Electrolyte Monitoring in Patients with Acute Kidney Injury
Electrolyte abnormalities must be closely monitored in all patients with AKI, particularly those receiving kidney replacement therapy (KRT), as these disturbances are extremely common and directly impact mortality and morbidity. 1
Key Electrolytes Requiring Monitoring
The primary electrolytes requiring close surveillance include:
Phosphate: Monitor for hypophosphatemia (serum levels <0.81 mmol/L), which occurs in 60-80% of ICU patients with AKI on KRT and is associated with respiratory failure, prolonged mechanical ventilation weaning, cardiac arrhythmias, and increased mortality 1
Potassium: Monitor for both hyperkalemia (common before KRT initiation) and hypokalemia (occurring in 12-25% of patients on prolonged KRT modalities) 1
Magnesium: Monitor for hypomagnesemia (serum levels <0.70 mmol/L), which occurs in 60-65% of critically ill patients on KRT, particularly when regional citrate anticoagulation is used 1
Sodium: Monitor for hyponatremia, which is common in kidney failure 1
Calcium: Monitor for hypocalcemia, frequently seen in AKI 1
Monitoring Frequency
For hospitalized patients with AKI, measure serum urea, creatinine, and electrolytes (sodium, potassium, bicarbonate) at least every 48 hours, or more frequently if clinically indicated 1. This includes:
- Patients at increased risk of AKI
- Those who have sustained AKI
- Patients with existing electrolyte abnormalities 1
Critical Clinical Context
Before KRT Initiation
At least one electrolyte deficiency occurs in 60% of patients and electrolyte excess in 67.6% of patients before starting KRT 2. The most common pre-KRT abnormalities are hyponatremia, hyperkalemia, hyperphosphatemia, and hypocalcemia 1.
After KRT Initiation
KRT paradoxically shifts the electrolyte profile from excess to deficiency 1. Intensive KRT modalities (CKRT, PIKRT) cause significant electrolyte removal, leading to:
- Hypophosphatemia becoming the dominant concern (prevalence up to 80%) 1
- Hypokalemia replacing hyperkalemia 1
- Hypomagnesemia, especially with citrate anticoagulation 1
Prevention Strategy
Use dialysis solutions containing potassium (4 mEq/L), phosphate, and magnesium to prevent electrolyte disorders during KRT rather than relying on intravenous supplementation 1. This approach:
- Prevents hypophosphatemia, hypokalemia, and hypomagnesemia more safely than IV supplementation 1
- Reduces clinical risk and workload associated with separate electrolyte infusions 1
- Can be used safely with regional citrate anticoagulation 1
Common Pitfalls to Avoid
Do not rely solely on standard KRT solutions (containing only 2 mmol/L potassium and no phosphorus), as these will inevitably cause electrolyte depletion during prolonged therapy 1.
Avoid intravenous electrolyte supplementation in patients on CKRT when possible, as this carries significant clinical risk; instead, modulate the KRT fluid composition 1.
Monitor for refeeding syndrome when initiating nutrition support, as carbohydrate administration can precipitate severe hypophosphatemia in the setting of KRT 1.
Prognostic Significance
Hyperphosphatemia before KRT initiation (≥4.5 mg/dL) predicts significantly higher 28-day mortality (71.2% vs 57.6%) and 90-day mortality in septic AKI patients, conferring a 2.2-fold and 2.6-fold increased mortality risk respectively 2. This underscores why electrolyte monitoring directly impacts patient survival.