Fluids Flashcards
what does a crystalloid solution contain?
water, electrolytes (like NaCl), small molecules like dextrose and buffers
what are the main osmotically active particles?
electrolytes, glucose, urea (also ketones and mannitol)
what is osmolarity?
the concentration of osmotically active particles in a solution, a function of the number of particles, NOT the size, molecular weight, or charge
what is an isotonic crystalloid?
a fluid where the concntration of Na and Cl is close to what is in the blood, aka, the intravascular space
what are the two scenarios you can use isotonic solutions in?
replacement for hypovolemia, or dehydration
what happens when you give isotonic cystalloids?
there is an increase in intravascular volume, which corrects hypovolemia, and then after 45 minutes 75% of the volume will diffuse into the interstitial space and correct dehydration
some of the ingredients in isotonic crystalloids are lactate, acetate, and gluconate. what do these do?
they are buffers and they absorb H+ ions to prevent acidosis
why are buffers added to fluids?
- many patients are acidotic
- the buffering molecules will produce bicarbonate which will bind to H+ ions and limit a change in pH
cystalloids with buffers are called what?
“balanced” crystalloids
0.9% NaCl has no buffer. What is the consequece of this?
the increase in Cl- when given will cause a decrease in bicarb, which can cause some acidosis. therefore, not the best kind of fluid to treat shock unless the patient is in hypochloremic metabolic alkalyosis (basic blood)
why is potassim added to fluid solutions? can you give potassium as a bolus?
it limits hypokalemia in the patient. it is usually added in amounts equal to the plasma. in small amounts it is okay to be given as a bolus, but if you need to supplement more for a maintenace infusion you can’t give it as a bolus because it will stop the heart
why is calcium an ingredient in a cystalloid?
it may improve contractility and vascular tone
what is the role of magnesium in a crystalloid?
it is an electrolyte that is commonly low in critical illness so this acts as a supplement to restore those levels
what are two examples of ways in which the fluids you give are incompatible with some drugs?
blood products: calcium will precipitate with the citrate in the blood product
medications: potassim phosphate will precipitate with calcium, so you cannot give with ringer lactate
what conditions can I treat with isotonic crystalloids?
hypovolemia (fluid remains in the IV space long enough to improve perfusion)
interstisial dehydration (equilibrates between IV and intersitial space within an hour)
NOT good for intracellular dehydration because there is no driving force to move fluids into this space
what is a contraindication for giving isotonic cystalloids?
be careful with patients at risk for edema or that might die if edema worsens, for example:
- hypoalbuminemia patients
- patients with anuric renal failure (kidneys can’t excrete)
- patients with cardiac disease
- pulmonary contusions (bruise in the lungs, fluids can cause these to pop and bleed)
- patients with brain injury (can cause increase in intracranial pressure and swelling)
- sepsis (water gets in easier if the patient is in sepsis, increase in increased permeability)
if you have to give isotonic fluids to a patient that may be at high risk (like a brain injury or CHF), how might you do this?
you can still give it, but you must do so slowly with very close monitoring
can you give hypotonic crystalloids as a bolus? why or why not?
you should not because they can have high potassium content
what is a maintenance fluid?
it is the volume and electroyte content that must be consumed to maintain the total body water and electroytes within normal limits
what happens when you give hypotonic fluids?
it expands the IV space a little bit, but it very quickly diffuses into the intersitial space and into cells (remember it’s hypotonic, so there’s lots of water, and the osmolarity is higher in the intersitial space and in cells, so the water moves out of the vessels and into where it’s more salty)
when should you give hypotonic fluids?
-when a patient needs fluid but they have cardiac disease (you want fluids with low sodium because this is less likely to cause edema, fluid wont stay in the vessels for very long and therefore will not overwhelm the heart)
- if you have a patient with hypernatremia ( provides free water to dilute the sodium)
- if the patient only requires fluid to compensate for normal physiologic losses like urination and panting (like if a dog is having surgery the next day and the dog can’t eat or drink anything but you need to restore these loses)
list some advantages and disadvantages of hypotonic crystalloids?
adv: can be used to treat hypernatremia or intracellular water deficits, it is balanced to replace daily metabolic losses, the low sodium decreases risk of volume overload in dehydrated patients with heart disease, compatable with most drugs/solutions for example there is no calcium for things to percipitate out
disadv: cannot use to treat shock, it leaves the IV space too quickly to treat shock
what is the effect of giving dextrose IV?
dextrose is immediately taken up by the cells shortly after delivery, leaving pure water to equilibrate between body compartments. therefore, it is considered equivalent to pure water
if giving dextrose is the same as giving pure water, why not just give pure water? why bother with the dextrose?
dextrose is added to provide osmolarity
