Clinical Case Scenario : QA
A 70-year-old man with known decompensated alcoholic liver cirrhosis presents to the ICU.
History
Laboratory Findings
Wrong Answer: A. Add 3% NaCl directly into the CRRT substitution/replacement fluid to match the patient’s serum sodium, thereby preventing rapid correction.
Right Answer: B. Infuse 3% NaCl as a separate infusion running via a central line and titrate rate to counteract sodium removal during CRRT.
Explaination The most dramatic symptoms of hypernatremia are witnessed when the increase in serum [Na+] has been either too large or too brisk. Chronic hypernatraemia is less symptomatic be- cause organic osmolytes (glutamine, glutamate, taurine and myo-inositol) enter brain cells and help restore normal brain volume.[1] A rapid decrease in serum sodium, particularly in chronic situations when compensation has occurred, can lead to significant water shifts into brain cells and cerebral edema. The rate of correction should not exceed 10-12 mmol/day (0.5 mmol/h).[2] ● Option A: Adding 3% NaCl directly into CRRT fluids is not safe or reliable. Commercial solutions are designed with specific osmolarity and any additional risks instability and dosing errors. ● Option B: Correct. The preferred and controlled way to prevent rapid sodium drop is to run CRRT with standard solutions while giving a separate 3% NaCl infusion titrated to the net sodium balance target (to cap correction at ≤ 8–10 mmol/L per 24 hr). ● Option C: Increasing dialysate sodium with 3% NaCl is unsafe and unstandardized since bag modification alters osmotic stability and leads to unpredictable shifts. ● Option D: Deferring CRRT risks worsening acidosis, hyperkalemia, and fluid overload; hypernatremia is not an absolute contraindication but requires careful Na⁺ balance management.
Wrong Answer: C. Increase dialysate sodium concentration by adding 3% NaCl into the dialysate bag and run CRRT at high efficiency to normalize sodium quickly.
Wrong Answer: D. Withhold CRRT until serum sodium is below 155 mmol/L, then initiate standard prescription to avoid osmotic shifts.
Clinical Case Scenario: QB
The same patient is started on continuous renal replacement therapy (CRRT). On day 1, his laboratory results are:
To buffer sodium loss, you decide to infuse 3% NaCl via a central line during CRRT.(Assume distribution volume of Na = 0.6 × body weight, and [Na] in 3% NaCl = 513 mmol/L).
Wrong Answer: A. 30 mL/hr
Wrong Answer: B. 50 mL/hr
Right Answer: C. 75 mL/hr. Infuse 3% NaCl at ~75 mL/hr as a separate central line infusion to buffer sodium losses during CRRT.
Explaination ● Serum sodium: 172 mmol/L ● Weight: 70 kg ● CRRT prescription: CVVHDF with dialysate Na⁺ concentration of 140 mmol/L, total effluent rate 25 mL/kg/hr ● No ongoing free water losses (insensible balanced by replacement) You want to prevent a serum sodium fall >10 mmol/L in 24 hours. To buffer this, you decide to run a continuous 3% NaCl infusion via central line alongside CRRT. Question: What is the approximate rate (mL/hr) of 3% NaCl infusion required to limit serum sodium drop to less than 10 mmol/L/day? (Assume distribution volume of Na⁺ = 0.6 × body weight, and [Na⁺] in 3% NaCl = 513 mmol/L) ________________________________________ Stepwise Reasoning TBW = 0.6 × 70 kg = 42 L Effluent volume/day = 25 × 70 = 1750 mL/hr = ~42 L/day Sodium lost/day = 172 × 42 = 7224 mmol Sodium replaced via CRRT fluids = 140 × 42 = 5880 mmol Net sodium loss = 7224 − 5880 = 1344 mmol/day Allowed loss = 10 × 42 = 420 mmol/day Required supplementation = 1344 − 420 = 924 mmol/day Volume of 3% NaCl = 924 ÷ 513 ≈ 1.8 L/day ≈ 75 mL/hr
Wrong Answer: D. 120 mL/hr
