Neurally adjusted ventilatory assist as a weaning mode for adults with invasive mechanical ventilation: a systematic review and meta-analysis.

BACKGROUND: Prolonged ventilatory support is associated with poor clinical outcomes. Partial support modes, especially pressure support ventilation, are frequently used in clinical practice but are associated with patient-ventilation asynchrony and deliver fixed levels of assist. Neurally adjusted ventilatory assist (NAVA), a mode of partial ventilatory assist that reduces patient-ventilator asynchrony, may be an alternative for weaning. However, the effects of NAVA on weaning outcomes in clinical practice are unclear. METHODS: We searched PubMed, Embase, Medline, and Cochrane Library from 2007 to December 2020. Randomized controlled trials and crossover trials that compared NAVA and other modes were identified in this study. The primary outcome was weaning success which was defined as the absence of ventilatory support for more than 48 h. Summary estimates of effect using odds ratio (OR) for dichotomous outcomes and mean difference (MD) for continuous outcomes with accompanying 95% confidence interval (CI) were expressed. RESULTS: Seven studies (n = 693 patients) were included. Regarding the primary outcome, patients weaned with NAVA had a higher success rate compared with other partial support modes (OR = 1.93; 95% CI 1.12 to 3.32; P = 0.02). For the secondary outcomes, NAVA may reduce duration of mechanical ventilation (MD = - 2.63; 95% CI - 4.22 to - 1.03; P = 0.001) and hospital mortality (OR = 0.58; 95% CI 0.40 to 0.84; P = 0.004) and prolongs ventilator-free days (MD = 3.48; 95% CI 0.97 to 6.00; P = 0.007) when compared with other modes. CONCLUSIONS: Our study suggests that the NAVA mode may improve the rate of weaning success compared with other partial support modes for difficult to wean patients.

Proportional assist ventilation versus pressure support ventilation for weaning from mechanical ventilation in adults: a meta-analysis and trial sequential analysis.

BACKGROUND: Pressure support ventilation (PSV) is the prevalent weaning method. Proportional assist ventilation (PAV) is an assisted ventilation mode, which is recently being applied to wean the patients from mechanical ventilation. Whether PAV or PSV is superior for weaning remains unclear. METHODS: Eligible randomized controlled trials published before April 2020 were retrieved from databases. We calculated the risk ratio (RR) and mean difference (MD) with 95% confidence intervals (CIs). RESULTS: Seven articles, involving 634 patients, met the selection criteria. Compared to PSV, PAV was associated with a significantly higher rate of weaning success (fixed-effect RR 1.16; 95% CI 1.07-1.26; I2 = 0.0%; trial sequential analysis-adjusted CI 1.03-1.30), and the trial sequential monitoring boundary for benefit was crossed. Compared to PSV, PAV was associated with a lower proportion of patients requiring reintubation (RR 0.49; 95% CI 0.28-0.87; I2 = 0%), a shorter ICU length of stay (MD - 1.58 (days), 95% CI - 2.68 to - 0.47; I2 = 0%), and a shorter mechanical ventilation duration (MD - 40.26 (hours); 95% CI - 66.67 to - 13.84; I2 = 0%). There was no significant difference between PAV and PSV with regard to mortality (RR 0.66; 95% CI 0.42-1.06; I2 = 0%) or weaning duration (MD - 0.01 (hours); 95% CI - 1.30-1.28; I2 = 0%). CONCLUSION: The results of the meta-analysis suggest that PAV is superior to PSV in terms of weaning success, and the statistical power is confirmed using trial sequential analysis.

Neurally adjusted ventilatory assist versus pressure support ventilation: a randomized controlled feasibility trial performed in patients at risk of prolonged mechanical ventilation.

