INTRODUCTION
Hypophosphatemia is a known issue during continuous renal replacement therapies (CRRT) reported in up to 80% of cases when standard CRRT solutions are used (Santiago MJ – 2009 [1]). RRT-related phosphate depletion should be avoided in critically ill patients and the adoption of phosphate-containing CRRT solutions could be helpful to reduce the incidence of hypophosphatemia and/or to minimize the need for parenteral phosphorus supplementation (Broman M – 2011 [2] (full text), Chua HR – 2012 [3], Morabito S – 2013 [4] (full text)).
The aim was to evaluate the effects on serum phosphate and phosphorus supplementation needs of a regional citrate anticoagulation (RCA) protocol for CRRT combining the use of citrate with a phosphate-containing CRRT solution.
METHODS
In heart surgery patients undergoing CRRT for acute kidney injury, we adopted RCA in CVVH or CVVHDF modality combining an 18 mmol/l citrate solution with a phosphate-containing replacement fluid acting as dialysate and/or replacement fluid (Figure 1).
RCA-CRRT was performed using the Prismaflex system (Gambro, Sweden) and PAES hemofilters (HF 1000, 1.15 m2; Gambro). The citrate solution rate was initially set to obtain an estimated circuit citrate concentration of 2.5-3 mmol/l, calculated in plasma water, with a target circuit Ca2+ (c-Ca2+) ≤0.5 mmol/l. Phosphate-containing replacement solution flow rate was adjusted to obtain a prescribed dialysis dose, corrected for pre-dilution, of at least 25 ml/kg/h. Calcium chloride (10%) was infused in a separate central venous line to maintain a target systemic Ca2+ (s-Ca2+) of 1.1-1.25 mmol/l.
Hypophosphatemia was defined as mild (<0.81 mmol/l), moderate (<0.61 mmol/l) and severe (<0.32 mmol/l).
Potassium, phosphate and magnesium losses with CRRT were replaced, when needed, respectively with potassium chloride, d-fructose-1,6-diphosphate (FDP; Esafosfina® 5 g/50 ml) and magnesium sulphate. In particular, FDP administration was scheduled in case of phosphate levels <0.9 mmol/l.
Nutritional support was provided mainly via parenteral route associated, if tolerated, with enteral route; energy and protein intake targets were 25 Kcal/Kg/day and 1.5 g/Kg/day with a phosphorus intake of about 20–30 mmol/day.
RESULTS
Over a two-years period (Sept 2011-Sept 2013) 48 patients were treated with RCA-CVVH or RCA-CVVHDF for at least 72 hours. RCA-CRRT initial parameters are showed in Figure 2 while patient’s characteristics at the start of the treatment are reported in Table I.
Gender |
15 F, 33 M |
Age, years |
69 (60-74) |
Oliguric AKI |
37/48 (77.1%) |
Mechanical ventilation |
42/48 (87.5%) |
Artificial nutrition |
48/48 (100%) |
APACHE II score |
32 (26-34) |
SOFA score |
13 (11-15) |
SOFA cardiovascular score |
3 (1-3) |
Serum creatinine, mg/dl |
2.1 (1.6-2.9) |
Blood urea nitrogen, mg/dl |
34.5 (28.5-55.2) |
Sodium, mmol/l |
140 (138-143) |
Potassium, mmol/l |
4.3 (4.1-4.6) |
Total Calcium, mmol/l |
2.1 (1.9-2.2) |
Phosphorus, mmol/l |
1.4 (1.16-1.8) |
Magnesium, mmol/l |
0.74 (0.7-0.95) |
pH, units |
7.40 (7.36-7.43) |
Bicarbonate, mmol/l |
22 (21-23) |
Base Excess |
-2 (-3 to -0.5) |
pCO2, mmHg |
37 (34-40) |
Lactate, mmol/l |
1.5 (1.2-2.4) |
Albumin, g/dl |
2.5 (2.2-2.8) |
Two-hundred and nineteen RCA circuits were used with a mean filter life of 57.1±41.7 hours (median 47, IQR 24-83, total running time 12.502 hours). RCA targets (c-Ca2+, s-Ca2+) were easily maintained without episodes of clinical relevant hypo- or hypercalcemia (Table II). RCA-CRRT provided an adequate control of acid-base status without the need for additional interventions on RCA-CRRT parameters (Table II). Serum phosphate was steadily maintained in a narrow range throughout RCA-CRRT days (Table II, Figure 3).
pH, units |
7.43 (7.40-7.47) |
Blood HCO3–, mmol/l |
25.3 (23.8-26.6) |
Base Excess |
0.9 (-0.7 to 2.4) |
Serum phosphate, mmol/l |
1.2 (0.97-1.45) |
Systemic Ca2+, mmol/l |
1.16 (1.12-1.21) |
Total serum calcium, mmol/l |
2.3 (2.18-2.41) |
Calcium ratio |
1.97 (1.87-2.07) |
Circuit Ca2+, mmol/l |
0.42 (0.36-0.48) |
Serum Na+, mmol/l |
134 (133-136) |
Serum K+, mmol/l |
4.2 (4-4.4) |
Serum Mg2+, mmol/l |
0.79 (0.73-0.84) |
CaCl2 infusion, mmol/h |
2.2 (1.9-2.6) |
KCl infusion, mmol/h |
2 (0-4) |
Magnesium sulphate infusion, g/24h |
3 (3-3) |
Phosphate supplementation need, n (%) |
20.8% (10/48) |
Supplementation (g/day) |
1.05±2.04 |
At some times during CRRT, only 10 out of 48 patients (20.8%) received a low amount of phosphate supplementation (FDP; Esafosfina® 1.05±2.04 g/day) for mild (n=7) to moderate (n=3) hypophosphatemia. Considering all patients, only 33 out of 513 serum phosphorus determinations met the criteria for mild (n=24) to moderate (n=9) hypophosphatemia.
CONCLUSIONS
- The use of a phosphate-containing CRRT solution, accounting for about 50-60% of CRRT dose in the setting of RCA-CVVH or RCA-CVVHDF, allowed to prevent CRRT-induced phosphate depletion in most of the patients minimizing the need for phosphate supplementation.
- Phosphorus levels were maintained in a progressively narrower near normal range throughout RCA-CVVH days.