


* Division of Paediatrics, Royal Womens Hospital, Melbourne, Australia
Departments of Obstetrics and Gynaecology and of Paediatrics, University of Melbourne, Melbourne, Australia
Department of Child Health, Queens University, Belfast, Northern Ireland
|| Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut
¶ Department of Pediatrics, McMaster University, Hamilton, Ontario, Canada
# Department of Pediatrics, Center for Clinical Research and Evidence-Based Medicine, University of Texas Medical School, Houston, Texas
| ABSTRACT |
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Methods. Randomized, controlled trials of postnatal corticosteroid therapy for prevention or treatment of CLD in preterm infants that reported rates of both mortality and CP were reviewed and their data were synthesized. Twenty studies with data on 1721 randomized infants met eligibility criteria. The relationship between the corticosteroid effect on the combined outcome, death or CP, and the risk for CLD in control groups was analyzed by weighted meta-regression.
Results. Among all infants who were randomized, a significantly higher rate of CP after corticosteroid treatment (typical risk difference [RD]: 0.05; 95% confidence interval [CI]: 0.02, 0.08) was partly offset by a nonsignificant reduction in mortality (typical RD: 0.02; 95% CI: 0.06 to 0.02). Consequently, there was no significant effect of corticosteroid treatment on the combined rate of mortality or CP (typical RD: 0.03; 95% CI: 0.01 to 0.08). However, on meta-regression, there was a significant negative relationship between the treatment effect on death or CP and the risk for CLD in control groups. With risks for CLD below 35%, corticosteroid treatment significantly increased the chance of death or CP, whereas with risks for CLD exceeding 65%, it reduced this chance.
Conclusions. The effect of postnatal corticosteroids on the combined outcome of death or CP varies with the level of risk for CLD.
Key Words: infant preterm survival cerebral palsy corticosteroids
Abbreviations: CLD, chronic lung disease CP, cerebral palsy RCT, randomized, controlled trial RR, relative risk RD, risk difference CI, confidence interval IQR, interquartile range
Improved survival of preterm infants has been accompanied by an increased rate of chronic lung disease (CLD),1 most often defined as a dependence on supplemental oxygen beyond 36 weeks postmenstrual age. From the mid-1980s, postnatal corticosteroids were increasingly prescribed for prevention or treatment of CLD, supported by evidence of benefit on some short-term outcomes, including earlier weaning from mechanical ventilation and a reduction in CLD.24 In the era before postnatal corticosteroid treatment, the long-term neurodevelopmental outcome for survivors with CLD was worse than that in similar infants without CLD.5,6 Therefore, a reduction in CLD might be expected to reduce the rate of adverse long-term sequelae. However, corticosteroids can have direct toxic effects on the developing brain, including neuronal necrosis, interference with healing, and inhibition of brain growth.7,8 There is currently concern about possible adverse long-term effects of postnatal corticosteroids, cerebral palsy (CP) having been reported to occur more frequently in some randomized, controlled trials (RCTs)911 and meta-analyses of RCTs.2,12 Recently, the European Association of Perinatal Medicine issued a warning about postnatal corticosteroids,13 and the American Academy of Pediatrics and the Canadian Pediatric Society stated that routine postnatal use of systemic dexamethasone (the most commonly prescribed corticosteroid) for prevention or treatment of CLD is not recommended.14
Clinicians currently have a dilemma when faced with an infant who is increasingly ventilator dependent: should they start corticosteroids in an attempt to reduce ventilator and oxygen dependence and possibly to improve long-term outcome, or should they avoid corticosteroids because they may be independently harmful? Interpreting the RCTs of postnatal corticosteroids is difficult as there are differences in the baseline risks for CLD, the timing and the dose of corticosteroids according to the protocol, and the rate of open-label corticosteroids given to infants in the placebo group (the "contamination" rate). The follow-up data also differ regarding the age of children at follow-up, the follow-up rate, and the expertise of the personnel involved in the follow-up assessments. Early death and CP among survivors are competing outcomes, and both must be considered when evaluating the effect of corticosteroid treatment. The aims of this report were to synthesize the data concerning mortality and CP from all RCTs of postnatal systemic corticosteroids for treatment or prevention of CLD in preterm infants and to test the hypothesis that the effect of corticosteroids is modified by the level of risk for CLD.
| METHODS |
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Data were analyzed in RevMan 4.2.2, with the endpoints being mortality before follow-up; CP; and, to allow for the competing risks of death and long-term morbidity, the combination of CP or death. The measures of treatment effect for individual trials included relative risk (RR); risk difference (RD); and, for the meta-analyses the typical RR and typical RD, all with their 95% confidence intervals (CIs). A fixed-effects model was assumed for meta-analysis, with significant statistical heterogeneity defined as P < .05. In addition to examining the effect of corticosteroids on death and CP in all of the trials taken together, we conducted subgroup analyses that were based on the postnatal age of starting corticosteroids (early and later) and on the contamination rate (no contamination, >0% to <35% contamination, and
35% contamination).
