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Comparison of inspiratory work of breathing between flow-triggered and pressure-triggered demand flow systems in
M Nishimura1, H Imanaka, I Yoshiya
1Department of Anesthesiology, Osaka University Medical School, Japan.
Objectives:
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.
Design:
Prospective evaluation using within-animal comparison of flow-triggering and pressure-triggering demand flow systems.
Setting:
The animal laboratory in a university hospital.
Subjects:
Six spontaneously breathing white rabbits, tracheostomized and intubated with 3- and 4-mm inner diameter endotracheal tubes.
Interventions:
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.
Measurements And Main 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.