PAV(Proportional Assist Ventilation),PPS
1. The concept and the purpose (Figure ; PAV) (Figure ; Volume gain : Excerpting from the instruction of EvitaXL) (Figure ; Flow gain : Excerpting from the instruction of EvitaXL)
The pressure P which is necessary that it is possible to swell a lung when there is an intake process when ventilating a lung by mechanical active-ventilation (CMV)VENTIt is shown by the type below "HA".
But, it is Ers : The pulmonary elasticity.
V : The capacity of the lung
Rrs : The resistance of the respiratory system
V' : The respiratory tract gas flow rate
Temporarily, in the lung, according to the actual measurement of V and V', it is P.VENTOnly it is decreased by the intake work volume if pressurizing at several % of pressure which is and helping in the ventilation. PVENTIt calls (a relative) gain in the ratio of the actual ventilating-pressure which does a boiling pair and the rate of the ventilation help of PAV changes according to the gain. A gain to Ers*V is called a volume gain and a gain to Rrs*V' is called a flow gain. However, if the gain is 1.0, at the simple model lung, which condition (the aspect) is stable in the condition as it bulged with the volume in that case. Even if the patient does intake and expiration from this condition, the work volume of the patient is helped to become 0. A machine is burdened only with the half of the work which is necessary for intake and the expiration if the gain is 0.5 temporarily. It is named "to be proportional" because it helps work at the constant rate to the necessary work in this way. This ventilation form is the mode that the optional degree of the spontaneous-respiration and the active-ventilation can be chosen theoretically. However, because there is a limit in the gain which can be set as following, it functions as the spontaneous-respiration mode to reduce breathing work volume in the condition which kept a spontaneous-respiration like PSV. Therefore, PAV isn't independent and it will be rational to use as SIMV+PAV instead of SIMV+PSV.
2. The component of PAV
1) The gain
A gain is always set to equal to or less than 1.0. In equal to or more than 1.0 setting, the system crashes (called RunAway) and the lung of the patient expands to the inspiratory-capacity. Because the actual lung doesn't always become as Ers and Rrs as the theory, it expects to be safe and equal to or less than 0.8 values are used as the empirical figure. Only the part is decreased about the possibility of PAV, too, because the gain which can be set in this way is limited.
2) The measurement of Ers and Rrs
Only the human being who reacts with the object having will resembles and difficulty is always accompanied by the measurement with these correct values. Also, be expressed by the simpler model actual Ers and Rrs can, they the simpler aren't. These on it must update in the regular interval because they change with the passage of time.
a) The measurement of Ers
At present, two measuring methods of Ers are proposed. As for one, by the intake fold law, by the ventilation with CMV or PAV, it provides a pose for the end of the end-of-suction and it measures Ers. It becomes Ers=(plateau pressure.-PEEP)/Vt. The system wakes up RunAway when exceeding peculiar Ers of the patient and the intake time and the taking air quantity of ventilation increase remarkably when another is called RunAway law and raises a gain (the absolute value) from the low value. The value of this switchover point is Ers.
b) The measurement of Rrs
Rrs can be fixed in (peak pressure-plateau pressure)/Vt. But, the resistance of the tracheal tube must be beforehand excluded beforehand. Because the resistance of the tracheal tube is constant with the tube size, it can use the fixed value to measure beforehand beforehand. However, Rrs, too, can fix RunAway law.
3) The back-up mechanism
The higher it makes a gain, system crash (RunAway) is a more inevitable problem and indispensable the safety-play is. Also, because the existence of the spontaneous-respiration is a presupposition about PAV, the back-up mechanism to the anaerosis, too, is indispensable. The intake time limit as the safety-play, the intake volume limitation, the inspiratory-pressure limitation in the present, SIMV and PCV and then, and then, in it, a back-up mechanism by A/C(Volume) is proposed to the anaerosis and the low expired volume per minute.
4) The performance of C-system
The the shorter the driver reaction time of the system is, the more V which can be also measured is highly precise, the the bigger the maximum intake gas flow rate which can flatter is, the better the reliability of the system becomes. Empirically, at the adult, it is an equal to or less than 100-ms driver reaction time, 12 The float rigger sensitivity below LPM, 180 It says that the intake gas supply ability above LPM is desirable.
