In modern clinical medicine, the ventilator, as an effective means of artificially replacing the spontaneous ventilation function, has been widely used in respiratory failure caused by various reasons, anesthesia respiratory management during major surgery, respiratory support treatment and emergency resuscitation. It occupies a very important position in the field of modern medicine. Ventilator is a vital medical equipment that can prevent and treat respiratory failure, reduce complications, save and prolong the life of patients.
Classification of ventilators
1. Classification by type of use or application
(1) Controlled mechanical ventilation (CMV)
a. Definition: A patient's breathing is produced, controlled, and regulated entirely by a mechanical ventilator in the absence of spontaneous breathing.
b. Applicable to: the disappearance or weakening of spontaneous breathing caused by diseases; the spontaneous breathing is irregular or the frequency is too fast, and when the mechanical ventilation cannot coordinate with the patient, the spontaneous breathing is suppressed or weakened artificially.
(2). Assisted Mechanical Ventilation (AMV)
a. Definition: A patient's spontaneous breathing that is assisted or augmented by a ventilator in the presence of the patient's breathing. The various types of mechanical ventilation are mainly triggered by the patient's negative inspiratory pressure or inspiratory flow.
b. Applicable to: Although spontaneous breathing exists and is relatively regular, but the spontaneous breathing is weakened and the patient is hypoventilated.
2. Classification by route of use of mechanical ventilation
(1) Intrathoracic or airway compression type
(2) Chest appearance
3. According to the switching mode of inhalation and exhalation
(1) Constant pressure type: After the pressure in the airway reaches the expected value, the ventilator opens the exhalation valve, and the chest and lungs passively collapse or exhale by negative pressure. When the pressure in the airway continues to drop, the ventilator passes the positive pressure again. Generates airflow and induces inhalation.
(2) Volume-fixed type: The estimated tidal volume is sent into the lungs through positive pressure. After reaching the estimated tidal volume, the air supply is stopped and the patient enters the exhalation state.
(3) Timing type: supply air according to the pre-designed inhalation and exhalation time.
(4) Mixed type (multifunctional type).
4. Air supply according to ventilation frequency
(1) High-frequency ventilation: ventilation frequency >60 times/min.
a. Advantages: low airway pressure, low intrathoracic pressure, little interference with circulation, no need to seal the airway.
b. Disadvantages: It is not conducive to the removal of carbon dioxide.
c. Classification: high-frequency positive pressure ventilation, high-frequency jet ventilation, high-frequency oscillatory ventilation.
(2) Constant frequency ventilation: ventilation frequency <60 times/min.
5. Classified by whether there is a synchronization device or performance
(1) Synchronous ventilator: The ventilator can be triggered when the patient's spontaneous breathing begins to inhale, so that it can supply air to the patient's airway and generate an inspiratory action.
(2) Asynchronous ventilator: the patient's breathing or inspiratory negative pressure cannot trigger the ventilator to supply air, and it is generally only used for patients with controlled mechanical ventilation.
6. Classified by applicable object
(1) Baby ventilator
(2) Children ventilator
(3) Adult ventilator
7. Classified by working principle
(1) Simple ventilator
(2) Membrane lung
Ventilator Modes and Functions
1. Main modes of mechanical ventilation
(1) Intermittent Positive Pressure Ventilation (IPPV): Inspiratory phase is positive pressure, expiratory phase pressure is zero.
a. Working principle: The ventilator generates positive pressure during the inspiratory phase, presses the gas into the lungs, and when the pressure rises to a certain level or the inhaled volume reaches a certain level, the ventilator stops supplying air, the exhalation valve opens, and the patient's chest And the lungs passively collapse, producing exhalation.
b. Clinical application: various patients with respiratory failure mainly based on ventilation function, such as COPD, etc.
(2) Intermittent positive and negative pressure ventilation (IPNPV): The inspiratory phase is positive pressure, and the expiratory phase is negative pressure.
a. How it works: The ventilator works in both the inspiratory and expiratory phases.
b. Clinical application: Negative pressure in the expiratory phase can cause alveolar collapse and cause iatrogenic atelectasis.
