Fluid Therapy

Question 1

Hypotonic fluid loss

Answer 1

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

Question 2

Causes of hypotonic fluid loss

Answer 2

• diabetes isipidus
• excessive panting
• chemical/post-obstructure diuresis
• decreased water intake

*all can lead to significant hypovolemia

Question 3

Neurological responses to hypovolemia and increased osmolality

Answer 3

1. increased osmolality > hypothalamus > releases ADH > increases water reabsorption in kidney > more concentrated urine
2. decreased stretch > aortic baroreceptors > stimulate thirst center in 3rd ventricle > increased water intake

Question 4

increased osmolality due to hypotonic fluid loss is reflected by an increase in what?

Answer 4

serum sodium

Question 5

Isotonic fluid loss

Answer 5

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

Question 6

Clinical causes of isotonic fluid loss

Answer 6

hemorrhage, vomiting/diarrhea, chronic kidney disease

*more common than hypotonic losses

Question 7

Patients demonstrating acute fluid loss leading to hypovolemia and severe dehydration deficits most likely show signs of ______, and should receive ______ doses of IV fluids

Answer 7

Shock; prevent complications of decreased oxygen delivery

Question 8

Replacement volume formula

Answer 8

Body weight (kg) x Percent Dehydration = Deficit (L)

Question 9

Fluid rate formula

Answer 9

Deficit (ml)/Time in hours = Rate (ml/hr)

Question 10

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

Answer 10

Subtracted

Question 11

How can ongoing losses be calculated?

Answer 11

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

Question 12

Maintenance Rates/Formulas

Answer 12

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)

Question 13

Fluid rate initially for those that have had fluid loss

Answer 13

Replacement rate + Ongoing losses rate + Maintenance

Question 14

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:

Answer 14

Ongoing losses rate + Maintenance

Question 15

Isotonic crystalloids

Answer 15

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

Question 16

What is the shock dose of an isotonic crystalloid solution?

Answer 16

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

Question 17

What are the concentrations of isotonic crystalloids?

Answer 17

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

Question 18

Hypotonic crystalloids

Answer 18

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

Question 19

D5W administration is restricted for what patients?

Answer 19

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

Question 20

Hypotonic Crystalloid Concentrations

Answer 20

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

Question 21

Hypertonic crystalloids

Answer 21

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

Question 22

Synthetic colloids

Answer 22

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

Question 23

A higher degree of substitution in synthetic colloids indicates what?

Answer 23

The slower the breakdown and elimination of the molecule; greater potential effects on coagulation

Question 24

What is the benefit of using synthetic colloids with isotonic crystalloids?

Answer 24

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

Question 25

Patients demonstrating acute fluid loss leading to hypovolemia and severe dehydration deficits most likely show signs of ______, and should receive ______ doses of IV fluids

Answer 25

Shock; prevent complications of decreased oxygen delivery