NAVA(Neurally Adjusted Ventilatory Assist)
1. The concept and the purpose (Figure ; Supplmentary of diaphragm line fast charge)
The idea which takes the muscle-potential of the diaphragm and moves a resuscitator was told by a lot of clinicians and engineers as "the dream of the next generation" but realistically, it didn't result in the coming to practical use readily. It became in 2006 and it was gradually practicalized as the mode, NAVA, in Servo i. The fact where the resuscitator which can control pressure ventilation freely by the electronic signal as the technical background of NAVA spread can not be ignored. NAVA means "breathing help which is controlled by the nerve" but the fact is the mode to give an airway pressure according to the amplitude of vibration (abbreviated with Edi or EAdi) of the muscle-potential of the diaphragm. It is adding an inspiratory-pressure with the value which hung constant amplification degree on the voltage of the muscle-potential as the technique to the PEEP pressure. Because the change of the airway pressure and the intake flow is the phenomenon which occurs after the respiratory muscle works, it becomes for breathing to have been able to be taken in the step with the earliness of one step by taking the muscle-potential of the respiratory muscle. In addition to NAVA's being the means of merely getting a trigger signal, with the size of the muscle-potential, the place to change an airway pressure realtime is peculiar. When the degree of the shrinkage of the respiratory muscle increases, the airway pressure, too, is an increasing mode. Edi is remarkable as the parameter which evaluates respiratory condition, too. In the meaning that the ventilation help follows faithfully to the request of the respiratory center, there is a side which has the characteristic which resembled PAV in NAVA.
2. The component
1) The sensing
It takes the activity of the respiratory muscle as the electric signal. Generally, the gullet catheter which combines an NG tube is used.
2) The information processing
It processes an electronic signal in the change to the form which is available to control a resuscitator.
3) The drive of the respiratory organs
It drives a resuscitator for the airway pressure to change according to the size with the potential of Edi. In the present situation, it uses Servo i. There is danger which is ornamented to the performance of Servo i in the evaluation of NAVA. In the future, if a license is supplied to the other manufacturer, the possibility of NAVA can be objectively evaluated right.
3. The control system
1) The controlling mechanism
It is done in MPU.
2) The operation theory (The figure of Edi and the airway pressure)
It equalizes (filtering processing) the action potential of Edi, or EAdi and the expressed diaphragm as the absolute value, and it spends electric amplification on the gotten voltage signal and it makes the reference signal of the inspiratory-pressure. If expressing processing around here in the notion, it imagines the VU meter which shows the strength of the sound to record which the tape recorder has and it is easy-to-understand if it is possible to get. Sound itself is the alternating current signal which contains a different frequency component but as for the movement of the meter, the amplitude of vibration of the meter is fixed by the size with sound wave energy. In NAVA, the strength of the sound corresponds to the action potential of the diaphragm. It should be possible to get by thinking that the amplitude of vibration of the VU meter changes an airway pressure. Actually, processing with a variety at the VU meter, too, is done. Which frequency does it think much of or there are a filter characteristic, logarithm processing, acceleration processing, delay processing, peak maintenance processing, equalization processing to the amplitude of vibration and so on.
4. The modification element
1) The means of taking the muscle-potential of the respiratory muscle
There are a transcutaneous sensor, a sutra gullet sensor, a direct line sensor and so on. NAVA catches the electromyogram of the diaphragm using the gullet sensor which combines a canal-of-stomach. Yet, there is room of the improvement about the shape of the sensor and the technique to fix the position of the pole. The success of NAVA is influenced by patient's making abdominal respiration main constituent or making thoracic respiration main constituent.
2) The linear fast charge signal conditioning
To avoid malfunction, filtering processing is indispensable. It chooses the signal of which frequency band, and it considers a noise level about delay by the time constant with which degree to spend and however of cutting, and so on, the signal to the constant strength is the point of the signal conditioning. In the present situation, it expects that the sensor of NAVA will be the processing of a cardiograph and similarity because it senses an electrocardiogram, too.
3) The amplification degree
The amplification degree which fixes correlation between the muscle-potential and the airway pressure is the important control index of NAVA. It makes an amplifying characteristic, too, linear, it does in the index function, it uses another function or there is a different alternative. In NAVA, a plateau law is recommended as the technique to fix best amplification degree but this resembles to use runaway phenomenon to fix a gain in PAV. Possible about the other way, too, in the future
4) The processing at the time of the NAVA maladjustment
As the processing when the muscle-potential can not be taken, it operates anaerosis back-up ventilation and PSV and PCV are used. Possible in the other method about this, too
5) The make-able expiration
It mistakes a muscle-potential because of the expiration (such as) the status(, e.g. the asthma) which has make-able expiration for intake and it malfunctions. The movement of the other involuntary muscle, too, can become the factor of the malfunction.