(3) Continuous Positive Airway Pressure (CPAP): It refers to artificially adding a certain positive airway pressure during the whole breathing cycle under the condition of the patient breathing spontaneously.
a. Working principle: The inhalation phase provides continuous positive pressure airflow, and the exhalation phase also provides certain resistance, so that the airway pressure in both inhalation and exhalation phases is higher than atmospheric pressure.
b. Advantages: The continuous positive pressure airflow during inhalation is greater than the inspiratory airflow, which saves the patient's inhalation effort, increases FRC, and prevents airway and alveolar collapse. Can be used for workouts before going offline.
c. Disadvantages: great disturbance to circulation and great barotrauma to lung tissue.
(4) Intermittent mandatory ventilation and synchronized intermittent mandatory ventilation (IMV/SIMV)
a. IMV: There is no synchronization device, the ventilator air supply does not need to be triggered by the patient's spontaneous breathing, and the time of each air supply occurring in the respiratory cycle is not constant.
b. SIMV: With a synchronization device, the ventilator gives the patient commanded breathing according to the pre-designed breathing parameters every minute, and the patient can breathe spontaneously without being affected by the ventilator.
c. Advantages: It exerts the ability to regulate breathing by itself; it has less impact on circulation and lungs than IPPV; to a certain extent, it reduces the use of shock and tranquilizers.
d. Application: It is generally considered to be used when offline. When R<5 times/min, a good oxygenation state is still maintained, and offline can be considered. Generally, PSV is added to avoid respiratory muscle fatigue.
(5) Mandatory Minute Ventilation (MMV)
a. When spontaneous breathing > preset minute ventilation, the ventilator does not command ventilation, but only provides a continuous positive pressure.
b. When spontaneous breathing < preset minute ventilation, the ventilator performs mandatory ventilation, increasing the minute ventilation to reach the preset level.
(6) Pressure Support Ventilation (PSV)
a. Definition: Under the premise of spontaneous breathing, receiving a certain level of pressure support for each inhalation increases the patient's inspiratory depth and inhaled gas volume.
b. Working principle: The inspiratory pressure starts with the patient's inspiratory action, and ends with the inspiratory flow rate reducing to a certain level or the patient's effort to exhale. Compared with IPPV, the supported pressure is constant and is regulated by the feedback of inspiratory flow rate; compared with SIMV, it can get pressure support for each inhalation, but the support level can be set according to different needs.
c. Application: SIMV+PSV: for preparation before weaning, which can reduce respiratory work and oxygen consumption
d. Indications: Exercising the ventilator; preparation before weaning; ventilator weakness due to various reasons; severe flail chest causing abnormal breathing.
e. Note: Generally not used alone, it will cause hypoventilation or hyperventilation.
(7) Volume Support Ventilation (VSV): Each breath is triggered by the patient's spontaneous breathing. The patient can also breathe without any support, and can reach the expected TV and MV levels. The ventilator will allow the patient to perform true autonomy. Breathing, the same goes for preparing before going offline.
(8) Capacity control of pressure regulation
(9) Biphasic or bilevel positive pressure ventilation
a. Working principle: P1 is equivalent to inspiratory pressure, P2 is equivalent to respiratory pressure, T1 is equivalent to inhalation time, and T2 is equivalent to exhalation time. b. Clinical application:
When P1=inhalation pressure, T1=inhalation time, P2=0 or PEEP, T2=expiration time, it is equivalent to IPPV.
When P1=PEEP, T1=infinity, P2=0, T2=0, it is equivalent to CPAP.
When P1 = inspiratory pressure, T1 = inspiratory time, P2-0 or PEEP, T2 = desired controlled breathing period, equivalent to SIMV.
2. Primary Mechanical Ventilation Functions
(1) Breath-hold at the end of inspiration
a. After the end of inhalation and before the start of exhalation, the ventilator does not supply air, and the exhalation valve continues to close for a period of time to maintain the pressure in the lungs at a certain level.
b. Clinical application:
The inhalation time is prolonged, which is conducive to the distribution of gas.