3. The control system
1) The controlling mechanism
The option can be had at BiPAP Vision of the Respironics Inc. and Evita4 of the Drager Inc., and so on 840 of the Bennett Inc.. Any model is MPU control system.
2) The control-theory
PAV is breathing mode to help the any percent to breathing work which the patient does. In other words, the resuscitator where PAV moves operates to read the signal (the signal which tries to move a respiratory muscle) which the respiratory center outputs in the movement coming of the respiratory muscle (the respiratory organs), and to amplify this and to help the move of the respiratory muscle at the respiratory organs and operates as the respiratory muscle power amplifier. Input signal however, load however, for the PAV resuscitator, there are respiratory organs of the patient, being. The unstable loop that the output of itself becomes an entry just as it is is made. Because a peculiar resonant frequency is fixed by the gain of the amplifier, and the characteristic, the characteristic of the load, it becomes an oscillator when the amplification degree exceeds a constant value. This condition can be provided with RunAway.
(Figure ; Feed Back in PAV)
It is the respiratory center that fixes an air quantity of ventilation and an air changes per hour, and the respiratory center receives a feedback-signal to the result of the ventilation from the living body sensor of patient himself and is correcting an error. Therefore, PAV can be expressed with one kind of the feedforward regulations. The feedforward regulation needs the following condition to be stable and to operate.
a) The feed-back-control mechanism functions right.
The respiratory center of the patient functions right and can react right to the hypoventilation and the hyperventilation, oxygen and the carbon dioxide, the pH in the arterial blood. The within-the-limits which the resuscitator system assumed has the characteristic of the respiratory organs.
b) Be reading the signal of the respiratory center right.
If supposing that the respiratory organs move about the signal of the respiratory center, it catches a resuscitator. As the technique to grasp the signal of the respiratory center specifically, it assumes that the lung of the patient is a model lung and it computes breathing work by the numerical formula which used pulmonary elasticity (Ers) and the resistance (Rrs) of the respiratory system. Then, it handles Ers and Rrs as the fixed number. However, at the actual patient, even if it is an identical patient, the intake quantity changes the value of Ers. Rrs, too, is never constant. Then, these change with the passage of time. To take breathing work of the patient correctly in this way is a defect on the principle which the PAV theory has in this difficultly.
c) The balance with feedback gain and the gain of the feed foward is in the appropriate range.
As for the feedback servo loop which exists between the respiratory center and the respiratory organs of the patient, it is "SONO". It does a the system-wide gain and the feedback gain of it in the quantification. It is very difficult but it is possible to estimate that the feedback gain which the living body has more than that the maximum gain of which PAV on being clinical is stable and it operates is about 80% is the degree which is higher a little than in 80% of gain values. It is RunAway in the condition which makes the gain of PAV high too much.
d) The driver reaction time of the feedforward regulation is shorter than the driver reaction time of the feed-back-control.
If a feed foward is delayed in that the reaction of the feed foward is more remarkable than the reaction of the whole respiration through systems of the patient and the lateness of it, the system becomes unstable and in some cases, it generates oscillation. It is possible to estimate that this, too, is 1 form of RunAway but this condition isn't defined by RunAway in PAV. However, a lot of clinicians are observing that the driver reaction time and the maximum intake gas supply ability of the resuscitator can not follow most patient often. As for marketing receptacle's not being readily sold in spite of PAV's being proposed and being passing long, the thing for which it was difficult to conquer these points, too, is cause.
4. The advantage and the fault
1) The setting of a parameter
PSV becomes a discussion by how to fix the optimal value of the end-of-suction end condition or how to fix the optimal value of the PSV level. In CMV however in the same way the intake time, the intake volume, the air changes per hour, the way of fixing "WO" By of ( which doesn't have the protocol which anyone can consent to concerned however the graphic display ) which feels that that a lot of clinicians fix these values empirically of the ventilatory-pattern of the patient is not a so difficult problem if the monitor is clear On the other hand, there is not such a problem in PAV theoretically. That the taking air quantity of ventilation, the intake time, the air changes per hour become an approximately constant value regardless of the value with gain on being clinical is observed. It explains that these values are the value which is peculiar to the patient which the patient wants and this, too, is said to that it does the advantage of PAV. The item which needs setting consequently in PAV is only a gain and the setting is simple. However, it isn't always possible to say sharpness about which value the best gain is. Moreover, it boils, and the volume gain and the flow gain are on about whether they set the gain that the one mentioned above 1 is desirable or that it is different and there is not broad knowledge.
