CRRT Explained: Modes, Settings and Alarms
How does CRRT work?
Continuous renal replacement therapy removes solutes and fluid gradually. CVVHD uses diffusion, CVVH uses convection, CVVHDF combines them, and SCUF primarily removes fluid. Understanding the transport mechanism and circuit location helps explain settings, effluent dose and pressure alarms. Assess patient instability separately from a circuit problem.
Key takeaways
- Diffusion follows a concentration gradient, while convection carries solutes with water through the filter.
- Effluent dose and net fluid removal describe different parts of the treatment.
- An alarm identifies a circuit finding requiring investigation, not a diagnosis by itself.
In this video
- What do CRRT pressures and alarms mean?
- When is CRRT used in the ICU?
- How do diffusion, convection, and ultrafiltration work?
- What is the difference between CVVHD, CVVH, CVVHDF, and SCUF?
- How do you read CRRT settings and effluent dose?
- What do access, return, filter, and TMP alarms mean?
- What complications should ICU nurses monitor during CRRT?
- How would you answer a CRRT interview question?
What is the difference between the CRRT modes?
Dialysate creates a concentration gradient for diffusion in CVVHD. CVVH uses ultrafiltration and replacement fluid for convective clearance. CVVHDF combines dialysate and replacement fluid. SCUF emphasizes fluid removal, with much less solute clearance.
Follow blood from the patient through the filter and back. Then identify which fluids enter and which leave the circuit. This is a more useful way to understand the mode than remembering the letters without the underlying transport mechanism.
What do CRRT settings and effluent tell you?
Blood flow moves blood through the circuit. Dialysate and replacement-fluid settings contribute to clearance, while the net fluid-removal target determines the intended fluid balance for the patient. These are related settings with separate jobs.
Effluent is the fluid leaving the treatment system. Interruptions reduce delivered treatment, so a prescription on the machine does not prove the patient received the intended clearance over the entire day. Follow actual treatment time and the patient’s laboratory and fluid-balance trends.
How should you reason through a CRRT pressure alarm?
Locate the pressure measurement first. Access pressure relates to blood entering the circuit, return pressure to blood going back, and filter pressures to movement through the filter. Transmembrane pressure describes a pressure relationship across the filter. Use the pattern and its trend to investigate the likely location.
Also assess the patient. A falling blood pressure and a rising filter pressure are different findings, even when they occur together. Review hemodynamics, electrolyte and acid-base changes, temperature, and anticoagulation effects alongside the circuit. Citrate monitoring requires attention to calcium balance and the patient’s ability to metabolize citrate.
