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561 - Perfusion Technology > Exam 8 - Hemodilution & Heat Exchangers > Flashcards

Exam 8 - Hemodilution & Heat Exchangers Flashcards

1
Q

History of hemodilution

A

1 - high/normal flow with real blood (no dilution)
-70-80 mls/kg/min
2 - low flow / no dilution (azygous principle - 10% of normal)
-30-35 mls/kg/min
3 - Hypothermia and no dilution (most low flow…some high flow)
-ASDs and VSDs

  • Early oxygenators required 3-5 L of prime….huge
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2
Q

John Gibbon

A

1st perfusionist

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3
Q

Homologous blood syndrome

A
  • happens if you prime with blood
  • decrease BP and VR
  • unpredictable migration of plasma from 3rd space
  • pooling in sphlanic circulation
  • portal hypertension (sludging)
  • metabolic acidosis
  • coag and renal failure
  • platelet aggregation
  • decrease surfactant activity
  • bleeding diastesis
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4
Q

Hemodilution in 1960’s - not just blood

A 
- 5% dextrose: Isotonic...then hypotonic
                          Patients alert / no pulmonary congestion
- Balanced crystalloid solutions:
           - serum electrolytes stable
           - minimal acidosis
           - decreased RBC damage
           - minimal post-op pulmonary problems
           - no renal problems
           - fluid retention
- Balanced solutions with colloid
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5
Q

Isotonic %

A

0.9%

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6
Q

Newtonian fluid

A
  • uniform fluid, constant viscosity as force is applied

- crystalloid

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7
Q

Non-newtonian fluid

A
  • varying viscosity as force is applied

- blood

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8
Q

Viscosity relationships

A
  • Temp: inverse / 5% up with 1 degree drop
  • Hct: direct / 50% decrease with 50% decrease in Hct
  • Flow: inverse
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9
Q

Rheology

A
  • study of deformation and flow of matter

- especially non-Newtonians

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10
Q

Shear stress

A
  • force required to move liquid between two plates

- directly proportional to viscosity

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11
Q

Shear rate

A
  • rate of flow during shear stress

- inverse to viscosity

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12
Q

Sickle cell

A
  • more viscous then normal RBC
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13
Q

Poiseuille’s law

A
  • Flow x Viscosity x SVR
  • R = viscosity x SVR
    So……
  • Flow = dP / (viscosity)(SVR)
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14
Q

Changing viscosity

A
  • as diameter decreases -> flow decreases -> shear rate down -> viscosity increases
  • Produces overall increase in R to flow in capillary (sludging)
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15
Q

So on CPB…what if you run lower than normal flow

A
  • decrease flow -> decrease shear rate -> increase viscosity -> increase SVR -> further decrease in flow….SLUDGING
  • Even more sludging when you cool patient
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16
Q

Affects of hemodilution on CPB

A
  • decrease perfusion pressure
    - decrease viscosity
    - change in body perception of pressure (can change flow better)
    - dilution of catecholamines (helps drop pressure)
  • decrease sludging (counteract hypothermia)
    - increase VR / flow through organs
  • decrease in post-op complications
    - Cerberal / pulmonary / renal
  • decrease in O2 carrying capacity
    - not good…but can make up with increased flow
  • decrease in colloid oncotic pressure
    - edema
  • change drug interactions
    - alter binding of proteins
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17
Q

Optimal Hct

A
  • low 30’s
  • lower on CPB…make up for with increase flow
  • problem when Hct is 10% or lower
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18
Q

CPB and metabolic acidosis

A

Hemodilute -> more flow -> more O2 consumption -> less acid

  • This is why CPB helps minimize metabolic acidosis
  • If Hct increases…..chance of acidosis increases
19
Q

Benefits of Hemodilution

A
  • Decrease exposure to blood products
  • Decrease viscosity
  • Improved regional blood flow
  • Improved O2 delivery
  • Improved blood flow at lower perfusion pressures
20
Q

How we hemodilute on CPB

A
  • Patients Hct and weight (estimated blood volume)
    - Infants (8-8.5) / Children and Male (7.5) / Female (7)
  • Circuit prime
  • Pre-bypass dilution (anesthesia and cath lab)
  • Pre-bypass removal (anesthesia and RAP/VAP)
    - maybe Hct too high? Bad….too viscous
21
Q

How much hemodilution is too much on CPB?

