UltraRounds: Applicability of Renal Resistive Index in the Coronavirus Patient

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The Pre-brief

  1. Acute Kidney Injury (AKI)  is commonly seen in patients with COVID-19, especially in those requiring intubation and mechanical ventilation.  
  2. Point-of-care ultrasound (POCUS) is widely used for the early recognition of and management of critically ill patients. 
  3. The use of point-of-care renal ultrasound in the ICU setting is currently limited, but certain measurements have shown potential in aiding in early recognition of AKI especially in septic and post-cardiac surgery patients. 
  4. Renal Resistive Index (RRI) is a noninvasive ultrasound test that may help in early recognition and management of AKI. 

What is the Renal Resistive Index? 

  1. RRI is the sonographic Doppler measurement of flow velocities in the intraparenchymal renal arteries. It has been shown to correlate with renal vascular impedance. 
  2. Generally, values above 0.7 are considered abnormal. Renal transplant patients with values above 0.8 are associated with higher mortality.  
  3. Critically Ill COVID-19 patients with AKI have been shown to have a higher RRI than those without AKI. 

How is RRI calculated? 

  1. Start with getting a long axis view of the kidney. 
  2. Apply color doppler to identify pulsatile flow in the kidney. 
  3. Place pulse wave doppler gate over the interlobar pulsatile vessels. 
  4. Peak systolic velocity (PSV) and End diastolic velocity (EDV) are measured. 

RRI = PSV-EDV/PSV  

  1. Values above 0.7 are considered abnormal. 

Limitations: 

  1. Many factors can influence RRI. These include age, mean arterial blood pressure, and serum lactate levels. 
  2. Research is ongoing looking at RRI as a predictor for AKI in patients with sepsis. 

The Debrief 

  1. RRI is a bedside ultrasound Doppler test that may help predict AKI in critically ill ICU patients. 
  2. Some studies have shown that RRI can help predict AKI in patients post-cardiac surgery and in septic shock. Larger studies are ongoing. 
  3. More research is needed, but RRI may help predict and prognosticate AKI in patients with COVID 19. 

References:

  1. Renberg, M., Jonmarker, O., Kilhamn, N. et al. Renal resistive index is associated with acute kidney injury in COVID-19 patients treated in the intensive care unit. Ultrasound J13, 3 (2021). https://doi.org/10.1186/s13089-021-00203-z
  2. Watchorn J, Huang DY, Joslin J, Bramham K, Hutchings SD (2020) Critically ILL COVID-19 patients with acute kidney injury have reduced renal blood flow and perfusion despite preserved cardiac function. Shock, A Case-Control Study Using Contrast Enhanced Ultrasound. https://doi.org/10.1097/shk.0000000000001659
  3. Di Nicolo P, Granata A (2019) Renal intraparenchymal resistive index: the ultrasonographic answer to many clinical questions. J Nephrol 32:527–538. https://doi.org/10.1007/s40620-018-00567-x
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6355884/

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