A total of 13 preterm infants with secondary NEC were enrolled in the NEC group, 1 patient was dead before discharge; 1 patient had severe secondary intracranial hemorrhage (IVH) discovered after operation, so the patient’s aEEG recordings was analyzed separately, but was not included in the follow-up of this study. And another patient was lost to follow up due to accidental death. A total of 16 normal preterm patients completed follow-up study. In NEC group there were 9 surgNEC patients. All surgical procedures were uneventful, and the vital signs were maintained at normal levels during the perioperative period. None of the infants were given sedative and analgesic treatment after postoperative anesthesia. All surgNEC patients were given fasting, gastrointestinal decompression (mean 8.5 days), respiratory support (mechanical ventilation for 16 days in 1 case, and the others 4.5 days in average), anti-infective treatment (broad-spectrum antibiotics were used), and correction of anemia (suspended red blood cells were transfused in 7 cases). All cases were transfused with plasma, albumin and intravenous nutritional support, and given dopamine therapy. There was 1 medNEC patient, the medical management of which included withdrawal of feeds for 7 days, intravenous nutritional support, antibiotic usage and symptomatic support. In the control group, the infants were fed normally with intravenous nutrition, respiratory support and symptomatic therapy during aEEG recordings. The conditions of the two groups in gender, gestational age, birth weight, Apgar score, IVH, highest serum C-reactive protein (CRP), ibuprofen treatment rates in patent ductus arteriosus (PDA), incidence of retinopathy (ROP) and CLD were shown in Table 1. As can be seen from the table, male proportion and the highest CRP value in NEC group were significantly higher than those in the control group. The highest CRP of the 5 infants in the NEC group was greater than 200mg/l, which was calculated as 200mg/l in the statistics.
Table 1
Epidemiological data of the study group.
Clinical characteristics | NEC | No NEC | P value |
Male | 10/10 | 6/16 | 0.001a |
Gestational age, weeks | 28.90(SD = 1.194) | 29.29(SD = 1.119) | 0.899b |
Birth weight, g | 1223.00(SD = 148.926) | 1323.75(SD = 157.729) | 0.119b |
Small for gestational age | 0/10 | 0/16 | / |
Apgar-1min | 8.00(SD = 1.160) | 9.00(SD = 1.000) | 0.336c |
Apgar-5min | 9.00(SD = 0.738) | 10.00(SD = 0.512) | 0.100c |
IVH grade I or II | 3/10 | 5/16 | 0.946a |
IVH grade III or IV | 0/10 | 0/16 | / |
Highest CRP(mg/l) | 150.78(SD = 49.010) | 10.89(SD = 8.462) | < 0.001b |
PDA treated by Ibuprofen | 1/10 | 3/16 | 1.000a |
ROP | 3/10 | 2/16 | 0.340 a |
CLD | 3/10 | 7/16 | 0.683 a |
Values are presented as medians (SD) or number/total number. aFisher’s exact test, bT test and cMann-Whitney U test were used. P < 0.05 was considered as statistically significant.
The aEEG features of NEC infants including discontinuous background not consistent with gestational age, absence of SWC and abnormal waveform like epileptic electrical activity. Here are two examples of the representative tracing analysis, which are shown in Figs. 1. The first infant (Fig. 1a) was 29 + 1 weeks’ gestation, whose birth weight was 1230 g and Apgar scores were 9-9-9. He was diagnosed NEC after born 9ds and underwent surgery the next day. aEEG at 24 ~ 72h hours postoperatively indicated functional inhibition of the brain (discontinuous, no cycling). The lower part of the figure (Fig. 1a) displayed abnormal burst-suppression background pattern at 12s in raw EEG. In fact, aEEG in preterm infants with cGA of 30+ 6 w is characterized by continuous background, visible but incomplete cycles, elevated lower borders, and immature bandwidth. The second infant (Fig. 1b) was 30 + 5 weeks’ gestation; birth weight was 1580 g and Apgar scores were 9-10-10. He was diagnosed NEC after born 6ds and underwent surgery on the same day. After surgery, he was found seizures, and his aEEG at 24 ~ 72h hours postoperatively indicated electrographic status epilepticus, and continuous low voltage was displayed in the following aEEG monitoring. The lower part of the figure (Fig. 1b) displayed epileptic electrical activity at 12s in raw EEG. Cranial MRI (corrected gestaional age (cGA) 41w) showed longer T1(a and b) and T2(c and d) abnormal signal changes, demonstrating severe cerebral hemorrhage in the right parietal temporal lobe, left parietal temporal lobe and bilateral external capsule area, with hydrocephalus (see Fig. 2 online only). He was not included in the follow-up and correlation studies. We’ve got a patient with medNEC, and his first aEEG Burdjalov score was 2 at 31 + 4w of cGA.