We examined the relationship between the corticosteroid effect on the combined outcome, death or CP, and the risk for CLD (indicated by the rate of CLD in the control group) by weighted meta-regression analysis in Stata (version 7.0)15 to test the hypothesis that the treatment effect on survival free of CP would be less favorable in trials that were conducted in populations at low risk for CLD and more favorable in trials that were conducted in populations at high risk for CLD. Meta-regression fits models with 2 additive components of variance, one representing the variance within studies, the other the variance between studies. Variance within studies is related to sample size, and larger studies contribute more to the overall results. We then adjusted for other important study design variables, including timing (early versus later) and total dose (
3.0 mg/kg, <3.0 mg/kg) of corticosteroids, the contamination rate (<35%,
35%), the follow-up rate (
90%, <90%), assessment by blinded experts (yes, no), and age of follow-up (
36 months, <36 months). These cutpoints were chosen either to be around the median (dose, contamination rate, and age of follow-up) or because they represented desirable features of follow-up studies (follow-up rate and outcome assessment). We then repeated the meta-regression analyses to examine the relationship between the rate of CLD in the control group and the corticosteroid effect on death and CP separately, without adjusting for the other study variables. For all analyses, P < 0.05 was considered statistically significant.
| RESULTS |
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Clinical characteristics of the studies varied widely (Table 1). In 9 studies, therapy started in the first week of life, and in 11, therapy started after the first week of life. The median cumulative dose of steroids (in mg/kg dexamethasone equivalent) according to the protocol was 3.0 (interquartile range [IQR]: 1.15.0), the median contamination rate (available for 17 studies only) was 33% (IQR: 16%49%), and the median control group rate of CLD at 36 weeks postmenstrual age in the 14 studies that reported this outcome was 50% (IQR: 28%69%). Follow-up method also varied widely (Table 1); the median age at assessment was 36 months (IQR: 1958 months); the follow-up rate was at least 90% in 70% (n = 14) of studies; and in 70% (n = 14) of studies, children were assessed by experts who were blinded to treatment allocation.
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In the subgroup analysis that was restricted to the studies that had a contamination rate from >0% to <35% (7 studies, 658 infants), there was no significant effect on mortality (typical RD: 0.01; 95% CI: 0.08 to 0.06; P = .75), a significant increase in CP among all randomized (typical RD: 0.09; 95% CI: 0.04 to 0.14; P < .001), and a significant increase in the combined outcome of death or CP (typical RD: 0.08; 95% CI: 0.01 to 0.16; P = .03). In the subgroup analysis that was restricted to studies that had a contamination rate
35% (8 studies, 767 infants), there was no significant effect on either mortality (typical RD: 0.02; 95% CI: 0.04 to 0.08; P = .50) or CP among all randomized (typical RD: 0.01; 95% CI: 0.05 to 0.04; P = .76) or the combined outcome of death or CP (typical RD: 0.01; 95% CI: 0.05 to 0.08; P = .69).
Meta-Regression Analysis: Relation of Treatment Effect to Control Risk for CLD
Fourteen studies reported the rate of CLD at 36 weeks postmenstrual age in the control group; this ranged from 9.5% to 73.8% (Table 1). Meta-analysis of these 14 studies found no significant effect on the combined rate of death or CP among children who were randomized (typical RD: 0.04; 95% CI: 0.02 to 0.09). However, there was a significant negative relationship between the RD for death or CP and the rate of CLD in the control group in these studies (Fig 1): for every 10% that the rate of CLD increased in the control group, the RD for death or CP fell by 3.8% (95% CI: 1.4% to 6.2%; P = .002). The regression line crossed 0 (no effect on death or CP) at a rate of CLD of
50%. At control rates of CLD below
35%, the lower bound of the 95% CI for the regression line was >0, indicating a significantly increased rate of death or CP with corticosteroid treatment. At control rates of CLD above
65%, the upper bound of the 95% CI for the regression line was <0, indicating a significant treatment benefit for this outcome.
