Troubleshooting Mechanical Complications in Continuous Renal Replacement Therapy
Lisa M. Milonovich, RN, MSN,
PCCNP, CPNP-AC, CCRN
Children’s Medical Center Dallas
Dallas, Texas, USA
Continuous renal replacement therapy (CRRT) is a widely accepted procedure for critically ill patients with acute renal failure or renal insufficiency. CRRT is better tolerated in critically ill, hemodynamically labile patients, giving it an advantage over standard hemodialysis. Fluid removal is slow and continuous and can be altered to account for increased intake with the addition of medications and blood products. Like all extracorporeal systems, however, CRRT is not without its complications, which can be divided in three general categories: patient-related complications, prescription complications or errors, and mechanical complications. This article focuses on the mechanical complications of CRRT, which often are more significant in pediatric patients because of the size of the vessels and equipment available for performing CRRT.
Several different systems are available for performing CRRT. While each system is slightly different, the general principles are the same. Each system has integrated alarms to warn the providers of complications or potential problems as they arise. It is important for bedside or dialysis nurses to be familiar with the alarm codes of the system used in their institution.
In most systems, alarms are both audible and visual. In many cases, the pump stops at the alarm, so the caregiver response should be prompt to prevent clotting of the filter or circuit. In addition, newer, more sophisticated systems may provide troubleshooting information on the alarm screen. The following is a general overview of the common alarms that occur during CRRT.
Pressure Alarms
While current systems generally are used to provide venovenous hemofiltration, the term arterial often is used to describe the blood removal or access side of the system. Venous describes the return side of the system.1, 2
Low arterial pressure alarms indicate a problem with Troubleshooting Mechanical Complications in Continuous Renal Replacement Therapy pulling blood from the patient’s catheter. This may be the result of a physical obstruction such as a clamp left in place, a kink in the catheter or tubing, or a clot in that portion of the system. It also may indicate that the pump speed is too fast for the size of the catheter, causing the catheter to pull against the side of the vessel and resulting in obstruction to outflow. In the pediatric patient, this also can occur when the pump speed is too fast for the central venous pressure or amount of blood available in the right atrium.
Venous pressure alarms indicate a problem with blood returning to the patient. High venous pressure results from an obstruction to blood return. Again, this can be the result of a clamp left engaged on the return side, a kink in the catheter or tubing, or a clot in the venous return system. Conversely, a low venous pressure alarm may occur when the system does not sense venous flow or positive pressure on the return limb of the circuit. This can result from a disconnection on the venous side of the system, obstruction between the filter and venous pressure sensor, or from a pump speed too low to produce positive pressure in a larger venous catheter.
Transmembrane pressure alarms indicate a change in the pressure across the membrane, between the blood and ultrafiltrate compartments. This is usually indicative of a failing filter. As the filter ages, microclotting occurs within the fibers, decreasing the area for filtration, thus increasing the transmembrane pressure to achieve the same ultrafiltration (UF) rate. On some systems, this alarm also can occur if a clamp inadvertently is left in place on the ultrafiltrate tubing; other machines have a separate UF alarm.
Fluid Balance Alarms
Current systems used for CRRT have a variety of alarms that indicate changes or problems with the prescribed fluid balance.1, 2 It is important to pay close attention to these, especially in the pediatric patient, as minimal changes in fluid balance can have significant patient consequences. One of these alarms is an ultrafiltration alarm indicating that the amount of UF prescribed is not being met. Another is a balance or bag volume/weight alarm indicating that the amount of ultrafiltrate, replacement fluid or dialysate is outside the prescribed volume. Each system has a small window/percentage of error to prevent the pump from sounding the alarm continuously. Once the weight or balance is outside this window, an alarm will sound. Typically, fluid balance alarms occur due to bags being clamped, the scales being moved after the pump is moved, or secondary to other concurrent alarms.
Other Alarms
In current CRRT systems, the presence of air in the venous system will cause an alarm.1, 2 When the alarm sounds, a clamp is engaged on the venous/return side to prevent the patient from receiving an air embolus. Blood leak alarms will be activated if the filter fibers split, causing blood to be lost in the ultrafiltrate compartment. Most systems also have malfunction or error codes that may signal during priming or therapy to indicate a problem with the system. These are specific to the system in use and providers should refer to their reference manuals to troubleshoot these alarms.
CRRT is an accepted therapy for the management of renal insufficiency or renal failure in critically ill patients from neonates to adults. The therapy is more technologically challenging in small infants and children due to the size of the vessels, which mandates the use of smaller catheters. Knowledge of the systems used, potential complications and alarm troubleshooting make the therapy feasible despite these challenges.
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