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Anaesthesia > Pharmacology of Fluid Therapy Agents > Flashcards

Pharmacology of Fluid Therapy Agents Flashcards

1
Q

Why is fluid therapy important?

A
  • ensure adeq circulation
  • considered a txt (prescribe as medication)
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2
Q

It is essential to ensure adequate

A

circulating volume

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3
Q

Why is fluid therapy essential

A

Optimizes & maintains CO thru adeq circulation, tissue perfusion, electrolyte concentration, acid-base balance

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4
Q

In fluid therapy, you want to avoid…

A

tissue oxygen debt & reduce organ failure

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5
Q

in fluid therapy, overinfusion can…

A

increase the risk of complications

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6
Q

Why is it essential to have good understanding of body fluid physiology for a patient receiving fluid therapy?

A

To ensure each animal receives
1. the correct fluid type
2. correct amount of fluid
3. at the correct rate
4. via an appropriate route

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7
Q

Overperfusion can cause…

A
  • Peripheral oedema
  • Pulmonary oedema
  • can overperfuse the blood possible
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8
Q

What are the goals of fluid therapy?

A
  • in intensive care: optimize CO
  • in anaesthesia: circulatory adequacy
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9
Q

Total body water =

A

60%

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10
Q

ECF makes up

A

20% Total body wt

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11
Q

Interstitial fluid makes up

A

15% of TBW

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12
Q

Intravascular fluid makes up

A

5% of TBW

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13
Q

intracellular fluid makes up

A

40% of TBW

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14
Q

What is dehydration?

A
  • loss of water from interstitum
  • due to intercompartmental shifts, ICF decreases too
  • severe dehydration can lead to hypovolaemia
  • must give prolonged fluids over many hours
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15
Q

What is hypovolaemia?

A
  • blood loss &/or water + solute loss (intra or pre-op)
  • boluses given to correct
  • absolute: vol loss from intravasc space only
  • relative: inappropriate fluid redistribution across compartments, pathological vasodilatory space
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16
Q

Osmosis

A

is the process where solvent molecules (most usually water) move through a semipermeable membrane from a diluted solution into a more concentrated solution (which becomes more diluted).

Mvmt of water from lots of water to little water to dilute high conc solutes

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17
Q

Osmotic pressure

A

The external pressure required so there is no net mvmt of solvent across a membrane

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18
Q

osmolality

A

osmoles/kg

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19
Q

osmolarity

A

osmoles/L

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20
Q

osmolality/osmolarity

A

number of osmotically active particles generated when a compound dissociates in 1 L of water

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21
Q

Normal serum osmolality in dogs

A

300 mOsm/kg

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22
Q

normal osmolality in cats

A

310 mOsm/kg

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23
Q

Oncotic pressure

A
  • Oncotic pressure = pressure exerted by larger molecules that sucks fluids into the vessel to maintain vascular volume
  • vascular endothelium freely permeable to water & electrolytes but selectively for larger molecules which exert osmotic pressure (Colloid pressure/oncotic pressure)

  • Sucks fluids into the vessel
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24
Q

Hydrostatic Pressure

A
  • increased pressures force fluid OUT of a space
  • independent of osmotic/oncotic pressure
  • arterial end of capillaries higher than ISF, fluid forced out
  • venous end of capillaries lower than ISF so oncotic & osmotic pressures favour mvmt of fluids back in vessels
  • push out of vessel
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25
Q

Filtration is where the fluid

A

exits capillary b/c capillary hydrostatic pressure > than blood colloidal osmotic pressure

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26
Q

Reabsorption is where…

A

At the venous end of a capillary, fluid re-enters capillary since capillary hydrostatic pressure is < blood colloidal osmotic pressure

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27
Q

No net movement of fluid means…

A

capillary hydrostatic pressure = blood colloidal osmotic pressure

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28
Q

What is the endothelial glycocalyx layer (EGL) theory?

