Getting the specialised
NAVA tube down safely
Key Message
The key message is that safe placement of ANY nasogastric tube is important. Malposition of a nasogastric tube especially within the airway is a never event. The enrolement of a patient in UK NAVA must never detract from this core principle.
Practical Approach
The NEX measurement allows the critical care team to place a nasogastric tube so that it can be used for feeding or drainage. As with standard feeding tubes, the NAVA catheter can be placed oro-gastrically - the NEX measurement must be adjusted accordingly. When using the NEX measurement, the healthcare professional inserting the NAVA catheter has to decide whether to use the NEX tool on the ventilator menu OR the coloured tool on the included tape measure.
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The internal ECG signal allows the position of the NAVA catheter to be fine tuned by small adjustments to the nasogastric tube. The latter may not be possible to use if there is no/minimal neural drive.
As with standard feeding tubes, the NAVA catheter can be placed orogastrically - the NEX measurement must be adjusted accordingly.
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Once the NEX measurement and internal ECG have permitted optimal location of the tube, the final length must be entered into the ventilator.
Perform cable function check - this will run automatically once the cable is connected to the module using the test connection which is attached to all cables. Essentially you are plugging the cable into itself to test that it is working correctly before you connect it to the nasogastric NAVA catheter in the patient. Sometimes the test connection port slides towards the ventilator and be difficult to locate.
The 'Edi Module test' that runs when the cable is plugged into itself is shown here (click on the image and wait a few seconds and you will see the self test happening on the screen). The NAVA catheter will function without this test but a warning message will continue to display.
Select the correct NAVA catheter size according to patient height. If you use the wrong catheter size, the electrodes across the diaphragm will not be correctly spaced for the size of the patient. For using the NAVA catheter insertion calculator the catheter size must be entered.
Either use the tape measure tool or the calculator on the ventilator to convert the NEX measurement to the insertion distance.
Once the Edi catheter is at the correct length by NEX measurement, it can be 'fine-tuned' by checking the internal ECG.
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QRS should be present in all 4 ECG leads. Ideally p waves should only be present in the upper two leads (closer to the heart). The QRS should become more negative as you go down the electrodes (because you are moving away from the heart).
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If neural drive is present, and the second and third leads are pink then the NAVA catheter is better positioned. If the upper two leads are pink then the catheter is in too far. If the lower two leads are pink then the catheter needs to be advanced.
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NEVER use the ECG locator tool to confirm the Edi catheter is in the oesophagus/stomach. This must only be done by the local ICU safety protocol.
The NAVA catheter positioning tool can be accessed from the main menu or from the 'quick link' and allows the position of the catheter and the initial neural drive to be set. If the neural drive is very flat, then the NAVA catheter may be completely outside the ECG detection window and the NEX position may need to be re-checked. As the position is adjusted, the neural drive will suddenly become very obvious. Of course a flat neural drive may also be due to over ventilation/over sedation/over oxygenation/phrenic nerve injury/brain-stem injury/high spinal cord injury. In this case the NAVA catheter is still not advanced enough because the neural drive is only being picked up on the lower NAVA electrodes.
Correctly located NAVA catheter
Case Study: what you see if NAVA catheter is inserted significantly too far. In this case the clinician advanced until a purple/pink 'neural drive' (actually artefact) was visible, but the electronics on the NAVA catheter were in the duodenum. The NEX measurement was significantly over-estimated (ear>xiphisternum was very short in reality). This emphasises the importance of doing basics well, and getting NEX measurement right, as well as having confidence that neural drive will display when the NAVA catheter is in the right place.
Case Study: Same patient with NEX remeasured and NAVA catheter pulled back. As you can see, the NAVA catheter is still in a little far (see the marker on the right hand side of the neural drive display. Although the Edipeak is 'similar' in magnitude, there is obviously a problem with the previous screen-the baseline is way too high.