Fluids Flashcards
By how much will the extracellular fluid volume be expanded after administration of 50mL of hypertonic solution? For how long?
By 150-250mL (3-5 times the volume administered)
It will last <30 min before electrolytes and fluids re-distribute
What is the composition of 0.9%NaCl, LRS, Plasmalyte-A (or Normosol)
0.9%NaCl: 154 mEq/L Na, 154 Cl (omsolality 308)
LRS: 130 Na, 109 Cl, 4 K, 1.5-3 Ca, 28 lactate (osmolality 273)
Plasmalyte-A: 140 Na, 98 Cl, 5 K, 1.5-3 Mg, 27 acetate, 23 gluconate (osmolality 294)
Name one patient population where administration of LRS is indicated and one where it is contra-indicated
- Indicated in neonates (use lactate as metabolic substrate)
- Contra-indicated in patients with liver failure (don’t metabolize lactate)
What is the recommended max osmolality to be administered via peripheral vein
600 mOsm/L
You have 7.2%NaCl available and need to make 3%NaCl. What do you do?
C1V1 = C2V2
-> to make 50mL of 3% NaCl, need V1 = (3*50)/7.2 = 20.8 mL of 7.2%
-> dilute 20.8mL of 7.2% NaCl in 29.2 (50-20.8) mL of sterile water
What fluid should be used to resuscitate a patient with hypovolemia and severe hyponatremia / hypernatremia
A fluid with a sodium content close to the patient’s sodium concentration (within 6 mmol/L) - might need to be home made
Between which 2 compartments is there an osmotic gradient in healthy individuals
Intracellular and interstitial
(NOT between intravascular and interstitial since the capillary membrane is freely permeable to sodium and glucose - fluid shifts determined by Starling’s law)
What is the best site to assess skin turgor
Over the top of the sagittal crest
What degree of interstitial dehydration is required to start causing hypovolemia
> 10-12%
What factors influence the assessment of interstitial hydration based on physical exam
- Age (elastic skin in puppies)
- Atropine administration (causes dry mucous membranes)
- Body fat content (skin turgor decreases with emaciation / increases with obesity)
How can interstitial / intravascular / intracellular volumes be assessed
Interstitial: markers of dehydration (MM moisture, skin turgor, corneal moisture, eye position in the orbit)
Intravascular: markers of perfusion (MM color, CRT, HR, pulse, temperature, etc.)
Intracellular: only based on the osmolality of the extra-cellular compartment (if osmolality is increased in extracellular fluid you know intracellular volume is decreased)
What is the maximum size of molecules able to move through the vascular endothelium
10-20 kDa
What is the definition of resting energy (or water) requirement
It is the amount of energy (or water) needed to maintain normal homeostatic functions while a patient is at rest, expelling no additional energy, in a fed state and thermoneutral environment
As a general rule, what is the recommended fluid type for:
- neonates
- patient with liver failure
- patient with traumatic brain injury
- Neonates: LRS (can use lactate as substrate for metabolism)
- Liver failure: PLA or 0.9NaCl (unable to metabolize lactate into bicarbonate)
- TBI: 0.9NaCl to avoid risk of decreasing osmolality and causing more cerebral edema
What are replacement fluids vs maintenance fluids
Replacement: isotonic crystalloids (0.9NaCl, LRS, PLA)
Maintenance: hypotonic crystalloids containing less Na/Cl and more K, intended to replace normal physiologic losses of Na
