(EAdi-signal) and - Topics in Intensive Care

NAVA (Neurally Adjusted Ventilatory Assist) :
A ventilation tool or a ventilation toy ?
Walter Verbrugghe, MD
Critical Care Department
Antwerp University Hospital
walter.verbrugghe@uza.be
08/12/2011

Indication for mechanical ventilation
• ↑ gas exchange
• ↓ respiratory muscle effort

From controlled mechanical ventilation to assisted mechanical ventilaton
Controlled mechanical
ventilation (CMV)
• Volume CMV : IPPV
• Pressure CMV : PCV
Assisted mechanical
ventilation
•SIMV
• ASB/PS
(Proportional) assisted
mechanical ventilation
• PAV
• NAVA

The NAVA (EAdi-)catheter
Guide-wire
lumen
Conection to
NAVA module
Feeding lumen

The NAVA (EAdi-)catheter

The NAVA (EAdi-)catheter

Positioning of the EAdi-catheter

Positioning of the EAdi-catheter (cont’d)
At least in 2/3 correct positioning using this formula
Barwing J et al. Int Care Med, 2009

The EAdi-signal

Correct positioning of the EAdi-catheter
p-wave
QRSwave

The ‘normal’ EAdi-signal

Interference from leaking ECG activity

Interference from IABP

Interference from transvenous pace maker activity

Setting up the NAVA ventilatory mode
1 st backup
2 nd backup

2. Pressure assist - slope
1. Inspiration - Cycle-on
The mechanical breating cycle
Inspiration Expiration
4. Expiration - Cycle-off
3. Assist amplitude

EAdi and ventilator triggering (cycle-on)
Flow/pressuretrigger
Pressure Support
Ventilation
Assisted breath
EAdi-trigger
NAVA

The NAVA-level : slope and amplitude + cycle-off
• EAdi-signal is sampled every 16ms
• The slope and the amplitude of the Eadi-signal determines the
slope and the amplitude of the mechanical inflation
• The NAVA-level serves as an amplifier of the EAdi-signal
Delivered assist (cmH20) =
instantaneous EAdi (µV) x NAVA-level (cmH20/µV)
• The mechanical inflation is terminated when the EAdi reaches
70% of the peak-EAdi

EAdi as a surrogate of the neural respiratory cycle
Number of active
inspiratory neurons ~
Inspiratory effort
Diaphragmatic
Activation ~
Edi (µV)
Mechanical assist ~
tidal volume

Neural
Mechanical
Chemical
The neuro-ventilatory coupling
Brain
Phrenic nerve
Diaphragmatic
contraction
Lung
distention
Alveolar
ventilation
Sinderby C et al. Clin Chest Med, 2008, 29, 329-342
?
Nerve afferents
Joint receptors
Baroreceptors
Chemoreceptors
Respiratory
neuron output
Nerve EMG
Diaphragmatic
EMG Edi
Flow Airway trigger
Pressure pressure trigger
PaO Blood
2/PaCO gas
2

NAVA takes advantage of (1) the diaphragmatic activity (EAdi-signal)
and (2) the neuro-ventilatory coupling mechanism
• The electrical activity generated by the diaphragm is captured
as the EAdi-signal, serving as a surrogate for the neural
respiration
• The timing and the intensity of the EAdi-signal determines the
timing and the intensity of the mechanical assist delivered by
the ventilator
• The delivered mechanical assist in NAVA is not only
synchronous with neural respiration but also proportional to the
ventilatory demand
• NAVA establises a ‘connection’ between the neuronal
respiratory centre output (patient) and the mechanical assist
delivered by the ventilator on a higher level in the neuroventilatory
coupling (compared to pneumatic triggered
breathing technology)

The meaning of the EAdi-signal
• The Eadi-signal = the electrical activity of the diaphragm as
measured at the crux diaphragmatica by a proper positioned
NAVA-catheter
• No ‘normal’ value for EAdi in a particular patient
• No inter-individual comparison between patients possible upon
absolute values of EAdi
• EAdi/TV ~ ventilatory efficiency
• High EAdi/TV ~ high neuronal output for rather small TV
• Low EAdi/TV ~ low neuronal output for rather normal TV
Sinderby C, Beck J. Neth J Crit Care, 2007

Setting up the NAVA-level

Setting the NAVA-level = implementation of the neuroventilatory
coupling principle in clinical practice 1
1 Brander L et al. Chest, 2009;135;695-703

The neuro-ventilatory tool

Setting up the NAVA-level
• Multiple methods described, optimal method unknown
• Steps : 0,1 µV � 0,2 µV � 0,5 µV ?
• Duration : 4 breaths � 3 minutes ?
• Low � high or high � low ?
• Always (always) set maximum pressure alarm at safe level
to avoid excessive inspiratory pressures in NAVA
• Probably absolute NAVA-level not so important as long as
situated in second response range at least in the presence
of intact neuro-ventilatory coupling
Barwing J et al. Int Care Med, 2009
Barwing J et al. Acta Anaesthesiol Scand, 2009
Viale CP et al. Crit Care Med, 1998

The neuro-ventilatory coupling and lung-protective ventilation
Terzi N et al. Crit Care Med, 2010
Spahija J et al. Crit Care Med, 2010

Lung protective ventilation contributing to the prevention of VILI ?
Brander L. et al. Intensive Care Med 2009;35(11):1979-1989.

