[Mortality risk factors in premature infants with respiratory distress syndrome treated by mechanical ventilation]

Respiratory distress syndrome (RDS) is the most common cause of respiratory failure and requirement for mechanical ventilation (MV) of newborns. RDS is also common cause of mortality and severe morbidity in premature infants. In developing countries, despite facilities for respiratory care of newborn infants, RDS mortality rate and percentage of complications still remain high in comparison to the developed countries. Survival rates of RDS infants requiring MV ranged from 25% in those newborns with birth weight <1000 grams up to 53% in those with birth weight >2500 grams. There have been limited data about causes of high mortality rate in infants with RDS from developing countries.

The objectives of the study were to determine (I) the incidence of severe RDS at Pediatric Intensive Care Unit (PICU), University Children's Hospital Skopje (UCHS) and main characteristics of infants with RDS, as well as (II) the survival rate and mortality risk factors of these infants.

The study included 126 premature infants with clinical and radiological signs of RDS requiring mechanical ventilation who were admitted to PICU, UCHS between January 1996 and December 2003. The mean gestational age (GA) of the infants was 31.5+/-2.5 weeks, and the mean birth weight (BW) was 1663+/-489 grams. The management of newborns with RDS at PICU, UCHS, follows the standard protocol, with emphasis on minimal manipulation, maintenance of thermoneutral environment, administration of humidified oxygen and noninvasive cardiorespiratory monitoring. Pressure-limited time-cycled mechanical ventilation with pediatric/neonatal ventilators was performed in all infants. In those newborn infants with clinical and radiological signs of RDS and need for MV with FiO2>0.4, synthetic (Exosurf) or natural (Survanta) surfactants were administered. Out of all newborns, 43 infants (34%) were not treated with surfactant, because it was not available at that time.

In the period 1996-2003, out of 1722 consecutive admissions to PICU, 693 hospitalized infants had neonatal RDS (40.2%). A total of 210 (30.3%) infants with RDS required intubation and PPV, and 126 met the inclusion criteria for this study. Surfactant replacement therapy (up to two doses) was given to 83 (65.8%) infants. Most of neonates (80 or 63.4%) were born at two maternity hospitals in Skopje, and others were transferred from regional maternity hospitals in Macedonia. The relation between perinatal characteristics, disease severity and outcome was illustrated in Table 2. There was higher risk of mortality in infants with lower birth weight, lower Apgar score (minutes 1 and 5), and shorter gestational age. Expected admission values of VI as well as other parameters of illness severity were not significantly associated with higher risk of mortality. The newborns with air-leak sy (any form) and pulmonary hemorrhage had significantly higher risk of dying, while the risk of mortality was significantly lower in infants with sepsis and BPD as complications in studied cohort. The findings of logistic regression analysis for mortality risk factors were presented in Table 3. The minimal model identified a number of factors as independently associated with significantly higher risk of mortality. Infant birth weight < or =1500 grams, admission VI > or =0.2 mmHg and air leak sy (any form) as complication significantly increased the risk of dying in infants with RDS. BPD was significantly associated with survival in studied cohort.

In spite of the implementation of high technology in Neonatal Intensive Care in our country, the mortality rate of the infants with RDS is high, but is not different from that in developing countries. The improvement of perinatal care and diminution of risk factors, common use of surfactant as well as antenatal steroids could most probably result in better outcome of neonatal RDS.