Initiating NAVA mode
In NAVA mode, the patient controls tidal volume and respiratory pattern.
​Initially set the NAVA level to 1. Allow the signal to stabilize over several breaths. An Edi of 5-20 uV would be the recommended target, although this will need to
A typical NAVA level would be 0.5 - 3.0 cm H2O of pressure support per uV of neural drive.​
Alternatively use the ECG locator window to allow the NAVA level to be previewed. The expected NAVA delivery can be compared with the current pressure delivery. An example of this is shown below in the case studies.
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Setting initial NAVA level
Transitioning from NAVA monitoring to NAVA mode
Patients will find the NAVA generally comfortable and well tolerated. In general transitioning to NAVA is usually simple and straightforward.
When ICU staff understand that NAVA represents a synchronised form of pressure support they become more willing to adopt this mode.
In NAVA, all breathing efforts are supported with less asynchrony which means the respiratory rate may be observed to increase, but the patient's respiratory rate will not be increased-in NAVA there are just no 'missed' breaths. There may also be less lung and diaphragmatic injury than with other support modes with more physiological gas distribution. The mode may reduce the risk of over- and under- assist from the ventilator.
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When initiating NAVA, the level can be set at 1.0 cm H2O pressure support per uV of neural drive. In patients with stable neural drive, this will provide similar levels of pressure support, to those given when pressure support is commenced at 15-20 cm water above PEEP (typical starting pressure support settings).
The NAVA level then up or down-titrated, a bit like setting the initial value of pressure support, where you start with an estimate of support patient might need and then titrate up/down by looking at the patient and the ventilator.
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Another method is to use the NAVA preview screen, which allows different NAVA levels to be set ('previewed') against the current mode of support, to predict the likely best opening NAVA level. This is shown here, where a NAVA level of 0.6 is selected. The patient is then transitioned without difficulty from pressure support into NAVA.
Patient transitions from Pressure Support to NAVA. The NAVA level is previewed and adjusted prior to initiating NAVA. The patient tolerated the transition from Pressure Support to NAVA uneventfully and was weaned using NAVA.
Patient with ARDS - ventilating in pressure control. The ECG positioning tool was used to indicate the nasogastric tube needed to be advanced. Then NAVA was established and neural drive increased as respiratory load being delivered by ventilator was reduced. Very easy transition: no issues reported by bedside nurses.
Patient with ARDS - ventilating in pressure control using PRVC. Very high Edi (>40uV). Very easy transition: no issues reported by bedside nurses. Because the Edi was very high, the NAVA level was set low. Of note, the patient could not tolerate pressure support but did tolerate NAVA. Further, it had not been possible to reduce sedation in pressure support, but in NAVA mode as sedation came down, Edi also reduced.
Patient with ARDS - recruited in APRV and then transitioned to NAVA. Very easy transition - no issues reported by bedside nurses.
Patient with cardiac failure and muscle weakness, had low neural drive when Edi catheter placed. The low neural drive signal gave an unreliable location. Occasional ECG strikes could be seen indicating catheter not actually in far enough. Advanced 5 cm from 65cm to 70cm and neural drive became immediately clear. The patient was then placed in NAVA without difficulty-the initial NAVA level was set against the existing pressure-support breath. This highlighted the importance of considering neural catheter position if drive appears flat. It also highlighted that if the neural drive signal is flat, occasional pink strikes on ECG positioning tool, may be unreliable, perhaps originating from background.
Patient with recovering ARDS and barotrauma (pneumothorax), delirium and ongoing sepsis. High spontaneous ventilatory drive.
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Overlay and positioning tool reviewed to demonstrate potential benefits of NAVA (improved synchrony) and how to determine the starting level of NAVA gain (in this case 1). When the NAVA level went below this the Edi rose steeply. Above a NAVA gain of 1.5 there were no advantages. The main issue appeared to be a high central ventilatory drive. NAVA appeared to provide a better spontaneous support mode than conventional pressure support. Transition from pressure support was reported to be uneventful and well tolerated by the patient. NAVA was assessed as being at least as effective as pressure support in this patient.
Patient with tracheostomy and speaking valve-he found it more comfortable to use the speaking valve in NAVA than when in pressure support. Despite a spinal cord injury at C5-6 he was generally significantly more comfortable in NAVA than pressure support.
Patient with severe bullous emphysema and viral community-acquired pneumonia. Could not be ventilated with conventional pressure support. Uncomplicated transition to NAVA.
