PRESSURE REGULATED

VOLUME CONTROL (PRVC)

Charles S. Williams RRT, AE-C

PRVC

First introduced on the Servo 300 ventilator. Is now available

on the Servo-I ventilator.

PRVC is defined as pressure controlled ventilation with a

volume target. (Volume-targeted pressure control).

It is considered a form of Dual-Mode ventilation.

PRVC combines the advantages of both volume-controlled

(VC) and pressure-controlled (PC) ventilation.

Intro

PRVC

PRVC will attempt to deliver the desired set tidal volume using

the lowest possible pressure.

Use clinically as you would “standard” Volume Control (VC)

Similar modes on other ventilators include:

1. AutoFlow (Drager Evita),

2. Adaptive Support Ventilation (Hamilton Galileo)

3. Volume Ventilation Plus (Puritan Bennett 840)

Intro

Volume-Control Ventilation (VCV)

Assist-Control Ventilation

Set mandatory (min) rate

Every breath delivered, either ventilator initiated (control)

or patient initiated (assist), are identical.

Peak inspiratory pressure (PIP) will vary depending on

lung mechanics. (compliance and airway resistance)

Volume Control

Volume-Control Ventilation (VCV)

Shown here is standard Volume Control mode.

The set tidal volume is 500.

Volume Control

*Screenshots have been modified for illustration purposes

Volume-Control Ventilation (VCV)

In VC, flow remains constant during inspiration.

Flowrate is normally a set parameter in VC.

*Screenshots have been modified for illustration purposes

Volume Control

Volume-Control Ventilation (VCV)

Pressure will vary depending on lung compliance, airway resistance, etc.

*Screenshots have been modified for illustration purposes

Volume Control

PRVC

When switching to PRVC mode, the ventilator first delivers a volume “test”

breath along with an inspiratory “hold” maneuver.

This is also done anytime ventilation has been interrupted, (opening the vent

circuit, suctioning, etc.)

Inspiratory Hold

PRVC

*Screenshots have been modified for illustration purposes

PRVC

The inspiratory hold maneuver determines the patient’s plateau pressure

(Pplat).

The measured Pplat is then used to deliver the patient’s very next breath.

PRVC

*Screenshots have been modified for illustration purposes

Pplat

PRVC

The ventilator then measures the exhaled tidal volume and compares it to the

set tidal volume.

Also note that pressure is now constant (with a square pattern) and flow has

become variable (with a decelerating ramp pattern ). Just as in Pressure

Control mode.

*Screenshots have been modified for illustration purposes

PRVC

PRVC

The ventilator then regulates the amount of pressure needed to obtain the

desired set tidal volume.

It will increase or decrease the amount of pressure on a “breath by breath”

basis. (+/-3 cmH20 per breath)

+3

PRVC

*Screenshots have been modified for illustration purposes

PRVC

MeasureTidal Volume

Compare to

set

Tidal Volume

Give same

Inspiratory Pressure

Increase

Inspiratory

Pressure

Less

Equal

More

Decrease

Inspiratory

Pressure

Test Breath

PRVC Flowchart

PRVC

“Guarantees” delivery of desired tidal volume.

Minimizes risks of barotrauma due to high peak

pressures.

Decelerating flow pattern may provide better distribution

of ventilation and oxygenation.

Can better meet patients inspiratory flow demands.

Advantages:

Advantages

PRVC

The ventilator may potentially increase pressures to

dangerously high levels as it attempts to maintain the

desired tidal volume.

1) The maximum delivered pressure is limited to 5cmH2O

below the set High Pressure alarm limit.

2) High Pressure alarm limit should be set at 35-40 cmH20.

Disadvantages:

Disadvantages

PRVC

Pressure delivered is dependant on the tidal volume

achieved from the previous breath.

If the patient intermittently makes a significant inspiratory

effort, it can result in variable tidal volumes than can be

higher or lower than the setting.

Disadvantages:

Disadvantages

PRVC

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.

*Screenshots have been modified for illustration purposes

Volume

(500ml)

PRVC

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.

*Screenshots have been modified for illustration purposes

Volume

(500ml)

PRVC

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.

*Screenshots have been modified for illustration purposes

Volume

(500ml)

PRVC

Automode/Volume Support

For patients that are making intermittent inspiratory

efforts, or breathing spontaneously, switching to

Automode may be better.

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).

Automode

PRVC

Automode/Volume Support

Volume Support (VS) mode works in 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.

Volume Support

Sources:

PRVC Dr. Charles Gomersall, Dept of Anaesthesia & Intensive Care,

The Chinese University of Hong Kong,

Prince of Wales Hospital

Golden Moments In Mechanical VentilationMaqet, INC.

Servo-I: Modes of Ventilation, Pocket GuideMaqet, INC.

Evidence Base for Newer Modes of Mechanical Ventilation Charles B. Spearman, MSEd, RRT, FAARC

Assistant Professor

Respiratory Care Programs

Department of Cardiopulmonary Sciences

Loma Linda University