Tissue Perfusion and Fluid Responsiveness Assessment in Critically Ill Patients. A Feasibility Pilot Study Using the Ikorus Urothelial Plethysmography Device (The Target-Up Study).

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).