BACKGROUND: The clinical effectiveness of neurally adjusted ventilatory assist (NAVA) has yet to be demonstrated, and preliminary studies are required. The study aim was to assess the feasibility of a randomized controlled trial (RCT) of NAVA versus pressure support ventilation (PSV) in critically ill adults at risk of prolonged mechanical ventilation (MV). METHODS: An open-label, parallel, feasibility RCT (n = 78) in four ICUs of one university-affiliated hospital. The primary outcome was mode adherence (percentage of time adherent to assigned mode), and protocol compliance (binary-≥ 65% mode adherence). Secondary exploratory outcomes included ventilator-free days (VFDs), sedation, and mortality. RESULTS: In the 72 participants who commenced weaning, median (95% CI) mode adherence was 83.1% (64.0-97.1%) and 100% (100-100%), and protocol compliance was 66.7% (50.3-80.0%) and 100% (89.0-100.0%) in the NAVA and PSV groups respectively. Secondary outcomes indicated more VFDs to D28 (median difference 3.0 days, 95% CI 0.0-11.0; p = 0.04) and fewer in-hospital deaths (relative risk 0.5, 95% CI 0.2-0.9; p = 0.032) for NAVA. Although overall sedation was similar, Richmond Agitation and Sedation Scale (RASS) scores were closer to zero in NAVA compared to PSV (p = 0.020). No significant differences were observed in duration of MV, ICU or hospital stay, or ICU, D28, and D90 mortality. CONCLUSIONS: This feasibility trial demonstrated good adherence to assigned ventilation mode and the ability to meet a priori protocol compliance criteria. Exploratory outcomes suggest some clinical benefit for NAVA compared to PSV. Clinical effectiveness trials of NAVA are potentially feasible and warranted. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01826890. Registered 9 April 2013.

Ventilation Strategies in Severe Bronchopulmonary Dysplasia.

Bronchopulmonary dysplasia (BPD) is an acquired, developmental chronic lung disease that is a consequence of premature birth. In the most severe form of the disease, infants may require prolonged periods of positive pressure ventilation. BPD is a heterogeneous disease with lung mechanics that differ from those in respiratory distress syndrome; strategies to manage the respiratory support in infants with severe BPD should take this into consideration. When caring for these infants, practitioners need to shift from the acute care ventilation strategies that use frequent blood gases and support adjustments designed to minimize exposure to positive pressure. Infants with severe BPD benefit from a chronic care model that uses less frequent ventilator adjustments and provides the level of positive support that will achieve the longer-term goal of ongoing lung growth and repair.

Neurally adjusted ventilatory assist (NAVA) versus pressure support ventilation: patient-ventilator interaction during invasive ventilation delivered by tracheostomy.

BACKGROUND: Prolonged weaning is a major issue in intensive care patients and tracheostomy is one of the last resort options. Optimized patient-ventilator interaction is essential to weaning. The purpose of this study was to compare patient-ventilator synchrony between pressure support ventilation (PSV) and neurally adjusted ventilatory assist (NAVA) in a selected population of tracheostomised patients. METHODS: We performed a prospective, sequential, non-randomized and single-centre study. Two recording periods of 60 min of airway pressure, flow, and electrical activity of the diaphragm during PSV and NAVA were recorded in a random assignment and eight periods of 1 min were analysed for each mode. We searched for macro-asynchronies (ineffective, double, and auto-triggering) and micro-asynchronies (inspiratory trigger delay, premature, and late cycling). The number and type of asynchrony events per minute and asynchrony index (AI) were determined. The two respiratory phases were compared using the non-parametric Wilcoxon test after testing the equality of the two variances (F-Test). RESULTS: Among the 61 patients analysed, the total AI was lower in NAVA than in PSV mode: 2.1% vs 14% (p < 0.0001). This was mainly due to a decrease in the micro-asynchronies index: 0.35% vs 9.8% (p < 0.0001). The occurrence of macro-asynchronies was similar in both ventilator modes except for double triggering, which increased in NAVA. The tidal volume (ml/kg) was lower in NAVA than in PSV (5.8 vs 6.2, p < 0.001), and the respiratory rate was higher in NAVA than in PSV (28 vs 26, p < 0.05). CONCLUSION: NAVA appears to be a promising ventilator mode in tracheotomised patients, especially for those requiring prolonged weaning due to the decrease in asynchronies.

Standardized Unloading of Respiratory Muscles during Neurally Adjusted Ventilatory Assist: A Randomized Crossover Pilot Study.

