sCMV, A/C(Volume)(synchronized Control Mechanical Ventilation, Volume Assisted Ventilation, ASSIST/CONTROL)
( figure ; The wave form of CMV
: in this ventilatory mode, ventilatory parameters are prescribed mechanically to the patient as, inspiratory flow rate, inspiratory time, inspiratory pose, expiratory time.
1. The concept and the purpose
The sure and rational ventilation can be provided if a patient being ventilated with intended parameters such as, fixed inspiratory time, fixed inspiratory gas flow rate, fixed inspiratory pose time, fixed expiratory time in mechanical positive pressure ventilationt. This kind of ventilatory mode is called CMV (Controlled Mechanical Ventilation, the mechanical mandatory ventilation). However, the problem of "stress of the patient" and "Fighting against the ventilator" may occur when you adapt this kind of ventilation to the patient who has a enough spontaneous-ventilation. To solve this problem, the technique was developed to decrease these faults by starting a mechanical mandatory ventilation synchronized with the beginning of the spontaneous-ventilation. This is called synchronized CMV. It sometimes expresses as, assisted CMV, triggered CMV, too.
Generally in Europe, the term of synchronized CMV is used for volume controlled mandatory ventilation. In other words, it is the concept that the mechanical controlled-ventilation synchronizes with the beginning of the spontaneous-ventilation is still in inside of the category of CMV persistently. It should be added, generally, the inspiratory pose time should be added, and lack of the pause time shold be regarded as meaningless. In this concept, it is accepted for you, not to expect a synchronism with the spontaneous-ventilation and "sedation" might be crucial in certain degree .
Genelally in America, on the other hand, it aims to coexist with the spontaneous-ventilation in not being particular about the concept of the mechanical controlled-ventilation. They Interprete the concept of volume controlled ventilation (Volume Ventilation) flexibly and adjusting it to the pattern of the spontaneous-ventilation of the patient. It is standard, to regard inspiratory pose time as being the cause of "Fighting", to regard it be harmful, to adopt inspiratory pause time only in the necessary time. There are a mechanism by which a patient is permitted to inspire inspiratory gas, that exceeds above the setted inspiratory gas flow rate, that exceeds above the setted inspiratory time. The decelalationg wave is a inovation to provide volume ventilation to a patient with enough spontaneous ability in flexible way. These ventilatory modes are termed as Assisted Volume Ventilation, Volume Assisted Breath, Mandatory Volume Breath, ASSIST/CONTROL, A/C(Volume) and so on. Recently, termination of A/C(Volume) is being increased according to the classification of the mode
Generally in North Europe(specifically the Siemens Inc.), they essentially use the term "CMV" as controlled mechanical ventilation, but recently, the American market gain in the business weight, that tthey adopt flexibility to their CMV ventilation. This kind of mandatory ventilation is termed as Volume Control Ventilation(VCV), that is the opposite termination of Pressure contorl Ventilation(PCV).
[Reference 1] Controlled Mechanical Ventilation and Contineous Mandatory Ventilation
The abbreviation of both words are CMV together. In the past, the concept of the former and the latter are resembled often (they are both volume ventilation, and A/C), and they are often confused. A term "CMV" is sometimes used as the mandatory volume ventilation in SIMV too. This encouraged the confuse in the concept of CMV !
If expressing correctly, the former means the volume cycled mandatory ventilation that is widely used in as a breathing mode in anesthesia. sCMV (which is the development type of CMV) were the 1st choice in the intensive care field, on a time in the past The classic sCMV is adaptated only in the limited case, because you can apply more supreme ventilatory mode (PRVC, AutoFlow and so on) in present.
The latter is the oposite term against Intemittent Mandatory Ventilation(IMV). The inevitability which distinguishes between the both terms has sternly occurred because the ventilation mode which do not use the classic CMV for the mandatory volume ventilation in SIMV mode were developed recently. The use of VAPS and AutoFlow, PCV, PRVC was popular in up-to date ventilatory management.
2. The component
1) The trigger mechanism
The trigger formula has three kinds of (1)pressure, (2)flow rates, (3)volumes. For the details, you should refer to the chapter of "trigger mechanism".
Because the trigger window is prepared in all span, if there is a problem in the respiratory center of the patient, a hyperventilation may occor. There is a model that have provided a refractory period for not to do a re-trigger immediately following the mandatory ventilation. If there is no trigger, the following mandatory ventilation stated if when it exceed the CMV cycle time (the 60-second/setting breathing rate).
2) The inspiratory gas flow rate
An inspiratory gas flow rate is fixed in the " taking air quantity of ventilation/at inspiratory time ". If there is time which is less temporarily than the required amount of the "SEYO"患 person, the patient feels choking. Also, it increases an inspiratory work volume. In this case, the airway pressure becomes a negative pressure. It increases pressure when there are too many inspiratory gas flow rates oppositely and it causes the extraordinary rise of the airway pressure.
3) The inspiratory time
It makes feel choking when the inspiratory time is shorter than the proper rhythm of the patient and it causes the tachypn ea. In some cases, it causes double cycling by the re-trigger and it sometimes wakes up Fighting, too. However, in the inspiratory time, it causes Fighting even if it is too long. But, if a taking air quantity of ventilation is sufficiently satisfied, the synchronism with the patient is better than the one that the one with the shorter inspiratory time is longer.
