Fluid Therapy: Colloids - DONE

what is the most permeable part of the vascular system?

capillary beds

what is permeability?

intravascular space

-->conducting vessels are relatively impermeable: arteries, arterioles, venules, veins

capillaries = semipermebale membrane

-->water

-->small ions (Na, K, Cl)

-->small molecules

what is permeability of the intracellular space

phospholipid bilayer

-->semipermable: water and glucose

what are colloids?

colloids are fluids that contain large, insoluble molecules that do not freely cross a semipermable membrane

colloids act to "hold" water within the vascular space for a longer duration of crystalloid

why are colloids important?

directly realted to plasma volume expansion

-->saline approximately 20% of infused volume

-->colloid thereotically 100% of infused volume (varies by type of colloid)

starling forces equation

which value in the starling equation helps to explain why a severely hypoproteinemic P develops a pitting limb edema, but not pulmonary edema?

reflection coefficient

lungs pretty much let anything pass (coefficient of 0)

-->free passage of proteins so we don't see edema

when there is not free passage (limbs), we will see edema

what is transcapillary fluid flux?

net movement of fluid into interstitium

returned to systemic circulation by lymphatic system (series of tubes with one-way valves)

what is the filtration coefficient (K)

correlates to permeability of vessel

varies along circulatory system

arteries and veins less permeable than capillaries

what is the reflection coefficient (o)?

degree to which membrane prevents trasnfer of colloid molecules

value between 0 and 1

-->0 indicates free passage, 1 is no passage

the lower the value, the less effect colloid will have on fluid dynamics

wht do changes in the filtration and reflection coefficients make it difficult to predict?

the pharacokinetcis of colloids in vivo

what is collid osmotic p (COP)?

the pressure exerted by large molecules

because, in health, these molecules do not easily leave the vasculature, they hold water within the vascular space

how do you measure COP?

using a colloid osometer

measures a change in P created by adding colloid solution to one side of a semipermeable membrane

as water diffuses across the membrane, it creates hydraulic pressure that can be measured

what is the major contributor to COP in the intravascular space?

albumin

what is normal COP for dog? cats?

dog: 15.3-26.3 mmHg

cat: 17.6-33.1 mmHg

albumin generates 80% of COP in normal states

whole blood vs plasma COP

significant difference between whole blood and plasma COP in healthy dogs

however, clinically the difference is minot and either can be used

rec same sample type

what are some proposed benefits of colloids?

longer intravascular effects

smaller volume requirements for intravacasular expansion

less dilutional coagulopathies

decreased tissue edema formation

if charge of the molecules are not considered, would sodium or albumin contribute most to serum osmolality?

exaclty equal if you remove charge

the size of the particle is unimportant so that a single ion (sodium) contributes as much to the serum osmolality as a single large portein miolecule

large molecules persist in the circulation longer

what is the pharamcology of colloids?

"the whole is greater than the sum of its parts"

molecular weight does not effect osmolality

charge is important

-->gibbs-donnan effect

what is the gibbs=donnan effect?

electroneutrality must be maintained

large proteins such as albumin are negatively charged and non-diffusable across semipermeable membrane

draws positive ions (Na) across membraen, pulling water with them

it inc COP by 7-8 mmHg

what are the natural colloids?

albumin

-->human albumin 5% and 25%

-->lyophilized canine albumin

blood products

-->fresh forzen plasma

-->whole blood

what are the synthetic colloids?

hydroxyethyl starch

gelatin

dextran

what is characteristic of albumin?

albumin has a unifom size

-->greater than 95% of particles have molecular weight of 69 kDa

-->the only monodisperse colloid known

highly preserved across species

accounts for 80% of colloid osmotic P in health

what are the roles of albumin?

carrier molecule

-->divalent cations (Ca and Zn)

-->hormones

-->drugs

maintain oncotic P

coagulation/inflammation

role in healing

what is lyophilized canine albumin?

purified canine albumin

sold as 5g vials

adverse reactions less frequent and less severe than human albumin in dogs

limited availability

what is human albumin?

human albumin 5% and 25%

may be used in critically ill Ps

adverse reactions

-->anaphylaxis

-->delayed hypersensitivity reactions

-->death

NEVER ADMINISTER TO A HEALTHY PATIENT OR A P THAT HAS RECEIVED HUMAN ALBUMIN IN THE PAST

what are the blood products?

fresh frozen plasma

whole blood

weak colloids

used primarily for replacement of clotting factors in Ps with coagulopathies

what is albumin deficit?

calculation to estimate amount of an albumin containing product is required to inc the albumin to a desired level

Alb dft = 10 [ALBdesired - ALBpatient] BW * 0.3

alb deficit = grams

ALBdes = g/dL

BW = kg

what are the synthetic collloids?

starches

-->hetastarch (hetastarch, hespan)

-->pentastarch

-->tetrastarch (voluven)

gelatins

dextrans (70 and 40)

what are some possible adverse effects of synthetic colloids?

acute renal failure

anaphylaxis

volume overload

coagulopathy

immunosuppression

what is hydroxyethyl starch?

primary synthetic colloid used in vet med

polydisperse solutions

-->made up of many size particles

-->reported molecular weight is a calculated value based on different particles sizes and distribution

described by molecular weight and degree of substiuton

degree of substitution is the proportion of glucose moieties that have been substituted with hydroxyethyl groups

-->ranges from 0 to 1

what are the types of hydroxyethyl starch?

6% hetastarch in 0.9% saline

-->molecule weight: 670 kDa

-->DS = 0.75

10% pentastarch

-->molecule weight: 200 kDa

--> DS = 0.5

6% tetrastarch (voluven)

-->molecular weight: 130 kDa

-->DS = 0.4

what are theadverse effecrs of hydroxyethyl starch?

acute renal failure

anaphylaxis

volume overload

coagulopathy

immunosuppression

which has a greater correlation with negative effects on coagulation

A: degree of substitution

B: molecular weigth

A

how does degree of substiution affect hydroxyethyl starches and coagulation?

higher degree of sibsitutuion correlates to greater negative effect on coagulation

interferes with factor VIII and vwF leading to platelet dysfunction

may also be incorporated into fibrin clot, weakening clot

how is hetastarch used in practice?

670/0.75

higher degree of substituotion so greater adverse effects on coagulation

daily rec maximum dosage is 20 mL/kg

larger molecules persist in the vasculature longer

-->however, minimal effect due to much fewe numbers of large molecules

administered as 2-5 mL/kg IV boluses

common practice is to use as CRI

how is voluven used in practive?

130/0.4

lesser degree of substitution so minimal effect on coagultion

daily rec maximum dosage is 40 mL/kg

shorter half life than hetastarch (16 vs 46 hours)

administered as 2-5 mL IV boluses

what is the COP of hetastarch 6%? voluven? human albumin 5%/25%? canine fresh frozen plasma?

hetastarch: 32%

voluvenL 37%

human albumin: 23%

canine fresh forzen plasma: 17%

how do you monitor colloid therapy?

refractometeric readings of total solids

-->COP should be used to monitor therapy bc of the minimal effects of synthetic colloids on TS

what is the effect of HES (670/0.75) on USG and osmolality in the dog?

dogs were administered 20 mL/kg HES

urine osmolality and speciifc gravity were measured

usually correlate, except in the presence of large molecules

urine specific gravity overestimated osmolality after administration of HES****** ON EXAM

the majority og the effect was within 2=3 houts after administration