A
  • not yet determined
  • determining factors: O2 delivery and flow distribution
  • <15% = maldistribution of coronary flow
  • > 34% = risk of MI
  • So… Acceptable = 16-27%???
  • OPTIMAL = 23-27% …but maybe lower (giving blood is bad)
22
Q

CPB and fluid balance

A
  • edema may contribute to post-op organ dysfunction

- adults gain 1-15 pounds

23
Q

Factors affecting fluid shifts

A
  • Temp
  • Pump flow rate
  • Urine output
  • Venous drainage
  • COP (colloid oncotic pressure)
  • Interstitial fluid pressure
  • Hemodilution
  • TIME ON BYPASS (25% contributer - biggest)
    • more complicated surgery… more time on bypass
  • Cardiac disease
24
Q

Osmotically active prime components and fluid balance

A
  • Albumin: less weight after CPB
  • Mannitol: less weight after CPB
  • Blood: MORE weight after CPB
25
Q

Hemodilution reversal

A 
Diuresis:
   - Mannitol - osmotic diuretic - if working kidneys
   - Lasix - loop diuretic
   - Edecrin - loop diuretic
   - Chlorothiazide - thiazide diuretic
   - Bumex - loop diuretic 
Ultrafiltration:
   - hemoconcentrate
Hemodialysis: 
   - machine / same as ultrafiltration / more complicated
26
Q

Why use hypothermia

A
  • decrease metabolic rate
  • protection:
    - cerebral / myocardial
27
Q

How to control temperature of circuit

A
  • Heat exchangers
    • integral and external
  • Room air
  • Heat/Cool blanket
  • Bear-hugger
28
Q

How heat exchangers work

A
  • two phases: blood and water
  • warming: heat from water to blood
  • cooling: heat from blood to water
29
Q

Solubility and temperature

A
  • Inverse…increase temp -> decrease solubility
  • Gas more soluble in cold
  • Don’t warm too fast….bubbles come out of solution
30
Q

Heat exchanger material

A
  • Biologically inert: reduce risk of clotting / coated
  • Aluminum: high conductivity / poor biocomp. / Al microemboli
  • Stainless steel: low conductivity / stronger / most used
  • Tried in past: plastic / polypropylene / polyurethane
    - much lower K (conductivity)
31
Q

Heat exchanger design

A
  • maximize heart exchange
  • countercurrent flow
  • increase surface area (good for exchange / bad for prime)
32
Q

Constraints to heat transfer

A
  • temp diff determines rate of exchange
  • thermal boundary
    • flow faster in middle of blood….warmer on outer part of flow
    • warmer on outer due to slower velocity
  • changing temp changes solubility
  • blood/H2O gradient: 6-10 is acceptable (most use 6)
33
Q

Convection

A
  • heat transfer via motion of gas or liquid
34
Q

Conduction

A
  • heat transfer via touching of molecule to molecule
35
Q

Heat capacity

A
  • heat required to raise 1 degree
36
Q

Specific heat

A
  • heat required to raise 1 gram by 1 degree
37
Q

Change in heat equation

A

Q = mcdT

Q = calories
M = grams 
T = Celsius
38
Q

Density of blood

A

1.045 gm/cm^3

39
Q

Specific heat of Blood

A

0.9 cal/gm*C

40
Q

Heat flow equation

A

Q/T = (c)(BF)(density)(dT)

c = cal/gm*C
BF = cm^3/min or ml/min
41
Q

Factors influencing rate of heat transfer

A
  • H-E material
  • thickness of conductor
  • k
  • heat loss
  • prime volume
  • blood path thickness
  • blood path resistance
  • water flow variation (little bit of turbulence good)
  • H-E design
42
Q

Coefficient of Heat Exchange

A

Che = (Tbo-Tbi) / (Twi-Tbi)

43
Q

How to increase heat flow

A
  • countercurrent exchange
  • chevrons (turbulent flow)
  • minimize thickness without integrity
  • increase time in path

561 - Perfusion Technology (12 decks)

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