Am. J. Respir. Crit. Care Med., Vol 150, No. 3, Sep 1994, 759-765.
Time course of changes in lung mechanics following fetal steroid treatment
CJ Lanteri, KE Willet, S Kano, AH Jobe, M Ikegami, DH Polk, JP Newnham, R Kohan, R Kelly and PD Sly
W.A. Research Institute for Child Health, Perth, Australia.
We studied the effect of a single-dose, corticosteroid treatment on preterm
lambs (gestational age: 128 d). A low, medium, or high betamethasone dose
(0.1, 0.5, and 2.0 mg/kg) or saline control was administered directly to
the fetus by ultrasound-guided intramuscular injection 48 h before
delivery. A second group received either the high dose of betamethasome or
saline 24 h before delivery. The lambs were delivered at 128 d gestation,
anesthetized with ketamine, and ventilated for 50 min. Respiratory system
elastance and resistance were measured at 10-min intervals using multiple
linear regression analysis of pressure, flow, and volume. Similarly,
estimates of lung mechanics were calculated from transpulmonary pressure.
The viscoelastic time constant (tau) was calculated by fitting an
exponential to the pressure changes occurring after occluding the airway
during expiration. Excised lung volume at 40 cm H2O and lung weight were
used to calculate specific elastance and resistance correcting for lung
size using volume or weight, respectively. Of the 13 lambs in the 48-h
high-dose betamethasone group, five developed pulmonary interstitial
emphysema (PIE) as did 3 of 11 animals in the high-dose group treated 24 h
before delivery. These animals were analyzed separately. The lambs
receiving medium- or high-dose (24 and 48 h predelivery) betamethasone had
significantly lower elastance and a trend toward lower resistance when
compared with the control groups. Ten minutes after delivery, the animals
that developed PIE all had elastance values comparable to that of the
control animals despite corticosteroid treatment.(ABSTRACT TRUNCATED AT 250
WORDS)