Facilitate the diffusion of gas
Facilitate the distribution and diffusion of aerosol inhaled drugs in the lungs
3. Can increase the burden on the heart.
(2) Positive end-expiratory pressure ventilation
a. At the end of expiration, the airway pressure does not drop to zero, but still maintains a certain level of positive pressure.
b. Clinical application: suitable for hypoxemia caused by intrapulmonary shunt, such as ARDS 3. PEEP corrects the mechanism of ARDS
Reduce alveolar collapse, reduce intrapulmonary shunt, and correct hypoxemia caused by intrapulmonary shunt
Reduce alveolar collapse and increase FRC, which is conducive to the full exchange of gas on both sides of the alveolar-capillary.
The increase in alveolar pressure increases the alveolar-arterial oxygen partial pressure, which is conducive to the diffusion of oxygen to the capillaries. The alveoli are always in a state of expansion, which can increase the diffusion area of the alveoli.
Increased alveolar inflation increases lung compliance and reduces work of breathing.
4. Main Side Effects of PEEP
a. Effects on hemodynamics
b. Barotrauma to lung tissue
c. Capable of compressing pulmonary capillaries. Decreased pulmonary blood flow may increase ineffective ventilation.
d. Can reduce alveolar surfactant.
5. The choice of the best PEEP: on the premise of maintaining FiO2<60%, the lowest PEEP level that can make PaO2>60mmHg.
6. Endogenous PEEP: Due to too short exhalation time or high respiratory resistance, the air in the alveoli is trapped, which can keep the alveolar pressure positive throughout the expiratory cycle, which is equivalent to the effect of PEEP. It can be caused by diseases or by Artificially caused by using a ventilator.
Prolonged expiratory and end-expiratory breath hold: suitable for patients with COPD and carbon dioxide retention.
Sigh: In every 50-100 breathing cycles, there are 1-3 deep inhalations equivalent to 1.5-2 times the tidal volume. In order to make the alveoli at the bottom of the lungs that are prone to collapse expand regularly and improve the gas exchange in these parts, Prevent atelectasis.
Inverse proportional ventilation (IRV)
Advantages: Prolong the inhalation time, which is beneficial to the dispersion and distribution of gas, and is beneficial to correct hypoxia.
Disadvantages: great disturbance to circulation and great barotrauma to lung tissue.
Development and application status of ventilator
1、 Degree of microcomputerization of ventilator The degree of microcomputerization of ventilator determines the grade of ventilator, which is manifested in:
a. There is a self-test function after starting up.
b. When a fault occurs, there will be a screen prompt, which is convenient for maintenance.
c. Perfect alarm function, such as oxygen supply, gas supply, minute ventilation, pressure upper limit, pressure lower limit, respiratory rate, tidal volume, apnea ventilation, background ventilation setting, machine disconnection, air leakage and air leakage volume, flow sensor , working status, oxygen flow and many other links to ensure the safety of the mechanical ventilation process, the clinician can adjust the alarm range set by the parameters according to the patient's status.
d. Other special functions, including sputum suction function, atomization function, breath-holding function (including inhalation and exhalation breath-holding to meet the needs of chest X-ray), lock function (to prevent ventilation parameters from being changed arbitrarily).
2、 Monitoring function of the ventilator The monitoring function of the ventilator is one of the key links in determining the grade of the ventilator. Perfect ventilator monitoring function is an important prerequisite to realize the ventilator suitable for the pathophysiological changes of the patient's lungs, not only to display routine ventilation and lung mechanical parameters, such as VTe, VT, R, c, f, airway temperature, Fio2, Pp resistance k, P, Pn a, VA, VAleak, I: E and can further display:
(1) Pressure-time, volume-time, flow rate-time curves can be displayed on one screen individually or simultaneously.
(2) spo2, ETCO2 and calculate VD/VTe, co2 output.
(3) Monitor the tracings of Paw-V, V-Flow, Flow-Paw, V-co2, Ptrach-V, Flow-Ptrach and other curve loops.
(4) Trend review (24-48 hours).
(5) The logbook is the review of the setting value of the ventilator application event.
(6) Calibration function, including co2, Flow, o2 calibration.
(7) Ventilation and various function settings: volume level, different combinations of screen display, arbitrary ventilation mode selection (more than 10 commonly used modes), multiple voice settings, etc.
(8) The ventilator allows the user to trace the P-V curve [1, 2, 3 J with a low flow rate method to further understand the patient's lung static compliance (c), resistance (R) and endogenous PEEP (PEEPi). Furthermore, it provides a basis for better adjustment of ventilation parameters. Through curve tracing, the upper and lower inflection points and the amount of recovery can be calculated, and the records can be printed online with the computer.