WHAT WE ALREADY KNOW ABOUT THIS TOPIC: WHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: Currently, there is no standardized method to set the support level in neurally adjusted ventilatory assist (NAVA). The primary aim was to explore the feasibility of titrating NAVA to specific diaphragm unloading targets, based on the neuroventilatory efficiency (NVE) index. The secondary outcome was to investigate the effect of reduced diaphragm unloading on distribution of lung ventilation. METHODS: This is a randomized crossover study between pressure support and NAVA at different diaphragm unloading at a single neurointensive care unit. Ten adult patients who had started weaning from mechanical ventilation completed the study. Two unloading targets were used: 40 and 60%. The NVE index was used to guide the titration of the assist in NAVA. Electrical impedance tomography data, blood-gas samples, and ventilatory parameters were collected. RESULTS: The median unloading was 43% (interquartile range 32, 60) for 40% unloading target and 60% (interquartile range 47, 69) for 60% unloading target. NAVA with 40% unloading led to more dorsal ventilation (center of ventilation at 55% [51, 56]) compared with pressure support (52% [49, 56]; P = 0.019). No differences were found in oxygenation, CO2, and respiratory parameters. The electrical activity of the diaphragm was higher during NAVA with 40% unloading than in pressure support. CONCLUSIONS: In this pilot study, NAVA could be titrated to different diaphragm unloading levels based on the NVE index. Less unloading was associated with greater diaphragm activity and improved ventilation of the dependent lung regions.

Effects of neurally adjusted ventilatory assist on air distribution and dead space in patients with acute exacerbation of chronic obstructive pulmonary disease.

BACKGROUND: Neurally adjusted ventilatory assist (NAVA) could improve patient-ventilator interaction; its effects on ventilation distribution and dead space are still unknown. The aim of this study was to evaluate the effects of varying levels of assist during NAVA and pressure support ventilation (PSV) on ventilation distribution and dead space in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). METHODS: Fifteen mechanically ventilated patients with AECOPD were included in the study. The initial PSV levels were set to 10 cmH2O for 10 min. Thereafter, the ventilator mode was changed to NAVA for another 10 min with the same electrical activity of the diaphragm as during PSV. Furthermore, the ventilation mode was switched between PSV and NAVA every 10 min in the following order: PSV 5 cmH2O; NAVA 50%; PSV 15 cmH2O; and NAVA 150% (relative to the initial NAVA support level). Ventilation distribution in the lung was evaluated in percentages in regions of interest (ROI) of four anteroposterior segments of equal height (ROI1 to ROI4 represents ventral, mid-ventral, mid-dorsal, and dorsal, respectively). Blood gases, ventilation distribution (electrical impedance tomography), diaphragm activity (B-mode ultrasonography), and dead space fraction (PeCO2 and PaCO2) were measured. RESULTS: The trigger and cycle delays were lower during NAVA than during PSV. The work of trigger was significantly lower during NAVA compared to PSV. The diaphragm activities based on ultrasonography were higher during NAVA compared to the same support level during PSV. The ventilation distribution in ROI4 increased significantly (P < 0.05) during NAVA compared to PSV (except for a support level of 50%). Similar results were found in ROI3 + 4. NAVA reduced dead space fraction compared to the corresponding support level of PSV. CONCLUSIONS: NAVA was superior to PSV in AECOPD for increasing ventilation distribution in ROI4 and reducing dead space. TRIAL REGISTRATION: Clinicaltrials.gov, NCT02289573 . Registered on 12 November 2014.

A diaphragmatic electrical activity-based optimization strategy during pressure support ventilation improves synchronization but does not impact work of breathing.

BACKGROUND: Poor patient-ventilator synchronization is often observed during pressure support ventilation (PSV) and has been associated with prolonged duration of mechanical ventilation and poor outcome. Diaphragmatic electrical activity (Eadi) recorded using specialized nasogastric tubes is a surrogate of respiratory brain stem output. This study aimed at testing whether adapting ventilator settings during PSV using a protocolized Eadi-based optimization strategy, or Eadi-triggered and -cycled assisted pressure ventilation (or PSVN) could (1) improve patient-ventilator interaction and (2) reduce or normalize patient respiratory effort as estimated by the work of breathing (WOB) and the pressure time product (PTP). METHODS: This was a prospective cross-over study. Patients with a known chronic pulmonary obstructive or restrictive disease, asynchronies or suspected intrinsic positive end-expiratory pressure (PEEP) who were ventilated using PSV were enrolled in the study. Four different ventilator settings were sequentially applied for 15 minutes (step 1: baseline PSV as set by the clinician, step 2: Eadi-optimized PSV to adjust PS level, inspiratory trigger, and cycling settings, step 3: step 2 + PEEP adjustment, step 4: PSVN). The same settings as step 3 were applied again after step 4 to rule out a potential effect of time. Breathing pattern, trigger delay (Td), inspiratory time in excess (Tiex), pressure-time product (PTP), and work of breathing (WOB) were measured at the end of each step. RESULTS: Eleven patients were enrolled in the study. Eadi-optimized PSV reduced Td without altering Tiex in comparison with baseline PSV. PSVN reduced Td and Tiex in comparison with baseline and Eadi-optimized PSV. Respiratory pattern did not change during the four steps. The improvement in patient-ventilator interaction did not lead to changes in WOB or PTP. CONCLUSIONS: Eadi-optimized PSV allows improving patient ventilator interaction but does not alter patient effort in patients with mild asynchrony. TRIAL REGISTRATION: Clinicaltrials.gov identifier: NCT 02067403 . Registered 7 February 2014.

