Ventilator Gas Switching Mode
Ventilator Gas Switching Mode
Different types of ventilators have different ways of converting the inspiratory phase and the expiratory phase. At present, there are mainly four forms of breathing phase switching in ventilators, the most basic of which are pressure switching and volume switching.
1. Time switching.
Negative pressure ventilators use time switching. Modern time-switched ventilators are controlled by electronic circuits. Various astable multivibrators are used to determine the period or frequency of breathing and the breathing ratio. These electronic circuits are used to activate regulating motors or air flow electrostatic valves. This form of gas switching is to preset a certain inhalation time first, and when the inhalation time reaches the preset value. The ventilator automatically changes the inspiratory phase to the expiratory phase. Its characteristic is that when the inspiratory time is fixed, when the patient's compliance and airway resistance change, the inspiratory pressure, volume and flow rate will change accordingly.
2. Capacity switching
The cyclic movement of breathing is determined by the volume of air delivered to the patient; when the volume of air delivered to the patient reaches the top value, the ventilator switches from the inspiratory phase to the expiratory phase. It is equipped with a pressure relief valve. During the process of delivering air to the patient, if the pressure exceeds the preset value, regardless of whether the air volume delivered to the patient is sufficient or not, as long as the pressure release valve works, the machine will automatically convert the inspiratory phase into the expiratory phase. In order to avoid causing serious damage to the patient, the advantage of this switching form is that it can maintain a stable ventilation volume.
3. Pressure switching
When the air pressure delivered to the patient exceeds the preset value. The ventilator switches the inspiratory phase to the expiratory phase at this time. Because the pressure is preset, when the patient's compliance and airway strength change, the tidal volume will change accordingly. It is characterized by the inability to maintain stable moisture levels.
4. Traffic switching
In the flow switching mode, the waveform of the gas flow rate changes with time during inhalation. When the flow rate reaches the preset value, the machine automatically converts the inhalation phase to the expiration phase.
Generally speaking, for a fully functional ventilator. The above four switching forms should all be available to meet different clinical requirements.