(9) The ventilator integrates other devices (respiratory mechanical monitor "Bi-core") to enhance the solution to problems that cannot be understood with respiratory parameters alone during ventilation, such as respiratory mechanical monitoring, placement of esophageal pressure, and intragastric pressure monitoring to understand Transpulmonary pressure, transdiaphragmatic pressure and dynamic auto-PEEP can further clarify the state of respiratory mechanics and provide research space for clinical professional physicians.
(10) After years of clinical practice, foreign ventilator manufacturers have timely integrated some useful parameters such as RVR, MIP, Po. 1. Put PlP and au grid P into the monitoring system to provide a basis for the adjustment and offline setting of clinicians. In recent years, the automatic off-line mode has quietly risen, and the ventilator integrates the important parameters of the patient, body weight, ideal ventilation parameters, and BGA, which improves the level of mechanical ventilation and shortens the time spent on the machine. In short, the microcomputerization and networking of the ventilator provide a scientific research platform for mechanical ventilation and promote the development of the application level of mechanical ventilation.
3、The development of the ventilator mode is an important manifestation of the level of the ventilator. Regardless of whether the ventilator is volume-controlled or pressure-controlled, it will lead to ventilator-induced lung injury (Ventilator-induced Lung Inj~y VILI) to varying degrees [3], in recent years , foreign countries have done a lot of basic and clinical research in this area, and have made major reforms on the basis of the original IPPV, IMV, SIMV, and PSV. Reduce the occurrence of VILI, and further expand the role of the ventilator as a clinical treatment.
(1) Today's ventilator applications range from neonates to adults, and only need to replace the humidifier and pipeline; mechanical ventilation is from non-invasive to invasive, and non-invasive ventilation has strong air leakage compensation.
(2) Adding Autoflow (autonomous airflow) or flow-by in the volume control ventilation mode can increase the autonomy of the patient, reduce the airway pressure, increase the comfort of the patient, and overcome the shortcomings of the volume ventilation mode.
(3) Breathing response time (30-40ms) of the ventilator, blowing waveform (square wave-constant current, deceleration wave), trigger sensitivity is adjustable by flow rate trigger, pressure trigger is discarded, expiratory sensitivity of PSV mode (Es. end) adjustable. Under ventilator monitoring, clinicians can easily adjust the patient's Esem, thus solving the human-computer interaction method can minimize the interference on cardiopulmonary function and the occurrence of VILI.
(4) International clinical practice has further confirmed that pressure ventilation is superior to volume control in maintaining positive airway pressure, reducing cardiopulmonary interference, and improving oxygenation, and minimizes the occurrence of VILI. On the basis of PCV, BiPAP/PS and APRV have been introduced in recent years. In particular, the BiPAP ventilation mode is adopted by many ventilator manufacturers because of its pressure control and good human-machine coordination. It is named: Bilevel, duoPAP and other different names.
(5) Spontaneous ventilation and closed-loop ventilation mode: Experiments and clinical applications show that the time of controlled ventilation is minimized, so as to minimize the occurrence of VILI, and the time with the machine is shortened. Many studies have shown that spontaneous breathing has many advantages, which is beneficial to the recovery of pathophysiological changes in patients. For spontaneous breathing, it is no longer the simple Spon mode in the past, but a servo mode (servo) and closed-loop ventilation mode. The biggest advantage lies in the system Internal output information can be precisely controlled. It can quickly reach a steady state under the premise of zero error, and can eliminate various external source interference. Mechanical ventilation techniques using closed-loop control principles can be quite simple or relatively complex. The simplest closed-loop control is to control an output variable, such as PSV, according to an input information. Relatively complex closed-loop control can continuously regulate multiple output variables according to multiple input information. Dual control is the synchronous control of output pressure and volume during one ventilation or each ventilation. The ventilation technique adopting the principle of dual control in one ventilation includes volume-guaranteed pressure support ventilation (Ⅵ) and pressure augmentation (PA). Its ventilation goal is to reduce the inspiratory work of the patient on the premise of ensuring the minimum inhaled tidal volume and minute ventilation volume. Others include: PRVC, autoflow, VTPC (Volume Calibration Pressure Control). The technical principle is that the ventilator follows the patient's respiratory mechanics. The characteristic change automatically adjusts the inspiratory pressure and inspiratory flow rate to ensure that vT tends to be constant during each ventilation. The ventilator performs negative feedback control on each breath. According to the principle of closed-loop ventilation control, closed-loop ventilation can be divided into: positive feedback ventilation (PAV), negative feedback ventilation (APV, ASV, PRvC), inter-breathing closed-loop ventilation (MMV, APV, ASV) and intra-breathing closed-loop ventilation (nw).
