A noninvasive method to identify ineffective triggering in patients with noninvasive pressure support ventilation.

BACKGROUND Ineffective inspiratory triggering efforts are a major cause of poor patient-ventilator interactions during mechanical ventilation, but their routine identification requires the insertion of an esophageal catheter. OBJECTIVES We developed a mathematical analysis of ventilatory tracings recorded under noninvasive pressure ventilation in order to identify ineffective triggering efforts and their consequences without recording esophageal pressure. METHODS We assessed 2,183 cycles from 44 pressure support tracings in 14 children with cystic fibrosis treated by noninvasive home ventilation. Airway pressure, flow and esophageal pressure time series were visually analyzed and manually counted. Airway pressure versus time and flow versus time were then analyzed using a dedicated algorithm written by us. Esophageal pressure was only used for validation. RESULTS A mathematical treatment of flow time series allowed us to draw phase portraits that had specific periodic trajectories for triggered ventilatory cycles and ineffective triggering efforts. From flow and pressure tracings, our algorithm correctly identified 100% of triggered cycles and 53/56 (94.6%) of ineffective triggering efforts. Ineffective triggering was associated with a significant reduction in minute ventilation, inspiratory flows and a significant increase in inspiratory efforts. CONCLUSIONS A noninvasive analysis of flow and airway pressure can reliably identify ineffective triggering efforts during noninvasive pressure support ventilation. This approach may be a valuable tool for evaluating patient-ventilator interactions and their consequences during long-term recordings.