The Effects of High Level Magnesium Dialysis/Substitution Fluid on Magnesium Homeostasis under Regional Citrate Anticoagulation in Critically Ill

Abstract

Background: The requirements for magnesium (Mg) supplementation increase under regional citrate anticoagulation (RCA) because citrate acts by chelation of bivalent cations within the blood circuit. The level of magnesium in commercially available fluids for continuous renal replacement therapy (CRRT) may not be sufficient to prevent hypomagnesemia.

Methods: Patients (n = 45) on CRRT (2,000 ml/h, blood flow (Qb) 100 ml/min) with RCA modality (4% trisodium citrate) using calcium free fluid with 0.75 mmol/l of Mg with additional magnesium substitution were observed after switch to the calcium-free fluid with magnesium concentration of 1.50 mmol/l (n = 42) and no extra magnesium replenishment. All patients had renal indications for CRRT, were treated with the same devices, filters and the same postfilter ionized calcium endpoint (<0.4 mmol/l) of prefilter citrate dosage. Under the high level Mg fluid the Qb, dosages of citrate and CRRT were consequently escalated in 9h steps to test various settings.

Results: Median balance of Mg was -0.91 (-1.18 to -0.53) mmol/h with Mg 0.75 mmol/l and 0.2 (0.06-0.35) mmol/h when fluid with Mg 1.50 mmol/l was used. It was close to zero (0.02 (-0.12-0.18) mmol/h) with higher blood flow and dosage of citrate, increased again to 0.15 (-0.11-0.25) mmol/h with 3,000 ml/h of high magnesium containing fluid (p<0.001). The arterial levels of Mg were mildly increased after the change for high level magnesium containing fluid (p<0.01).

Conclusions: Compared to ordinary dialysis fluid the mildly hypermagnesemic fluid provided even balances and adequate levels within ordinary configurations of CRRT with RCA and without a need for extra magnesium replenishment.

Trial registration: ClinicalTrials.gov Identifier: NCT01361581.

Conflict of interest statement

Competing Interests: The novel fluid has been used so far only locally in the author´s department. The EU patent (EP2609915B1) was granted on 27th April 2016.

Figures

Fig 1. Configuration of the CRRT circuit under citrate anticoagulation.

Qb, blood flow (L/h); Qc—4% citrate flow (L/h); Qd—dialysis flow (L/h); Qeff,—effluent flow (L/h); UF indicates ultrafiltration, that is, net fluid removal (L/h).

Fig 2. Flow chart of the 27 hour sequential exposure study.

Ultrafiltration (i.e. net fluid removal) was always administered according to haemodynamic needs (4%TSC trisodium citrate, Qb blood flow, Qd dialysis flow).

Fig 3. Magnesium inputs (black squares for CVVHDF and white squares for CVVH, both above zero) vs magnesium losses (black triangles for CVVHDF and white triangles for CVVH).

The final balances at each study time (black and white circles) are in the middle. Median, IQR in boxes, Min-Max in whiskers.

Fig 4. Arterial Mg levels in CVVHDF (black squares), CVVH (white squares) at each study time.

Median, IQR in boxes, Min-Max in whiskers.

Fig 5. Calcium inputs (black squares for CVVHDF and white squares for CVVH, both above zero) vs calcium losses (black triangles for CVVHDF and white triangles for CVVH).

The final balances at each study time (black and white circles) are in the middle. Median, IQR in boxes, Min-Max in whiskers.