FAQs

What is UK NAVA and why is it happening?

Half of all patients who require an admission to critical care, end up receiving invasive mechanical ventilation. UK NAVA aims to see if we can show that patients can be made more comfortable whilst receiving mechanical ventilation and whether we can help to get them of the ventilators faster. If we can get patients off ventilators faster then they may get less ventilator-induced lung injury and muscle injury (eg diaphragm wasting). They may also get less damage to their airways and less effects from sedation and global muscle wasting.
UK NAVA is a randomised trial that compares the use of NAVA technology to provide ventilatory support versus other standard ventilator modes without NAVA technology. Both treatments are approved methods for providing ventilatory support in the UK. The trial is 'open label' which means that ICU staff, patients and families can see which treatment a patient is getting.
The trial is important because there is a discrepancy between published evidence that suggests NAVA should be superior to standard pressure support, and its actual use. In addition, there are no adequately powered trials to confirm that NAVA technology is more effective than standard care. This includes knowing whether it helps patients in the long-term. We also want to see if NAVA technology saves money.

What is NAVA technology?

NAVA technology has two parts - it allows monitoring of a patient's neural drive (electrical activity of the diaphragm -Edi) which displays as a wave form on the ventilator AND it allows this neural drive to TRIGGER and SHAPE the pressure support breaths. This contrasts with the uniform delivery of standard pressure support breaths which can be delayed or 'cycle off' at the wrong time and which do not allow physiological breath-breath variation.

What are the inclusion criteria for the UK NAVA trial?

The UK NAVA team are trying to test the clinical effectiveness of NAVA technology in as wide a group of patients as possible. Any adult patient who has a medical reason why they are unlikely to extubate within 48h can be enrolled provided there are no exclusions. The reason for potentially prolonged weaning can be an acute diagnosis such as severe pneumonia, ARDS, multiple organ failure, shock, complex polytrauma AND/OR a chronic health disorder such as obesity, COPD, heart failure, frailty, or cognitive impairment.
It is important to remember that your ICU team can randomise a patient into UK NAVA at any point in their ICU journey. It is possible to place a NAVA catheter at the initial intubation or at subsequent timepoints eg after a failed extubation or following a tracheostomy.

What are the exclusion criteria for the UK NAVA trial?

We exclude any patient where there is a contraindication for placing an NG/OG tube. This includes facial/oesophageal trauma, recent oesophageal/gastric surgery and we also exclude patients with known or suspected oesophageal varices.
We exclude any patients who require neuroprotective ventilation (eg for raised intracranial pressure following traumatic or neurovascular brain injury).
We exclude any patients where the nerve signal down the phrenic nerve is compromised by pathology (eg Guillain-Barre Syndrome, Myaesthenia gravis, Spinal Cord Injury above C6; or phrenic nerve trauma).
We exclude all patients on long-term ventilation or who have been referred to /accepted by a long-term ventilatory support unit.
We exclude all patients who are actively dying or receiving palliative care only.
We exclude anyone who has a temporary or permanent pacemaker.

In many of these patient groups, NAVA technology has important utility, but the full intervention (NAVA monitoring + NAVA mode) cannot be reliably and fairly applied in a trial setting, particularly by clinical staff who may be using NAVA technology for the first time. However, it does not mean that NAVA technology cannot be used in some of these groups in normal clinical care. Indeed, NAVA technology has many important uses in many of the exclusion groups.

Is it difficult to use NAVA technology?

NAVA technology uses two things that are very familiar to ICU teams-an NG tube and a form of Pressure Support. Once ICU professionals become familiar with the technology, they will find it is not difficult to use. Patients do report feeling more comfortable with NAVA than standard pressure support. The protocol is also carefully designed to work well in busy ICUs who may be less familiar with the technology. One important part of the protocol is to ensure that NAVA monitoring continues even if NAVA mode is not being used because of difficulty with this mode. If standard Pressure Support (or Volume Support) is being used then simply document the reason why NAVA is not being used AND ensure that NAVA monitoring is restarted (overlay the Edi signal and record peak Edi hourly). NAVA should be tried again at least once every 24 hours.

Can you use a NAVA catheter to feed a patient and give enteral drugs like a normal NG or OG tube?

