Medical Ventilator

Classification of ventilator

1、Classification by type of use or application

（1）Controlled mechanical ventilation (CMV)

 1.Definition: when the patient's spontaneous respiration is weakened or disappeared, it is completely generated, controlled and regulated by the mechanical ventilator. 

2.It can be applied to: the disappearance or weakening of autonomic respiration caused by diseases; when the autonomic respiration is irregular or the frequency is too fast, and the mechanical ventilation cannot coordinate with the patient, the autonomic respiration can be inhibited or weakened by artificial methods.

（2）Auxiliary mechanical ventilation (AMV) 

1. Definition: in the presence of breathing, the ventilator assists or enhances the patient's autonomous breathing. All kinds of mechanical ventilation are mainly triggered by the patient's inspiratory negative pressure or inspiratory air flow.

 2. It is applied to the patients whose spontaneous respiration is regular, but the spontaneous respiration is weakened and the ventilation is insufficient.

 2、Classification according to the use way of mechanical ventilation

（1）Intrathoracic or airway compression type

（2）Pleura

（3）Classification according to the switching mode of suction and expiratory phase

（1）Constant pressure type: when the pressure in the respiratory tract reaches the expected value, the ventilator opens the exhalation valve, and the thorax and lung are passively collapsed or the negative pressure produces the exhalation. When the pressure in the airway keeps decreasing, the ventilator again generates the airflow through the positive pressure, and causes the inhalation.

（2）Constant volume type: send the predicted tidal volume into the lung through positive pressure. When the predicted tidal volume is reached, stop air supply and enter the expiratory state.

（3）Timing type: air supply according to the pre-designed inspiratory and expiratory time. 

（4） Hybrid (multifunctional).

4、Air supply according to ventilation frequency

（1）High frequency ventilation: ventilation frequency > 60 times / min.

 1.Advantages: low airway pressure, low chest internal pressure, little interference to circulation, no need to seal the airway.

 2.Disadvantages: not conducive to the removal of carbon dioxide.

 3.Classification: high frequency positive pressure ventilation, high frequency jet ventilation, high frequency oscillation ventilation.

（2）Normal frequency ventilation: ventilation frequency < 60 times / min.

5、Classification by synchronisation or performance

（1）Synchronous ventilator: the ventilator can be triggered at the beginning of the patient's self breathing inspiration to supply air to the patient's respiratory tract and generate inspiration action.

（2）Nonsynchronous ventilator: the negative pressure of the patient's breath or inhalation can not trigger the supply of air to the ventilator, which is generally only used for patients with controlled mechanical ventilation.

6、Classification by applicable object

（1）Baby ventilator

（2）Infant ventilator 

 (3)  Adult ventilator

7、Classification by working principle

（1） Simple ventilator

（2） Membranous lung

The mode and function of ventilator

Ventilator block diagram

1、Main mechanical ventilation mode

（1）Interstitial positive pressure ventilation (IPPV): positive pressure in inspiratory phase and zero pressure in expiratory phase.

 1. Working principle: the ventilator generates positive pressure in the inspiratory phase, presses the gas into the lung, when the pressure rises to a certain level or the inhaled capacity reaches a certain level, the ventilator stops supplying air, the expiratory valve opens, the patient's thorax and lung passively collapse, and produces exhalation.

 2. Clinical application: all kinds of respiratory failure patients with ventilation function, such as COPD, etc.

（2）Intermittent positive and negative pressure ventilation (ipnpv): positive pressure in inspiratory phase and negative pressure in expiratory phase.

 1. Working principle: the ventilator can work in both inspiratory and expiratory phases. 

2. Clinical application: negative pressure of expiratory phase can cause alveolar collapse and iatrogenic atelectasis.

（3）Continuous positive airway pressure (CPAP): refers to the patient's artificial positive airway pressure during the whole respiratory cycle under the condition of autonomous respiration.

