Am. J. Respir. Crit. Care Med., Vol 154, No. 4, 10 1996, 1049-1054.
Patient-triggered ventilation in neonates: comparison of a flow-and an impedance-triggered system
HD Hummler, T Gerhardt, A Gonzalez, J Bolivar, N Claure, R Everett and E Bancalari
University of Miami School of Medicine, Florida, USA.
We conducted a study with the objective of comparing the performance of two
different systems for patient-triggered ventilation in neonates (impedance
versus flow/volume-triggered) by measuring response time, autotrigger and
trigger failure rates, ventilation, and gas exchange. The two ventilator
systems were applied in random order in 10 preterm neonates (median
gestational age: 30.5 wk; range: 27 to 34 wk; body weight: 1,266 g; range:
840 to 2,240 g) using identical ventilator settings. The median (range)
response time was 169 (98 to 305) ms for the impedance system and 115 (79
to 184) ms for the flow/volume system (p < 0.01). The longer and more
variable response time of the impedance system was secondary to a phase lag
of the impedance signal caused by chest wall distortion. Although 13.1 (0.2
to 29.4)% of mechanical breaths were autotriggered with the impedance
system, there were no autotriggered breaths using the flow/volume system (p
< 0.01). The rate of trigger failures was not significantly different
with the two systems, at 1.2 (0 to 4.4)% (impedance) versus 3.1 (0 to 6.4)%
(flow/volume). Minute ventilation was smaller with the impedance system (p
< 0.001), because of the larger number of breaths triggered late in
inspiration or during expiration. We conclude that the flow/volume-
triggered system is less prone to autotriggering and has a shorter and more
consistent response time than the impedance-triggered system. The
impedance-triggered system is more susceptible to artifacts and chest wall
distortion.
