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8 Minutes, Let You Quickly Understand The Ventilator!

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Update time : 2023-08-27 17:30:00
Ventilators are a useful tool for respiratory support and are a common treatment for critically ill patients today. The quality of respiratory support is directly related to the rescue level of critically ill patients.
 
The role of ventilator mechanical ventilation
1. Maintain proper ventilation, so that the alveolar ventilation can meet the needs of the body.
2. Improve gas exchange function and maintain effective gas exchange.
3. Reduce the work of respiratory muscles.
4. Intrapulmonary atomization inhalation treatment.
5. Preventive mechanical ventilation, used for preventive treatment of respiratory failure after thoracotomy or in cases of sepsis, shock and severe trauma.
6. It can play an internal support role for patients with floating chest walls.
Relative contraindications to ventilator therapy
1. Asphyxiating respiratory failure caused by massive hemoptysis or severe misaspiration
2. Respiratory failure with bullae
3. Patients with tension pneumothorax
4. Respiratory failure secondary to myocardial infarction
Indications for ventilator therapy
1. Respiratory rate >30-35 times/min, or <5-10 times/min
2. Nasal catheter nasal congestion or mask oxygen inhalation blood gas analysis: PO2<60mmHg or PCO2>55mmHg
3. COPD: PO2<55-60mmHg or PCO2>70-80mmHg
Assisted ventilation modes commonly used by ventilators
Intermittent Positive Pressure Ventilation (IPPV)
IPPV is also called mechanically controlled ventilation (CMV). In this mode, the ventilator will provide the patient with intermittent positive pressure ventilation according to the preset ventilation parameters regardless of the patient's spontaneous breathing. Mainly used for patients who are not breathing spontaneously.
Synchronized intermittent mandatory ventilation (SIMV)
It means that the ventilator gives the patient mandatory breathing according to the preset breathing parameters (frequency flow rate, flow rate, volume, breathing, etc.) within each minute.
 
