Skip to main content

Patient-ventilator asynchrony during conventional or automated pressure support ventilation in difficult-to-wean patients


Patient-ventilator asynchrony, defined as a mismatch between patient's inspiratory time and the ventilator insufflation time, occurs in nearly 25% of intubated patients. High asynchrony rates are associated with higher incidence of weaning failure and tracheostomy, and prolonged mechanical ventilation. The aim of this study was to compare the asynchrony rate during conventional pressure support ventilation (PSV) and automated PSV (SmartCare; Draeger) in difficult-to-wean patients.


A prospective, crossover study in difficult-to-wean patients (patients who required up to three spontaneous breathing trials (SBTs) or as long as 7 days to achieve successful weaning). Patients were ventilated with an Evita XL ventilator for two consecutive 3-hour periods applied in random order: with conventional PSV managed by the attending physicians; and with PSV managed by SmartCare. The periods were administered in the afternoon (3:00 to 9:00 pm) and in the night (12:00 pm to 6:00 am). In both periods, the starting PS level with either conventional or automated PSV was the basal level before enrolment. During every period, airway pressure, flow and volume signals were continuously recorded on a PC connected to t he ventilator using dedicated software (VentView). These signals were analyzed offline by two clinicians. The asynchrony index was defined as the number of asynchronies (wasted efforts, double cycles, premature cycling off ) divided by the total respiratory rate (ventilator cycles + asynchrony events), multiplied by 100.


Sixteen patients were enrolled (age 64 ± 11 years; SAPS II 66 ± 14; COPD 25%; days of mechanical ventilation before enrollment 9 ± 4, number of SBTs 3 ± 1). The asynchrony index was lower with Smartcare (10% vs. 14%, P = 0.01), but not different between afternoon and night. Mean PS level (11 vs. 12 cmH2O) was not different between conventional and automated PSV, although the coefficient of variability of PS level was greater with Smartcare (20% vs. 0%, P < 0.01). No differences were observed in PaCO2 (36 vs. 36 mmHg), PaO2 (106 vs. 102 mmHg), total respiratory rate (22 vs. 23), and P0.1 (1.4 vs. 1.6 cmH2O) between conventional PSV and Smartcare.


As compared with conventional PSV, Smartcare may reduce asynchronies in difficult-to-wean patients, possibly because of greater variability of the PS level. This needs to be further confirmed.

Author information

Authors and Affiliations


Rights and permissions

This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and Permissions

About this article

Cite this article

Bitondo, M., Aguirre-Bermeo, H., Moccaldo, A. et al. Patient-ventilator asynchrony during conventional or automated pressure support ventilation in difficult-to-wean patients. Crit Care 16, P126 (2012).

Download citation

  • Published:

  • DOI:


  • Pressure Support Ventilation
  • Prolonged Mechanical Ventilation
  • Spontaneous Breathing Trial
  • Successful Weaning
  • Asynchrony Index