4) The inspiratory corrugation
A dwindling wave, a climbing-pulse, a square wave, a signature wave are prepared but as for being general, a square wave and a dwindling wave are used. In the past, the square wave was average but the model which standardized on a dwindling wave by dwindling wave's recently bringing about the effect which is equal to PCV because it was ideal more, too, appears (T Bird of the Bird Inc.). The signature wave is the corrugation which is near the spontaneous-ventilation pattern but clinical evaluation about the positive pressure type ventilation law isn't established. There seems to be permitted to be quantity ventilation to ventilate in the inspiratory corrugated pattern (fixing the shape of the dwindling from the pulmonary compliance and the airway resistance value) which imitated PCV but coming to practical use isn't done. But this should become the same as PRVC theoretically in the ideal state Because the ventilation can be provided without using feedback servo control when seeing from the viewpoint of the control system, there is an advantage which that inspiratory gas is delayed to the tachypn ea can provide ventilation with little good response for.
5) The taking air quantity of ventilation
It raises up a re-trigger immediately after the inspiratory-phase ends if less than the required amount of the patient. It causes Fighting if surplus. The required amount of the patient changes to the troublesome thing.
6) The inspiratory pose
As the means of improving oxygenation ability, it closes an inspiratory valve and an exhalation-valve in the end of the end-of-suction and it maintains them as the inspiratory condition. The pulmonary static-compliance can be measured in this period. At the equipment which is made in the Europe, the inspiratory pose is the option handling is always added but to add it only at the necessary time at the equipment which is made in America.
7) The expiratory-phase
ZEEP or PEEP is added.
3. The control method
There are a mechanical method, a new Mattick method, an electronic circuit method, a microprocessor method. At present, the microprocessor method is mainstream.
4. The advantage and the fault
There is an advantage that the sure air quantity of ventilation can be secured but it is a fault that that Fighting occurs makes synchronize with the proper rhythm (expiration's beginning specifically) of the patient difficultly to the patient who has a spontaneous-ventilation. Also, there is possibility to cause a hyperventilation because of the respiratory center fault and the psychological reason. The peak airway pressure is high compared with PCV if being the same air quantity of ventilation. PSV(Pressure Support Ventilation) The average airway pressure, too, tends to become high because it is difficult to get the cooperation of the patient when comparing.
[Reference 2] The synchronization of the mandatory ventilation and patient breathing
To solve this problem, inspiratory gas flow rate revision feature (Servo 900, Servo 300, Bear 3, Bear 5, Erica, Elvira) and the corrugated control of inspiratory, the setting of a refractory period, the development of the SIMV mechanism were done (To divide at the time of SIMV compromises with the mechanical ventilation).
To evaluate the advantage of the 従量 type ventilation in Americanism, to copy the inspiratory pattern of the patient by the category of the quantity ventilation and to suppress a peak airway pressure, the techniques such as the use of the dwindling wave and the control of the inspiratory gas flow rate generalized. On the other hand, the Siemens-Elema Inc. in North Europe developed the same purpose to improve the fault of CMV in the direction which uses PCV for the mandatory ventilation. PRVC is this result. America however, recently, it evaluated PCV and PCV became loaded into the equipment which is made in America, too. Moreover, new mandatory ventilation modes such as PSV, and Pressure Augumentation (the Bear Inc.) and VAPS (the Bird Inc.), AutoFlow (the Drager Inc.) which repeated quantity ventilation, too, are proposed.
[Reference 3] The spontaneous-ventilation and the trim to make side
To confirm the synchronism of the spontaneous-ventilation and the mechanical artificial ventilation, the monitor by the graphic display with pressure, flow, volume is indispensable.
In the compulsion quantity ventilation, it makes an inspiratory load when the setting inspiratory flow rates are fewer than the inspiratory flow rates of the patient and it isn't always possible to reach in the purpose of the artificial ventilation. If approximate to that, it thinks that the synchronism is good but if a sudden rise is shown to the end, there is possibility to be surplus and in PCV of inspiratory-pressure's changing smoothly compared with the required amount of the patient in the taking air quantity of ventilation. If there is not a rise of the pressure in the early stages of inspiratory, the possibility that the efficiency of the ventilation help is bad is suggested. If the change of the air quantity of ventilation and the inspiratory time is big in each ventilation aspect of SIMV, there is possibility that the setting of the SIMV number of times and the taking air quantity of ventilation by the PSV level, the mandatory ventilation are improper.
If the ending of the inspiratory flow and the ending of the inspiratory time are synchronous in the compulsion pressure ventilation, it thinks that the synchronism is good. In this case, the pressure pattern draws a smooth square wave. If the inspiratory flow lasts in the end of the inspiratory time, the efficiency of the ventilation is bad and can not be called valid pressure ventilation. If the inspiratory time lasts for the inspiratory flow to have ended oppositely, it becomes the compulsion of the unnecessary inspiratory time and it compromises the advantage of the pressure ventilation. The change of the taking air quantity of ventilation has the possibility that the setting of a ventilating-pressure is improper. (By PSV inside the time of the PCV mode in PC-SIMV after PCV ventilation) The phenomenon that the taking air quantity of ventilation decreases gradually and that it changes periodically has the possibility that the patient is weary because there is too much little setting of a ventilating-pressure and there is too much little number of times of PC-SIMV in it.