of invasive ventilation Prevent patient ventilator asynchrony Be applicable to a wide variety of patients

and automatically adapt to changes in lung and respiratory mechanics

Goals of Advanced Modes of Ventilation

Modes and Ventilator Names

Ventilator Modes and Available Ventilators on the Market

PRESSURE REGULATED VOLUME CONTROL

(PRVC)

Short History

PRVC was introduced in 1991 created by Siemens Servo 300 ventilator.

PRVC is also called…

Auto flow Adaptive pressure ventilation Volume control + (VC+) Volume targeted Pressure control Pressure control volume guaranteed

GALILEO

SERVO 300

What is PRVC?

Pressure regulated volume control delivers pressure controlled breaths with a target tidal volume

However PRVC can increase or decrease the vent will just adjust the inflation pressure to achieve target volume.

In other words PRVC has an average minimal tidal volume but not a max.

PRVC is pressure limited and time cycled

CONTINUED

The ventilator will measure tidal volume delivered if the delivered tidal volume is less or more the ventilator will increase or decrease pressure delivered until set tidal volume and delivered are equal

How does PRVC differ from AC-PC?

The pressure level adjust on a breath to breath analysis to reach a target tidal volume.

SETTINGS???

Target tidal volume Inspiratory time Rate Rise time FIO2 PEEP Sensitivity Pressure limit (in alarms) On SIMV same settings add PS or VS

HOW DOES PRVC WORK??

The ventilator assesses the previous breath and adjust pressure from 1-3 cm H20 while assessing the tidal volume.

First breath

Which is known as the test breath is 5-10 cm H20 above peep

The test breath consists of an inspiratory hold to obtain a plateau pressure on the next breath.

During the next three breaths pressure is increased to 75 percent needed for set tidal volume.

After that the pressure will only change +/- 3 cm H20 per breath

Time ends inspiration

Quick review

https://www.youtube.com/watch?feature=player_detailpage&v=iCeDnlou04Y#t=0

https://www.youtube.com/watch?feature=player_detailpage&v=Aq0dHapIPCc#t=5

What we should keep in mind..

The vent will ALARM when delivered pressure rises to 5 cm H20 below the set upper pressure limit.

Flow varies automatically to patient demands.

During each breath there is a constant pressure however the pressure varies from breath to breath

Disadvantages to PRVC

Mean airway pressure varies Can cause auto peep or make it worse When patient demand is increase pressure level may

diminish when support is needed. Sudden increase in RR and demand may result in a

decrease in vent support. Since the pressure delivered is dependent on tidal

volume from the previous breath sudden inspiratory effort such as cough or yawning can result in different volumes that can be higher or lower than the setting.

Advantages to PRVC

Helps maintain a low PIP Targeted tidal volume Little WOB requirement Decelerating flow waveform for improved

gas distribution

INDICATIONS..

Patients who require the lowest PIP and a target tidal volume

Acute lung injury/ARDS to help limit PIP to protect the lung

Patients requiring high or variable flow Patient with the possibility of changing lung

compliance or Raw

COOL thing about PRVC.. Is that it combines volume ventilation and

pressure control Targeted tidal volume Vent adjust level of pressure control breath

by breath analysis Can provide better synchrony for the patient

because it adapts to pt changing output. Ventilator estimates volume/pressure

relationship with each breath Inverse relationship between volume and

pressure if the pressure goes up volume goes down if the volume goes up the pressure will go down

When not to use PRVC..

Patients with erratic breathing patterns Cheynes stokes breathing Excessive coughing seizures

PRVC with volume support weaning protocol

1.) switch to PRVC-SIMV with VS2.) decrease tidal volume by 10-20 percentAssess weaning parametersRSBI < 100RR< 30VE <10 L/minSp02>92%Pa02> 60mmHgHemodynamically stable

Weaning continued

MIP <-20 cmH20 MVV > 20 L/min Watching vital signs decrease to 50 percent

of original tidal volume Volume support 5-10 cmH20 Abg normalized Call physican for order to extubate!

