Bowel sonography in sepsis with pathological correlation: an experimental study

Background Sepsis predisposes full-term infants to necrotizing enterocolitis (NEC). As such, experimental induction of NEC was applied to a sepsis model to evaluate the potential role of US in the early diagnosis of NEC in fullterm infants. Objective To evaluate the resistive index (RI) of the superior mesenteric artery (SMA) on Doppler sonography in experimentally induced sepsis and correlate it with the pathological findings. Materials and methods Fifteen 1-week-old New Zealand white rabbits (control group n=3, sepsis group n=12) were used in this study. We injected 1 mg/kg of E. coli O55-B5 lipopolysaccharide (LPS) into 12 rabbits to induce sepsis. Then we conducted grayscale evaluation of the caliber of the abdominal aorta as well as bowel wall thickness and echogenicity. In addition, we measured peak systolic and end-diastolic velocities and SMA RI on Doppler sonography. Pathological findings were analyzed and correlated with RI readings. Peak systolic and end-diastolic velocities and SMA RI values were analyzed statistically at each hour using the Wilcoxon rank sum test; the control and sepsis groups were compared using the Mann-Whitney test. Results The bowel wall thickness in the sepsis group was significantly increased after LPS injection. The caliber of the abdominal aorta in the sepsis group was significantly decreased after LPS injection. There were echogenic foci (<10 in axial plane) in the bowel wall after LPS injection. Peak systolic velocity in the sepsis group was not significantly changed, but end-diastolic velocity was decreased. SMA RIs in the sepsis group were significantly increased post-LPS injection from baseline. In the control group there were no significant changes in bowel wall thickness, abdominal aorta caliber, bowel wall echogenicity or peak systolic and end-diastolic velocities and RIs. Pathologically, eight of the 12 rabbits in the sepsis group showed grade 1 intestinal injury, three showed grade 2 injury and one showed grade 3 injury. SMA RIs were higher in grades 2 and 3 than in grade 1 when measured at 2 h and 4 h. Conclusion Sepsis caused necrotic injury in the animal models, and these findings were accompanied by significant changes on Doppler US. These findings could facilitate early detection of intestinal injury in septic infants with NEC.