2) The trigger mechanism
PAV is made more favorable about the malfunction of the trigger mechanism, too. There is an evil that the waking-up inspiratory-phase has begun malfunction in PSV and sCMV when making sensitivity high too much. There is necessity which suppresses sensitivity low necessitously to avoid this (However, it is solving this, too, recently by the device of filtering algorithm). Because it operates theoretically for the trigger mechanism to merely reduce a work volume to the change not necessary only, an artifact by the hiccup and the cadiac beat is rarely influenced to it in PAV.
3) The circuit leak
a) The inspiratory-phase
As for the inspiratory-phase, as for the leak of the patient circuit and the tracheal tube, it is easy for PAV to undergo influence. Because the intake or the leak of the patient can not be distinguished between, mistaking for the bigger intake effort when there is a leak, the resuscitator causes assist surplus (overassist) consequently. In the conventional ventilation mode which is represented by PCV and sCMV, the air quantity of ventilation decreases when there is a leak but PAV is one of the few modes that the air quantity of ventilation increases. As for this point, it hears that an advanced leak revision measure is accomplished in BiPAP Vision.
b) The expiratory-phase
On the other hand, if there is PEEP in the expiratory-phase, too, PAV has the lurk-ability which causes malfunction by the leak. This measure is to add a trigger condition to the beginning of the intake of PAV but this is big contradiction with the point at issue about the advantage of PAV to the malfunction of the 2) trigger mechanism oppositely.
This is the problem which is peculiar to PAV but it is easy the nearer the gain is 1, the more RunAway occurs. Around the early stages, in the gain, it was hearing that equal to or less than 0.5 was desirable but it is recommending to lay as 0.8 recently in the gain. However, this basis is empirical and feels a big doubt to the point at issue that the setting of 1) parameter is clear. If saying oppositely, there is not a sharp protocol that anyone can be consented to about the setting method with gain. Also, because a range with gain is necessitously limited, there is limitation in the ability to help intake, too. Therefore, it is a limit on the principle that there is a limit in the clinical application and that PAV has. The cause lies in the point that PAV theory is constructed based on the simple model theory, too.
It says that it is difficult for PAV to cause Auto-PEEP consequently because it operates to help breathing work to Auto-PEEP, too.
6) The application range
In PAV, the thing with the normal function of the respiratory center is a presupposition. Therefore, the patient with the function which isn't normal becomes tabooing. Moreover, the patient as the respiratory-acidosis progresses in spite of the management in appropriate PAV isn't suitable for PAV. Depending on the example, because there are few breathing work volumes (being zero if having made a controlled-respiration), to be adaptable to the disease which has the possibility that the increase of the work volume brings about an evil like the cardiac insufficiency and the angina in PAV, CMV needs note.
7) The airway pressure
The peak airway pressure of four ventilation modes (PCV, PSV, PAV, CMV) is identical to the theoretically identical taking air quantity of ventilation if the gain of PAV is near 1 boundlessly, the ventilation capacity of the patient is limitless and is near (PAV and PSV aren't formed if being zero) zero. In the resuscitator, if the same about the work volume to be burdened with, because PCV can be ventilated by the average airway pressure of PAV, the peak airway pressure is lower in PCV. However, when the ventilation capacity of the patient assumes a condition with certain degree, because the work volume which a resuscitator is burdened with, too, is the same if breathing work volume which a patient is burdened with is the same, the peak airway pressure is lower as expected in PCV than in PAV. On the other hand, because the gain of PAV can the higher the ventilation capacity of the patient is, the lower are set to CMV, PAV gets for the maximum airway pressure to be low according to the gain compared with CMV. It isn't possible to say that the maximum airway pressure will be low but than PCV that is lower compared with CMV PAV than PSV. Breathing work volume is shown at the area which was surrounded by the pressure and quantity curve. Žd in PAV
The thing quantity is the area of A+B. The work volume by PCV is the area of A+C. The area of both is equal. Of course, PCV becomes lower about the peak airway pressure. The PCV pressure is equal to the average airway pressure of PAV.
