With the large-scale infection of the new coronavirus pneumonia in the world in the past two years, the number of critically ill patients in the ICU has increased significantly. The ventilator that sends oxygen-containing air into the lungs and expels carbon dioxide gas from the body to improve the ventilation of the respiratory system has become an important medical material. However, many medical workers are not familiar with the principles and precautions of ventilator use.
ICU Ventilator application field
As an important means of mechanical ventilation, ventilator can relieve respiratory failure caused by severe hypoxemia and hypercapnia , increased intracranial pressure , neuromuscular paralysis and other diseases. Buy time and conditions for the rescue, and finally restore the patient to effective spontaneous breathing.
With the advancement of modern mechanical ventilation technology, there is no absolute contraindication to the use of ventilators . However , in the application of bullae, pneumothorax, hypovolemic shock, myocardial infarction and other diseases, the ventilation pressure should be reduced and the frequency should be increased.
Common parameters of ventilator
There are multiple parameters displayed on the control panel of the ventilator, and clinicians set appropriate thresholds to intervene in patient ventilation according to the patient’s condition and respiratory function.
1. Tidal volume (TV) : The amount of gas delivered by the ventilator to the patient each time, the set value is 6-8 mL/kg .
2. Respiratory Rate (RR/RF) : The number of breaths a patient takes per minute, expressed in units of breaths per minute.
3. Inspiratory ratio (IE) : the ratio of inspiratory and expiratory time, generally set to 1: 1.5～2 .
4. Minute ventilation (MV) : The amount of gas the ventilator delivers to the patient every minute. MV=RR×TV.
5. Oxygen Concentration : The percentage of oxygen in the gas delivered by the ventilator. The oxygen concentration should ensure that the patient ‘s blood oxygen saturation ( SpO ₂）>96%。
6. Positive end- expiratory pressure (PEEP) : The airway at the end of expiration is maintained at a level higher than atmospheric pressure, which can prevent alveolar collapse and promote oxygenation. The general setting value is 15cmH2O .
7. Peak airway pressure (P-Peak) : The highest pressure during the ventilation process of the ventilator, the higher the airway pressure, the greater the P-Peak.
Multiple parameters on the ventilator control panel
Common ventilation modes of ventilator
1. Controlled ventilation : for patients with severe respiratory depression or apnea.
However, this mode completely “ignores” the patient’s spontaneous breathing, which can easily lead to human-machine confrontation , that is, the abnormal human-machine relationship caused by the different rhythms of the two breathing pumps of the ventilator and spontaneous breathing, aggravating the underlying cardiopulmonary diseases.
Pressure-Time Curves for Controlled Ventilation
2. Assisted ventilation : It is used for patients whose respiratory center function gradually recovers as a transitional measure for weaning.
In this mode, the ventilator delivers air at the actual air demand of the patient , and the human inhalation is synchronized with the ventilator delivery, also known as synchronous ventilation . However, when the patient breathes very slowly, the ventilation rate of the ventilator is also very small, and the ventilation is insufficient; and when the patient breathes quickly, the assisted breathing rate of the ventilator will also increase, and the ventilation is excessive.
Pressure-Time Curves for Assisted Ventilation
3. Spontaneous ventilation : used for patients recovering from spontaneous breathing as a preparation for weaning.
The patient breathes spontaneously, and the ventilator detects that the airway pressure is lower than expected and triggers the initiation of inspiration, and provides ventilation support as preset. Unlike assisted ventilation, the patient can choose to switch between breathing and breathing .
Pressure-time curve of PSV in support mode of spontaneous breathing
During the initial setting of the ventilator, the doctor can select the appropriate ventilation mode according to the needs of the patient. All ventilation modes are derived from three modes: controlled ventilation, assisted ventilation, and spontaneous ventilation .
Scope of application of common modes of ventilator
1. Spontaneous/time-controlled mode (S/T mode): It is suitable for patients with relatively stable spontaneous breathing, but at the same time, there may be respiratory arrest or respiratory weakness.
2. Continuous positive airway pressure mode (CPAP mode): Help patients reduce airway resistance and maintain open upper airway. For type I respiratory failure, acute and chronic heart failure, obstructive sleep apnea syndrome.
CPAP mode
The pressure-controlled ventilation mode (PCV mode) performs forced ventilation according to the set parameters, and is generally only used in emergency situations.
ventilator use
– practical guidance
1. Application of ventilator in COPD complicated with obstructive sleep apnea syndrome:
l Daytime S/T mode: IPAP: 12-20 cmH 2 O; EPAP: 4-6 cmH 2 O; pressure rise time: 50-100 ms; expiratory sensitivity: 2-3 gears; inspiratory time: 0.8- 1.2 seconds; alternate breathing rate: 12-15 times/min;
l Night S/T mode: IPAP: 12-20 cmH 2 O; EPAP: 6-8 cmH 2 O to eliminate snoring; pressure rise time: 50-100 ms; expiratory sensitivity: 2-3 gears; night: ST mode ; Inspiratory time: 0.8-1.2 seconds; Standby breathing rate: 12-18 times/min.
2. Application of ventilator in acute exacerbation/stable COPD:
l Preferred S/T mode , IPAP: 12-20 cmH 2 O, EPAP: 4-6 cmH 2 O; pressure rise time: 50-100 ms; expiratory sensitivity: 2-3 gears; inspiratory time: 0.8- 1.2 seconds; alternate breathing rate: 12-15 breaths/min.
Application of ventilator in cardiogenic pulmonary edema
l The first choice is CPAP mode . The initial CPAP setting is mostly 5-8 cmH 2 O. According to the patient’s comprehensive clinical conditions such as blood gas and pulse oxygen circulation function, it is adjusted every 5-10 minutes, with an increment of 2 cmH 2 O each time; CPAP setting The range is generally 6-12 cmH 2 O.
l For patients whose CPAP exceeds 12 cm H 2 O and is still difficult to improve in a short time, it is recommended to switch to tracheal intubation for invasive ventilation.
Ventilators play an important role in the adjuvant treatment of various diseases
The fundamental purpose of ventilator use is to maintain effective alveolar ventilation and improve oxygenation, so as to gain time and conditions for the treatment of underlying causes. Therefore, it is still necessary to comprehensively treat patients after using a ventilator, including nebulization, drainage, etc., to improve the patient’s ventilation function and maintain better human-machine coordination.
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