Purpose
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.

Methods
In a prospective observational study, 24-h recordings were obtained in 110 patients on the 1st day 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 3rd day (n = 37) and on the 6th day (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 1st day data of patients with ≥16 h of recording (1st day group).

Results
The analysis included 2931 h 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 1st day group (n = 79) was associated with the risk of being on mechanical ventilation ≥8 days 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)].

Conclusions
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.