Influence of different flow-triggering levels on the breathing effort of mechanically ventilated patients

Although a sensitive flow triggering (FT) level is supposed to be associated with reduced breathing effort, the incidence of autotriggering (AT) is likely to be increased. The actual effects of various FT levels on the work of breathing and occurrence of AT in mechanically ventilated patients are unknown. We investigated the effects of different FT levels (1-8 L/min) on breathing effort and incidence of AT in mechanically ventilated patients under pressure support ventilation using a Puritan-Bennett 840 ventilator.

Eight FT levels were randomly studied in mechanically ventilated patients under pressure support ventilation. The triggering effort (pressure-time product of triggering, PTPtr) was assessed by quantitating a segment of the pressure-time product of the esophagus (PTPes). The total PTPes, inspiratory work of breathing (Wi) and P0.1 were determined.

Nine patients with appropriately recorded signals were included. The incidence of AT significantly decreased with increasing FT level (FT1, 1 L/min: 30.7%, FT8: 0.2%). PTPtr significantly increased with increasing FT level (0.020 ± 0.004 cmH2O • S in FT1 to 0.190 ± 0.017 cmH2O • S in FT8), but P0.1 remained similar. PTPtr accounted for only1-3% of total PTPes. Wi and PTPes were significantly lower only at FT1, but there was no significant difference in Wi and PTPes at different FT levels when AT breaths were excluded.

A higher FT level was associated with lower incidence of AT, but without a significant increase in breathing effort. A higher FT level may be more reasonable in mechanically ventilated patients with this particular ventilator.