Electrolyte Replacement and mEq Calculations

Understanding Milliequivalents

Milliequivalents (mEq) measure the chemical activity of electrolytes in the body. Common electrolytes include potassium (K+), sodium (Na+), calcium (Ca2+), and magnesium (Mg2+). The PTCB exam may ask you to calculate mEq from weight or concentration.

Potassium chloride (KCl) is one of the most frequently tested electrolytes. It is available in various forms including oral tablets (10 mEq, 20 mEq), oral solutions, and IV concentrates that must be diluted before administration.

IV Electrolyte Calculations

IV potassium must be diluted and infused slowly to prevent cardiac arrhythmias. A typical order might read "add 20 mEq KCl to 1000 mL NS and infuse over 8 hours." Knowing the concentration of KCl stock solution (commonly 2 mEq/mL) allows you to calculate the volume needed.

Normal saline (0.9% NaCl) contains 154 mEq of sodium per liter. Half-normal saline (0.45% NaCl) contains 77 mEq/L.

Exam Resources

Electrolyte questions combine clinical knowledge with math skills. Review with PTCB flashcards and practice with timed exams.