Volume Support Mode (VS)

VS is an entirely spontaneous mode that assists with patients who are breathing spontaneously in order to help them achieve a “target” volume.

Pressure limited, Volume targeted, and flow cycled Basically, VS is pressure support with a set “target” Vt. It adjusts pressure (up or down) to achieve the target

volume. Maximum adjustment in pressure from breath-to-breath

is 1-3 cm H2O If flow reaches within 5% of peak flow during the breath,

the ventilator will cycle off.

What is Volume Support?

Ventilation Graphics in Volume Support Mode (VS)

Helps to decrease a patient’s WOB and assists with weaning for patients who are breathing spontaneously.

It automatically weans patient off of pressure support as long as the minimum Vt is being met.

Gives pressure supported breaths using the lowest required pressure

Allows patient to control I:E time Breath to breath analysis and varies minute

ventilation to meet patient demand.

Benefits of VS

May tend to give smaller tidal volumes Varying MAP If auto-PEEP is present, the mode may not

work properly A sudden increase in RR or patient demand

may result in a decrease in ventilator support (coughing, hiccups, seizure, etc.)

Disadvantages of VS

Available with the Servo I and Galileo ventilators

When the patient begins to breathe, the ventilator automatically switches from PRVC to Volume support.

If there are no spontaneous breaths, the ventilator switches to PRVC.

PRVC with Auto-mode and Volume Support

MANDATORY MINUTE

VENTILATION (MMV)

Mandatory minute ventilation

MMV is also known as minimum minute ventilation or augmented minute ventilation.

However this mode is not widespread due to limitations and lack of understanding.

History..

MMV is an original mode of mechanical ventilation introduced by Hewlett et al. in 1977 in this mode the patient is guaranteed a predetermined minute volume called preset minute volume. If the patient is able to spontaneously breath and reach the preset minute volume the ventilator does not deliver any mechanical breaths. If however the spontaneous breathing does not reach the minute ventilation the needed minute ventilation will be delivered.

How does it work?

Rt sets a minimum minute ventilation which is usually between 70-90 percent of patients current minute ventilation.

The ventilator will provide the part of minute ventilation that the patient is unable to accomplish.

This is done by increasing the breath rate or the preset pressure.

Indications

Used on any patient who is spontaneously breathing and is deemed ready to wean

Patients with unstable ventilatory driveAdvantages:-Full to partial ventilatory support-Allows spontaneous ventilation with safety net-Patients minute ventilation stays stable-Prevents hypoventilation

Disadvantages

Adequate minute ventilation may not be sufficient (shallow breathing)

High rate alarm must be set low enough to alert for RSB

Mean airway pressure is variable Inadequate set minute ventilation can lead to

inadequate support and patient fatigue Excessive minute ventilation with no spontaneous

breathing can lead to total support.

Limitations when using MMV

Development of fast and ineffective breathing

Development of auto peep Delivering dangerously high tidal volumes Increased dead space

Adaptive Support

Ventilation (ASV)

ASV is a new ventilatory mode, which uses a closed-loop controlled mode between breaths.

The ventilator allows the clinician to set a maximum plateau pressure and desired minute ventilation based on the patient's ideal weight.

It automatically selects the target ventilatory pattern based on user inputs, as well as taking into account the respiratory mechanics data from the ventilator monitoring system (resistance, compliance, auto-PEEP).

This mode can be safely used during initiation, maintenance, or weaning phases of the mechanical ventilation.

ASV's goal is to ensure an effective alveolar ventilation level, minimize the WOB, and lead the patient to an optimal ventilatory pattern in order to reduce complications such as volutrauma or barotrauma and air trapping.

What is ASV?

ASV evolved as a form of mandatory minute ventilation (MMV) implemented with adaptive pressure control, and described by Hewlett in 1977.

 ASV first clinical application was described in 1994 by Laubscher et al. It became commercially available in Europe in 1998, but it was not until 2007 that it was marketed in the United States.

Background History of ASV

The machine selects a Vt and frequency that the patient's brain would presumably select if the patient were not connected to a ventilator.

