Patient characteristics of infants with no NEC and definite NEC.

Data are expressed as median (range) or as numbers unless specified otherwise. Abbreviations: NEC—necrotizing enterocolitis; NIRS—near-infrared spectroscopy; PDA—patent ductus arteriosus; PNA—postnatal age; RBC—red blood cell. Circulatory failure was defined as hemodynamic instability and scored by the need for volume expansion or the use of inotropes or both, from one hour before NEC onset until the first forty-eight hours after NEC onset, or until surgery, whichever came first. Statistical differences between the two groups are marked by * (除非另有说明，数据均以中位数（范围）或例数形式呈现。缩写说明：坏死性小肠结肠炎（necrotizing enterocolitis, NEC）、近红外光谱（near-infrared spectroscopy, NIRS）、动脉导管未闭（patent ductus arteriosus, PDA）、出生后年龄（postnatal age, PNA）以及红细胞（red blood cell, RBC）。循环衰竭定义为血流动力学不稳定，其评分依据为需进行容量复苏或使用正性肌力药物，或两者兼具，统计时段为坏死性小肠结肠炎（NEC）发作前1小时至发作后最初48小时，或直至手术干预，以先发生者为准。两组间的统计学差异以*标记（