An analytical method was developed for the determination of unsymmetrical dimethylhydrazine ( UDMH ) in soil samples by gas chromatography-mass spectrometry with the pretreatment of alkaline distillation and ultrasonic derivatization. After pretreated by the alkaline distillation, the quantitative analysis of UDMH was conducted in selected ion monitoring ( SIM ) mode by using salicylaldehyde as derivatization reagent and ultrasonic to accelerate the derivative reaction. The characteristic ion of the derivative product named salicylaldehyde dimethylhydrazone was m/z 164 . Impact factors including types of the alkaline distillation and the derivative conditions with ultrasonic were investigated. The conditions of derivatization were optimized. Under the optimal conditions, linear range of the method was 0. 4-30 mg/L. The limit of detection (LOD, S/N=3) was 0. 0078 mg/kg. The method was used to detect total UDMH in real soil samples with known concentration. The recoveries ranged from 76% to 108% with relative standard deviations ( RSD) of 12%-19% at different spiked concentration levels from 10 mg/kg to 100 mg/kg. In comparison with the methods of spectrophotometry and Soxhlet extraction-ultrasonic derivatization, this method had lower detection limit, and could be used to detect total UDMH in soil samples.

Objective:To investigate the attitude of neonatologists toward the treatment of extremely preterm infants (EPIs) in China.Methods:A cross-sectional survey was conducted using a questionnaire designed and posted on Wenjuanxing, a web-based survey platform, from June to July 2021. The respondents were neonatal physicians in various provinces and cities in China. The questionnaire covered the basic information, treatment experience and attitude towards EPIs, and opinions on the current definition of the preterm infant in China. The results were described or analyzed using the Chi-square test.Results:A total of 1 066 valid replies were collected. The respondents included 322 males and 744 females, among whom 78.1% (832/1 066) were assistant director physicians or director physicians, 82.8% (882/1 066) were from tertiary hospitals, and 83.0% (885/1 066) had the experiences of treating EPIs. In terms of the attitude toward the treatment of EPIs, 63.0% (672/1 066) of the respondents suggested that the lower limit of gestational age for EPIs requiring active resuscitation should be defined at 25 gestational weeks or less. Moreover, 57.1% (609/1 066) considered that the current domestic definition of preterm infants as 28 gestational age or above was inappropriate, and 75.2% (458/609) considered that the lower limit defined as preterm infants should be 25 gestational weeks or less. Concerning the treatment experience in EPIs, 54.3% (579/1 066) of the respondents suggested that in their hospital, withdrawing treatment in EPIs was common or very common, and 83.3% (888/1 066) considered that the main reason for withdrawing treatment was family members' concerns about the prognosis. Those who hesitated about treating the EPIs accounted for 71.6% (763/1 066), and 83.9% (640/763) hesitated due to the poor prognosis and possible medical disputes. Moreover, 32.7% (349/1 066) of the respondents or their colleagues had been involved in medical disputes about whether to treat EPIs, and 74.8% (797/1 066) believed that the patients should be the decision-maker on whether to treat EPIs or not.Conclusion:Most neonatal physicians in this survey hold a positive attitude toward the treatment of EPIs and believe that the lower limit of gestational age for preterm infants should be lowered. However, a hesitating attitude to the care of EPIs is still common, and uncertainty about the prognosis of EPIs remains a concern.

Objective:To develop a risk prediction model for identifying bronchopulmonary dysplasia (BPD) associated pulmonary hypertension (PH) in very premature infants.Methods:This was a retrospective cohort study. The clinical data of 626 very premature infants whose gestational age <32 weeks and who suffered from BPD were collected from October 1 st, 2015 to December 31 st, 2021 of the Seventh Medical Center of the People′s Liberation Army General Hospital as a modeling set. The clinical data of 229 very premature infants with BPD of Hunan Children′s Hospital from January 1 st, 2020 to December 31 st, 2021 were collected as a validation set for external verification. The very premature infants with BPD were divided into PH group and non PH group based on the echocardiogram after 36 weeks′ corrected age in the modeling set and validation set, respectively. Univariate analysis was used to compare the basic clinical characteristics between groups, and collinearity exclusion was carried out between variables. The risk factors of BPD associated PH were further screened out by multivariate Logistic regression, and the risk assessment model was established based on these variables. The receiver operating characteristic (ROC) area under curve (AUC) and Hosmer-Lemeshow goodness-of-fit test were used to evaluate the model′s discrimination and calibration power, respectively. And the calibration curve was used to evaluate the accuracy of the model and draw the nomogram. The bootstrap repeated sampling method was used for internal verification. Finally, decision curve analysis (DCA) to evaluate the clinical practicability of the model was used. Results:A total of 626 very premature infants with BPD were included for modeling set, including 85 very premature infants in the PH group and 541 very premature infants in the non PH group. A total of 229 very premature infants with BPD were included for validation set, including 24 very premature infants in the PH group and 205 very premature infants in the non PH group. Univariate analysis of the modeling set found that 22 variables, such as artificial conception, fetal distress, gestational age, birth weight, small for gestational age, 1 minute Apgar score ≤7, antenatal corticosteroids, placental abruption, oligohydramnios, multiple pulmonary surfactant, neonatal respiratory distress syndrome (NRDS)>stage Ⅱ, early pulmonary hypertension, moderate-severe BPD, and hemodynamically significant patent ductus arteriosus (hsPDA) all had statistically significant influence between the PH group and the non PH group (all P<0.05). Antenatal corticosteroids, fetal distress, NRDS >stage Ⅱ, hsPDA, pneumonia and days of invasive mechanical ventilation were identified as predictive variables and finally included to establish the Logistic regression model. The AUC of this model was 0.86 (95% CI 0.82-0.90), the cut-off value was 0.17, the sensitivity was 0.77, and the specificity was 0.84. Hosmer-Lemeshow goodness-of-fit test showed that P>0.05. The AUC for external validation was 0.88, and the Hosmer-Lemeshow goodness-of-fit test suggested P>0.05. Conclusions:A high sensitivity and specificity risk prediction model of PBD associated PH in very premature infants was established. This predictive model is useful for early clinical identification of infants at high risk of BPD associated PH.