 1. Working principle: the inspiratory phase is provided with continuous positive pressure air flow, and the expiratory phase is also provided with certain resistance, so that the airway pressure of the inspiratory and expiratory phases is higher than the atmospheric pressure. 

2. Advantages: when inhaled, the continuous positive pressure air flow is greater than the inhaled air flow, so that the patient's inspiratory effort is saved, FRC is increased, and airway and alveolar collapse are prevented. It can be used for exercise before offline. 

3. Disadvantages: large disturbance to circulation and large air pressure injury to lung tissue.

（4） IMV and IMV / SIMV 

1. IMV: there is no synchronization device, the ventilator supply does not need the patient's spontaneous breathing trigger, and the time of each supply in the respiratory cycle is not constant. 

2. SIMV: it has a synchronous device. The ventilator gives the patient mandatory respiration according to the designed respiratory parameters in each minute. The patient can breathe autonomously without the influence of the ventilator.

 3. Advantages: give full play to the ability of self-regulation of respiration in offline; have less influence on circulation and lung than IPPV; reduce the use of seismostatic medicine to a certain extent. 

4. Application: it is generally considered to be used when offline. When R < 5 times / min, it still keeps a good oxygenation state. Offline can be considered, and PSV is generally added to avoid respiratory muscle fatigue.

（5）Command ventilation per minute (MMV) 

1. When autonomous respiration > preset minute ventilation, the ventilator does not command ventilation, only provides a continuous positive pressure. 

2. When the autonomic breathing is less than the preset minute ventilation, the ventilator will give instructions to ventilate and increase the minute ventilation to reach the preset level.

（6）Pressure support ventilation (PSV)

 1. Definition: under the premise of autonomous breathing, each inhale receives a certain level of pressure support, increasing the inhaled depth and amount of gas. 

2. Working principle: the inspiratory pressure starts with the patient's inspiratory action and ends with the decrease of inspiratory flow rate to a certain extent or the patient's efforts to exhale. Compared with IPPV, the support pressure is constant and regulated by the feedback of suction flow rate; compared with SIMV, the pressure can be obtained in each suction

（8）Volume support ventilation (VSV): each breath is triggered by the patient's autonomous respiration. The patient can also breathe without any support, and can reach the expected TV and MV levels. The ventilator will allow the patient to carry out real autonomous respiration, which is also suitable for preparation before offline.

（8）Capacity control of pressure regulation

（9）Working principle: P1 is equivalent to inspiratory pressure, P2 is equivalent to respiratory pressure, T1 is equivalent to inspiratory time, T2 is equivalent to expiratory time. 2. Clinical application: (1) when P1 = inspiratory pressure, T1 = inspiratory time, P2 = 0 or peep, T2 = expiratory time, it is equivalent to IPPV. (2) When P1 = peep, T1 = infinity, P2 = 0, T2 = O, it is equivalent to CPAP. (3) When P1 = inspiratory pressure, T1 = inspiratory time, p2-0 or peep, T2 = desired controlled respiratory cycle, equivalent to SIMV.

2、Main mechanical ventilation function

（1）At the end of inhalation and before the beginning of exhalation, the ventilator does not supply air, and the exhalation valve continues to close for a period of time to keep the pressure in the lung at a certain level. 2. Clinical application: (1) prolonging the inspiratory time is beneficial to the gas distribution. (2) It is beneficial to the diffusion of gas (3) it is beneficial to the distribution and diffusion of atomized drugs in the lung (3) it can increase the burden on the heart.

（2） Positive end expiratory pressure ventilation 1. At the end of expiratory, the airway pressure did not drop less than 0, and still maintained a certain level of positive pressure. 2. Clinical application: it is suitable for hypoxemia caused by intrapulmonary shunt, such as ARDS 3. The mechanism of peep to correct ARDS 

(1) to reduce alveolar collapse and intrapulmonary shunt, correct hypoxemia caused by intrapulmonary shunt .

