IV Potassium Replacement Calculation: A Practical Guide
For rapid IV potassium correction in hypokalemia, use 20 mEq potassium chloride in 100 mL normal saline infused over 1 hour, which typically raises serum potassium by approximately 0.25 mEq/L per dose. 1
Estimating Total Body Potassium Deficit
Calculate the deficit using: Deficit K+ (mEq) = (K+ target - K+ actual) × 0.5 × ideal body weight (kg), where 0.5 represents the distribution volume of potassium in extracellular and intracellular spaces 2. However, this formula has significant limitations—transcellular redistributions from insulin, alkalosis, or catecholamines can dramatically alter serum potassium without changing total body potassium, and continuous losses from diuretics, diarrhea, or vomiting require repeated calculations 2.
Critical caveat: Serum potassium is an inaccurate marker of total-body potassium deficit 3. Only 2% of body potassium is extracellular, so small serum changes reflect massive total body deficits 4, 2. For example, in diabetic ketoacidosis, typical deficits are 3-5 mEq/kg body weight (210-350 mEq for a 70 kg adult) despite initially normal or elevated serum levels 2, 5.
Standard IV Dosing Protocol
Initial Dose Based on Severity
For serum potassium 1.8 mg/dL to lower end of normal range: 0.16-0.31 mmol/kg phosphorus (0.23-0.46 mEq/kg potassium) 5
For serum potassium 1.0-1.7 mg/dL: 0.32-0.43 mmol/kg phosphorus (0.47-0.63 mEq/kg potassium) 5
For serum potassium <1.0 mg/dL: 0.44-0.64 mmol/kg phosphorus (0.64-0.94 mEq/kg potassium), up to a maximum single dose of phosphorus 45 mmol (potassium 66 mEq) 5, 6
Practical Infusion Parameters
Standard concentration and rate: 20 mEq potassium chloride in 100 mL normal saline infused over 1 hour (200 mEq/L concentration at 20 mEq/hour rate) is safe via central or peripheral vein 1, 7. This approach increased mean serum potassium from 3.2 to 3.9 mEq/L (mean increment 0.25 mEq/L per 20 mEq dose) without life-threatening arrhythmias in 495 infusion sets 1.
Maximum peripheral infusion rate: 10 mEq/hour through peripheral vein; continuous ECG monitoring is recommended for higher rates 6. For central lines, rates up to 20 mEq/hour are acceptable with appropriate monitoring 1.
Maximum concentration limits:
- Peripheral line (adults/pediatrics ≥12 years): phosphorus 6.8 mmol/100 mL (potassium 10 mEq/100 mL) 6
- Central line (adults/pediatrics ≥12 years): phosphorus 18 mmol/100 mL (potassium 26.4 mEq/100 mL) 6
- Pediatric <12 years (peripheral): phosphorus 0.27 mmol/10 mL (potassium 0.4 mEq/10 mL) 6
- Pediatric <12 years (central): phosphorus 0.55 mmol/10 mL (potassium 0.8 mEq/10 mL) 6
Critical Pre-Administration Checks
Before giving ANY IV potassium:
- Verify serum potassium is <4.0 mEq/L; if ≥4.0 mEq/L, use an alternative phosphorus source 6, 5
- Check and normalize calcium first—potassium phosphates are contraindicated in hypercalcemia 6
- Confirm adequate urine output (≥0.5 mL/kg/hour) to establish renal function 5
- Check magnesium levels immediately—hypomagnesemia (target >0.6 mmol/L) is the most common reason for refractory hypokalemia and must be corrected first 2, 5
Special Clinical Scenarios
Diabetic Ketoacidosis (DKA)
Add 20-30 mEq/L potassium (2/3 KCl and 1/3 KPO4) to each liter of IV fluid once K+ falls below 5.5 mEq/L with adequate urine output 5, 8. Pediatric patients may require 20-40 mEq/L in maintenance fluids 5, 8. If K+ <3.3 mEq/L, delay insulin therapy until potassium is restored to prevent life-threatening arrhythmias 2. Monitor electrolytes every 2-4 hours during active treatment 5, 2.
Moderate Renal Impairment
In patients with eGFR 30-60 mL/min/1.73 m², start at the low end of the dose range and monitor serum potassium, phosphorus, calcium, and magnesium closely 6, 5. Severe renal impairment (eGFR <30 mL/min) and end-stage renal disease are contraindications to potassium phosphates injection due to life-threatening hyperkalemia risk 6.
Monitoring Protocol
Recheck potassium within 1-2 hours after IV correction to ensure adequate response and avoid overcorrection 2. Continue monitoring every 2-4 hours during acute treatment until stabilized 2. The timing should be based on severity of initial hypokalemia, presence of cardiac symptoms or ECG changes, and underlying comorbidities like kidney disease or heart failure 2.
Common Pitfalls to Avoid
Never administer potassium phosphates undiluted—it is only for infusion after dilution into normal saline or D5W 6. Direct IV push can cause cardiac arrest 2.
Never infuse with calcium-containing IV fluids—this causes precipitation and pulmonary vascular emboli 6.
Never supplement potassium without checking magnesium first—this is the most common reason for treatment failure 2. Magnesium depletion causes dysfunction of potassium transport systems and increases renal potassium excretion 2.
Avoid aggressive potassium repletion in patients on high-dose insulin therapy—moderate hypokalemia (2.5-2.8 mEq/L) may be acceptable, as animals treated with aggressive potassium repletion during high-dose insulin-euglycemia therapy developed asystole 5.
Do not tie potassium delivery to insulin infusion rates—maintain separate infusion lines to allow independent titration based on glucose response versus potassium levels 2.