Birth weight and early lung compliance as predictors of short-term outcome in premature infants with respiratory distress syndrome
The original publication is available at http://www.samj.org.za
In addition to birth weight (BW), respiratory mechanics measured during the first week of life have been reported to predict outcome in ventilated newborn infants with respiratory distress syndrome(RDS). Most measuring techniques are invasive, requiring the placement of an oesophageal tube or balloon. In the present study the compliance (Crs) and resistance (Rrs) of the total respiratory system were measured without an oesophageal tube, using a commercially available system (PEDS; MAS Inc., Hatfield, Pa.). The Crs and Rrs were determined once, within 24 hours of birth, in 28 preterm infants requiring mechanical ventilation for RDS. Variables such as gestational age (GA) and BW were also evaluated for their predictive role in outcome. Poor outcome was defined as death from respiratory failure or the development of bronchopulmonary dysplasia (BPD) at 28 days. All non-survivors died of refractory respiratory failure, at a median age of 6 days. The median Crs of the 21 survivors was 0.5 ml/cm H2O and of the non-survivors 0.21 ml/cm H2O (P = 0.01). Crs below 0.45 ml/cm H2O predicted 15 of the 16 infants who either developed BPD or died (positive predictive value 100%; negative predictive value 92%; sensitivity 94%; specificity 100%). Nine survivors, who subsequently developed BPD, had a median Crs of 0.38 ml/cm H2O. Their Crs was significantly lower than that of the infants without evidence of BPD (Crs = 0.61 ml/cm H2O) (P = 0.01). All of the 12 babies without BPD who survived had median Crs values above 0.45 ml/cm H20. The median Rrs of the 9 infants with BPD (96 cm H2O/l/s) was also significantly higher than the Rrs value of the non-BPD group (59 cm H2O/l/s) (P = 0.05). When stepwise multiple logistic regression was applied to predict outcome, the only variable that could be entered at a 0.05 level of significance was BW. Uncorrected compliance entered the second step, but did not reach statistical significance. We conclude that in premature infants with RDS, BW is a strong predictor of outcome. Although determination of the Crs within the first 24 hours after birth did not add significance to this predictive model, it was nevertheless a useful parameter to determine respiratory morbidity and mortality.
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