(Figure ; PV curve of PAV and PCV)
8) The characteristic of the ventilation
PCV and PSV are the mode that the gain becomes the value that the gain is about 1 gradually, exceeding 1 roughly in the early stages of intake if expressing in the PAV logic and declining with the passage of time finally but approaching the end of the end-of-suction. Therefore, in PSV, because it becomes exaggerated assist, there are much PCV and intake quantity in the early stages of intake in the early stages of intake compared with PAV. Therefore, the characteristic to be low comparatively is in the importance which resembles and is on and the fault, that the decision procedure of the end-of-suction end condition is ambiguous, doesn't become a so serious problem about at which time to do end-of-suction end in PCV and PSV.
9) The oxygenation ability
There is not a clinical dater which was compared about the improvement of the oxygenation ability but theoretically, the pressure ventilation is estimated to be more favorable.
10) The synchronism to the spontaneous-respiration
As for PSV, an end-of-suction end recognition condition, a control mechanism in the intake start-up time and so on are being improved and the synchronism with the spontaneous-respiration is improving. Likewise, because it is improving PAV, too, as for comparing both sweepingly, it is empty. Rather, it will should review this problem from the affinity with the active-ventilation mode to combine.
5. The evaluation of PAV
1) The comparison with the other ventilation mode
PAV was loaded into the different resuscitator and the clinical application became easy but when evaluative, being always high, it is in the saying difficulty. In other words, it is aroused, but the theoretical interest can not admit absolute advantage to the conventional ventilation mode and is a truth. The problem of RunAway that the decision procedure with the gain which the range which can be clinically applied as the reason is limited to isn't clear isn't solved. The one of the spontaneous-respiration which doesn't have advantage in the oxygenation ability like PCV that a malfunction to the leak isn't solved As the slave which is faithful to the intention of the respiratory center which is the ventilation law which presupposes existence There is always not a primariness which solves the essential problem which the conventional ventilation mode has in the "NADOGA" problem that the output is theoretically unstable C-system which returns to the entry which is an operating ventilation mode. The PAV mode is option handling in a lot of cases and the cost to have added a license fee to inevitably becomes need. There are few users who buy PAV about paying an expensive option fee because it isn't possible to find advantage on being clinical readily compared with the other ventilation mode. Moreover, the other ventilation mode has to do the favorable which can be used for the cheapness because the license fee is unnecessary for most.
2) The clinical adaptation
For the PAV ventilation to succeed, the following condition is indispensable. 1) The respiratory center of the patient functions right. 2) It is kept, that the patient certain degree of of the ventilation capacity is done and there is ability to reflect the function of the respiratory center. 3) The resuscitator can grasp breathing work of the patient correctly. The condition of 1)2) is the condition to be severe to a lot of patients who need an artificial respiration therapy. 3) is the condition which is severe on the resuscitator. If saying paradoxically, it is possible to say that the degree which the patient who receives an artificial respiration therapy needs in the artificial respiration therapy from the beginning if these conditions can be achieved was low, too. There is a characteristic the more ventilation requests (the air quantity of ventilation) of the patient there are in PAV, the more the ventilation help increases. The ventilation mode to have the characteristic which is the same as this was loaded into WEANY of the eye mosquito Inc. as AAV(Adaptive Assist Ventilation). Of this mode however, the SIMV number of times increases to the extent that the ventilation requests of the patient are many and also the taking air quantity of ventilation, too, increases. On the other hand, it is EMMV that is built by the opposite philosophy. This is the ventilation mode that the machine helps a part of patient's not being able to achieve to the set expired volume per minute. The ventilation help decreases when the ventilation request (the air quantity of ventilation) of the patient increases in EMMV. In other words, the responsibility which maintains an air quantity of ventilation in PAV and AAV is in the respiratory center of the patient and in EMMV, it is in the resuscitator. Therefore, in the independence of PAV from the operation theory, the respiratory muscle receives a fault in some cause but the patient (for example, are the patient of the muscular dystrophy and so on) that there is not a fault in the respiratory center and the respiratory organs will be good adaptation. In the chronic lung-disease, there is not a fault in the respiratory center and the respiratory muscle but the affinity with PAV may be good for the patient who the gas exchange ability in the lung has a fault. However, in the viewpoint, the low invasion of the therapeutic effect and the lung, the pressure ventilation like PCV will be rational more. In the future, it will should expand clinical adaptation by the mode to combine PAV and the other ventilation mode. For example, it has the possibility that it is possible to make up EMMV+PAV of, SIMV+PAV and then each of PAV/PSV which begins PAV and PSV at the same time like VAPS faults.