Yes, The NAVA catheter has all of the usual safety features of any NG or OG feeding tube. This includes the purple safety connector at the top of the feeding tube. The NAVA catheter is pre-lubricated, so it does not need any gel to insert. Instead the NAVA catheter should just be dipped into clean water before insertion-this will activate the lubricant. The NAVA catheter is no more difficult to insert than any other NG tube. It is important to use your local safety guidelines in relation to inserting any NG/OG tube to confirm GASTRIC location. There is nothing in NAVA technology that replaces standard rules around placement.

What are NAVA catheters made of?

NAVA catheters are made of medical grade polyurethane with embedded stainless steel. The MDR specification permits 7-day use.

Why does the NAVA catheter have a second small blue plastic port.

There is a separate narrow port and tube that runs down the main feeding tube. In the UK, most ICUs doe not use this port. In some European ICUs it is used to give some medications and to give enteral water.

Is the NAVA catheter MRI compatable?

No. The NAVA catheter contains embedded electronics made of stainless steel. These mean that the NAVA catheter is not MRI compatible. Prior to an MRI, the NAVA catheter should be removed. The same catheter or a fresh NAVA catheter can then be reinserted when the patient returns.

Does the NAVA catheter stop working after 7 days

No. The NAVA catheter will continue to function after 7 days. However, it is important for the UK NAVA team to be clear about the CE mark (MDR specification) of the NAVA catheter. IF the clinical team believe there is a clinical justification for using the NAVA catheter beyond 7 days, then the risk passes from our sponsor to the clinical team and we ask that the team clearly docoment the reason for prolonged use.

How does a NAVA catheter differ from a normal NG tube?

A NAVA catheter can be used as a nasogastric tube. It is radio-opaque for X-ray identification and is actually easier to see on a CXR than some NG tubes. It has the same purple safety connector as standard NG tubes and meets all safety requirements. Importantly, NAVA catheters must be placed using all safety measures to ensure gastric placement according to your local policy (commonly confirmation by low pH or CXR). The main differences with a standard NG tube, are that NAVA catheters are lubricated with water only (the water activates the pre-lubricant) and they are slightly stiffer. In general, they are just as easy to place. They are also NOT MRI compatible. Finally, it is recommended to change NAVA catheters once every 7 dys as per the technical specification from Getinge. However, this is a clinical decision. NAVA catheters continue to function after 7 days, but the justifcation for prolonged use needs to be documented. We do not recommend that patients are discharged with NAVA catheters in place.

How do you know if a NAVA catheter is in the right place?

NAVA catheters should be placed like any naso/oro-gastric tube. Gastric placement MUST be confirmed according to local protocols (eg pH testing or CXR). The initial length of a NAVA catheter is determined by the NEX measurement (NOSE>EAR>XIPHISTERNUM). This is the straight-line measurement between these landmarks. It is very important to get this measurement correct and it it is good practice to get a second checker. In the event of NAVA technology not working, the NEX measurement should be re-checked. The left hand ventilator screen panel has an embedded calculator that allows you to enter the NAVA catheter size and NEX measurement. It will provide the insertion distance. Of note, there is a field on the ventilator where the final insertion distance can be recorded. There is a 'fine tuning' positional tool that uses the internal ECG signal from the heart to allow clinicians and nurses to ensure the embedded electronics are centred across the diaphragm. If the NEX measurement has been measured correctly, then usually only very small adjustments (1-2cm) will be needed using the ECG locator screen. When an ICU team becomes experienced they will generally insert the NAVA catheter and fine tune the position before confirming gastric placement. THE ECG LOCATOR TOOL DOES NOT CONFIRM GASTRIC PLACEMENT.

What is NAVA Monitoring and how do I do it?

NAVA monitoring is one of the two key parts of NAVA technology. The NAVA monitoring displays a continuous waveform reflecting the neural drive in microvolts of the patient. As soon as you connect the NAVA catheter to the ventilator via the NAVA cable and module, the NAVA monitoring waveform will appear automatically at the bottom of the screen. It is then required, to overlay the same signal on the yellow pressure-time curve, but gently pressing your finger on the ventilator control screen over the yellow curve and selecting the Edi overlay option instead of 'none'. This will then allow doctors, nurses and therapists to see whether the patient's breathing is syncronised with the ventilator control or support breaths. The nurses should ensure that the peak Edi is recorded in the patient observations hourly. This may happen automatically in an electronic system (eg EPIC, Cerner, GE, ICCA or Metavision flow sheets), but the UK NAVA team also provide paper observation charts.

