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Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
Travancore Medicity, Kollam
India
editor
Mechanical ventilation breaths can be considered as
Controlled
Assist- controlled
Assisted-spontaneous
(Fully) Spontaneous breaths
according to the settings selected for :
Breath initiation
Inspiration
Cycling to exhalation
Breath Type | Breath Initiation | Inspiration | Cycling to exhalation |
Controlled | Machine Frequency setting | Volume control or Pressure Control | Machine Inspiratory time setting |
Assist-control | Patient Inspiratory trigger
Machine Frequency setting
| Volume control or Pressure Control | Machine Inspiratory time setting |
Assisted spontaneous | Patient
Inspiratory trigger | Pressure control Pressure Support | Pateint Expiratory trigger |
Spontaneous | Patient Inspiratory trigger | Pressure control PEEP/CPAP setting | Patient Expiratory trigger |
1.Breath Initiation
Breath may be initiated either by the machine or by the patient.
Machine Initiation
Breath is initiated at a pre-set time, according to the setting for respiratory frequency.
Machine-initiation can take place only in the modes that include a control for frequency (Controlled and assist controlled breaths).
Patient Initiation
Patient initiation means that breath is initiated by the patient's inspiratory effort, by means of a pressure or flow based trigger.
Patient initiation can take place during assist control, assisted spontaneous and spontaneous breathing modes.
Assist Control Breaths
|
2.Inspiration
It can be either volume control or pressure controlled
Volume controlled inspiration
It is based on control of inspiratory flow, delivered for the set inspiratoy time and according to the set flow pattern, to achieve the set tidal volume.
At any point of time during a volume controlled inspiration the pressure developed in airway depends on Inspiratory flow and volume change produced by ventilator and resistance, compliance and intrinsic PEEP of the lungs.
Pressure controlled inspiration
The ventilator applies a positive pressure above the baseline pressure. The ventilator generates a rapid increase in pressure to the user-set level, and then maintains that pressure throughout inspiration.
At any point of time during a pressure controlled inspiration, the inspiratory flow and volume depends on the balance between inspiratory pressure and passive impedance of respiratory system.
3. Cycling to exhalation
When the exhalation is controlled by the machine, it is time based.
Time cycling means that the ventilator switches to exhalation as soon as the set inspiratory time has elapsed (Ti).
The inspiratory time (Ti) may be set in a ventilator as
Duty cycle (Ti%) or the Inspiration : Expiration Ratio (I:E) combined with frequency.
Inspiratory peak flow combined with tidal volume and flow pattern.
Time cycling is used in controlled and assist control breaths.
Patient controlled cycling is used in assisted spontaneous and fully spontaneous breaths.
It is based on expiratory trigger that allows the automatic adaptation of the ventilator Ti to patient's own Ti.
Updated on 20/9/2015
Reference
Patient Centered Acute Care (PACT) . Mechanical Ventilation 2011.
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emmedonline
Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
Travancore Medicity, Kollam
India
editor