The ventilator is an artificial mechanical ventilation device to assist or control the patient's spontaneous breathing movement to achieve the function of gas exchange in the lungs and reduce the consumption of the body to facilitate the recovery of respiratory function.
The clinical application of ventilators is divided into two categories. One type is mainly respiratory diseases, including pulmonary infection, lung insufficiency, asthma, pulmonary edema, etc., which affect the gas exchange function in the lung. At this time, the treatment of the ventilator mainly improves the gas exchange in the lungs, increases the oxygen concentration in the blood, and removes carbon dioxide. The second type is mainly surgery, which is conducive to the recovery of anesthesia, maintain normal respiratory function, reduce respiratory muscle movement, and reduce oxygen consumption.
(1) The basic working principle of the ventilator
Any ventilator works on the pressure difference of the gas.
The positive airway ventilator increases the gas pressure and connects with the patient's respiratory cannula through the pipeline. The gas flows directly to the alveoli through the airway and bronchus. At this time, it is inhalation; when exhaling, the ventilator is connected to the atmosphere, and the alveoli are Above atmospheric pressure, the gas in the alveoli is self-excluded until it is equal to atmospheric pressure.
(two) ventilator type
According to the working principle of the ventilator, it can be divided into two categories:
1 Constant pressure type ventilator sets the pressure value. When the ventilator produces a positive pressure, the airflow enters the respiratory tract, causing the alveoli to expand, and the airway pressure continues to rise until the predetermined pressure value, the ventilator stops supplying air, that is, the end of the inspiratory period begins to exhale. Applying a constant pressure type ventilator, the airflow speed is fast, the predetermined pressure is low, the inhalation time is short, and the tidal volume is small; while the airflow speed is slow, and the predetermined pressure is high, the inhalation time is long. The tidal volume is affected by the compliance of the lung. Under the same predetermined pressure, the compliance of the lung is good, the tidal volume is large, and the compliance of the lung is poor, and the tidal volume is significantly reduced. Therefore, in clinical applications, constant pressure ventilators are more prone to ventilatory transition or insufficient ventilation.
2 Quantitative ventilator sets the tidal value. When the ventilator delivers air, regardless of the patient's intrapulmonary resistance, the set tidal volume is sent to the airway; when exhaled, the respiratory pressure drops and the atmosphere is passed, and the alveolar gas is removed from the body. . The quantitative ventilator is not affected by the lesions in the patient's lungs, ensuring adequate ventilation. However, there must be a pressure alarm device. When the pressure in the airway exceeds the set range, the respiratory exhalation valve opens, communicates with the atmospheric pressure, and the gas is expelled from the body to prevent the airway pressure from being too high, the alveoli rupture, and serious complications such as pneumothorax.
(three) common indicators of ventilators
- Tidal volume (TV): refers to the amount of air inhaled or exhaled every time you breathe calmly.
- Pressure: Generally refers to peak airway pressure (PIP).
- Absorption frequency: number of breaths per minute, tidal volume × respiratory rate = ventilation per minute.
- Breathing cycle: The sum of inspiratory time and expiratory time, generally exhaling time is longer.
- Breathing ratio: The ratio of inspiratory time to expiratory time.
- Positive end expiratory pressure (PEEP): Under the premise of intermittent positive pressure ventilation, the level of end-expiratory airway is maintained above atmospheric pressure, which can prevent small airway, alveolar inconvenience, increase functional residual capacity and Lung compliance, plays an important role in the treatment of respiratory distress syndrome, non-cardiogenic pulmonary edema, pulmonary hemorrhage.
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