AMERICAN JOURNAL OF PERINATOLOGY/VOLUME 9, NUMBER 5/6

Sept/Nov 1992

CHARACTERISTICS ASSOCIATED WITH SUCCESSFUL WEANING IN VENTILATORDEPENDENT PRETERM INFANTS Elaine M. Sillos, M.D., Mirta Veber, M.D., Marjorie Schulman, M.D., Alfred N. Krauss, M.D., and Peter A.M. Auld, M.D.

Eighteen ventilator-dependent preterm infants with hyaline membrane disease were studied for 24 hours before and after an attempt at extubation. All were treated with theophylline prior to weaning and achieved average levels of 8.9 ±1.7 |jig/ml (49 ± 9 ixmol/liter) in 13 successfully weaned infants and 8.4 ± 1.1 |xg/ml (47 ± 6 (xmol/liter) in 5 infants not extubated, p > 0.05. Infants successfully weaned were significantly (p < 0.01) older, more mature (29 ± 1 versus 26 ± 2 weeks' gestational age) and heavier (1107 ± 236 versus1016 ± 256gm)than infants not successfully extubated. Infants successfully weaned differed only in developing a greater maximal inspiratory force (33.8 ± 12.3 versus 23.3 ± 15.0 cm H2O) and higher compliance (1.1 ± 0.3 versus 0.7 ± 0.3) during the preweaning treatment period. These results indicate that maturity and size play a significant role in the ability to wean a preterm infant from the ventilator successfully, that maximal inspiratory force and compliance are higher in preterm infants who can be successfully extubated, and that methlyxanthines do not uniformly improve pulmonary function in all potentially extubatable preterm infants.

Weaning preterm infants from ventilatory assistance may be unsuccessful because of apnea, hypercapnia, or progressive atelectasis. The ability to wean adult patients with pulmonary failure has been correlated with inspiratory muscle strength.1 Maximum inspiratory pressure, a measure of inspiratory muscle strength, has also been shown to correlate with successful extubation in neonates and infants.2 It has been suggested that adjuvants to weaning, such as theophylline, may act to improve pulmonary function, as central stimulants to ventilation, or to increase the strength of the inspiratory muscles.34 The present study was undertaken in order to determine whether maximal inspiratory force (MIF) was predictive of successful extubation in ventilator-dependent preterm infants treated with theophylline.

SUBJECTS AND METHODS The subjects of this study were 18 preterm infants, described in Table 1. Gestational ages ranged from 24 to 31 weeks, and postconceptional age at time of study ranged from 24 to 33 weeks. Birthweights ranged from 740 to

1420 gm. All infants were studied with their parents' knowledge and consent under a protocol approved by the local human research review committee. No patient experienced any ill effects as a result of participation in this protocol. All patients in this study were ventilator-dependent preterm infants with hyaline membrane disease, diagnosed by standard clinical and radiographic criteria. Patients were selected for this study because they appeared to be ready for extubation. This decision was reached by the clinicians caring for the infant and was not made by the investigators. The decision to wean the patient from ventilatory support was based on the ability to maintain an arterial pH over 7.3 and an arterial oxygen tension (PO2) over 50 torr with a ventilator providing not more than 5 breaths per minute, supplemental oxygen less than 30%, and the absence of clinically significant apnea. Infants unable to maintain these levels of arterial pH, carbon dioxide, and oxygen at an inspired oxygen concentration not exceeding 40% were judged to be ventilator-dependent. When it became clinically apparent that infants were approaching these levels of respiratory support, parental consent for study was obtained. The infant was then given a loading dose of theophylline of 6 mg/kg (33 |xmol/kg),

The Perinatology Center, Department of Pediatrics, New York Hospital—Cornell University Medical College, New York, New York Reprint requests: Dr. Krauss, Perinatology Center, Department of Pediatrics, New York Hospital—Cornell University Medical College, 525 East 68th Street, New York, NY 10021 374

Copyright © 1992 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.

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ABSTRACT

RESPIRATOR WEANING PRETERM INFANTS/Sillos, et al. Demographic Data of Subjects in This Study.*

Successfully Unsuccessfully Birthweight Gestational age (weeks) Postconceptional age (weeks) Weight at time of study (g) Age at time of study

Extubated

Extubated

p Value

1143 ± 225 28.8 ± 1 . 4

813 ± 67 26 ± 2

Characteristics associated with successful weaning in ventilator-dependent preterm infants.

Eighteen ventilator-dependent preterm infants with hyaline membrane disease were studied for 24 hours before and after an attempt at extubation. All w...
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