A
  • re-eval of Starling forces
  • web of membrane-bound glycoproteins & proteoglycans on luminal side of endothelial cells that regulates fluid mvmt
  • controls vol of layer, fluid mvmt & avoidance of cell adhesion/clot formation
  • EGL compromised in systemic inflammatory states, hyperglycaemia, Sx, Sepsis
29
Q

tonicity is the equivalence of

A

effective osmolality

30
Q

Tonicity is the ability of an extracellular solution to make water

A

move into or out of a cell by osmosis

31
Q

tonicity is influenced only by…

A

solutes that cannot cross the membrane as these only exert effective osmotic pressure

32
Q

Solutes able to freely cross the membrane do not

A

affect tonicity b/c they will always equilibriate w/ equal conc on both sides of the membrane w/o net solvent mvmt

33
Q

Hypertonic

A

effective osmolarity > normal
fluid moves out of cell
Fluid moves INTO intravascular space (blood stream)

34
Q

Hypotonic

A

effective osmolarity < normal
fluid fills cell & may burst
fluid moves OUT of intravascular space (into interstitial space)

35
Q

Isotonic

A

shifts are similar each way
no net fluid mvmt

36
Q

how do we describe fluids?

A
  • content: crystalloid vs colloid
  • tonicity: isotonic vs hypertonic vs hypotonic
  • Fxn: resuscitation, replacement, maintenance; alkalinizing or acidifying
37
Q

Crystalloid

A

aqueous sln of mineral salts or water-soluble molecules

38
Q

Colloid

A

sln of large solutes, either naturally occurring or synthetic

39
Q

If resuscitation is needed to re-establish haemodynamic stability through restoring intravascular volume, what fluids could be used?

A
  • balanced crystalloid: Hartmann’s sln, Ringer’s acetate, Plasma-lyte 148
  • Crystalloid: 0.9% NaCl
40
Q

If replacement fluid therapy is required to provide daily maintenance requirements & replacement of any ongoing abnormal losses, what fluids should be used?

A
  • Balanced crystalloid: Harmann’s sln, Ringer’s acetate, Plasma-Lyte 148
  • Crystalloid: 0.9% NaCl
41
Q

If fluid therapy is necessary for providing daily maintenance requirements, what fluids could be used?

A
  • 0.18% NaCl/4% dextrose
  • 0.45% NaCl
  • 5% dextrose
42
Q

Replacement fluids are used to…

A

replace lost body water & electrolytes

43
Q

Replacement fluids may be used for…

A

short-term maintenance

44
Q

What are some isotonic fluids

A

CSL (Hartmann’s sln)
Lactated Ringer’s
NaCl 0.9%

45
Q

maintenance fluids provide

A

water in far excess than electrolytes

46
Q

maintenance fluids replaces losses through

A

sensible & insensible losses

47
Q

Maintenance fluids should not be…

A

bolused, or used until patient is stabilised

48
Q

Advantages of maintenance fluids

A
  • Commonly available incl large bags for horses/cattle
  • Economical
  • Replace interstitial deficits
  • Often restore effective circulating vol
  • Good replacement solns for V, D, diuresis losses
49
Q

Disadvantages of maintenance fluids

A
  • Rapidly redistributed in the interstitium –> About 20% retained intravascular w/I about 3 hrs or so, Large vol req.’d
  • Interstitial oedema –> Cerebral, pulmonary, systemic interstitial (kidneys cannot keep up)
  • Haemodilution: RBCs, Albumin, Coag factors (esp if very tiny P, easy to overload)
50
Q

Compound sodium lactate, Hartmann’s (Similar to LRS)

Uses, Treats, Contraindications

A
  • used as replacement & alkaliniser fluid
  • treats dehydration, hypovolaemia, metabolic acidosis
  • contains Ca2+ –> unsuitable for use w/ blood products, cannot give in same line as blood transfusion
51
Q

NaCl 0.9% (saline solution)

Clinical Uses, Type of Fluid, AE/contraindications

A

Type: isotonic crystalloid
Clinical uses: hyponatraemia (never change serum Na lvls faster than 0.5 mmol/kg/hr), hypochloraemia, hypercalcaemia, when you need to avoid administering K+, txt of metabolic acidosis, ECF replacement esp if pre-pyloric V, w/ no D

