Am. J. Respir. Crit. Care Med., Vol 157, No. 1, 01 1998, 135-143.
Effects of flow triggering on breathing effort during partial ventilatory support [In Process Citation]
P Aslanian, S El Atrous, D Isabey, E Valente, D Corsi, A Harf, F Lemaire and L Brochard
Medical Intensive Care Unit and INSERM U296, Paris XII University, Hopital Henri Mondor, Creteil, France.
The effects of flow triggering (FT) as compared with pressure triggering
(PT) on breathing effort have been the focus of several studies, and
discrepant results have been reported. In the initial part of our study, a
lung model was used to quantify triggering effort (airway pressure-time
product, PTPaw) for a range of sensitivity settings in nine new-generation
ventilators. A ventilator providing both FT and PT was then used to compare
these systems during pressure- support (PSV) and volume-targeted
assist-control ventilation (ACV) in eight ventilator-dependent patients,
using sensitivity settings (2 L/min for FT and -2 cm H2O for PT) that had
proven significantly different in the initial bench study. Indexes of
effort included the esophageal and transdiaphragmatic pressure-time
products and inspiratory work of breathing per minute (PTPes/min,
PTPdi/min, and Wi/min, respectively). The experimental study revealed
significant differences between ventilators in PTPaw at commonly used
settings. In two of three ventilators featuring both systems, PTPaw was
significantly lower with FT than PT (p < 0.001). In the clinical study,
FT as compared with PT, was associated with reductions in all indexes of
breathing effort during PSV: 16 +/- 6% (p < 0.001), 13 +/- 10% (p <
0.01), and 14 +/- 12% (p < 0.05) for PTPdi/min, PTPes/min, and Wi/min,
respectively. By contrast, no differences were found when FT was used
during ACV. Although FT reduced triggering effort in both modes (p <
0.001), the effects observed during the post-trigger phase differed, and
explained the discrepant results between the two modes. We conclude that FT
more effectively reduces breathing effort when used in conjunction with a
pressure-targeted mode than with a volume-targeted mode, especially when
flow delivery is close to or below demand.
