Outcomes
All outcome parameters were measures/recorded prior to administration
and 30 minutes after completion of each dose of medication. The primary
study outcome was the absolute difference in expiratory flow at 75% of
exhalation (EF75), measured directly from the ventilator flow volume
loops (Figure 1) 30 minutes post study medication administration
compared to immediately prior to administration (post – pre treatment).
Measurement of EF75 was accomplished by calculating the exhaled volume
at 25% of the breath (tidal volume x 0.25) and then recording flow at
this point on the expiratory side of the flow volume loop (Figure 1).
Measurement of EF75 has not been used in prior studies with mechanically
ventilated neonates and was chosen as a measurement that would not
require specialized equipment or the need to alter the mechanical
ventilator mode or settings to perform measurements. Although the
measurement was not performed under conditions of forced exhalation, we
reasoned that the measurement would be made over the effort-independent
portion of the flow-volume curve, especially in a population of patients
with obstructive lung disease. With the administration of a
bronchodilator, we anticipated that the EF75 would become higher with
small airway dilation.
Secondary outcomes were the proportional change in peak inspiratory
pressure (PIP) required to deliver the participant’s set tidal volume,
minute ventilation, total respiratory rate, blood oxygen saturation
level (SpO2), heart rate (HR), and the occurrence of any
abnormal heart rhythm pre- and post- treatment.