Blogs
Mechanical Ventilation- Basic Ventilation Modes
Date: November 29, 2023 | Posted by: Vikram Aditya Tirthani
Date: November 29, 2023 | Posted by: Vikram Aditya Tirthani
CMV stands for controlled mandatory ventilation. Breaths in CMV mode are volume-controlled and mandatory. In the Inspiratory phase, a set tidal volume is delivered to the patient with a constant flow or at a selected flow pattern within a set inspiratory time for gas delivery time at a specific respiratory rate.
The ventilator always delivers the set tidal volume hence pressure in the airway can increase or decrease depending on the resistance and compliance of the patient’s lungs.
To protect the patient’s lungs it is important to carefully set an upper pressure limit.
The following figure shows typical waveforms in CMV mode.
V-A/C stands for Assist/controlled mandatory ventilation. Breaths in this mode are volume-controlled and mandatory. In the Inspiratory phase, a set tidal volume is delivered to the patient with a constant flow or at a selected flow pattern within a set inspiratory time for gas delivery time at a specific respiratory rate. During the expiratory phase, V-A/C mode supports synchronization triggers. In V-A/C mode synchronization window is activated and in case patient triggers during synchronization window, inspiratory breath is initiated and hence the breath is synced with the patient’s effort
The breath can be triggered by the ventilator or by the patient. If the breath is spontaneous (triggered by the patient), the inspiratory rate may increase.
The following figure shows typical waveforms in V-A/C mode.
If a breath is not triggered by patient effort within a preset time, the ventilator delivers a set tidal volume with a constant flow or operator-selected flow pattern for a set inspiratory time at a set respiratory rate.
V-SIMV is volume-synchronized intermittent mandatory ventilation mode. The SIMV mode combines attributes of the V-A/C and PSV modes, delivering volume-controlled mandatory breaths or pressure-supported spontaneous (patient-triggered) breaths.
V-SIMV provides the minimum number of mandatory breaths based on the preset intermittent mandatory ventilation frequency ensuring that the set target volume is delivered during the mandatory breaths. After the mandatory breath is delivered, the patient is free to take any number of spontaneous breaths for the remainder of the V-SIMV breath interval.
Each SIMV breath interval includes a trigger window during the expiratory phase, If the patient triggers a breath during the Trigger window, the ventilator immediately delivers a mandatory breath once. Mandatory volume control breath is also delivered once if it is not triggered at the end of the trigger window.
The following figure shows typical waveforms in V-A/C mode.
If the patient triggers a breath outside the trigger window, the ventilator delivers a pressure support.
The duration of the trigger window is 5s for adults and 1.5s for pediatrics and neonates. If the expiratory time is less than the duration of the trigger window, the trigger window covers the expiratory time. The following figure shows typical waveforms in V-SIMV mode.
PCV is a ventilation mode where the patient’s airway pressure rises to a preset level during the inspiration phase, remaining at that level until the end of the inspiration time, followed by the expiration phase.
In this mode, the ventilator maintains a constant pressure, with the gas flow having a decelerating pattern. The delivered volume depends on the pressure settings, inspiration time, and the patient’s lung resistance and compliance.
The following figure shows typical waveforms in PCV mode
During inspiration, if the delivered gas volume exceeds the high alarm limit for tidal volume, the system transitions to expiration promptly.
P-A/C is a ventilation mode where the patient’s airway pressure rises to a preset level during the inspiration phase, remaining at that level until the end of the inspiration time, followed by the expiration phase.
In this mode, the ventilator maintains a constant pressure, with the gas flow having a decelerating pattern. The delivered volume depends on the pressure settings, inspiration time, and the patient’s lung resistance and compliance.
During inspiration, if the delivered gas volume exceeds the high alarm limit for tidal volume, the system transitions to expiration promptly.
The following figure shows typical waveforms in P-A/C mode
In the expiratory phase, the system supports synchronization triggers, meaning that when the ventilator detects the patient’s inspiratory effort, it immediately delivers the next mechanical ventilation breath. This mode ensures controlled and effective ventilation while adapting to the patient’s needs.
P-SIMV is a pressure-synchronized intermittent mandatory ventilation mode. The PIMV mode combines attributes of the P-A/C and PSV modes, delivering volume-controlled mandatory breaths or pressure-supported spontaneous (patient-triggered) breaths.
P-SIMV provides the minimum number of mandatory breaths based on the pre-set intermittent mandatory ventilation frequency ensuring that the set target pressure is delivered during the mandatory breaths. After the mandatory breath is delivered, the patient is free to take any number of spontaneous breaths for the remainder of the P-SIMV breath interval.
Each SIMV breath interval includes a trigger window during the expiratory phase, If the patient triggers a breath during the Trigger window, the ventilator immediately delivers a mandatory breath once. Mandatory volume control breath is also delivered once if it is not triggered at the end of the trigger window.
If the patient triggers a breath outside the trigger window, the ventilator delivers a pressure support.
The following figure shows typical waveforms in P-A/C mode
The duration of the trigger window is 5s for adults and 1.5s for pediatrics and neonates. If the expiratory time is less than the duration of the trigger window, the trigger window covers the expiratory time. The following figure shows typical waveforms in P-SIMV mode.
PSV, or Pressure Support Ventilation, is a mode where the ventilator delivers pressure support when it senses the patient’s inspiratory effort reaching a pre-set trigger level. The user sets the time for pressure rising and the level of pressure support. At the start of the inspiratory phase, the patient’s airway pressure rises to the predetermined level within the set time, maintaining this pressure until the system detects the patient’s inspiratory flow reaching the expiration trigger level. During this phase, the delivered gas flow decelerates, varying with the resistance and compliance of the patient’s lungs. The inspiratory phase is limited to a maximum time limit by a control parameter Timax, which ensures that if by that time the patient’s breath does not reach the expiratory trigger level, the expiratory phase will compulsorily start.
When pressure support is set to zero, the ventilator functions like a conventional CPAP mode, where the airway pressure is consistently held at a user-set positive level throughout the ventilation cycle. CPAP provides a continuous positive pressure that supports the patient’s airway and breathing while allowing them to maintain control over their respiratory parameters.
Here is a typical waveform for PSV/CPAP mode –
In CPAP, the patient breathes spontaneously, determining their own breathing frequency, tidal volume, and breath time.
The system initiates apnea ventilation if it detects that the patient has not continuously performed spontaneous breathing for a duration exceeding the pre-set apnea time.
Get in touch with us using our contact form.
