Pharmacology, Fluid and Electrolyte Therapy, and Dose Calculations
Pharmacology essentials
Know the high-alert infusions - vasopressors, insulin, heparin, opioids, concentrated electrolytes, chemotherapy - and their double-check requirements, standard concentrations, and rate limits. Know common antidotes and reversal agents (protamine for heparin, vitamin K and PCC for warfarin, naloxone for opioids, flumazenil for benzodiazepines, glucagon/dextrose for hypoglycemia). Know monitoring: vancomycin trough or AUC, aminoglycoside levels, aPTT/anti-Xa for heparin.
Fluids and electrolytes
Isotonic fluids (0.9% sodium chloride, lactated Ringer's) expand the extracellular volume. Hypotonic fluids (0.45% sodium chloride) move water intracellularly and risk hyponatremia and cerebral edema. Hypertonic fluids (3% saline, concentrated dextrose) require central access and close monitoring. Potassium is never given by IV push - always diluted and rate-limited, with cardiac monitoring for high rates. Assess for hyperkalemia (peaked T waves), hypokalemia (U waves, arrhythmia), and for signs of overload (crackles, edema, jugular venous distention).
Calculations
Use dimensional analysis and check that the units cancel. Common forms: mL/hr from a dose; gtt/min = (volume × drop factor) ÷ time in minutes; weight-based mcg/kg/min; unit-per-hour heparin infusions; and pediatric doses per kg.
Trap: mixing micrograms and milligrams, or forgetting to convert hours to minutes in gravity drip problems.
Worked example: 1000 mL over 8 hours with a 15 gtt/mL set. 1000 × 15 = 15,000 drops ÷ 480 minutes = 31 gtt/min.
Rule of thumb: calculate the answer, then ask whether it is physiologically plausible - an adult heparin rate of 400 mL/hr or a pediatric dose larger than the adult dose means the arithmetic is wrong.