Sodium at two in the morning: how to control the rate of correction on CVVH by customizing the bags

🎧 Listen: Weekly · Nov 2, from 17:44.

The problem

Commercial CVVH replacement solutions contain about 140 mmol/L of sodium. Used unmodified in a patient with severe chronic hyponatremia, serum sodium can rise faster than intended; in profound hypernatremia, it can fall faster than intended. The plasma-to-replacement-fluid gradient, the effluent dose and concurrent sodium and water inputs together set the rate and direction of change, which makes the effluent dose part of the prescription.

Hyponatremia: dilute the bag

• Adding sterile water to a 5-liter bag lowers its sodium: 500 mL gives 5.5 L at about 127 mmol/L; 1,000 mL gives 6.0 L at about 117 mmol/L.
• The review's correction target is no more than 8 mmol/L over the first 24 hours, and about 4 to 6 mmol/L in patients at very high risk for osmotic demyelination, in line with current hyponatremia treatment standards.
• The catch: water dilutes every solute, not just sodium. With 1,000 mL added, potassium, calcium, magnesium, bicarbonate and phosphate all fall to about 83% of baseline. Post-dilution concentrations must be calculated for the specific product, with close monitoring and supplementation as needed.
• If sodium is rising faster than planned, dilute further and/or reduce the effluent dose temporarily.

Hypernatremia: add hypertonic saline

• Remove a calculated volume of baseline fluid and replace it with the same volume of 3% saline (about 513 mmol/L), so the bag stays at 5.0 L. The formula is V(mL) = 5000 × (target Na − 140) / (513 − 140).
• Approximate volumes: 67 mL for a target of 145 mmol/L, 134 mL for 150, 201 mL for 155 and 268 mL for 160. If 3% saline is added without removing base fluid, the final concentration must be recalculated on the true final volume.
• Correction of chronic hypernatremia should not exceed 8 to 10 mmol/L per day.

Safety and practice

Measure serum sodium every 4 to 6 hours initially and after any change in settings, adjusting subsequent bags and the effluent dose. Modifications should follow a written, pharmacy-approved local protocol with aseptic compounding by pharmacy or trained ICU staff rather than ad hoc preparation at the bedside, and every modified bag should be labeled with the additive volume, the calculated final sodium, the date and time, and the preparer. The review covers CVVH only; dialysate-based approaches have different kinetics.

Why it matters, and what the evidence is

Two things are worth stating plainly, and they go beyond the review. First, there is a live debate about how dangerous faster correction of hyponatremia really is and how strict the classic speed limits need to be. Second, the concern as it applies to CRRT is extrapolated from the general hyponatremia literature: the review describes no case of osmotic demyelination caused by CRRT itself. What it leans on are case reports, small series and protocolized single-center experiences, which the author says support feasibility but do not establish comparative efficacy or safety.

Our take: wherever that debate lands, there will be nights when you need to control how fast the sodium moves, and the standard bag will not do it for you. This review is a practical, reproducible method for doing it, and the tables are worth having to hand. If your ICU has no sodium protocol for CRRT, that is the thing to write before the next two a.m. call.

The source: Alrashidi FS. Updated Management of Sodium Disorders During Continuous Venovenous Hemofiltration. Semin Dial. Published online October 29, 2026. doi:10.1111/sdi.70053 Read the original

Also discussed:

• Spasovski G. Hyponatraemia — treatment standard 2024. Nephrol Dial Transplant. 2024;39(10):1583-1592. doi:10.1093/ndt/gfae162 Link

🎧 Listen: Weekly · Nov 2, from 17:44.

Physician-led, AI-assisted. Dr. Wael Hussein chooses every item NephSpace covers and reviews and edits every story before it is published. The first draft was written in our own words with AI (Claude, by Anthropic) from the full text of the review and checked against our reading notes; Dr. Hussein then reviewed and edited it. For education and information only, not medical advice. Please talk to your own physician or care team about your health. Clinicians: read the original before changing practice. See our disclaimer and disclosures. Spotted an error? Tell us.