Weaning: Neuro Ventilatory Efficiency

Christer Sinderby Department of Critical Care

Keenan Research Center at the Li Ka Shing Knowledge Institute of St. Michael's Hospital

Faculty of Medicine, University of Toronto, Canada

Disclosure: Dr. Sinderby has made inventions related to neural control of mechanical ventilation that are patented. The license for these patents belongs to

Maquet Critical Care. Use of this technology provides financial benefit to Dr. Sinderby through royalties. Dr Sinderby owns 50% of Neurovent Research Inc

(NVR). NVR is a research and development company that builds the equipment and catheters for research studies. NVR has a consulting agreement with

Maquet Critical Care.

Conflict of interest• Disclosure: Dr. Sinderby has made inventions related to neural

control of mechanical ventilation that are patented. The license for

these patents belongs to Maquet Critical Care. Commercial use of

this technology provides financial benefit to Dr. Sinderby through

royalties. Dr Sinderby owns 50% of Neurovent Research Inc (NVR).

NVR is a research and development company that builds the

equipment and catheters for research studies. NVR has a

consulting agreement with Maquet Critical Care.

Neuro-ventilatory efficiency = Vt/EAdi (ml/µV)

Sinderby & Beck, Neurally Adjusted Ventilatory Assist in

Principles and Practice of Mechanical Ventilation, Third Edition

Editor: Tobin MJ, McGraw-Hill Medical 2013

EAdi and Vt in health and disease

Principle for Vt/EAdi

Vt

EAdi

We evaluated whether extubation failure could be characterized

by increased respiratory drive and impaired efficiency to generate

inspiratory pressure and ventilation.

Following PSV of 10 cm H2O and PEEP of 5 cm H2O: 52

patients underwent 30-minutes of spontaneous breathing on

CPAP of 5 cmH2O.

Data was compared between successfully extubated patients and

those patients that either failed spontaneous breathing or passed

but failed within 48 h.

• Purpose: To compare breathing pattern descriptors and diaphragm

electromyographic activity (EAdi) during a spontaneous breathing trial (SBT) in

patients successfully and unsuccessfully separated from the ventilator and to assess

their performance as a potential marker to discriminate these two categories of

patients.

• Methods: Fifty-seven ready-to-wean patients were included in a prospective

observational study. During a 30-min SBT (pressure support 7 cmH2O, zero end

expiratory pressure), tidal volume (VT) and respiratory rate (RR) were obtained

from the flow signal at baseline of PSV and at 3, 10, 20 and 30 min during the

SBT.

Note that this study describes the inverse of Neuro-Ventilatory Effiency

ConclusionsEAdi-derived indices collected via the NAVA catheter during the SBT provide

reliable predictors of successful separation from the ventilator. These indices

can discriminate early in the SBT the ongoing success or failure of separation

from the ventilator. However, the performance of these indices is not better

than the performance of the rapid shallow breathing index. Therefore, the

benefit of EAdi-derived indices during the SBT remains unclear.

• In this pilot study we compared the EAdi to conventional weaning parameters in

difficult-to-wean patients scheduled for a spontaneous breathing trial. Our primary

goal was to observe the expected increase in the EAdi. A secondary goal was to

compare the conventional weaning parameters to those derived from the EAdi.

• We studied 18 mechanically ventilated patients considered difficult to wean. For a

spontaneous breathing trial (SBT) the patients were disconnected from the

ventilator and given oxygen through a T-piece. The SBT was evaluated using

standard criteria.

This observational study included 12 patients breathing with neurally

adjusted ventilatory assist (NAVA). When a spontaneous breathing trial

(SBT) with pressure support of 7 cm H2O and PEEP was unsuccessful,

NAVA was used and the level was adjusted to obtain an EAdi of 60% of

maximal EAdi during SBT. VT and EAdi were recorded continuously.

We compared changes in NVE between NAVA and SBT at the first failed

and first successful SBT.

ConclusionsThese results suggest that in patients after respiratory failure and prolonged

mechanical ventilation, changes in VT and NVE, between SBTs are indicative

of patient recovery. Larger clinical trials are needed to clarify whether changes

in NVE reliably predict weaning in patients ventilated with NAVA.

Conclusion

4 studies in 138 patients indicate that neuroventilatory efficiency

(Vt/EAdi) is reduced in weaning failure patients. Thus, clinical

use of mechanical ventilation to unload inspiratory muscles due

to weakness or load is justified.

Vt/EAdi as a predictor of weaning during SBT equals that of

Fb/Vt.

Future studies of comparing patient-chosen changes in Vt,

Vt/EAdi, and Fb/Vt between NAVA and SBT may introduce

better prediction of weaning outcome.

Thank You

VentQuest.ca