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Meta-regression of RD for death alone against the rate of CLD in the control group showed a nonsignificant negative relationship (Y = 3.7 0.17X; P = .11). For every 10% increase in the rate of CLD in the control group, the RD for death fell by 1.7% (95% CI: 0.4% to 3.9%). Meta-regression of RD for CP alone against the rate of CLD in the control group showed a significant negative relationship (Y = 14.1 0.23X; P = .023). For every 10% that the rate of CLD increased in the control group, the RD for CP fell by 2.3% (95% CI: 0.3% to 4.3%)
| DISCUSSION |
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The 20 studies included in this review were all randomized trials. Although all studies reported effects on some long-term outcomes, none was designed primarily to assess long-term effects of treatment. We attempted to obtain as complete a data set as possible by contacting the investigators and requesting any unpublished data concerning long-term outcomes. In the included studies, children were assessed mostly early in childhood, before the diagnosis of CP can be certain,46 not always by experts who were blinded to treatment group, not always using explicit and reproducible criteria for the diagnosis of CP, and sometimes with potentially important (>10%) loss to follow-up.
Corticosteroids that are given after birth to preterm infants with lung disease have proved short-term benefits, including reductions in ventilator and oxygen dependence and in incidence of CLD.24 These short-term benefits might be expected to lead to a reduction in adverse neurodevelopmental outcomes associated with CLD in preterm infants. However, among all trials, we found no evidence of benefit of postnatal corticosteroid treatment on the rate of CP, regardless of whether the competing risk for death before follow-up was taken into account. In fact, the direction of effects was generally that of harm, reaching statistical significance for CP among all randomized and among survivors examined.
The subgroup analyses that were based on contamination rates of control groups in the various trials support the interpretation of a causal relationship, overall, between postnatal corticosteroid treatment and CP, in that this relationship was stronger in the trials with no or less contamination and weaker or nonexistent in the trials with high rates of contamination. In trials with low or no contamination, there was a tendency for corticosteroid treatment to reduce mortality. This pattern suggests that, overall, postnatal corticosteroid treatment, although maybe reducing mortality, causes CP in survivors.
Corticosteroid treatment was associated with a significant increase in CP in the early treatment but not the later treatment subgroup; however, even in the later treatment subgroup, there was no trend toward benefit. Given that preterm infants are more unstable in the first days after birth, when events such as cerebrovascular hemorrhage are prone to occur, it is possible that any adverse effects of corticosteroids might be exacerbated at that time and that the marked adverse effects noted in the early treatment subgroup could be attributed to postnatal age per se.
However, the result of the meta-regression shown in Fig 1 suggests an alternative explanation for the adverse effects observed in the early treatment trials. Postnatal corticosteroids in the doses used might not only have had direct toxic effects on the developing brain7,8 but also an indirect benefit to the brain by improving lung function. The early treatment trials enrolled infants who were generally at lower risk for CLD. Thus, infants who were treated early might have experienced net harm because they had less to gain in terms of the indirect benefit, but all were exposed to the direct harmful effects of corticosteroid treatment. The significant negative association between treatment effect on death or CP and risk for CLD supports this interpretation. None of the potential confounding variables was significantly related to the corticosteroid effect on the combined outcome of death or CP. Moreover, adjustment for these variables, including the time of starting treatment, did not eliminate the statistically significant negative relationship between the risk for CLD in controls and the effect on the rate of death or CP.
We recognize that there are limitations of our meta-regression analysis to explore effect modification arising from risk for CLD. First, the analysis was limited to a subset of studies (14 of 20) in which the control rate of CLD was reported. Second, in taking the control rate of CLD as a measure of control risk, we used data that were unavailable at trial entry. Future application of these results in identifying suitable candidates for corticosteroid treatment would require accurate prediction of CLD in at-risk populations. Third, we did not have access to individual patient data, which would allow more sensitive analysis of the relations between risk factors known at baseline, subsequent development of CLD, and corticosteroid effect on death or CP. Fourth, the list of potential confounding variables that we examined was limited by the data available and does not include other possible confounders, such as differences between studies in mechanical ventilation strategies used.
The main focus of our study was on CP because this is the outcome that has been most controversial. We have also taken into account the competing outcome of death. Data on the effects of steroids on other neurologic outcomes are also important but are much more limited and are discussed in the existing Cochrane reviews.24 There were too few studies that reported both the effects of corticosteroids on neurologic outcomes other than CP and the rate of CLD in the control group to allow us to examine those associations in meta-regression analyses.
Future research should be directed toward trying to prevent CLD and hence the need for corticosteroids, to more accurate early prediction of CLD47 to allow targeting of any postnatal corticosteroids to those most likely to experience long-term benefit, and to determination of the lowest dose of corticosteroid that is effective in reducing ventilator and oxygen dependence and the incidence and severity of CLD, without causing long-term harm. The analyses reported here support future randomized trials of postnatal corticosteroids specifically in preterm infants who are accurately predicted to be at high risk for CLD, with effects on neurodevelopment and mortality as primary outcomes.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Reprint requests to (L.W.D.) Department of Obstetrics and Gynaecology, Royal Womens Hospital, 132 Grattan St, Carlton 3053, Australia. E-mail: lwd{at}unimelb.edu.au
No conflict of interest declared.
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