(2) to reduce alveolar collapse and increase FRC, which is conducive to the full exchange of gas on both sides of alveolar capillary.

 (3) The increase of alveoli pressure is beneficial to the diffusion of oxygen to capillaries. The alveoli are always in the state of expansion, which can increase the diffusion area of alveoli.

 (4) The increase of alveolar inflation can increase lung compliance and reduce respiratory work.

4. The main side effects of PEEP

 (1) the influence on hemodynamics.

 (2) the barotrauma of lung tissue .

(3) the compression of pulmonary capillaries. Reduce pulmonary blood flow, may increase ineffective ventilation. 

(4) It can reduce alveolar surfactant.

5. The best choice of PEEP: keeping the feo2 < 60%, the lowest peep level of PaO2 < 60mmhg can be achieved. 6. Endogenous peep: due to the short expiratory time or high respiratory resistance, the gas in the alveoli is detained, which can keep the positive pressure of the alveoli in the whole expiratory cycle, which is equivalent to the effect of PEEP, which can be caused by disease or by the application of ventilator. （3） Prolonged expiratory and end expiratory breath holding: it is suitable for COPD patients with carbon dioxide retention. （4） Sigh: 1-3 deep inspirations of tidal volume equivalent to 1.5-2 times in every 50-100 respiratory cycles. In order to make the alveoli at the bottom of the collapsed lung expand regularly, improve the gas exchange at these parts, and prevent atelectasis. （5） Advantages: prolonging the inspiratory time is beneficial to the dispersion and distribution of the gas and to the correction of hypoxia.

2. Disadvantages: large disturbance to circulation and large air pressure injury to lung tissue

The development and application of ventilator

1. The degree of ventilator computerization determines the grade of ventilator, which is manifested in: (1) self checking function after startup. (2) There is screen prompt in case of failure, which is convenient for maintenance. (3) Perfect alarm functions, such as oxygen supply, gas supply, minute ventilation, upper pressure limit, lower pressure limit, respiratory frequency, tidal volume, suffocation ventilation, background ventilation setting, machine disconnection, air leakage and air leakage, flow sensor, working state, oxygen flow and many other links to ensure the safety of mechanical ventilation process. Clinicians can adjust the report set according to the patient's state Alarm range. (4) Other special functions, including sputum suction function, atomization function, breath holding function (including inspiratory and expiratory breath holding, to meet the needs of chest radiography), locking function (to prevent ventilation parameters from being arbitrarily changed).

(2) the monitoring function of ventilator the monitoring function of ventilator is one of the key links to determine the grade of ventilator. The perfect monitoring function of ventilator is an important prerequisite for the realization of ventilator's adaptability to the pathophysiological changes of patients' lungs. It is not only necessary to display the values of conventional ventilation and lung mechanical parameters, such as VTE, VT, R, C, F, airway temperature, FiO2, PP resistance K, P, PN-1, VA, valeak, I: e, but also to further display: (1) Pressure time, capacity time, flow rate time curve can be displayed on a single screen or at the same time. (2) The output of VD / VTE and CO2 were calculated. (3) Monitoring the tracing of the curve rings of paw-v, v-flow, flow paw, v-co2, pch-v, flow PCH, etc. (4) Trend review (24-48 hours). (5) Logbook is the review of ventilator application event settings. (6) Calibration function, including CO2, flow, O2 calibration. (7) Ventilation and settings of various functions: volume, different combinations of screen display, arbitrary ventilation mode selection (more than 10 common modes), multiple voice settings, etc. (8) The ventilator allows the user to trace the P-V curve [1,2,3 J] with low flow rate method to further understand the static compliance (c), resistance (R) and endogenous peep (PEEPi). The curve can be used to calculate the upper and lower inflexion points, the complex tensor, and print the record with the computer online. (9) The ventilator integrates other devices (respiratory mechanics monitor "Bi core") to enhance the solution of the problem that the respiratory parameters alone cannot be understood during the ventilation process, such as respiratory mechanics monitoring, placement of esophageal pressure, intragastric pressure monitoring to understand the trans pulmonary pressure, trans diaphragmatic pressure and dynamic auto peep, which can further clarify the status of respiratory mechanics and provide scientific research space for clinical doctors. (10) After years of clinical practice, foreign ventilator manufacturers timely integrate some useful parameters such as RVR, MIP, po.1, PLP, Au grid P into the monitoring system to provide basis for the adjustment and offline setting of clinicians. In recent years, the automatic off-line mode has risen quietly ﹐ 5.5. The ventilator integrates the important parameters, body weight, ideal ventilation parameters and BGA of patients, improves the level of mechanical ventilation, and shortens the time of taking the ventilator. In a word, the computerization and networking of ventilator provide a scientific research platform for mechanical ventilation and promote the development of the application level of mechanical ventilation.

