Diagnosis: Acute Tubular Necrosis (ATN) Requiring Continuous Renal Replacement Therapy (CRRT)
Case Summary: Great work! This case is complex, let’s take a look back.
Here we have a patient presenting with shock likely secondary to pneumonia who subsequently develops acute respiratory distress syndrome (ARDS) and acute kidney injury (AKI). Take a moment to review our infographic on AKI:
Based on this patient’s oliguria (low urine output), “muddy brown” granular casts on urine sediment, and fractional excretion of sodium (FENa, which should always be taken with a grain of salt…) > 1.0%, the most likely cause of his AKI is acute tubular necrosis (ATN).
Despite maximal supportive care in the ICU, the patient continues to decompensate. He develops volume overload due to his oliguria, and his net intake/output balance is significantly positive. This volume overload in addition to ARDS is making the patient very difficult to ventilate, as seen by his hypoxia and hypercarbia on arterial blood gases. He also develops hyperkalemia and worsening metabolic acidosis. These derangements beg the question, does the patient need renal replacement therapy (RRT)?
Of note, there are multiple studies and a good deal of controversy surrounding when to start renal replacement therapy in critically ill patients. Take a look at this great summary from Renal Fellow Network here for more discussion and a summary of the landmark trials.
Once we have determined this patient requires renal replacement therapy, we must decide which modality to use. Intermittent hemodialysis (HD) Is the standard modality for most institutions. Other acute RRT modalities include peritoneal dialysis (PD), continuous renal replacement therapy (CRRT), and other hybrid therapies such as prolonged intermittent renal replacement therapy (PIRRT).
The main considerations for choosing CRRT over an intermittent therapy tend to include hemodynamic instability and fluid/volume goals. This oliguric patient with hypotension requiring vasopressors as well as high daily intake (multiple IV medications) would likely be considered a good candidate for CRRT. Of note, however, the evidence has not shown significant benefit in patient outcomes using CRRT over intermittent therapies.
More on CRRT in an upcoming case, but check out this Renal Fellow Network post and figure below summarizing the different modalities:
Different institutions use various types of CRRT, including continuous veno-venous hemodialysis (CVVHD), continuous hemofiltration (CVVH/CVVHF), and contiuous veno-venous hemodiafiltration (CVVHDF). Some use anticoagulation strategies with citrate, others use heparin, or no anticoagulation. Take a look at this AJKD Core Curriculum, and keep an eye out for future CRRT cases!