How A Ventilator Works
Wiki Article
Respiratory support is one of the most important means to save the lives of critically ill patients. Therefore, the ventilator has become an indispensable device in clinical treatment. Mastering the basic knowledge and basic operation methods of ventilator is a necessary basic knowledge and skill for clinicians.
The basic principle of ventilator: the inspiratory action during spontaneous ventilation creates negative pressure in the thoracic cavity, and the passive expansion of the lung causes negative pressure in the alveoli and airway, which constitutes the pressure difference between the airway orifice and the alveoli to complete the inhalation; after inspiration, the thoracic cavity And the lungs contract elastically, creating an opposite pressure difference to complete the exhalation. Therefore, normal breathing is due to the "active negative pressure difference" between the alveoli and the airway openings in the body to complete the inhalation through the breathing action. The elastic recoil of the chest and lungs after inhalation creates a passive positive pressure differential between the alveoli and airway openings and expiration. Meet the needs of physiological ventilation. Ventilator ventilation is driven by an external mechanical force to create a positive pressure differential between the airway openings and the alveoli, and expiration is the passive positive pressure differential between the alveoli and the airway openings after exhalation of the external mechanical driving pressure. That is, there is a "passive positive pressure differential" in the breathing cycle to complete the breath.
According to the working characteristics of the ventilator, it can be divided into the following categories:
1. Constant pressure ventilator
When inhaling, the ventilator pumps a certain pressure of gas into the airways to inflate the alveoli, and the airway pressure gradually increases. When the predetermined pressure is reached, the airflow ceases and becomes the expiratory phase. The tidal volume of this type of ventilator is related to the preset pressure of the ventilator, inspiratory time, flow rate, etc. If the flow rate is low, the inspiratory time is short, the predetermined pressure is low, and the tidal volume is small, otherwise the tidal volume is increased. Tidal volume may decrease if lung compliance decreases or bronchospasm increases airway resistance.
The disadvantage of this type of ventilator is that tidal volume cannot be guaranteed when airway pressure increases. The advantage is that when the airway leaks, it must also maintain some pressure and maintain proper ventilation. In conclusion, the pressure of this ventilator does not guarantee capacity.
2. Constant volume ventilator
A ventilator pumps a fixed amount of gas into a patient's airways and lungs, producing inspiration and expiration. The advantage of this type of ventilator is that a certain amount of tidal volume can be guaranteed in a closed airway state within a safe pressure range. The disadvantage is that the airway leakage cannot be compensated, the airway pressure is too high, and the ventilation is insufficient. In short, this ventilator capacity does not guarantee pressure.
3. Timed ventilator
With a timed, pressure-limited constant-flow ventilator, the ventilator generates airflow into the airway for a predetermined period of time, where inspiration stops and expiration occurs. During the exhalation phase, there is still low pressure airflow in the airway. Inhalation time, breathing rate, inhalation/hit rate and inspired oxygen concentration can be adjusted.
The above classification is based on inspiratory and expiratory phase changes. It is also classified according to control method and use. There is also a high-frequency ventilation ventilator , which is characterized by high respiratory rate and low tidal volume.
https://www.arshinemedical.com/news/how-a-ventilator-works-58528719.html