Abstract
BackgroundNeurally Adjusted Ventilatory Assist (NAVA) is a proportional ventilatory mode that uses the electrical activity of the diaphragm (EAdi) to offer ventilatory assistance in proportion to patient effort. NAVA has been increasingly used for critically ill patients, but it has not been evaluated during spontaneous breathing trials (SBT). We designed a pilot trial to assess the feasibility of using NAVA during SBTs, and to compare the breathing pattern and patient-ventilator asynchrony of NAVA with Pressure Support (PSV) during SBTs.MethodsWe conducted a crossover trial in the ICU of a university hospital in Brazil and included mechanically ventilated patients considered ready to undergo an SBT on the day of the study. Patients underwent two SBTs in randomized order: 30 min in PSV of 5 cmH2O or NAVA titrated to generate equivalent peak airway pressure (Paw), with a positive end-expiratory pressure of 5 cmH2O. The ICU team, blinded to ventilatory mode, evaluated whether patients passed each SBT. We captured flow, Paw and electrical activity of the diaphragm (EAdi) from the ventilator and used it to calculate respiratory rate (RR), tidal volume (VT), and EAdi. Detection of asynchrony events used waveform analysis and we calculated the asynchrony index as the number of asynchrony events divided by the number of neural cycles.ResultsWe included 20 patients in the study. All patients passed the SBT in PSV, and three failed the SBT in NAVA. Five patients were reintubated and the extubation failure rate was 25% (95% CI 9–49%). Respiratory parameters were similar in the two modes: VT = 6.1 (5.5–6.5) mL/Kg in NAVA vs. 5.5 (4.8–6.1) mL/Kg in PSV (p = 0.076) and RR = 27 (17–30) rpm in NAVA vs. 26 (20–30) rpm in PSV, p = 0.55. NAVA reduced AI, with a median of 11.5% (4.2–19.7) compared to 24.3% (6.3–34.3) in PSV (p = 0.033).ConclusionsNAVA reduces patient-ventilator asynchrony index and generates a respiratory pattern similar to PSV during SBTs. Patients considered ready for mechanical ventilation liberation may be submitted to an SBT in NAVA using the same objective criteria used for SBTs in PSV.Trial registrationClinicalTrials.gov (NCT01337271), registered April 12, 2011.
Highlights
Adjusted Ventilatory Assist (NAVA) is a proportional ventilatory mode that uses the electrical activity of the diaphragm (EAdi) to offer ventilatory assistance in proportion to patient effort
The asynchrony index had a median of 24.3% (6.3–34.3) in Pressure Support Ventilation (PSV) and 11.5% (4.2–19.7) in Neurally Adjusted Ventilatory Assist (NAVA) (p = 0.033). In this crossover pilot trial including intubated patients considered ready for mechanical ventilation liberation, we found that an spontaneous breathing trials (SBT) in NAVA was usually well tolerated, had similar respiratory rate and tidal volumes to an a b c d e f
Previous studies had shown lower tidal volumes and greater respiratory rates in NAVA compared to PSV, and such a pattern could interfere with the interpretation of an SBT
Summary
Adjusted Ventilatory Assist (NAVA) is a proportional ventilatory mode that uses the electrical activity of the diaphragm (EAdi) to offer ventilatory assistance in proportion to patient effort. NAVA has been increasingly used for critically ill patients, but it has not been evaluated during spontaneous breathing trials (SBT). The process of liberation usually involves the application of spontaneous modes of ventilation like Pressure Support Ventilation (PSV), and more importantly, daily assessment of readiness to undergo a spontaneous breathing trial (SBT) [5, 6]. An SBT consists of removing or minimizing ventilatory support for 30–120 min and observing if the patient tolerates the challenge. This can be accomplished either using a t-tube or with low levels of ventilator support, using continuous positive airway pressure (CPAP) or 5–7 cmH2O of pressure support. There is no consensus as to what is the best method to perform the SBT [7, 8]
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