CCHT Electrolyte Balance 2 — Questions and Answers
Question 1: A patient's pre-dialysis potassium level is 6.8 mEq/L with peaked T waves on ECG. Which dialysate potassium concentration would be most appropriate?
- 3.0 mEq/L
- 2.0 mEq/L
- 1.0 mEq/L (Correct answer)
- 0 mEq/L potassium bath
Correct answer: 1.0 mEq/L
Severe hyperkalemia with ECG changes requires aggressive potassium removal using a 1.0 mEq/L dialysate, which maximizes the gradient for potassium diffusion from blood to dialysate.
Normal dialysate potassium is 2.0 to 3.0 mEq/L. With a serum K+ of 6.8 and ECG changes (peaked T waves = early hyperkalemia sign), rapid removal is essential. Using 1.0 mEq/L dialysate maximizes the concentration gradient. However, dropping potassium too rapidly can also cause cardiac arrhythmias; clinical judgment and physician order guide the exact choice.
Question 2: What is the physiological consequence of using dialysate with a calcium concentration lower than the patient's serum calcium?
- Calcium will move from blood into dialysate, potentially lowering serum calcium (Correct answer)
- Calcium will move from dialysate into blood, raising serum calcium
- No change occurs because calcium does not cross the dialyzer membrane
- Phosphorus will increase to compensate for calcium loss
Correct answer: Calcium will move from blood into dialysate, potentially lowering serum calcium
When dialysate calcium is lower than serum calcium, the concentration gradient causes calcium to diffuse out of the blood into the dialysate, lowering serum levels.
Standard dialysate calcium is 2.5 mEq/L (1.25 mmol/L). If serum ionized calcium is higher, net calcium removal occurs during dialysis. Patients with hypercalcemia (from calcium-based phosphate binders or vitamin D excess) may benefit from lower calcium dialysate, while hypocalcemic patients may need higher calcium dialysate.
Question 3: Which acid-base disturbance is most common in ESRD patients before dialysis treatment?
- Metabolic alkalosis
- Respiratory acidosis
- Metabolic acidosis (Correct answer)
- Respiratory alkalosis
Correct answer: Metabolic acidosis
ESRD patients develop metabolic acidosis because the kidneys can no longer excrete acid or regenerate bicarbonate, causing accumulation of organic acids.
In ESRD, the kidneys fail to excrete daily acid load (~1 mEq/kg/day from protein metabolism) and cannot regenerate bicarbonate. This causes metabolic acidosis with low serum bicarbonate (typically 15 to 18 mEq/L in ESRD). Dialysis corrects acidosis by delivering bicarbonate from the dialysate. Target post-dialysis bicarbonate is 22 to 26 mEq/L.
Question 4: Why is hyperphosphatemia particularly dangerous for hemodialysis patients beyond the known bone disease effects?
- It directly causes cardiac arrhythmias
- It promotes vascular and soft tissue calcification, increasing cardiovascular mortality (Correct answer)
- It reduces EPO effectiveness, worsening anemia
- It directly impairs the dialyzer membrane
Correct answer: It promotes vascular and soft tissue calcification, increasing cardiovascular mortality
Elevated phosphorus combines with calcium to form calcium-phosphate deposits in blood vessels and soft tissues (vascular calcification), dramatically increasing cardiovascular risk.
When the calcium x phosphorus product exceeds 55 mg2/dL2, calcium-phosphate crystals precipitate in vascular walls, heart valves, and soft tissues. This metastatic calcification causes arterial stiffness, coronary artery calcification, valvular dysfunction, and left ventricular hypertrophy. ESRD patients have 10 to 30 times higher cardiovascular mortality than the general population, with hyperphosphatemia as a major independent risk factor.
Question 5: What effect does bicarbonate concentration in dialysate have on the patient's serum pH?
- Higher bicarbonate dialysate decreases serum pH
- Higher bicarbonate dialysate increases serum pH by adding bicarbonate to blood (Correct answer)
- Dialysate bicarbonate has no effect on serum pH
- Dialysate bicarbonate only affects serum pH in patients with intact kidney function
Correct answer: Higher bicarbonate dialysate increases serum pH by adding bicarbonate to blood
Bicarbonate in dialysate diffuses into the blood down its concentration gradient, increasing serum bicarbonate and normalizing low pH (metabolic acidosis).
Standard dialysate bicarbonate is 35 to 40 mEq/L, much higher than the typical pre-dialysis serum bicarbonate of 15 to 18 mEq/L. This concentration gradient drives bicarbonate into the blood, correcting metabolic acidosis. The bicarbonate concentration is adjusted based on the patient's pre-dialysis bicarbonate levels. Too much correction causes post-dialysis metabolic alkalosis.
Question 6: A patient on dialysis has a serum magnesium of 0.8 mEq/L. Standard dialysate contains 0.75 to 1.0 mEq/L of magnesium. What would you expect to happen to magnesium levels during dialysis?
- Magnesium will continue to decrease during dialysis
- Minimal change or slight increase since dialysate and serum levels are similar (Correct answer)
- Magnesium will increase significantly due to high dialysate concentration
- Dialysis will have no effect on magnesium levels
Correct answer: Minimal change or slight increase since dialysate and serum levels are similar
Since serum magnesium (0.8) is near standard dialysate magnesium (0.75 to 1.0), the small concentration gradient produces minimal net movement.
Magnesium balance during dialysis depends on the gradient between serum and dialysate concentrations. With serum Mg at 0.8 mEq/L and dialysate at 0.75 to 1.0 mEq/L, the gradient is near zero, producing little net transport. Standard dialysate is designed to maintain near-normal serum magnesium in most patients.
CCHT Electrolyte Balance 2
A patient's pre-dialysis potassium level is 6.8 mEq/L with peaked T waves on ECG.
Which dialysate potassium concentration would be most appropriate?