This pattern is assumed to encourage the patient to generate spontaneous breaths.

This mode provides specific minute ventilation and a breathing pattern optimized to the point of the smallest total energy expenditure, and it is based on patient's requirements.

About ASV

Among the closed-loop systems available are Proportional Assist Ventilation (PAV), Neurally Adjusted Ventilatory Assistance (NAVA), Knowledge-Based Systems (KBS), and ASV. The first three (PAV, NAVA, and KBS) are basically advanced versions of Positive Pressure Support Ventilation (PSV) and therefore are considered to be "ventilatory modes".

On the other hand, ASV combines various ventilatory modes:

PSV, if the patient's respiratory rate (RR) is higher than the target

Pressure controlled ventilation, if there is no spontaneous breathing

Synchronized intermittent mandatory ventilation (SIMV), when patient's RR is lower than target. 

ASV vs. “other modes”

1. Proximal Flow Sensor The proximal flow sensor precisely measures the

pressure, volume, and flow directly at the patient’s airway opening. This provides the required sensitivity and response time, and prevents dead space ventilation. The patient is better synchronized and has less work of breathing as a result. 

2. Volumetric Capnography3. Integrated SpO2 Sensor

Hamilton ASV Sensors

ASV vent settings:1. Height of the patient (based on this, the vent will

automatically calculate ideal body weight and dead space)2. Gender3. % Min Vol: 25-350%

Normal 100%, Asthma 90%, ARDS 120%, Others 110% Add 20% if body temp is >101.3 degrees Fahrenheit Add 5% for every 1640 feet above sea level (500 m)

4. Trigger: flow trigger of 2 L/min5. Expiratory trigger sensitivity: Start with 25% and 40% in

COPD6. Tube resistance compensation: Set to 100%7. High pressure alarm limit: 10 cm H 2 O be the limit of ↓ and ↑

least 25 cm H 2 O of PEEP/continuous positive airway pressure (CPAP)

8.  PEEP9. FiO2

What The User Sets

Dead space based on the ideal weight (dead space [Vd ] = 2.2 ml/kg)

ASV selects the respiratory pattern in terms of RR, VT, Inspiratory:Expiratory time (I:E ratio) for mandatory breathing and reaches the respiratory pattern selected. Thus, it is volume and pressure limited. Basically, ASV uses the Otis et al. and Mead et al. equation developed in 1950, that states that for a given level of alveolar ventilation, there is a particular RR which achieves a lower WOB. Therefore it is more energy efficient to minimize the cumulative effects of elastic and resistive load imposed on the respiratory system.

What the Ventilator Calculates Automatically

How Does ASV Work?

Closed-loop feedback system. The operator presets a target tidal volume (VT), through a feedback signal, the system measures the tidal volume of the patient (VT observed). The target VT and VT observed are compared (added or subtracted) and then an error signal is sent to the controller, which regulates the received signal and makes adjustments as needed to send an output signal, resulting in a desired breathing pattern, which can be eventually measured 

In the closed-loop system, the output of gas is measured by providing a feedback signal that can be compared with the input value. The classical system of negative feedback control differentiates between input and output of gases, thus generating an error signal used to adjust the output so that it matches the input. The feedback control forces the gas output to become stable in the presence of environmental changes (such as leakage of the circuit, changes in lung mechanics, and respiratory muscle strain). This also automatically applies lung protection strategies, reducing the risk of errors committed by the operators.

How The “Closed-loop” System Works

Point A shows that in order to maintain alveolar ventilation with very low RR, it is needed to use large VTs, which implies a high level of WOB. On the other hand, Point B, shows that a high amount of muscular effort is required to maintain adequate alveolar ventilation at high RRs (and low volume) in an attempt to overcome the resistance to flow. However, there is an optimal RR, which is the least costly in terms of WOB (Point C). 

The operator sets % VM, Pmax , PEEP and FiO 2 . The system by calculations and by a dual closed-loop system (RR goal and target VT) it calculates the RR and volume in which there is the lowest WOB (thus more efficient ventilation) within safety margins, adjusting inspiratory pressure and I:E ratio to achieve the desired goals.

