Pulmonary Response to an Inhaled Bronchodilator in Chronically Ventilated Preterm Infants with Suspected Airway Reactivity

Abstract

Background

Airway reactivity is a common clinical problem in infants who require prolonged ventilator support. The decision to utilize inhaled bronchodilator therapy is frequently based on the patient's history and on the presence of intermittent wheezing and bronchospasm during examination. The response to this therapy is often difficult to quantify.

Methods

We retrospectively analyzed dynamic compliance (C_dyn) and total respiratory-system resistance (R_I [inspiratory], R_E [expiratory], R_tot [total]) by esophageal manometry and pneumotachography before (PRE) and 20 minutes after (POST) 1 actuation (90 µg) of albuterol sulfate via the endotracheal tube in 25 intubated infants (mean [SD] weight at study 1.65 [1.05] kg, mean [SD] age at study 6.6 [4.6] weeks, and mean [SD] gestational age 28 [4] weeks). These infants had been receiving mechanical ventilation and were suspected of having increased airway reactivity. Functional residual capacity (FRC) had been determined by helium dilution prior to study.

Results

There were no significant differences between PRE and POST values of tidal volume, minute ventilation, or peak airway pressure, Cdyn, R_tot, or R_I R_E was significantly reduced POST (p < 0.05). Ten infants had a greater than 25% decrease in R_tot after albuterol, whereas 9 babies had less than a 25% decrease in R_tot. An additional 6 neonates had a greater than 25% increase in R_tot when compared to their PRE value. Tidal flow-volume-loops revealed evidence of tracheobronchomalacia (TBM) in 4 of 9 nonresponders in PRE treatment testing, and in 2 of 6 negative responders in POST-treatment testing. R was lower PRE in the negative-response group compared to the positive-response and no-response groups.

Conclusion

Measurement of lung function may be helpful in assessing response to bronchodilator therapy in preterm infants, and unnecessary use of this therapy can be avoided in patients who do not have a positive response. Such studies may also predict which infants will not respond to inhaled bronchodilator therapy. Increased airway reactivity may be clinically indistinguishable from fixed airway obstruction or TBM.