Clusters of ineffective efforts during mechanical ventilation: impact on outcome.

Abstract

The aim of this study was to investigate the role of ineffective efforts (IEs), specifically clusters of IEs, during mechanical ventilation on the outcome of critically ill patients. In a prospective observational study, 24-h recordings were obtained in 110 patients on the 1stday of assisted ventilation (pressure support or proportional assist), using a prototype monitor validated to identify IEs. Patients remaining on assisted ventilation were studied again on the 3rdday (n=37) and on the 6thday (n=13). To describe the clusters of IEs, the concept of an IEs event was developed, defined as a 3-min period of time containing more than 30 IEs. Along with all patient data, to minimize selection bias by time of recording, analysis was performed only on 1stday data of patients with ≥16h of recording (1stday group). The analysis included 2931h of assisted ventilation and 4,456,537 breaths. Neither the IEs index (IEs as a percentage of total breaths) in general nor a value above 10% was correlated with patient outcome. Overall, IEs events were identified in 38% of patients. In multivariate analysis, the presence of events in the 1stday group (n=79) was associated with the risk of being on mechanical ventilation ≥8days after first recording [odds ratio 6.4, 95% confidence interval (1.1-38.30)] and hospital mortality [20 (2.3-175)]. Analysis of the data for all patients revealed similarly increased risks for prolonged ventilation [3.4 (1.1-10.7)] and mortality [4.9 (1.3-18)]. Clusters of IEs are often present in mechanically ventilated critically ill patients and are associated with prolonged mechanical ventilation and increased mortality. Studies to find ways of improving patient-ventilator interaction are warranted.