NEC is an idiopathic inflammatory disease characterized by extensive hemorrhage and necrosis of the small intestine and colon. It is the leading cause of emergency gastrointestinal surgery during the neonatal period and is a leading cause of death in preterm infants between 2 weeks and 2 months of age [6, 7]. In clinical practice, NEC can be controlled in approximately half of infants after fasting, antibiotic treatment, and supportive treatment. However, some children require surgical intervention due to the progressive aggravation of the disease. Therefore, early recognition of the clinical manifestations of NEC deterioration and timely diagnosis and treatment are extremely important to reduce the mortality of NEC.
Similar to the results of some previous studies, our study found that children with a lower gestational age and birth weight were more likely to receive surgical treatment. Many scholars have also reached similar conclusions. Bazacliu et al.  found that the morbidity and mortality of NEC were inversely proportional to the gestational age. In a 2-year national study in the United Kingdom, the incidence of NEC was 11% in infants born at 24 weeks of gestation but decreased to 0.5% in infants born at 31 weeks of gestation . Hull et al.  found that the probability of receiving surgery in children with NEC decreased with increasing birth weight, namely, for every 100 g increase of birth weight, the probability of undergoing surgery was reduced by approximately 5%. In a study on the incidence rates of NEC in infants of different races, the authors found that the proportion of infants with preterm birth and low birth weight was higher in Hispanic and non-Hispanic black infants; thus, they speculated that premature birth and low birth weight, rather than ethnic factors, led to the higher incidence of NEC . These findings can be explained by the immature intestinal development of preterm infants. The gastrointestinal tract supports the immune system and nervous system, which may be a determinant of intestinal injury and inflammation in infants with NEC. Pathogenic microorganisms invade the immature intestinal tract, resulting in increased morbidity and mortality. In addition, many infants with NEC achieve a high volume of enteral feeding at the time of onset, but the increase in intestinal volume may provide more substrate for the growth of pathogenic microorganisms and place greater pressure on the intestine. In contrast, the development of gut microbiota in preterm infants differs from that in full-term infants . Studies have shown that preterm infants have lower gut microbial diversity, different colonized microbes in the intestine, and more potential pathogenic bacteria [13, 14]. A multivariate analysis of the above factors showed that only lower gestational age was an independent predictor of the incidence of sNEC.
In our study, we found that NEC occurred earlier in children who required surgical treatment than in those who required only medical treatment. This result was confirmed by Duci et al. . The intestinal tract matures gradually over time after birth, which may reduce the probability of undergoing surgery in infants with severe NEC. There is controversy regarding whether there is a correlation between patent ductus arteriosus (PDA) and the occurrence of NEC. It has been reported that compared with NEC patients without PDA, NEC patients with PDA have a better prognosis . However, another study found that the presence of PDA increased the mortality of NEC patients . In addition, extremely low birth weight infants have a significantly higher incidence of PDA, which is commonly treated with nonsteroidal anti-inflammatory drugs (NSAIDs). Another study has shown that the incidence and severity of NEC are related to the use of NSAIDs . In our study, we found that many children with NEC had received NSAIDs to treat hsPDA, which was found to be related to an increased probability of receiving surgical treatment. We speculated that the deterioration of the condition of NEC patients with hsPDA might be due to the decreased intestinal perfusion and decreased oxygenation caused by hsPDA. Multivariate analysis showed that clinical early-onset NEC and hsPDA that required treatment were associated with an increased probability of surgical treatment in NEC patients and were independent predictors for sNEC.
In some studies, sepsis has been identified as a risk factor for NEC [19, 20]. The onset of NEC can be likened to that of early onset sepsis, which is rapid and fatal and has serious consequences for patients. Studies have shown that the incidence of NEC in children with sepsis is almost 3 times that in children without sepsis . Antibiotics are the most commonly used drugs in neonatal intensive care units, especially for extremely premature infants. The use of antibiotics reduces the biological diversity of gut microbiota, delays the colonization of beneficial microbes, and promotes the excessive growth of pathogenic bacteria. At least 3 cohort studies have found that the empirical use of antibiotics for more than 4 days increased the risk of NEC [22,23,24]. Alexander et al.  reported that the incidence of NEC was 3 times higher in newborns who received prophylactic antibiotics for more than 10 days. A univariate analysis found that the failure of infants to achieve complete enteral feeding before the onset of NEC was associated with an increased probability of receiving surgical treatment. The reason may be that these infants were born at lower gestational ages, and immature intestinal development caused them to fail to achieve complete enteral feeding. In addition, compared with full-term infants, preterm infants have significantly delayed gastric emptying.
To date, clinical indicators are not reliable for predicting when NEC will occur or which children will develop NEC. Laboratory test results, such as increased or decreased white blood cell count, thrombocytopenia, metabolic acidosis, unstable glucose levels, and elevated C-reactive protein levels, can be observed in patients with NEC. However, these results still lack sensitivity and specificity [25, 26]. In our study, low platelet count, low serum HCO3−, and increased standard base excess were associated with an increased probability of receiving surgical treatment in NEC patients. However, in the multivariate analysis, only low serum HCO3− was identified as an independent predictor of an increased probability of undergoing surgery in NEC infants. Low serum bicarbonate can lead to metabolic acidosis, causing poor circulation or severe bicarbonate loss. Therefore, the abnormal serum HCO3− and standard base excess in the sNEC group were not surprising because serum HCO3− and standard base excess reflect the infants’ metabolic state.
Similar to other retrospective studies, this study has some inherent and unavoidable limitations. First, our study was based on a single center and might be affected by various biases. In general, multicenter and large-sample studies have less bias. Second, the data used in this study were collected from records in our electronic medical record system, and some important data might have not been recorded. Therefore, further prospective studies are needed to elucidate the reasons for the increased probability of surgical treatment in preterm infants with NEC.