Discussion
We found that the mortality rate of preterm infants
with MAS was 33.7%, which was
similar to that in the study of Louis et al [8].
As mentioned above, this life-threatening condition remains a relatively
high case fatality rate. Identifying the specific prediction risk
factors of poor prognosis might be helpful to improved survival of
preterm infants affected by MAS.
In this study, persistent pulmonary hypertension was considered as an
independent risk factor associated with mortality in preterm infants
with MAS. It was reported that PPHN increased the risk of death in
infants diagnosed with MAS in the study of Louis and colleague[8]. PPHN is more commonly associated with diverse
lung pathologies including MAS, perinatal asphyxia, congenital
diaphragmatic hernia, pneumonia and
respiratory distress
syndrome[13]. MAS cause parenchymal lung disease
with variable degrees of chemical pneumonitis, surfactant inactivation
and release of inflammatory mediators, leading to hypoxemia, acidosis
and hypercapnia, ultimately results in pulmonary
vasoconstriction[14,15]. In clinical MAS,
persistent pulmonary hypertension of the newborn is the leading cause of
death in MAS. The overall mortality of infants with PPHN has been
reported to be 12%-29% [16-18].
Pulmonary hemorrhage was another independent risk factor associated with
mortality in preterm with MAS in our study. It occurs mainly in preterm
infants with severe respiratory distress syndrome. Risk factors for
pulmonary hemorrhage include severity of associated illness,
intrauterine growth restriction, prematurity, PDA, coagulopathy and
surfactant therapy [12,19]. Meconium aspiration
may lead to uneven airway obstruction and dysfunction of ventilation,
finally result in pulmonary hemorrhage. Pulmonary hemorrhage is
associated with significant high mortality, which is as high as 50% to
82% [20-22].
Female was found to be another risk factor associated with mortality in
preterm infants with MAS in our study, whereas relevant evidence was
insufficient. The development and prognosis of some neonatal diseases
(eg, neonatal respiratory distress syndrome, glucose-6-phosphate
dehydrogenase deficiency, and congenital diaphragmatic hernia) were
considered gender-related [23-25]. Although we
can’t find any strong evidence to explain the effect of gender on
increasing the rate of mortality in preterm infants with MAS. Our
finding is meaningful and deserves further exploration in the future
research.
Lin et al [10] analyzed 314 cases of MAS between
1995 and 2001, and found that infants who required resuscitation in the
delivery room, with birth asphyxia, developed persistent pulmonary
hypertension and pneumothorax were associated with increased mortality
in MAS. Another retrospective study reported that myocardial
dysfunction, birth weight, and higher initial oxygen requirement were
independent predictors of mortality in neonates with MAS[8]. These above studies included infants
irrespective of gestational age, additionally, our study included a
relatively small quantity of patients, which may explain the different
conclusions of our studies.
Our study has several limitations. The sample size of our study is
relatively small. As a case–control study, the inherent shortcomings of
a case-control design (eg, selection bias and recall bias) were
difficult to avoid. Some of the patients were transferred to our center
from other hospitals, and information with regard to the details of
treatment protocols performed outside of our hospital were limited.