POCUS in Renal Failure

Ray and I have been teaching bedside ultrasound to the medical students at NOSM for the last couple of years. I taught them Renal/Bladder EDE last month. Kudos to Andrew Skinner from St. Paul’s in Vancouver for creating the powerpoint. I added measurement of the kidney in the long axis to the Renal part of the talk. One should measure the longest axis obtainable. If it is below 9 cm, then it’s a definite positive. This cutoff is set at a level that is very specific, but it gives up a bit of sensitivity. There is some variability around this number. Women and smaller people have smaller kidneys. Kidneys normally get smaller with age as well. One indication for measuring the kidney would be in the setting of acute and previously unknown renal failure. Look for a distended bladder and hydro to rule out post-renal failure. Do IVC and cardiac EDE to add data points to your assessment of possible pre-renal failure. And if the kidney is normal in size, then that is one data point against chronic renal failure (CRF) and suggests a purely acute intrinsic cause. See the image for an example of a small kidney. You’ll notice that the black part of the kidney (cortex/medulla) also gets thinner with CRF.