6) The end-of-suction end recognition condition
Theoretically, it makes recognize a trigger and a termination like PSV and it is changing the intake and the expiration of the resuscitator intentionally because to recognize intake beginning and end-of-suction end isn't necessary but there is a problem of the noise in NAVA actually. Such supplementary processing, too, is the element which influences the performance of NAVA.
5. The advantage and the fault
A. The advantage
1) The forgiveness to the leak
The biggest advantage of NAVA is a forgiveness to the leak. Because the sensing takes the move of the respiratory muscle of the diaphragm purely, it doesn't undergo influence even if there is a leak in the patient circuit. It is possible for low invasion "NAAKUSESU" not to depend on the tracheal-intubations such as nose mosquito Nyura and pernasality trachea mosquito Nyura for to ventilate, too. Therefore, NIV is the best adaptation of NAVA. Because it doesn't need the acquirement of the patient like general NIV, it becomes for NIV to have been able to be more easily introduced.
2) The synchronism and the response
The uniqueness of NAVA lies in the point which is excellent about the synchronism with the respiratory-pattern of the patient. Because the ventilation help efficiency is good, the ventilation help to the patient finishes in the least. Therefore, the weaning, too, is early. Another is to do the improving of the response to patient breathing. It is possible to reply, moreover, that 10ms-100 ms are earlier than to detect the change of the pressure and the flow theoretically. Therefore, "the newborn baby of the tachypn ea" that the delay becomes a problem becomes good adaptation. However, at the adult that the delay doesn't become a problem too much, little beneficence occurs.
3) The index of breathing
In the stable ventilation, the strength, the rhythm, the baseline of Edi are stable. The strength of Edi, and the rhythm, "BE"-"SURAIN" are loose when the problem is in the ventilation condition oppositely and becomes make-ability breathing. Therefore, to monitor Edi becomes the good index which evaluates respiratory condition. Best PEEP and the good guideline which fixes ventilation setting can be gotten by the Edi monitor. However, it isn't synonymous with NAVA's being a best ventilation mode with being the index which Edi may make a monitoring-respiration. However, even if it doesn't depend on Edi, because total carbon dioxide emission quantity is correlated with the energy consumption, it is possible for the information on the expiration CO2 monitor to evaluate in the same way.
4) The forgiveness to the exaggerated assist
In PSV, the exaggerated assist changes PSV into the more compulsory character and compromising a synchronism to the expiration beginning by it Therefore, it says that PSV by the high pressure isn't practical and that PCV is good for it if anything in the case. On the other hand, in NAVA, the exaggerated assist becomes a problem hardly.
It says that voluntary SIGH of the patient is possible in NAVA but the point which can be SIGH by the will of the patient even if it is NAVA and it is PSV is the same. Even if SIGH happens in PSV, the airway pressure doesn't change. However, in the intake time, it extends and the intake flow rate and the air quantity of ventilation, too, are increasing. The auxiliary form of the ventilation is merely different only.
6) The simple of the setting
Because the item which NAVA sets is only gain, it is very simple. Because there are many items such as the pressure, the intake time, the air quantity of ventilation to set in the conventional ventilation mode, there is danger which these have been improperly set to. Moreover, because NAVA is tolerant to the exaggerated assist, too, it can do appropriate setting easily.
B. The fault
1) The fragilitas of the sensing
To take the activity of the respiratory muscle with the electromyogram, it sometimes malfunctions with the movement of the other muscle. The fragility of the sensings such as the heave and the cough, the difference of the sensing catheter by body is a maximum fault.
2) The theoretical problem
Theoretically, because NAVA is the mode which operates as the slave of the respiratory center like PAV, it is unsuitable for the clinical condition that the respiratory centers such as the respiratory-care behind the art don't function normally. Also, the clinical condition must be stable, to be certain degree of. The ability for the respiratory center to be able to control breathing doesn't become adaptable in case of not being. The adaptation is limited like PAV and is the theoretical defect of NAVA. Also, because PCV "NADO" is ideal more to improve that the pulmonary can of oxygen is done, it is unsuitable for the diseased lung.