Patient-ventilator asynchrony

Discrepancy between neural respiration and mechanical assist
Mechanical respiratory cycle
Neural respiratory cycle
Beck J et al. AJRCCM, 2001
Colombo D et al. Crit Care Med, 2008
Aslanian P et al. AJRCCM, 1998
Goulet R et al. Chest, 1997
Tobin MJ et al. Crit Care Med, 2001
80-550 ms
200 ms

Timing asynchrony : inspiration (cycle-on)
Inspiratory trigger delay
Autotrigger
Wasted effort Double trigger

Timing asynchrony : expiration (cycle-off)

Assist asynchrony : slope and amplitude asynchrony

Determinants of patient-ventilator asynchrony
• Patient-related factors
• PEEPi and dynamic hyperinflation 1 (e.g. COPD)
• Shortening of inspiratory muscle and flattening of diaphragm with
horizontal position � compromised diaphragmatic force
• Delayed inspiratory triggering and continued inflation after beginning
of the neural expiration
• Excessive PS � excessive tidal volume
• Hering-Bruer reflex
• Respiratory alkalosis
� depression of neural inspiration
• Sedation level 2
• Technical factors
• Inadequate setting of the inspiratory (pneumatic) trigger
trigger (too sensitive or not sensitive enough)
• Inadequate setting of the expiratory (flow) trigger
• Air leaks in the ventilator circuit (non-invasive ventilation)
1 Jain M et al Critical Care, 2007, 11:206
2 De Wit M et al. J Crit Care, 2009, 24, 74-80

Asynchrony, pneumatic triggering and PEEPi 1
1 Jain M et al Critical Care, 2007, 11:206

Importance of patient-ventilator asynchrony
• Incidence : > 25% of mechanically ventilated patients
• Who : COPD-patients, children,… but many more
• Asynchrony Index (AI) > 10% ~ association with
potential complications 1,2
1. Increased need for sedation and muscle relaxants
• ↑ critical illness polyneuropathy or critical illness myopathie
• ↑ ICU‐delirium (� mortality?)
2. Increased ventilatory pressures � risk barotrauma and VILI
(Ventilator Induced Lung Injury)
3. Increased duration of mechanical ventilation and weaning
� mortality
1 Thille AW et al. Intensive Care Med.2005, 32, 1515-1522
2 Sinderby C et al. Neth J Crit Care 2007:11(5): 243-252.

Patient-ventilator asynchrony in PSV vs NAVA
Spahija J et al. Crit Care Med, 2010

Patient-ventilator asynchrony with NIV

EAdi as monitoring tool of diaphragm activity and prevention of VIDD ?
PSV NAVA
In Yearbook of intensive Care and Emergency Medicine, 2007. Ed Vincent JL

EAdi as monitoring tool of diaphragm activity and prevention of VIDD ?

EAdi as monitoring tool of diaphragm activity and prevention of VIDD ?
1 Levine S et al. NEJM, 2008, 358, 1327-1335

Respiratory muscle weakness is associated with
prolonged mechanical ventilation
De Jonghe B et al. Crit Care Med, 2007

The Edi-pattern of VIDD ?

The evolution of the Edi-signal
Start abdominal breathing excercise

The evolution of the Edi-signal

EAdi as monitoring tool of diaphragm activity and prevention of VIDD ?
• Animal data and human data suggests that even short
term diaphragmatic inactivity is associated with muscle
fiber atrofy 1 .
• VIDD is not uncommon, its prevalence is estimated 25 –
50% in mechanically ventilated ICU patients 2
• There is indirect evidence VIDD is associated with
weaning failure in humans 1
• This may occur even in assisted ventilator modes due to
persistent inactivity of the diaphragm
• Particularly in PSV the patient may receive the full assist
only with the use of accessory muscles (even if pneumatic
trigger not too sensitive)
1 Levine S et al. NEJM, 2008, 358, 1327-1335
2 Decramer M et al. Am J Respir Crit Care Med, 2004, 170, 1140-1141

Conclusions

Conclusions : potential benefits of NAVA/Eadi-monitoring ?
NAVA = proportional and synchronous assist with preservation of variable breathing
pattern integrated in the neuro-ventilatory coupling mechanism with direct
visualisation of diaphragmatic muscle activity
Potential benefits :
• Better patient comfort ? Invasive but also non-invasive ventilation (no
interference from air leaks)
• Less need for sedation – muscle relaxants ?
• Less risk for ICU delirium ?
• Better sleep quality ?
• Improved lung protective ventilation ? Prevention VILI ?
• Faster transition from controlled mechanical ventilation to assisted mode ?
• Less duration of mechanical ventilation – faster weaning ?
• Diaphragmatic muscle training (abdominal breathing excercise ?)
• Prevention of VIDD ?
Delisle S et al. Ann Intensive Care, 2011
De Jonghe B et al. Crit Care Med, 2007

Conclusions : potential indications ?
NAVA
• Non-invasive ventilation
• Much better patient-ventilator synchrony and comfort; new standard ?
• Invasive ventilation
• Patients with major patient-ventilator asynchrony
• COPD
• Children
• The “difficult-to-wean” or “non-weanable” patient ?
• Diaphragmatic disuse/atrophy (prevention is better than cure ?)
• Patient with critical illness polyneuropathy/-myopathy ?
Monitoring the EAdi-signal
• Direct visualisation of diaphragmatic muscle activity
• Prediction of weaning success/failure ?
• Prediction of re-intubation ?

Conclusion
• NAVA is a novel ventilatory mode capable of delivering a
ventilatory assist synchronous with the neural ventilation on a
breath-to-breath basis
• NAVA has the potential to train the most important respiratory
muscle, the diaphragm, whereas other (pneumatically
triggered) (assisted) ventilatory modes may actually
consolidate diaphragmatic disuse
• The rationale for NAVA has a sound physiological basis, but
remains to be proven in clinically trials with relevant clinical
eindpoints
• The adoption of NAVA as a new ventilatory mode will require a
drastical lowering of the cost of the NAVA-catheter
• If NAVA as a ventilatory mode is not applicable; the monitoring
of the Eadi-signal alone may provide important information to
the clinician and needs further research

hank you