How should we use NAVA monitoring to improve patient care?

Like any ICU monitoring, NAVA monitoring will not improve patient outcome unless it is linked to beneficial changes in management. Whenever a patient is being assessed or handed over, please review the trend in neural drive (Edi) using the trend display on the left hand screen menu. The trend options can be changed in their order by 'drag and drop' and we recommend having Edi at the top for patients in UK NAVA. In addition the current Edi value should be reviewed along with a simple assessment of synchrony. Changes to sedation and ventilation may be possible. Commonly, ventilatory weaning can be accelerated and optimised. This may allow you to get the patient off the ventilator quicker. Although NAVA monitoring does not 'do' anything to the patient, it commonly empowers the ICU team to make important changes to the patient support (eg decreasing ventilatory support levels and/or sedation).
NAVA monitoring also reveals the effect of changes in neural drive associated with changes in sedation (eg boluses) and changes in mode or levels of ventilatory support. Typically, NAVA monitoring may lead to more confidence when weaning.
NAVA monitoring may be effectively used by physiotherapists when devising airway or ventilatory support weaning plans, and allow quantitative assessment of the effect of downsizing of a tracheostomy; cuff deflations and/or addition of speaking valves.
Importantly NAVA monitoring can be used post extubation. This is because sometimes the NAVA catheter will remain in place, and the neural drive (and trend) can be monitored with the ventilator in standby, to optimise post-extubation support.

Why is the Edi waveform flat in my patient?

It is quite common to see a suppressed Edi neural drive waveform when you first connect the NAVA catheter to the ventilator. The first thing to check is that the NAVA catheter is inserted to the correct length according to the NEX measurement. It is surprising how often this is wrong when you check it. If there is NO EDi signal you cannot use the ECG fine tune location screen to centre the NAVA catheter. If the NAVA catheter length is correct then the common causes for a suppressed or absent neural drive are 'sedation', 'off-loading of the respiratory muscles through 'over-ventilation' or 'over-oxygenation. Of course, sedation and ventilatory support may be entirely appropriate for critical illness support, but it is still important to be aware that neural drive is suppressed and that the diaphragm will not be contracting. As sedation and ventilatory support is reduced, then the neural drive should appear. This may be improved by standard measures eg talking to the patient.

What is a 'normal' Edi?

In health the neural drive, reflected by the Edi, will be low. In the ICU population, we use the standard range of 5-20 uV. In practice this is a very useful range to use clinically. It provides ICU staff with a sensible target range.

Why does the Edi go up in disease?

In disease states, the respiratory muscles may not perform efficiently, and the central neural centres in the brain increase their signal output to increase the number of muscle units being activated in the diaphragm as well as additional 'accessory' muscles. The Edi signal therefore increases in magnitude. The closer the patient state is to the normal state of healthy physiology, the lower will be the Edi. Low Edi also suggests that spontaneous ventilation is sustainable and has some reserve.
In COPD, sometimes more than 40% of.the maximum capacity of the diaphragm is used. This limits exercise tolerance, and also means that patients can quickly become unwell (decompensation) if they develop a new acute problem like pneumonia. This concept will be very familiar to ICU staff. As COPD approaches the end-stage of disease, the background Edi will become higher and higher until it is unsustainable. This is reflected by patients spending more time in hospital, and the intervals that they are able to be at home become shorter. When using NAVA, the target Edi in such patients will need to be decided, but it will obviously never be 5-20uV. It will just be the range that will permit weaning from pressure support (either IMV or NIV), and eventually weaning will become impossible and patients will become ventilator-dependent and may use NIV at home. NAVA monitoring in such patients will also enable hypoxic drive to be monitored, as the effect high FiO2 can be safely reviewed.

What are the key differences between NAVA mode vs standard Pressure Support?