Limited predictability of maximal muscular pressure using the difference between peak airway pressure and positive end-expiratory pressure during proportional assist ventilation (PAV).

BACKGROUND: If the proportional assist ventilation (PAV) level is known, muscular effort can be estimated from the difference between peak airway pressure and positive end-expiratory pressure (PEEP) (ΔP) during PAV. We conjectured that deducing muscle pressure from ΔP may be an interesting method to set PAV, and tested this hypothesis using the oesophageal pressure time product calculation. METHODS: Eleven mechanically ventilated patients with oesophageal pressure monitoring under PAV were enrolled. Patients were randomly assigned to seven assist levels (20-80%, PAV20 means 20% PAV gain) for 15 min. Maximal muscular pressure calculated from oesophageal pressure (Pmus, oes) and from ΔP (Pmus, aw) and inspiratory pressure time product derived from oesophageal pressure (PTPoes) and from ΔP (PTPaw) were determined from the last minute of each level. Pmus, oes and PTPoes with consideration of PEEPi were expressed as Pmus, oes, PEEPi and PTPoes, PEEPi, respectively. Pressure time product was expressed as per minute (PTPoes, PTPoes, PEEPi, PTPaw) and per breath (PTPoes, br, PTPoes, PEEPi, br, PTPaw, br). RESULTS: PAV significantly reduced the breathing effort of patients with increasing PAV gain (PTPoes 214.3 ± 80.0 at PAV20 vs. 83.7 ± 49.3 cmH2O•s/min at PAV80, PTPoes, PEEPi 277.3 ± 96.4 at PAV20 vs. 121.4 ± 71.6 cmH2O•s/min at PAV80, p < 0.0001). Pmus, aw overestimates Pmus, oes for low-gain PAV and underestimates Pmus, oes for moderate-gain to high-gain PAV. An optimal Pmus, aw could be achieved in 91% of cases with PAV60. When the PAV gain was adjusted to Pmus, aw of 5-10 cmH2O, there was a 93% probability of PTPoes <224 cmH2O•s/min and 88% probability of PTPoes, PEEPi < 255 cmH2O•s/min. CONCLUSION: Deducing maximal muscular pressure from ΔP during PAV has limited accuracy. The extrapolated pressure time product from ΔP is usually less than the pressure time product calculated from oesophageal pressure tracing. However, when the PAV gain was adjusted to Pmus, aw of 5-10 cmH2O, there was a 90% probability of PTPoes and PTPoes, PEEPi within acceptable ranges. This information should be considered when applying ΔP to set PAV under various gains.

Impact of prolonged assisted ventilation on diaphragmatic efficiency: NAVA versus PSV.

BACKGROUND: Prolonged controlled mechanical ventilation depresses diaphragmatic efficiency. Assisted modes of ventilation should improve it. We assessed the impact of pressure support ventilation versus neurally adjusted ventilator assist on diaphragmatic efficiency. METHOD: Patients previously ventilated with controlled mechanical ventilation for 72 hours or more were randomized to be ventilated for 48 hours with pressure support ventilation (n =12) or neurally adjusted ventilatory assist (n = 13). Neuro-ventilatory efficiency (tidal volume/diaphragmatic electrical activity) and neuro-mechanical efficiency (pressure generated against the occluded airways/diaphragmatic electrical activity) were measured during three spontaneous breathing trials (0, 24 and 48 hours). Breathing pattern, diaphragmatic electrical activity and pressure time product of the diaphragm were assessed every 4 hours. RESULTS: In patients randomized to neurally adjusted ventilator assist, neuro-ventilatory efficiency increased from 27 ± 19 ml/µV at baseline to 62 ± 30 ml/µV at 48 hours (p <0.0001) and neuro-mechanical efficiency increased from 1 ± 0.6 to 2.6 ± 1.1 cmH2O/µV (p = 0.033). In patients randomized to pressure support ventilation, these did not change. Electrical activity of the diaphragm, neural inspiratory time, pressure time product of the diaphragm and variability of the breathing pattern were significantly higher in patients ventilated with neurally adjusted ventilatory assist. The asynchrony index was 9.48 [6.38- 21.73] in patients ventilated with pressure support ventilation and 5.39 [3.78- 8.36] in patients ventilated with neurally adjusted ventilatory assist (p = 0.04). CONCLUSION: After prolonged controlled mechanical ventilation, neurally adjusted ventilator assist improves diaphragm efficiency whereas pressure support ventilation does not. TRIAL REGISTRATION: ClinicalTrials.gov study registration: NCT02473172, 06/11/2015.