According to the scoring system developed by Burdjalov and colleagues[16],the Burdjalov total scores and separate entities such as continuity, SWC and bandwidth were compared with the reference indicators, which were considered normal if the score met or exceeded the level of corrected gestational age, and abnormal if the score lagged behind the corrected gestational age. The results showed that compared with no NEC group, the incidence of abnormal Co (7/10:0/16), Cy (8/10:0/16), LB (6/10:0/16), B (8/10:0/16) and Total score(9/10:0/16) were significantly increased in the NEC group (p ≤ 0.01). However, in 2nd aEEG, 3rd EEG and 4th aEEG recordings, the incidence of abnormal T (2/10:0/16; 2/10:0/16; 0/10:0/16) was not significantly different between both groups.
A total of 12 NEC infants had received cranial MRI examination, among which 5 cases presented widened inter-parenchymal space with cerebral tissue volume lessened (2 cases among these had decreased myelination). One of the infants was 28 + 1 weeks’ gestation, birth weight was 1260 g and Apgar scores were 7-9-9. He was diagnosed NEC after born 10ds and underwent surgery the next day. aEEG at 24 ~ 72h hours postoperatively indicated functional inhibition of the brain (total score 3), and the Burdjalov scores at 1w, 2w and 3w were 4, 9, 13 separately. Ultrasonography indicated white matter and gray matter damage 5ds after surgery. The brain MRI (correct gestational age (cGA) 38 + 4w) showed brain retardation (like premature infants). Bilateral basal ganglia region, both cerebral cortical and subcortical diffuse patchy distribution of longer T1, longer T2 and lower Flair T2 abnormal signal changes, with local gyrus slightly swollen. This case was lost to follow up, for he died accidentally when he was 8-month old (see Fig. 3). In the control group, 16 infants received MRI examination, while no obvious abnormalities were found.
To assess intelligence and motor outcome, GDS were used on 10 NEC patients and 16 normal preterm infants at 12- to 18-month of age. The GDS DQ assessment indicated that NEC children had inferior performance and lower mean scores in the sub-domains of gross motor (73.12 ± 10.742:94.13 ± 10.366, P < 0.001), fine motor (68.15 ± 10.323:100.04 ± 12.608, P < 0.001), adaptive behavior (74.79 ± 9.774:100.24 ± 12.175, P < 0.001), language (68.59 ± 12.593:96.37 ± 11.493, P < 0.001), personal-social responses (82.36 ± 16.013:97.58 ± 11.834, P = 0.010) and in overall DQ (73.08 ± 8.901::98.02 ± 9.289, P < 0.001). In NEC group, there were 2 children with scores < 70, 7 children with scores 70–84, 1 child with normal score (= 85). In the contrast group, there were 2 children with scores of 70–84, 14 children with normal scores (≥ 85).
In this study, we found that among 13 infants with neurodevelopmental delay (DQ < 85), 9 (69.23%) infants had NEC; among 13 infants with normal neurodevelopmental outcome(DQ ≥ 85), 1 (7.69%) infant had NEC.The difference in the proportion of NEC among patients with normal neurodevelopmental outcome versus delay neurodevelopmental outcome was statistically significant (P < 0.001). Logistic binary regression analysis was performed for the influencing factors of poor neurodevelopmental outcome. Considering the exclusive criteria in all enrolled infants: intrauterine distress, neonatal asphyxia, intracranial hemorrhage (III degree and above), hydrocephalus, periventricular leukomalacia (PVL), HIE, bilirubin encephalopathy, intracranial infection, hypoglycemic encephalopathy, brain malformations, severe chronic lung disease (sCLD), intrauterine growth retardation, complex congenital heart disease, chromosomal disorders and genetic metabolic diseases. Therefore, the factors included in the study were financial difficulties, parental education(below middle school), maternal age ≥ 35 years, male, hCRP, platelets < 100×10^9/l, and NEC. After univariate analysis, statistically significant factors were included in the logistic binary regression analysis, and the results revealed that NEC patients had a significantly increased risk of abnormal neurodevelopmental outcome compared to no NEC patients (aOR = 27.00, 95% CI 2.561–284.696, P = 0.006) after adjusting for male, hCRP > 50mg/l and platelets < 100×10^9/l.
Following Spearman’s rank correlation analysis, there was a positive correlation between 1st Burdjalov score of aEEG and neurodevelopmental outcome (r = 0.603, p = 0.001), but no significant difference with the 2nd Burdjalov sore (r = 0.337, p = 0.092) and 3rd Burdjalov score (r = 0.337, p = 0.092). And the 4th Burdjalov scores all reached the normal level according to cGA in both groups.
When we worked on the assumption that infants with abnormal 1st Burdjalov scores to postconceptional age would be likely to suffer from neurodevelopmental delay, and infants with normal Burdjalov scores would be likely to be neurologically normal in later life, the area under the receiver operator characteristic curve(ROC) was 0.806 (p = 0.010), the sensitivity was 61.74%, the specificity was 84.62%, the positive predictive value was 80.00%, and the negative predictive value was 68.75%.