In the past 20 years, PSVE has been welcomed by clinicians, and the success rate of weaning ventilator-dependent patients has increased. Since PSV is a constant-pressure inspiratory support, at low levels of Ps, the generation of VT must be over-supported, and the support is equivalent. There are less than three stages of support. This mode has inspiratory delay and exhalation delay. When this mode is applied, it is easy to cause human-machine asynchrony. In recent years, many manufacturers have added expiratory sensitivity adjustment (Esens) to the expiratory phase, which greatly reduces the occurrence of man-machine asynchrony and improves the clinical application effect. However, clinicians still have many difficulties in identification and adjustment, and cannot observe waveforms. Very easy to identify. In the past 10 years, PAV or PPS mode ventilation has become the focus of contemporary critical illness research. This mode provides pressure support proportional to the patient's respiratory effort to solve the human-machine incoordination in PSV ventilation. By understanding the changes in patient resistance and compliance, or The setting of the ventilator (VA and FA) is adjusted by the target adjustment method. The setting pressure of the ventilator is too high, the volume is too high and the apnea ventilation alarm ensures the safety of this mode, reduces the dependence on the ventilator and significantly shortens the process of taking the machine. At present, there are DI in the world. ea company, PB company, and Weikang company have this mode, and PB840 has also adopted the automatic setting method to make the use of this mode more convenient. This closed-loop model is being recognized by clinicians. (6) Automatic catheter compensation (AT°C) Automatic catheter compensation is to instantly compensate the resistance pressure generated by different diameters and flow rates of artificial airway catheters. Different diameters and different flow rates have different compensation resistance pressures. The compensation range is from 0-100% different. The ventilator can be reflected in curves and waveforms. The setting of ATC is convenient for clinicians to observe and evaluate the spontaneous breathing ability, and it is easy to achieve weaning when performing low-assisted ventilation.
4、 Adjustment of the ventilator The modern ventilator adopts a single-knob adjustment method instead of the single function of multiple knobs in the past, which is convenient for clinical use. The use of digital adjustment increases the accuracy of parameter setting. At the same time, clinicians are required to have a wealth of theoretical and practical experience in order to make the parameter setting more in line with the patient's condition. The ventilator also stipulates the safety range of conventional parameters, and confirmation is required when exceeding the range, which increases the safety of mechanical ventilation. Due to the enhanced monitoring and display function of the ventilator, the set parameters are clearly displayed, which is beneficial for clinicians to evaluate the patient's condition, and can be transmitted through the network to facilitate the management and guidance of mechanical ventilation.
5、 Purchasing Principles of Ventilator Ventilator is a useful tool for respiratory support and a common treatment method for critically ill patients today. The quality of respiratory support is directly related to the rescue level of critically ill patients. The following principles should be followed when purchasing a ventilator:
(1) Understand the development and application status of ventilator, monitoring, and ventilation mode determine the grade of ventilator.
(2) According to the scale of the hospital, whether it is a comprehensive ICU or a specialized ICU, it is estimated that the type of disease admitted is an application-oriented unit or a large hospital for medical, teaching, and research.
(3) According to the experience of using ventilators and the level of ICU doctors, do not buy high-end ventilators one-sidedly. The development of ventilators is the same as that of other medical devices, and they are updated quickly. It is necessary to solve clinical problems and avoid waste of resources. To sum up, ventilator treatment for intubated patients is a complex systematic project, that is, the level of the ventilator involved is more related to the level of the doctor using the ventilator, the respiratory management of the nurses and the overall strength of the hospital (all auxiliary departments). One-sided pursuit of high-end machines may not necessarily improve the success rate of respiratory failure rescue. 
