Healthcare Facts for Simulation Technology Specialists: The Fun "Fizzyology" of IV Fluids


Blog post by Kim Baily

Healthcare Facts for Simulation Technology Specialists: The Fun "Fizzyology" of IV Fluids

This is the second post in a series (read part one here) designed to help sim techs new to simulation or who need a refresher understand how the body functions. Simulation technicians can help create fidelity in simulation by understanding the physiology and/or pathophysiology behind each scenario. Missing data or typical equipment can confuse learners and leave them guessing about their next action. The appropriate cues from lab reports, IV therapy, 12 lead EKG, patient complaints, catheter placements and moulage can help guide learners.

Did you know that the composition of sea water and human body fluid is very similar?

When certain compounds are dissolved in water, charged particles or ions (electrolytes) are produced that can conduct an electric current. Movement of charged ions into and out of human cells play a key role in many physiological mechanisms such as nerve conduction and cardiac function. The principle cations (positive ions) of the human body are sodium, potassium, magnesium and calcium. The principle anions (negative ions) are chloride, phosphate, and chloride. However, these ions are not found in equal concentrations in the various body compartments.


The concentration differences across cells is important for normal physiological function although ion concentrations can shift rapidly during events such as nerve conduction, muscle cell contraction or cardiac function. A 5 mEq/L increases or decrease extracellular sodium results in a relatively small percentage change in sodium concentration (around 3%) whereas a 5mEq/L increase in extracellular potassium would double the concentration of potassium. Relatively small changes in extracellular potassium can have serious effects on cardiac and neuromuscular function. Since potassium administration via IV fluids must be carefully controlled and monitored, simulation is an ideal methodology to enhance learner knowledge of fluid maintenance.

The most common IV fluid is normal saline aka 0.9% sodium chloride. This concentration is the go to IV bag hung in emergencies since its concentration matches human plasma (and sea water) and will not cause fluid or electrolyte shifts. Normal saline is said to be isotonic i.e. similar concentration of particles to plasma. It is the only fluid that can be hung with blood transfusions. Hanging blood with a hypotonic solution such as 0.225% sodium chloride with cause water to move into the red cells causing them to swell and burst (lyse). Hanging hypertonic solutions such as 3% sodium chloride will cause the red cells to shrink as water moves out of cells. In a simulation involving blood transfusions always have IV bags of varying concentrations available. Surprisingly some learners grab the first bag they see and do not bother to check the IV content.

Normal saline is made from dissolving 0.9 grams salt (sodium chloride) in 100 mL of water or 9 grams in one liter.