Application of neurally adjusted ventilatory assist in neonates.

Neurally adjusted ventilatory assist (NAVA) uses the electrical activity of the diaphragm (Edi) as a neural trigger to synchronize mechanical ventilatory breaths with the patient's neural respiratory drive. Using this signal enables the ventilator to proportionally support the patient's instantaneous drive on a breath-by-breath basis. Synchrony can be achieved even in the presence of significant air leaks, which make this an attractive choice for invasive and non-invasive ventilation of the neonate. This paper describes the Edi signal, neuroventilatory coupling, and patient-ventilator synchrony including the functional concept of NAVA. Safety features, NAVA terminology, and clinical application of NAVA to unload respiratory musculature are presented. The use of the Edi signal as a respiratory vital sign for conventional ventilation is discussed. The results of animal and adult studies are briefly summarized and detailed descriptions of all NAVA-related research in pediatric and neonatal patients are provided. Further studies are needed to determine whether NAVA will have significant impact on the overall outcomes of neonates.

Asynchrony, neural drive, ventilatory variability and COMFORT: NAVA versus pressure support in pediatric patients. A non-randomized cross-over trial.

PURPOSE: To determine if neurally adjusted ventilatory assist (NAVA) improves asynchrony, ventilatory drive, breath-to-breath variability and COMFORT score when compared to pressure support (PS). METHODS: This is a non-randomized short-term cross-over trial in which 12 pediatric patients with asynchrony (auto-triggering, double triggering or non-triggered breaths) were enrolled. Four sequential 10-min periods of data were recorded after 20 min of ventilatory stabilization (wash-out) at each of the following settings: baseline PS with the ventilator settings determined by the attending physician (1-PS(b)); PS after optimization (2-PS(opt)); NAVA level set so that maximum inspiratory pressure (P(max)) equaled P(max) in PS (3-NAVA); same settings as in 2-PS(opt) (4-PS(opt)). RESULTS: The median asynchrony index was significantly lower during NAVA (2.0%) than during 2-PS(opt) (8.5%, p = 0.017) and 4-PS(opt) (7.5%, p = 0.008). In NAVA mode, the NAVA trigger accounted on average for 66% of triggered breaths. The median trigger delay with respect to neural inspiratory time was significantly lower during NAVA (8.6%) than during 2-PS(opt) (25.2%, p = 0.003) and 4-PS(opt) (28.2%, p = 0.0005). The median electrical activity of the diaphragm (EAdi) change during trigger delay normalized to maximum inspiratory EAdi difference was significantly lower during NAVA (5.3%) than during 2-PS(opt) (21.7%, p = 0.0005) and 4-PS(opt) (24.6%, p = 0.001). The coefficient of variation of tidal volume was significantly higher during NAVA (44.2%) than during 2-PS(opt) (19.8%, p = 0.0002) and 4-PS(opt) (23.0%, p = 0.0005). The median COMFORT score during NAVA (15.0) was lower than that during 2-PS(opt) (18.0, p = 0.0125) and 4-PS(opt) (17.5, p = 0.039). No significant changes for any variable were observed between 1-PS(b) and 2-PS(opt). CONCLUSIONS: Neurally adjusted ventilatory assist as compared to optimized PS results in improved synchrony, reduced ventilatory drive, increased breath-to-breath mechanical variability and improved patient comfort.

Effect of adaptive servo-ventilation on 1-year prognosis in heart failure patients.

