Weaning with NAVA
Principles of NAVA
The way that NAVA mode drives pressure support is important to understand.
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In contrast to standard pressure support the trigger for the pressure support is a neural trigger from the Edi signal rather than from a change in flow/pressure in the ventilator circuit.
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Breath-to-breath variability is permitted
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The contour of each breath will also track patient preferences
While increasing or decreasing the NAVA support level may result in changes to neural drive (Edi) which may lead to less or no change in the resulting pressure support.
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The patient will often breath at a higher recorded respiratory rate in NAVA mode compared with pressure support. This is usually because there are far fewer missed breaths, so all patient breaths are represented in the respiratory rate. With experience, nurses and medical staff become more accustomed to this. Further, as NAVA monitoring becomes more commonly used, ICU staff become aware of 'missed' breaths in other modes of control or support ventilation.
Weaning Strategies with NAVA mode
As with conventional pressure support there is a surprising lack of evidence around optimal approaches to weaning with NAVA. There is even disagreement around related topics such as definitions of sedation holds or spontaneous breathing trials.
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In addition, again similar to conventional pressure support, there is probably no one 'right' way of using NAVA to wean, partly because not all prolonged or failed weaning has the same underlying cause. Weaning difficulty or failure is obviously not a single disease. For example, different patients may have different contributions from left heart failure, right heart failure; airway issues; muscle weakness; phrenic nerve injury; diaphragmatic injury; lung parenchymal injury. Further, different patient will have different chronic health trajectories and comorbidities in addition to different acute critical illnesses.
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Weaning can be progressive where NAVA level is reduced steadily in steps of 0.1-0.2 OR split into 'rest' (night and day blocks if needed) and 'sprint' blocks of higher patient work. Magnitude of sprints can be set using lower levels of NAVA gain (or CPAP) and/or extending duration of 'sprints'.
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Sedation, analgesia can be adjusted in parallel. Other considerations eg optimal fluid balance; optimal cardiovascular support (eg left/right ventricular support); treatment of sepsis; and optimal PEEP, all remain important.
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NAVA level reduction, like conventional pressure support should be reduced using a structured weaning plan which is calibrated by looking at the patient clinically; using trends in blood gases and measures such as the rapid shallow breathing index. P 0.1 can also be used.
Some ICUs will try to accelerate weaning by finding the peak Edi on zero NAVA and then adjusting the NAVA level to produce an Edi of 50-60%.
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The bottom line is that weaning from ventilatory support should be structured; agreed and coordinated across the whole inter-professional team AND involve all aspects of patient pathophysiology and support, including psychological. NAVA monitoring - NAVA mode should contribute usefully to this holistic approach. In UK NAVA this general approach should be used whether the patient is in NAVA technology NAVA Monitoring - NAVA mode arm or conventional pressure support arm.
Weaning with NAVA mode is performed in a similar way to pressure support. Either there is a gradual step-wise reduction in the support level (by weaning NAVA gain) or the patient can be exposed to more challenging 'sprints' with blocks of rest (eg at night) in between. In this case the critical care service decided to gradually reduce the NAVA level from a starting level of 1 ,which the patient tolerated very well. Sedation was also weaned quite quickly and resistant delirium also settled. Two consecutive days are shown. On the second day, the patient was awake and communicating with family.
The respiratory rate in patients on NAVA tends to be slightly higher than in pressure support but this is because there are no missed breths - all patient breaths are supported.
