Superior mesenteric artery Doppler parameters across sepsis severity spectrum and their discriminative performance for refractory septic shock

Background This study aimed to characterize the evolution of superior mesenteric artery (SMA) Doppler parameters across the sepsis-severity spectrum, evaluate their exploratory discriminative performance for refractory septic shock, and explore whether waveform characteristics change after successful resuscitation. Methods In this single-center retrospective observational study, 96 patients were enrolled: non-septic ICU controls ( n = 22), sepsis ( n = 29), septic shock ( n = 22), and refractory septic shock ( n = 23). Bedside SMA Doppler ultrasound measured PSV, EDV, TAMV, RI, PI, and BF. SMA Doppler parameters were compared across the four groups; correlations with illness-severity markers and norepinephrine-dose-stratified analyses were performed. Cross-sectional discrimination for refractory septic shock was assessed using Firth's penalized logistic regression and ROC analysis with bootstrap internal validation (1,000 replicates) in acute-phase shock patients. In a subgroup of 20 shock patients who achieved successful resuscitation, paired pre- and post-resuscitation measurements were obtained. Results 96 patients were enrolled. SMA hemodynamic profiles differed significantly across four acute-phase cohorts (all p < 0.001). Sepsis patients exhibited compensatory hyper-dynamic mesenteric features; with advancing illness towards refractory septic shock, SMA flow velocities and resistance indices declined significantly. PSV, RI and PI were inversely associated with SOFA score, lactate, norepinephrine dosage and creatinine (all p < 0.001). Despite stable mean arterial pressure, RI and PI decreased progressively with escalating norepinephrine dose. Among acute-phase shock patients( n = 45), PSV and RI showed apparent AUCs of 0.898 and 0.874, respectively; optimism-corrected AUC after bootstrap internal validation were 0.858 for PSV and 0.823 for RI. In the paired subgroup, PSV and RI increased after successful resuscitation ( p < 0.001), whereas TAMV and calculated BF did not change significantly. Conclusion Bedside SMA Doppler ultrasonography may capture a non-linear mesenteric hemodynamic trajectory across sepsis severity. A low-resistance, low-velocity SMA Doppler phenotype is associated with more severe shock and may serve as an exploratory discriminative marker for refractory septic shock.