Renal Resistive Index in Patients With Shock

Acute Kidney Injury (AKI) is a severe complication developing in intensive care patients as a result of hypovolemic, cardiogenic or septic shock. It is defined by an abrupt decrease in kidney function. It encompasses both direct injury to the kidney as well as acute impairment of function, including decreased glomerular filtration rate (GFR). Its prevention is crucial because AKI increases morbidity and mortality (1). Mechanisms comprise ischemia/reperfusion, oxidative stress, inflammation and toxicity (2).The common pathophysiological pathway includes endothelial damage to microvessels leading to impaired macro- and microvascular flow and this will aggravate ischemia (3).

Up to now, much controversy exists about

• the changes in renal blood flow during different kinds of shock
• the relation between renal blood flow, glomerular filtration rate and the development of AKI
• the relation between renal blood flow and markers of the systemic and microcirculation

In this prospective observational study, three study measurement will be performed in two groups of critically ill patients (shock and no shock).

• The Renal Resistive Index (RRI) will be determined using Renal Doppler Ultrasound . The renal resistive index (RRI) is a sonographic index assessing resistance of the intrarenal arcuate or interlobar arteries and is used to assess renal arterial disease. It is measured as RRI = (peak systolic velocity - end diastolic velocity)/peak systolic velocity. The normal value is ≈ 0,60, with 0,70 being around the upper limits of normal.
• The sublingual microcirculation will be quantified using side stream dark field imaging (SDF)
• Fluid status will be determined by Bioelectrical impedance analysis (BIA) using the Akern device.

In addition, routinely measured markers of circulation, renal function and fluid balance will be collected for analysis.

Inclusion criteria

First group (patients with shock):

• Critically ill patients admitted to the intensive care unit (ICU) with cardiogenic shock or shock due to sepsis/SIRS or hemorrhage
• Age > 18 years
• Noradrenalin support
• ICU admission < 24 hours
• Signed informed consent

Second group (patients without shock):

• Critically ill patients admitted to the intensive care unit (ICU) without shock, without vasopressor support and without fluid-dependent circulation
• Age > 18 years
• ICU admission < 24-h
• Signed informed consent

In both groups, written consent will be obtained if and when the patients are awake and able to communicate ('deferred consent')

Exclusion criteria

• Severe pre-admission chronic renal insufficiency (eGFR < 30 ml/min)
• Dialysis dependency
• Renal transplantation