Case 55: Diagnosis & Conclusions

Case submitted by: Dr. Sonali Gupta (@Neph_sg), Dr. Maureen Brogan (@Maureen1Brogan)
Case Published: November 2022

Case 55 Index

Diagnosis: Acute Tubular Necrosis (ATN) with complications of continuous kidney replacement therapy (CKRT)

Case Summary: Great work! Let’s review this case.

Here we have a critically ill patient who develops acute kidney injury requiring kidney replacement therapy. The initial decision of dialysis modality, specifically intermittent hemodialysis versus continuous kidney replacement therapy (CKRT), is largely influenced by this patient’s cerebral edema. The goal in these cases is to maintain hemodynamic stability and minimize changes in serum osmolality to prevent worsening cerebral edema or midline shift.

This patient is initiated on continuous veno-venous hemodialysis (CVVHD) for solute clearance and volume management. Other options for CKRT include continuous venous-venous hemofiltration (CVVH) and continuous veno-venous hemodiafiltration (CVVHDF), which are outlined in the diagram below from the Renal Fellow Network.

continuous renal replacement therapy modalities

Once this patient is initiated on CKRT, several issues are encountered. It is crucial as a nephrology fellow or even a member of the ICU team to be able to recognize and respond to circuit issues! In order to do this, we need to understand several terms.

Pressures Along the Continuous Kidney Replacement Therapy (CKRT) Circuit
Access Pressure
Pressure created by pulling blood from the patient to the filter (negative pressure)
Return Pressure
Pressure created by returning blood to the patient from the filter (positive pressure)
Effluent Pressure
Pressure will be positive or negative depending upon if fluid is being pushed or pulled from the blood compartment to the fluid compartment
Filter Pressure
Pressure needed to push the blood through the filter (typically positive pressure)
Transmembrane Pressure (TMP)
Pressure exerted on the filter membrane; reflects pressure difference between the blood compartment and the fluid compartment of the filter.
Filter Pressure Drop (∆P Filter)
Reflects pressure changes in the hollow fibers

Understanding these pressures helps to create a differential diagnosis for what is going wrong with the circuit. Issues can be identified at the level of the patient, dialysis access/catheter, as well as the filter itself. In particular, the calculated values of Transmembrane Pressure (TMP) and Filter Pressure Drop (∆P Filter) are key to troubleshooting!

Take a look at the following figures outlining mechanisms for circuit issues.
Clotting vs. Clogging
Access Clotting vs. Filter Clotting

Having a better understanding of the workings of CKRT can help prevent complications. Take a comprehensive approach and investigating potential causes at the level of the patient, the circuit, catheter, lines and tubes.

Take a look at the following references to learn more:

  1. Ricci Z, Baldwin I, Ronco C: Alarms and troubleshooting. In: Continuous Renal Replacement Therapy, edited by Kellum J, Bellomo R, Ronco C, 2009
  2. Neyra JA, Yessayan L, Bastin ML, Wille K, Tolwani AJ. How to prescribe and troubleshoot continuous renal replacement therapy: A case-based review. Kidney360 2: 371-384, 2021

Case Published: October 2022

Case 55 Index
Case 55 Introduction
Case 55 Physical Exam
Case 55 Diagnostic Testing
Case 55 Next Steps