Contraindications
* unbalanced
* slightly higher Na conc than plasma
* higher Cl concentration –> admin can lead to hyperchloraemic metabolic acidosis, dilutes bicarb, no K+ or Ca2+ ions, key difference btw this & the plasma

  • ECF acidifer –> produces metabolic acidosis
52
Q

Ringer’s Solution (No lactate)

Fluid type, Anions/cations, Missing?, Use

A
  • isotonic crystalloid
  • contains higher Na & Cl conc
  • no lactate (buffer)
  • normally used as lab sln
53
Q

Plasmalyte A & Normosol-R

Contains? Contraindications

A
  • contains acetate as buffer (Normosol-R) or acetate + gluconate (Plasmalyte A)
  • NOT RECOMMENDED FOR DKA
54
Q

Dextrose solutions (w/ or w/o electrolytes)

A
  • rapid glucose metabolism
  • initially isotonic, become hypotonic once dextrose is metabolised
  • used when fluid lost is pure water (heatstroke, hypernatraemia, hypodipsia)
  • SHOULD NOT BE YOUR MAIN SOURCE OF FLUIDS
55
Q

Hypertonic Saline (7.5% NaCl)

A
  • Plasma vol expander
  • used in txt of shock
  • causes intracellular dehydration, follow w/ isotonic sln
  • causes intravascular expansion
  • immediate vol expansion seen
  • improves microcirculation & microperfusion
  • reduces ICP
56
Q

Disadvantages of Hypertonic Saline (7.5% NaCl)

A
  • short duration of action
  • hyperchloraemic metabolic acidosis
  • rapid administration
  • vein irritation
  • intravascular haemolysis
  • ventricular arrhythmias
57
Q

Colloids are solutions w/ large solutes that do not readily

A

cross vascular membrane, pull fluid from the interstitium

58
Q

What are the main Synthetic colloids

A

HES
Dextrans
Gelatins

59
Q

Natural colloids

A

Plasma
Whole blood
Oxyglobin
Albumins

60
Q

Elimination of colloids..

A

small molecules excreted by kidneys
large molecules by liver

61
Q

In colloids, the size of the molecules determines

A

duration of effect

62
Q

in colloids, the number of molecules determines

A

the degree of osmotic effect

63
Q

Advantages of colloids

A
  • 60-80% retained in intravascular space
  • in intravascular space for days
  • excellend blood vol support, smaller resuscitation vol
  • often used in combo w/ crystalloids
64
Q

Indications of Colloids

A
  • shock, hypotension, resuscitation
  • protein loss
  • hypoproteinaemia, oedema
65
Q

Disadvantages of colloids

A
  • do not replace interstitial fluids, just for vascular expansion, not completely balanced so keep crystalloid too
  • poor replacement fluids for GI losses
  • Haemodilution: RBCs, Coag factors
  • rebleeding from damaged BVs –> can cause rebleeding
  • coagulopathy
66
Q

Gelatins

A
  • polydispersible sln formed by hydrolysis of bovine gelatin
  • Gelofusine –> succinylated gelatin in NaCl, improves water retention w/i circulation, short term 4-6 hrs, kidney excretion, can cause anaphylaxis
  • Characteristics: variable sizes, 274 mOsm/L
  • T1/2 8 hrs, vol expansion lasts 3 hrs, renal excretion
  • AE: anaphylaxis, haemodilution w/ large vol, increased clotting times, vol overlaod
67
Q

HES (Hydroxyethyl starches)

A
  • Synthetic polymer derived from amylopectin
  • up to 24 hr intravascular retention
  • renal complications –> increases w/ increasing dose & risk of mortality
  • coagulopathies
  • vol overload
  • pro-inflammatory efects
  • restricted use: not in sepsis, burns, critically ill
68
Q

Dextran solutions

A
  • polysaccharide
  • plasma expander
  • hyperoncotic compared to plasma –> reduces blood viscosity, improves microcirculatory flow
  • Anaphylaxis possible
  • interferes w/ haemostasis
  • can make ligatures slip

Anaesthesia (23 decks)

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