DUAL CONTROLLED

MODES OF

MECHANICAL

VENTILATION

UĞUR KOCA

Advantage of Volume control modes:

- Guarantee a preset tidal volume and minute ventilation

Advantage of Pressure control modes:

- The abilitiy to determine and maintain peak airway pressure and inspiratory

time

- The variable and decelerating inspiratory flow pattern

Dual control modes have been developed to provide the benefits of both volume

control and pressure control ventilation

Dual control modes are closed-loop systems that switch between pressure

control and volume control in a single breath or breath to breath on

measured patient characteristics

Dual control modes change the output (pressure) based on a measured input

(volume)

The dual-control modes can be patient-triggered or time-triggered, and flow-

cycled or time-cycled

I. Dual control within a breath modes

Volume-assured PS (VAPS): Bird 8400 STi, TBird, Avea

Pressure Augmentation (PA): Bear 1000

II. Dual control breath to breath modes

Pressure limited, Flow cycled:

Volume support (VSV): Servo 300

Variable PS: Venturi

Pressure limited, Time cycled :

Pressure Regulated Volume Control (PRVC): Servo 300

Autoflow: Evita 4

Variable Pressure Control: Venturi

Volume Control Plus: Puritan Bennett 840

Adaptive PS: Gallileo

III. Combination Modes

Adaptive Support ventilation: Gallileo

Automode: Servo 300

Dual control within a breath- Volume assured pressure support (VAPS)- Pressure augmentation (PA)

The ventilator switches from PC or PS to VC during the inspiratory

phase of individual breaths based on the patient’s inspiratory effort

and ability to achieve the clinican set minimum tidal volume

This technique combines the high initial flow of pressure limited

breath with possibility of switching to constant flow (volume limited

breath).

The advantage of dual control with in a breath is reduced work of

breathing while maintaining a minimum guaranteed tidal volume and

minute ventilation.

Dual control within a breath

Once the breath triggered (patient or time) the ventilator attempts to reach the

pressure support setting as quickly as possible. This portion of breath is the

pressure limited portion and associated with a high variable flow.

As the pressure support level is reached, the ventilator measures delivered flow

and volume and starts a continuous comparison between the volume that has

been delivered and the desired tidal volume.

If the delivered tidal volume and set tidal volume are equal, the breath is a

pressure support breath

If the delivered tidal volume remains greater than the set minimum, the ventilator

operates in the pressure support mode and makes no maniplations.

Dual control within a breath

If the micropressor finds that the measured flow is inadequte to achieve

the set tidal volume in the set inspiratory time, inspiration continues

according to the peak flow setting until the set minimum tidal volume

has been delivered; that is the breath changes from pressure limited

to volume limited.

In this situation, airway pressure will rise above the set pressure support

level. If inspiratory time longer than 3 seconds, breath will be

automatically time cycled.

Because of the airway pressure may rise above the set pressure support

setting during the volume limited portion of the breath, the high

pressure alarm is important.

Dual control within a breath

Choosing the appropriate pressure and flow settings is critical

- If the pressure is set too high and minimum tidal volume is set low

all breaths will be pressure support breaths and minimum tidal

volume guarantee will be provided without any feedback operation.

- If the peak flow is set too low, the switch from pressure to volume

will occur late and inspiratory time may be prolonged.

Dual control within a breath

PS setting

PS setting at a level equivalant to the plateau pressure obtained

during a volume control breath at a desired tidal volume can be

used

Peak flow setting

Peak flow should be adjusted to allow for the appropriate

inspiratory time and inspiratory to expiratory ratio required by

the patient

Volum Assured PSPressure Augmentation

Pressure at PS

setting

Given Vt≥set Vt

İnsp flow>set peak flow

Switchs to flow control at

set peak flow

Paw<PS setting

given Vt=set Vt

yes

Inspiration ends

no

no

no

yes

yes

yesİnsp flow=%25

of peak

inspiratory flow

no

Inspiration ends

yes

trigger

Dual control breath to breath modes

Pressure limited, Flow cycled: Volume support (VSV),Variable PS

These modes are closed loop control of pressure support ventilation.

Tidal volume is used as a feedback control for continiously

adjusting the pressure support level.

The peak pressure is adjusted to ensure delivery of the target tidal

volume based on the compliance measured during the previous

breath.

Dual control breath to breath modes ;Pressure limited, Flow cycled

VSV

A test breath is delivered with an inspiratory pressure of 10 cmH2O

above PEEP and ventilator measures delivered tidal volume and

calculates the total system compliance. The following three breaths are

delivered at a peak pressure of 75% of the pressure that calculated to

deliver the minimum set tidal volume.

All breaths are patient triggered, pressure limited and flow cycled

pressure support breaths

The maximum pressure change breath to breath is ≤3 cmH2O and can

range from 0 cmH2O above PEEP to 5 cmH2O below high pressure alarm

setting.

Dual control breath to breath modes ;Pressure limited, Flow cycled

Respiratory frequency, inspiratory time and flow are determines by

the patient.