BACKGROUND: Adaptive servo-ventilation (ASV) has been used as therapy for heart failure (HF). The objective of the present study was to estimate the effect of ASV on 1-year prognosis in HF patients. METHODS AND RESULTS: After optimizing medical therapy, a 1-year follow-up study was conducted of 85 HF patients (mean age, 72 ± 10 years; 46 men), categorized as New York Heart Association class II-IV. The patients were classified into 2 groups based on adherence to ASV therapy. Use of ASV for ≥ 4h/night was designated as good adherence, and use of ASV for <4h/night was designated as poor adherence. The incidence of fatal cardiovascular events including death from progression of HF, cardioembolic stroke, and fatal cardiac arrhythmias was tracked. Fifty-seven patients were classified into the good adherence group. After 1-year follow-up, the survival rate calculated using Kaplan-Meier analysis was significantly higher in the good adherence group than in the poor adherence group (P=0.0046, log-rank test). In a Cox proportional hazards model, the odds ratio (95% confidence interval) of fatal cardiovascular events was 0.53 (0.27-0.99) for the good ASV adherence group (P=0.046). CONCLUSIONS: ASV prevents fatal cardiovascular events and improves survival in HF patients.

Neurally adjusted ventilatory assist in patients with critical illness-associated polyneuromyopathy.

PURPOSE: Diaphragmatic electrical activity (EA(di)), reflecting respiratory drive, and its feedback control might be impaired in critical illness-associated polyneuromyopathy (CIPM). We aimed to evaluate whether titration and prolonged application of neurally adjusted ventilatory assist (NAVA), which delivers pressure (P (aw)) in proportion to EA(di), is feasible in CIPM patients. METHODS: Peripheral and phrenic nerve electrophysiology studies were performed in 15 patients with clinically suspected CIPM and in 14 healthy volunteers. In patients, an adequate NAVA level (NAVAal) was titrated daily and was implemented for a maximum of 72 h. Changes in tidal volume (V (t)) generation per unit of EA(di) (V (t)/EA(di)) were assessed daily during standardized tests of neuro-ventilatory efficiency (NVET). RESULTS: In patients (median [range], 66 [44-80] years), peripheral electrophysiology studies confirmed CIPM. Phrenic nerve latency (PNL) was prolonged and diaphragm compound muscle action potential (CMAP) was reduced compared with healthy volunteers (p < 0.05 for both). NAVAal could be titrated in all but two patients. During implementation of NAVAal for 61 (37-64) h, the EA(di) amplitude was 9.0 (4.4-15.2) µV, and the V (t) was 6.5 (3.7-14.3) ml/kg predicted body weight. V (t), respiratory rate, EA(di), PaCO(2), and hemodynamic parameters remained unchanged, while PaO(2)/FiO(2) increased from 238 (121-337) to 282 (150-440) mmHg (p = 0.007) during NAVAal. V (t)/EA(di) changed by -10 (-46; +31)% during the first NVET and by -0.1 (-26; +77)% during the last NVET (p = 0.048). CONCLUSION: In most patients with CIPM, EA(di) and its feedback control are sufficiently preserved to titrate and implement NAVA for up to 3 days. Whether monitoring neuro-ventilatory efficiency helps inform the weaning process warrants further evaluation.

A physiologic comparison of proportional assist ventilation with load-adjustable gain factors (PAV+) versus pressure support ventilation (PSV).

PURPOSE: To compare patient-ventilator interaction during PSV and PAV+ in patients that are difficult to wean. METHODS: This was a physiologic study involving 11 patients. During three consecutive trials (PSV first trial--PSV1, followed by PAV+, followed by a second PSV trial--PSV2, with the same settings as PSV1) we evaluated mechanical and patient respiratory pattern; inspiratory effort from excursion Pdi (swing(Pdi)), and pressure-time products of the transdiaphragmatic (PTPdi) pressures. Inspiratory (delay(trinsp)) and expiratory (delay(trexp)) trigger delays, time of synchrony (time(syn)), and asynchrony index (AI) were assessed. RESULTS: Compared to PAV+, during PSV trials, the mechanical inspiratory time (Ti(flow)) was significantly longer than patient inspiratory time (Ti(pat)) (p < 0.05); Ti(pat) showed a prolongation between PSV1 and PAV+, significant comparing PAV+ and PSV2 (p < 0.05). PAV+ significantly reduced delay(trexp) (p < 0.001). The portion of tidal volume (VT) delivered in phase with Ti(pat) (VT(pat)/VT(mecc)) was significantly higher during PAV+ (p < 0.01). The time of synchrony was significantly longer during PAV+ than during PSV (p < 0.001). During PSV 5 patients out of 11 showed an AI greater than 10%, whereas the AI was nil during PAV+. CONCLUSION: PAV+ improves patient-ventilator interaction, significantly reducing the incidence of end-expiratory asynchrony and increasing the time of synchrony.