NAVA mode is still a form of pressure support, and so it is important that ICU nurses, doctors and AHPs like physiotherapists are confident that many aspects of pressure support they are familiar with still apply when using NAVA. With NAVA, the amount of pressure support the patient receives is more in the control of the patient. The shape and magnitude of each breath will determine the level and shape of the support. This is much more physiological than standard pressure support. The pressure support breaths will vary breath-to-breath, and the patient can place pauses or bigger deeper breaths into their breathing cycle. In addition, the trigger is much more synchronised with the patient neural drive initiation, and so the various forma of asynchrony (eg delayed trigger, missed breaths, premature cycle off) will no longer occur.

Why does a patient's respiratory rate sometimes seem to go up when I go from Pressure Support to NAVA?

The patient's respiratory support is not really going up. In standard Pressure Support, some patient breaths are 'missed' by the ventilator, whereas in NAVA, there are no missed breaths. It may be more comfortable for the patient if all of their breaths are supported and hopefully the UK NAVA trial will help us to understand this.

How do you wean NAVA mode?

NAVA mode is a form of (more synchronised) pressure support. However, it is still weaned using similar strategies to pressure support. The two most common are to employ slow step-wise reduction (0.1 to 0.2 cm of pressure support per uV of neural drive) or to employ 'sprints' with rest periods. Here, short bursts of low NAVA (<0.5 cm water pressure support per uV of neural drive) are interspersed with rest periods. The difference with pressure support weans may be that there is a degree of automation in the weaning and because rest may be better, as the higher levels of support are more synchronised.

What should we do once the patient is extubated?

The NAVA catheter may be left in place once the patient is extubated. Whilst you are not required to continue NAVA monitoring, it is recommended for the first 48 hours after extubation (until the patient is confirmed as being successfully extubated. The NAVA monitoring will continue to be visible if you select the correct standby option on the ServoU. It can also be very useful to monitor a patient's neural drive following extubation to optimise support (eg with high flow or NIV) and also detect deterioration or improvement early. We strongly recommend that patients do not leave the ICU with a NAVA catheter still in place unless there is an overwhelming clinical justification, which is documented and clear plan for review and removal (eg by critical care outreach).

How do we identify patients who are suitable for the UK NAVA Trial?

All current ICU patients and future admissions should be screened for eligibility for participation in UK NAVA. NAVA technology can be applied safely in most ICU patients. We provide clear guidance on exclusions which will be familiar to any ICU staff. Critical Care Outreach Teams that cover wards and Emergency Departments can confirm eligibility and randomise at the point of intubation. However, this is not mandated-patients can be screened and randomised at ANY point of their ICU stay. The UK NAVA team have provided maximium flexibility to our sites. If critical care interventions are needed (eg intubation, sedation hold, tracheostomy) then patients can be randomised under a waiver. This is because our ethics committee understood that nasogastric/orogastric tube insertions are part of standard care, and may be done as part of emergency procedures or where time-critical decisions are taken. Our UK NAVA sites can very much decide themselves how they want to maximise safe and effective participation in UK NAVA.

How can we enrol a patient into UK NAVA?

All current ICU patients and future admissions should be screened for eligibility for participation in UK NAVA. NAVA technology can be applied safely in most ICU patients. We provide clear guidance on exclusions which will be familiar to any ICU staff.
Once a patient is identified, eligibility should be confirmed by a delegated member of the team (they do not need GCP or whole trial training).
Patient can be randomised under waiver or following professional/personal legal consent. Telephone consent is permitted.
If a patient is randomised to standard care please do NOT place a NAVA catheter in this patient: a standard NG/OG tube should be used according to your unit policy.
If a patient is randomised to NAVA technology, a NAVA Catheter should be placed as soon as possible and definitely within 6 hours. It must be connected to the ventilator. NAVA monitoring should commence immediately (overlay the Edi curve onto the Pressure-time curve and record PeakEdi hourly). NAVA mode should be used in preference to pressure support when the patient is ready for a support mode. If Pressure Support (or Volume Support) are used instead of NAVA, please document WHY and review this at least once every 24h. Patients allocated NAVA technology who receive Pressure Support or Volume Support MUST continue to receive NAVA monitoring.