Fluid Therapy Flashcards
Hypotonic fluid loss
body looses part of the TBW as part of a pathological process (water has little to no solute content); increased osmolality of ECF > movement from ICF to ECF - deleterious neuro effects
Causes of hypotonic fluid loss
- diabetes isipidus
- excessive panting
- chemical/post-obstructure diuresis
- decreased water intake
*all can lead to significant hypovolemia
Neurological responses to hypovolemia and increased osmolality
- increased osmolality > hypothalamus > releases ADH > increases water reabsorption in kidney > more concentrated urine
- decreased stretch > aortic baroreceptors > stimulate thirst center in 3rd ventricle > increased water intake
increased osmolality due to hypotonic fluid loss is reflected by an increase in what?
serum sodium
Isotonic fluid loss
loss of TBW due to fluid loss that has solute concentration similar to that of ECF; no water movement occurs b/t ECF and ICF
- most commonly seen in vet med
Clinical causes of isotonic fluid loss
hemorrhage, vomiting/diarrhea, chronic kidney disease
*more common than hypotonic losses
Patients demonstrating acute fluid loss leading to hypovolemia and severe dehydration deficits most likely show signs of ______, and should receive ______ doses of IV fluids
Shock; prevent complications of decreased oxygen delivery
Replacement volume formula
Body weight (kg) x Percent Dehydration = Deficit (L)
Fluid rate formula
Deficit (ml)/Time in hours = Rate (ml/hr)
If a shock bolus has been given, this volume can be _____ from the total deficit and the remaining volume given over the time in hours that was considered appropriate for replacement
Subtracted
How can ongoing losses be calculated?
Either measuring urine output in animals with polyuria disease, and measuring/estimating volume of diarrhea/vomit animal is losing per hour in animals w/ GI signs; better to overestimate these losses
Maintenance Rates/Formulas
30 (BW in kg) + 70 = total volume (ml/24hrs) 70x[BWkg]^0.75 = total volume (ml/24hrs): small animals <2kg or very large animals >40kg 40-60 ml/kg/day (40-50 for cats/geriatrics)
Fluid rate initially for those that have had fluid loss
Replacement rate + Ongoing losses rate + Maintenance
Once replacement volume has been delivered and if the patient is considered euvolemic and no longer showing signs of shock, fluid rate is decreased to:
Ongoing losses rate + Maintenance
Isotonic crystalloids
Uses: Replacement fluids, commonly maintenance fluids, hypovolemic shock Electrolyte containing w/ composition close to ECF - rapidly diffuses SE: volume overload esp w/ low oncotic pressure, inflammatory states (sepsis), and oligo-anuric renal dysfunction, pulmonary edema if overhydrated Agents: 0.9% NaCl, LRS, Plasmalyte, Normosol-R
What is the shock dose of an isotonic crystalloid solution?
Approximately one blood volume 90ml/kg in dog, 50ml/kg in cat 1/3-1/2 shock dose given ASAP; within 15 min of original exam
What are the concentrations of isotonic crystalloids?
Osmolality: 295-308 (close to that of ECF)
Na+: 130-154
K+: 0-5
Cl: 98-154* very high (as in ECF)
Mg: 0-3
Ca: 0-3
Hypotonic crystalloids
Uses: maintenance, replenish free water, tx hypernatremia secondary to hypotonic fluid loss Contain much lower electrolyte amounts (homeostasis); contain higher K load Large Vd and distribute to ECF and ICF more readily SE: NEVER used for shock/poor perfusion - may cause fatal cerebral edema due to drop in plasma osmolality Better tolerated in cardiac/renal dysfunction patients b/c of restricted Na and Cl Agents: 0.45% NaCl, 1/2 LRS + 2.5% Dextrose, Plasmalyte-56, Normosol-M, D5W Water + 5% Dextrose
D5W administration is restricted for what patients?
Animals with water deficit and evidence of hypernatremia on bloodwork; NEED to monitor electrolytes q6hr Use Free Water Deficit formula to determine how much can be given over safe period of time
Hypotonic Crystalloid Concentrations
Osmolality: 150-265 (relatively normal)
Na: 40-130
K: 0-13
Cl: 40-77 (much lower than normal)
Mg: 0-3
Ca: 0-3
D5W- no electrolytes
Hypertonic crystalloids
Most common: hypertonic saline, 7-7.5% NaCl MOA: transient osmotic shift of water from extravascular to intravascular compartment > transient expansion of intravascular volume Uses: hemorrhagic shock and traumatic brain injury decreases blood viscosity to increase microcirculatory perfusion, increases CO (incr preload, mild vasodilation), decrease inflammatory response
Synthetic colloids
Do not readily filter across vascular membrane Hydroxyethyl starch molecules in isotonic crystallography solution MOA: Hyperoncotic to normal animal and pull fluid into vascular space - incr blood volume > infused volume + retain fluid in intravascular space in the animal w/ normal capillary permeability Uses: resuscitation and to increase oncotic pressure, treating shock if crystalloids don’t work/contraindicated (pulm/cardiac dz) Maintain vascular volume for longer than crystalloids b/c do not redistribution Agents: Hextend, Hespan, Hetastarch, VetStarch3, Voluven4 SE: should be avoided in animals with kidney dysfunction, sepsis, and risk of coagulopathies
A higher degree of substitution in synthetic colloids indicates what?
The slower the breakdown and elimination of the molecule; greater potential effects on coagulation
What is the benefit of using synthetic colloids with isotonic crystalloids?
Maintain adequate plasma volume expansion with lower interstitial fluid volume expansion and to expand the intravascular space with smaller volumes over a shorter time period
Patients demonstrating acute fluid loss leading to hypovolemia and severe dehydration deficits most likely show signs of ______, and should receive ______ doses of IV fluids
Shock; prevent complications of decreased oxygen delivery