The development of ventilator mode is an important manifestation of ventilator level. Whether the ventilator is volume control or pressure control, it will lead to ventilator-induced lung inj ~ y in varying degrees VILI) E3], in recent years, many basic and clinical researches have been made abroad in this field, and significant reforms have been made on the basis of the original IPPV, IMV, SIMV, PSV, etc. many studies have shown that the independent mode of pressure can well realize the non protective strategy, minimize the occurrence of VILI, and further expand the role of ventilator as a clinical treatment means. (1) Today's ventilator application from newborn to adult, only need to replace humidifier and pipeline; mechanical ventilation from non-invasive to invasive, non-invasive ventilation has strong air leakage compensation. (2) In the volume control ventilation mode, the increase of autoflow or flow by can increase the patients' autonomy, reduce airway pressure, increase patients' comfort, and overcome the shortcomings of volume ventilation mode. (3) The response time of ventilator (30-40ms), the air supply waveform (square wave constant current, deceleration wave), the trigger sensitivity is that the flow rate trigger is adjustable, the pressure trigger is abandoned, and the breath sensitivity (es. End) of PSV mode is adjustable. Under the monitoring of ventilator, it is easy for clinicians to adjust the patient's ESEM, so as to solve the human-computer interaction mode, which can minimize the interference on cardiopulmonary function and the occurrence of VILI. (4) International clinical practice further confirmed that pressure ventilation is superior to volume control in maintaining positive airway pressure, reducing cardiopulmonary interference, improving oxygenation, and minimizing the occurrence of VILI. On the basis of PCV, BiPAP / PS and APRV have been launched in recent years. In particular, BiPAP ventilation mode is used by many ventilator manufacturers for its pressure control, good man-machine coordination, and universal ventilation mode. It is named bilevel, DUOPAP and other different names. (5) Autonomous ventilation and closed-loop ventilation: the experimental and clinical application shows that the control ventilation time is shortened to the greatest extent, so as to minimize the occurrence of VILI, and to shorten the on-board time. Many studies have shown that autonomic breathing has many advantages, which is conducive to the recovery of patients' physiological changes. For autonomic breathing, it is no longer a simple spin mode in the past, but a servo mode and closed-loop ventilation mode. The biggest advantage is that the output information in the system can be accurately controlled. It can reach steady state quickly under the premise of zero error, and can eliminate all kinds of external interference. The mechanical ventilation technology based on the closed-loop control principle can be quite simple or complex. The simplest closed-loop control is to control an output variable according to the input information, such as PSV. The relatively complex closed-loop control can continuously control multiple output variables according to multiple input information. Dual control is to control the output pressure and volume synchronously in one ventilation or each ventilation. The ventilation technology based on the principle of dual control in one ventilation has capacity guaranteed pressure support ventilation (Ⅵ) and pressure amplification (PA). The ventilation goal is to reduce the inspiratory work of patients on the premise of ensuring the minimum inspiratory tidal volume and minute ventilation volume. The other aspects include: PRVC, autoflow, VTPC (volume calibration pressure control). The technical principle is that the ventilator will exhale with the patients.