Fluid and Electrolytes

Four Important Takeaways

We're 60% Water

All of that water is divided into several different compartments which you need to know!

Insensible losses add up

You need to understand that insensible losses from the human body, whether it's urine, gastrointestinal loss or sweat add up so make sure to take them into account when you're looking at fluid balance.

Hypovolemia, Baroreceptors, and Stretch

Make sure you understand the different maintenance fluids.  That lactated ringers is an isotonic solution but has less sodium than the plasma so will drive sodium levels down.  If you're going to give a fluid, know what's in it!

What fluid to replace?

Let's say you've lost blood, what fluid do you replace it with?  How about a nasogastric tube with 1500ml of output?  What fluid?  How about a high ileostomy output?  What fluid?

Notes from the Video

What You're Going to Learn from This Video on Fluid and Electrolytes


In this video we're going to get comfortable with fluid compartments in the body! 


We're also going to go deep into the various intravenous fluids available and when you may need to decide which fluid to use.


You're going to be confidence with the following:


1.). Understand the fluid compartments of the body


2.). What fluid goes where?


3.). Obligatory fluid and electrolytes losses and how to replace them



Fluid compartments in the body are critical for the proper functioning of various physiological processes. The human body is composed of approximately 60% water, which is distributed between several fluid compartments.


The major fluid compartments in the body are the intracellular fluid (ICF) and the extracellular fluid (ECF).


The ICF is the fluid inside the cells, which makes up approximately two-thirds of the body's total water content.


The ECF is the fluid outside the cells, which makes up approximately one-third of the body's total water content.


The ECF is further divided into interstitial fluid and plasma.


The interstitial fluid is the fluid between the cells, while the plasma is the liquid component of blood. The plasma contains several important proteins, such as albumin and globulins, which help to maintain osmotic pressure and transport various substances in the blood.


The movement of water and solutes between the different fluid compartments is regulated by osmosis, diffusion, and active transport.


Osmosis is the movement of water across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration. Diffusion is the movement of solutes from an area of high concentration to an area of low concentration. Active transport is the movement of solutes against a concentration gradient, requiring energy in the form of ATP.


The concentration of solutes, such as electrolytes and proteins, differs between the different fluid compartments, which helps to maintain the balance of fluids and electrolytes in the body. The ECF contains a higher concentration of sodium, chloride, and bicarbonate, while the ICF contains a higher concentration of potassium, magnesium, and phosphate.  The concentration of proteins is also higher in the plasma than in the interstitial fluid.


Changes in the concentration of solutes in one compartment can cause water to move from one compartment to another, leading to alterations in fluid balance. For example, if the concentration of sodium in the ECF increases, water will move from the ICF to the ECF to maintain osmotic balance, leading to dehydration of the cells.


The kidneys play a vital role in regulating the volume and composition of the ECF by filtering the blood and excreting excess water and electrolytes. The body maintains fluid balance through a variety of mechanisms, including thirst, hormone regulation, and the renin-angiotensin-aldosterone system.


Thirst is stimulated when the body is dehydrated, leading to an increase in water intake. Hormones such as antidiuretic hormone (ADH) and aldosterone help to regulate water and electrolyte balance by increasing or decreasing the reabsorption of water and electrolytes in the kidneys.


Disturbances in fluid balance can have significant consequences for the body, including dehydration, electrolyte imbalances, and edema. Dehydration can lead to decreased blood pressure, decreased urine output, and impaired organ function.


Electrolyte imbalances, such as hyponatremia or hyperkalemia, can cause cardiac arrhythmias and other serious complications. Edema, or the accumulation of excess fluid in the interstitial space, can lead to swelling, pain, and impaired tissue function.


Fluid compartments in the body are essential for the proper functioning of various physiological processes. The proper balance of fluids and electrolytes in the body is maintained through a complex interplay of mechanisms, including osmosis, diffusion, active transport, hormone regulation, and the function of the kidneys. Disturbances in fluid balance can have significant consequences for the body, emphasizing the importance of maintaining proper fluid balance for optimal health and well-being.




References:

Guyton AC, Hall JE. Textbook of Medical Physiology. 13th ed. Philadelphia: Elsevier; 2016