If inspiratory time exceeds 80% of the total cycle time a secondary

cycling mechanism is activated.

Decrease in patient respiratory frequency causes automatically

increase in the tidal volume target to maintain the minute volume

constant

Dual control breath to breath modes ;Pressure limited, Flow cycled

Setting alarms for minute ventilation, high pressure and respiratory rate is

important for safely using these modes

Increases in pressure level to maintain the tidal volume may increase autoPEEP

at the patients who has airflow obstruction.

As the autoPEEP increases the same pressure results in a smaller tidal volume.

In this situation, the algorithym increases the pressure limit, increasing the

pressure worsens air trapping.

This vicious circle of increasing pressure support, worsening air trapping causes

to inability to trigger the ventilator. Decreasing in respiratory rate results

in further increase in tidal volume to maintain the same minute volume.

Dual control breath to breath modes ;Pressure limited, Flow cycled

In cases of hyperpnea ventialtor decreases pressure support. If

the cause of hyperpnea is increase in metabolic demand,

decreasing the pressure support level is opposite response.

The inability of all dual modes to distinguish between improved

pulmonary compliance abd increased patient effort (increased

metabolic demand)

Dual control breath to breath modes ;Pressure limited, Flow cycled

These modes allow automatic reduction of pressure support as lung

mechanics improve and patient effort increases

These modes can be used as a weaning mode by clinician reduction

of the target tidal volume

If the clinician sets minimum tidal volume greater than the patient

demand, the patient may remain at that level of support and

weaning may be delayed.

Dual control breath to breath modes: Pressure limited, Time cycledPressure Regulated Volume Control, Autoflow, Variable Pressure Control, Volume

Control Plus, Adaptive PS

These modes are closed loop control of pressure control ventilation.

The pressure limit is adjusted using the clinician set desired tidal

volum as the negative feedback control.

The primary advantage of these modes is reduction in peak

inspiratory pressure associated with a declerating flow pattern,

combined with the guaranteed delivery of minute volum.

These modes enable the ventilator to adjust inspiratory flow

according to patient flow demand combined with maintenance of

constant tidal volum.

Dual control breath to breath modes: Pressure limited, Time cycled

All breaths in these modes are time or patient triggered, pressure

limited and time cycled.

These modes allow dual control breath to breath by using either

continuous mandatory ventilation or SIMV except PRVC that allows

continuous mandatory ventilation.

During SIMV the mandatory breaths are the dual control breaths

Dual control breath to breath modes: Pressure limited, Time cycled

PRVC

The pressure limit fluctuates between 0 cmH2O above PEEP

level to 5 cmH2O below the upper pressure alarm limit.

Upper pressure alarm limit is critic. If the desired tidal volum is

not delivered with the pressure of 5 cmH2O below the upper

pressure alarm limit, the ventilator will alarm.

Hipoventilation may occur if the desired tidal volume and

maximum pressure alarm limit settings are incompatible

Combination Modes

Adaptive Support ventilation, Automode

Automode

Automode designed for automated weaning from pressure control to

pressure support and for automated escalation of support if

patient efort diminishes below a selected threshold.

It combines volume support ventilation and PRVC into a single mode;

This mode provides a continuous weaning from pressure control to

pressure support or from volume control to volume support with

guaranteed tidal volum

Combination Modes

Automode

The ventilator provides PRVC breaths if the patient is paralyzed. All breaths are

mandatory, time triggered, pressure limited and time cycled. The pressure limit

increases or decreases to maintain the desired tidal volum.

If the patient triggers 2 consecutive breaths, the ventilator switches to volume

support. In this case, all breaths are patient triggered, pressure limited and

flow cycled.

If the patient becomes apneic for 12 seconds (8 seconds for pediatric, 5 seconds

for neonatal patient) the ventilator switches to PRVC.

The switches PRVC to VS are accomplished at equivalant peak pressure.

References

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Branson RD Techniques for automated feedback control of mechanical ventilation. Semin Respir Crit Care Med. 2000;21(3):203-9

Rose L, Advanced modes of mechanical ventilation: implications for practice. AACN Adv Crit Care. 2006 Apr Jun;17(2):145-58

Singh PM, Borle A, Trikha A. Newer nonconventional modes of mechanical ventilation. J Emerg Trauma Shock. 2014 Jul;7(3):222-7

Branson RD, Johannigman JA. What is the evidence base for the newer ventilation modes? Respir Care. 2004 Jul;49(7):742-60

Tehrani F, Rogers M, Lo T, Malinowski T, Afuwape S, Lum M, Grundl B, Terry M. A dual closed-loop control system for mechanical ventilation.

J Clin Monit Comput. 2004 Apr;18(2):111-29

Singer BD, Corbridge TC. Pressure modes of invasive mechanical ventilation. South Med J. 2011 Oct;104(10):701-9

Burns SM. Pressure modes of mechanical ventilation: the good, the bad, and the ugly. AACN Adv Crit Care. 2008 Oct-Dec;19(4):399-411