【Advantages of SIMV】
1. It can ensure the effective ventilation of the patient.
2. Clinically, adjust the frequency and TV of SIMV appropriately according to the changes of the patient's own TV, f and MV, which is beneficial to the exercise of respiratory muscles. SIMV has become a necessary means before evacuating the ventilator.
3. In the absence of blood gas detection, when PaO2 is too high or too low, the patient can adjust it through spontaneous breathing, which reduces the chance of hypoventilation or overventilation.
Pressure Support Ventilation (PSV)
It is an assisted ventilation method, that is, under the premise of spontaneous breathing, each inhalation receives a certain level of pressure support to assist and enhance the patient's inspiratory depth and inhaled volume.
Positive end-expiratory pressure (PEEP)
It means that the ventilator generates positive pressure during the inspiratory phase and presses the gas into the lungs; but at the end of expiration, the airway pressure does not drop to zero, but remains at a certain positive pressure level. The function of maintaining a certain level of positive pressure at the end of exhalation is called PEEP. The main indication is hypoxemia caused by intrapulmonary shunt.
The main role of PEEP
1. The supporting effect of positive end-expiratory pressure → the opening of small airways at the end of exhalation → facilitating the discharge of CO2. For example, in patients with COPD, when appropriate PEEP is added, the small airway can be supported to prevent the formation of a "valve" in the small airway during exhalation, which is conducive to the discharge of CO2.
2. End-expiratory alveolar expansion → Functional Residual Capacity (FRC) → Oxygenation, such as hypoxemia, especially ARDS, oxygenation alone does not improve FiO2 oxygenation, adding PEEP can increase oxygenation content.
3. For pneumonia and emphysema, the addition of PEEP can not only increase oxygenation, but also help to reduce edema and inflammation.
4. Prevention and treatment of atelectasis after major surgery.
It is generally believed that the choice of PEEP with 2-5cmH2O in COPD patients can have a good ventilation and oxygenation effect without causing adverse reactions. A particularly cautious attitude is required for PEEP above 8 cmH2O.
It takes 15 minutes for the body to adapt to the new level of PEEP; increase every 15 minutes by 2cmH2O each time. Reduce PEEP by 2-5cmH2O each time, with an interval of 1-6 hours.
Continuous Positive Airway Pressure (CPAP)
The patient breathes spontaneously under the continuous positive pressure airflow system on demand, so that the airway pressure is higher than the atmospheric pressure during the inspiratory and expiratory periods. Maintain the airway pressure basically constant at the pre-adjusted CPAP level with small fluctuations.
In this mode, patients feel comfortable, but it will affect the circulatory system.
Pressure Support Ventilation (PSV)
It is an assisted ventilation method, that is, under the premise of spontaneous breathing, each inhalation receives a certain level of pressure support to assist and enhance the patient's inspiratory depth and inhaled volume.
The patient can completely control F, I:E by himself; VT is jointly determined by the patient and the PASB given by the ventilator.
The patient feels comfortable and can overcome the resistance brought by the pipeline.
CPAP
(biphasic positive airway pressure Bipap): It is the assisted ventilation mode. Breathing and giving the patient airway pressure support when inhaling, and setting a certain resistance in the airway when exhaling, so as to achieve a continuous low-level positive pressure state. It can be used in the COPD rehabilitation period, and can also be used to treat sleep apnea syndrome. , but not for severe respiratory failure such as ARDS. Pressure support with PEEP.
Basic steps for using a ventilator
1. Determine whether there is an indication for mechanical ventilation.
2. Determine whether there is a relative contraindication to mechanical ventilation, and carry out necessary treatment.
3. Determine controlled breathing or assisted breathing.
4. Determine the mechanical ventilation method (IPPV, SIMV, CPAP, PSV, PEEP, CPAP).
5. Determine the minute ventilation (MV) of mechanical ventilation, generally 8-12ml/kg.
6. Determine the frequency (f), tidal volume (TV) and inspiratory time (IT) required for supplemental mechanical ventilation MV.
7. Determine FiO2: adjust the oxygen concentration in combination with the positive end-expiratory pressure to achieve the target blood oxygen saturation (>88-90%).
8. Determine PEEP: When PaO2 is still less than 60mmHg under high-concentration oxygen inhalation, PEEP should be added to reduce FiO2 to below 0.5. The adjustment principle of PEEP is to increase gradually from small to achieve the best gas exchange and the smallest circulation impact.
9. Determine the alarm limit and airway safety valve. The alarm parameters of different ventilators are different, please refer to the manual for adjustment. The airway pressure safety valve or pressure limitation is generally adjusted to maintain positive pressure ventilation peak pressure 5-10cmH2O.
10. Adjust the temperature and humidifier. Generally, the temperature of the humidifier should be adjusted to 34-36 degrees Celsius.
11. Adjust the synchronization trigger sensitivity. Adjust according to the size of the patient's spontaneous inspiratory force. Generally -2~-4cmH2O or 0.1L/S.
Ventilator parameter settings
Ventilator tidal volume setting
For adults, the frequency of mechanical ventilation can be set to 8-20 times/min. For patients with acute and chronic restrictive ventilatory dysfunction, a higher frequency of mechanical ventilation (20 times/min or higher) should be set. After 15 to 30 minutes of mechanical ventilation, the frequency of mechanical ventilation should be further adjusted according to the arterial oxygen partial pressure, carbon dioxide partial pressure, and pH value. The frequency of mechanical ventilation should not be set too fast to avoid gas occlusion in the lungs and the generation of endogenous positive end-expiratory pressure.
Ventilator Mechanical Ventilation Frequency Setting
For adults, the frequency of mechanical ventilation can be set to 8-20 times/min. For patients with acute and chronic restrictive ventilatory dysfunction, a higher frequency of mechanical ventilation (20 breaths/min or higher) should be set. After 15 to 30 minutes of mechanical ventilation, the frequency of mechanical ventilation should be further adjusted according to the arterial oxygen partial pressure, carbon dioxide partial pressure, and pH value. In addition, the frequency of mechanical ventilation should not be set too fast to avoid gas trapping in the lungs and the generation of endogenous positive end-expiratory pressure. Once an endogenous positive end-expiratory pressure is generated, it will affect lung ventilation/blood flow, increase the patient's work of breathing, and increase the risk of barotrauma.
Ventilator breath ratio settings
During mechanical ventilation, the setting of the I/E ratio of the ventilator should take into account factors such as the impact of mechanical ventilation on the patient's hemodynamics, oxygenation status, and spontaneous breathing level.
1. For patients with spontaneous breathing, when the ventilator assists breathing, the air supply of the ventilator should be matched with the patient's inhalation to ensure that the two are synchronized. Generally, it takes 0.8 to 1.2 seconds to inhale, and the breath-to-breath ratio is 1:1.5 to 1:2.
2. For patients with controlled ventilation, generally longer inspiratory time and higher inspiratory-expiratory ratio can increase mean airway pressure and improve oxygenation. However, to prolong the inspiratory time, attention should be paid to monitoring the changes in the patient's hemodynamics.
3. If the inspiratory time is too long, the patient is not easy to tolerate, and sedatives or even muscle relaxants are often required. Furthermore, a short expiratory time can lead to an intrinsic positive end-expiratory pressure that exacerbates circulatory disturbances. Care should be taken in clinical application.
Ventilator Inspiratory Oxygen Concentration Setting
During mechanical ventilation, the setting of the inspired oxygen concentration of the ventilator generally depends on the target level of arterial partial pressure of oxygen, the level of positive end-expiratory pressure, the mean airway pressure, and the hemodynamic status of the patient. Because inhalation of high concentrations of oxygen can cause oxygen toxic lung injury, it is generally required that the inhaled oxygen concentration be lower than 50% to 60%. However, in the selection of inhaled oxygen concentration, not only the lung injury effect of high concentration oxygen, but also the lung injury effect of high airway and alveolar pressure should be considered. For patients with severe oxygenation disorders, the inhaled oxygen concentration should be set under the premise of adequate sedation, muscle relaxation, and an appropriate level of positive end-expiratory pressure to make the arterial oxygen saturation > 88% to 90%.
After the patient receives ventilator-assisted breathing, it is generally required to perform blood gas analysis for half an hour on the machine, adjust the parameters of the ventilator according to the results, and then repeat the inspection every 2 hours to prevent concurrent hyperventilation or hypoventilation.
Generally, when the inhaled oxygen concentration is below 0.4 and the blood oxygen partial pressure is 60mmHg, a blood gas analysis is allowed every 24 hours.
When performing blood gas analysis, the body temperature and oxygen concentration of the patient should be marked when the blood is drawn.
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