ASV mode is based on lung protective strategies, which aim to reach the RR and VT target, inside a security boundary area, where the highest energy efficiency is obtained and complications such as apnea, volutrauma, barotrauma and/or dead space ventilation are avoided

 

Safety limits calculated based on these parameters.

Once started, ASV provides a series of test breaths or test mode P-SIMV (with RRs between 10 and 15 min according to ideal body weight and assigned to inspiratory pressure above 15 cm H 2 O pressure basal), in which it measures the expiratory time constant for the respiratory system, and uses this along with the estimated dead space and normal minute ventilation in order to calculate an optimal breathing frequency in terms of mechanical work. During this breathing test, the ventilator measures compliance, Rce , VT, and RR based on selected inspiratory time (Ti ), mandatory rate (f), and inspiratory pressure (Pinsp ), according to the height (adult or pediatric age range) that the operator sets. In order to have a VT and RR target are determined within safety limits.

This means that the pressure limit is automatically adjusted to achieve an average delivered VT equal to the target. The ventilator continuously monitors the mechanics of the respiratory system and adjusts its settings accordingly.

ASV Initiation

Changes to Make Based Off ABG

Can be used safely and effectively in over 98% of patients.

Reduce time on the ventilator by over 50% 2 controlled studies show that while less user interaction is

required and fewer alarms occur, ASV also facilitates shorter time on the ventilator: 6 hours with ASV as compared to 14 hours with conventional ventilation.

Studies show that ASV: can be used to ventilate virtually all intubated patients whether

active or passive and regardless of the lung disease requires less user interaction, adapts to the patient’s breathing

activity more frequently and causes fewer alarms adapts to changes in the patient’s lung mechanics over time works comparable to experienced clinicians allows shorter weaning times allows shorter ventilation times

ASV adapts to lung mechanics by automatically applying lower tidal volumes in ARDS patients.

Benefits of ASV

Start weaning at intubation The unique closed-loop ventilation system ASV

automatically promotes spontaneous breathing for patients in all ventilation modes and phases. It encourages spontaneous activity right from the start of ventilation and promotes weaning from first deployment.

Studies show the results: a shorter length of ventilation and a shorter weaning time.

 ASV employs lung protective strategies to minimize complications from AutoPEEP and barotrauma. ASV also prevents apnea, tachypnea, excessive dead space ventilation and excessively large breaths.

Benefits (continued)

Studies show that: In passive patients, ASV selects different tidal volume /

respiratory rate combinations for normal lung, COPD, and ARDS patients (Arnal 2008).

In active patients, ASV decreases work of breathing and improves patient-ventilator synchrony (Wu 2010, Tassaux 2010). 

In the ICU, ASV decreases the weaning duration in medical patients (Chen 2011) and COPD patients (Kirakli 2011).

In post-cardiac surgery, ASV allows earlier extubation than conventional modes (Gruber 2008, Sulzer 2001) with fewer manual adjustments (Petter 2003) and fewer ABG analyses performed (Sulzer 2001). 

Further ASV Research

Advantages and Disadvantages of ASV

Advantages/Disadvantages (cont.)

Clinician's lack of understanding results in inappropriate programming.

Inability to recognize dead space ventilation or shunts to make adjustments to ventilation.

In clinical conditions where lung physical parameters remain unchanged (pulmonary embolism), the mode fails to adapt to patients requirements.

Auto PEEP may become problem in chronic obstructive pulmonary disease (COPD) patients needing longer expiratory times which are currently unaccounted in current protocols of automatic adjustments.

Drawbacks/Limitations of ASV

Conventional vs. Adaptive Weaning

The FUTURE of Advanced Ventilation Modes

History of Ventilation

NEGATIVE PRESSURE VENTILATIORS

FROM THE 19TH CENTURY

Closed-loop adaptive ventilators

Cutting Edge Ventilators of Today

Hamilton S-1

Galileo

Future Ventilator Capabilities

https://youtu.be/P1lrr0BrE94

ASV Set Up And Use On A Real Patient

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Citations