Tissue perfusion and fluid responsiveness assessment in critically ill patients: a feasibility pilot study using the Ikorus urothelial plethysmography device (The Target-Up Study)
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Authors
Wong, Adrian
McDonald, Rory
Roslan, Nurul Liana
Bramham, Kate
Hutchings, Sam
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Issue Date
2026
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Article
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BACKGROUND: Accurate assessment of tissue perfusion is challenging. Commonly used markers like lactate levels and central venous oxygen saturation are indirect, intermittent, and provide a global picture of circulatory status which may not reflect perfusion at the organ level. The Urethral Perfusion Index (UPi), measured through a specialized urinary catheter, is a novel technique that offers continuous, real-time monitoring of perfusion in a central tissue bed, potentially providing more immediate and targeted clinical information. OBJECTIVES: 1. The aims of the study were (1) to assess the correlation between changes to left ventricular outflow tract velocity time integral (LVOT VTi) and UPi following a fluid challenge and (2) To assess the relationship between UPi and other markers of tissue perfusion. DESIGN: Interventional, feasibility pilot study. SETTING: Single-center, study conducted at a tertiary-level institution in the United Kingdom. All patients were mechanically ventilated adults, whom the primary clinical team thought would benefit from a fluid challenge. INTERVENTION: A fluid challenge (FC) was defined as a 250 mL bolus of crystalloid solution. MAIN OUTCOME MEASURES: Focused transthoracic echocardiogram measured LVOT VTi and UPi, measured before and after FC. RESULTS: There were no reported complications associated with device use or insertion. Mean duration of data recorded was 19 h and the Signal Quality Index of the UPi trace was high (93%). There was a moderate positive correlation between the time matched values of UPi and LVOT VTi (Spearman r = 0.55, P < 0.0001), R 2 value of 0.272. However, there was no discernible correlation seen between change in UPi and VTi following fluid (Spearman r = 0.24, P = 0.14). Patients with below-average UPi at baseline had evidence of poorer systemic tissue perfusion, as measured by lactate concentration and capillary refill time, and received more vasoactive drugs. CONCLUSION: UPi may be a marker of tissue perfusion in a diverse group of critically ill patients. With further evaluation it may, therefore, present a future therapeutic target. Although there is some relationship between LVOT VTi and UPi, it is not precise enough to be used as a marker of fluid responsiveness. TRIAL REGISTRATION: London Southeast Research and Ethics Committee (22/LO/0911).
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Shock
Volume
65
Issue
1