Joe Basha’s PerfWeb #25 — Acute Kidney Injury (AKI). Drivers Of Urine Production — Perfusion

The learner will be able to describe the physiologic principles of urine production and discuss how cardiopulmonary bypass affects urine production and the potential development of Acute Kidney Injury (AKI). Urine Production. Renal Anatomy. Nephron What is Acute Kidney Injury? It is the SUDDEN decrease in renal function that leads to the build-up of waste in the blood, fluid overload, and electrolyte imbalances. What are the causes of Acute Kidney Injury? There are three causes, which are based on location. The first is known as prerenal injury and this is an issue with the perfusion to the kidneys that leads to decreased renal function. A second cause is known as intrarenal injury, and this is due to damage to the nephrons of the kidney. Lastly, postrenal injury is due to a blockage located in the urinary tract after the kidney that can extend to the urethra. This is causing the backflow of urine, which increases the pressure and waste in the kidneys. Stages of Acute Kidney Injury: There are four stages of acute kidney injury, which include initiation, oliguric, diuresis, and recovery stage. The initiation stage starts when a cause creates an injury to the kidney and then signs and symptoms start to appear. This leads to the oliguric stages. The patient will void less than 400 mL/day of urine during this stage and will experience increased BUN/creatinine levels, azotemia, hyperkalemia, hypervolemia, increase phosphate, and decreased calcium levels along with metabolic acidosis. After this stage, the patient can progress to the diuresis stage and this is where the patient will void 3-6 Liters of urine per day due to osmotic diuresis. The patient is at risk for hypokalemia, dehydration, and hypovolemia. The last stage is recovery and the patient's glomerular filtration rate has returned to normal. Therefore, the kidneys are able to maintain normal BUN and creatinine levels, electrolyte, and water levels.