Comparison of inspiratory work of breathing between flow-triggered and pressure-triggered demand flow systems in rabbits.
OBJECTIVE
Flow-triggered continuous positive airway pressure decreases the inspiratory work of breathing in adults when compared with pressure-triggered continuous positive airway pressure. However, the effect of flow-triggered continuous positive airway pressure on work of breathing in neonates is not known. Our objective was to determine if flow-triggering was superior to pressure triggering in the presence of narrow endotracheal tubes, such as those tubes used in neonates.


METHODS
Prospective evaluation using within-animal comparison of flow-triggering and pressure-triggering demand flow systems.


METHODS
The animal laboratory in a university hospital.


METHODS
Six spontaneously breathing white rabbits, tracheostomized and intubated with 3- and 4-mm inner diameter endotracheal tubes.


METHODS
The animals were connected to a ventilator through a standard respiratory circuit. The ventilator was randomly operated in the following modes: flow-triggered continuous positive airway pressure, pressure-triggered continuous positive airway pressure, flow-triggered with 5 cm H2O pressure support ventilation, and pressure-triggered with 5 cm H2O pressure support ventilation.


RESULTS
Esophageal pressure, airway pressure, and flow signals were monitored. Control data were obtained while the rabbits were breathing room air through the endotracheal tube. With 3-mm inner diameter endotracheal tubes, the negative deflection of esophageal pressure during flow-triggered continuous positive airway pressure was significantly less than control; however, negative deflection of esophageal pressure during pressure-triggered continuous positive airway pressure did not significantly differ from control. The application of 5 cm H2O pressure support ventilation with flow-triggering decreased negative deflection of esophageal pressure significantly compared with flow-triggered continuous positive airway pressure, pressure-triggered continuous positive airway pressure, and control. With endotracheal tube inner diameter of 4 mm, flow-triggered continuous positive airway pressure and pressure-triggered continuous positive airway pressure did not show any differences compared to control. Negative deflection of esophageal pressure differed under all conditions except control when results with the 3-mm inner diameter endotracheal tube were compared with the 4-mm inner diameter endotracheal tube.


CONCLUSIONS
Flow-triggering is superior to pressure-triggering in the presence of a 3-mm inner diameter endotracheal tube. This difference was not clear with a 4-mm inner diameter endotracheal tube. The size of the endotracheal tube may be the most important variable in evaluating the approach used to ventilate small neonates.
Nishimura
M
M
Department of Anesthesiology, Osaka University Medical School, Japan.
Imanaka
H
H
Yoshiya
I
I
Kacmarek
R M
RM
D000399:Air Pressure; D000704:Analysis of Variance; D000818:Animals; D004947:Esophagus / Q000502:physiology; D005069:Evaluation Studies as Topic; D007442:Intubation, Intratracheal / Q000295:instrumentation / Q000379:methods; D011175:Positive-Pressure Respiration / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D011446:Prospective Studies; D012123:Pulmonary Ventilation / Q000502:physiology; D011817:Rabbits; D011897:Random Allocation; D014160:Transducers, Pressure; D014939:Work of Breathing / Q000502:physiology*