Exam 3 Flashcards
Colloid
a substance microscopically dispersed evenly throughout another substance. Colloids contain larger insoluble molecules, such as gelatin or albumin. Blood is a colloid; mixture of two different phases of matter
Crystalloids
are aqueous solutions of mineral salts or other water-soluble molecules. Normal saline is a crystalloid; dissolved- no suspended
Osmolality
is a measure of the osmoles of solute per kilogram of solvent (osmol/kg or Osm/kg); per mass
Osmolarity
is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per liter (L) of solution (osmol/L or Osm/L); per volume
Colloid Osmotic Pressure (Oncotic Pressure)
osmotic pressure exerted by proteins in blood plasma that pulls water into the circulatory system
Tonicity
the state of being hypertonic, hypotonic, and isotonic, is related to how much osmotic pressure is exerted on a membrane by a fluid; measure of the osmotic pressure gradient (defined by water potential of the 2 solutions) of two solutions separated by semipermeable membrane
Osmotic Pressure
is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane
What was the ECC primed with during early years?
“Fresh” heparinized homologous blood
Mannitol
aka. Osmitrol; oncotic agent, pulls fluid into blood stream; crystalloid
Crystalloid Prime Consists of….
Dextrose
pH balanced crystalloid fluids
mannitol (Osmitrol)
Advantages of crystalloid prime
Easy to handle during priming/de-airing
Cheaper
No anaphylactoid reactions
Crystalloid Solution Examples
Plasmalyte Normosol 0.9% Normal Saline Lactated Ringers D5 0.9% NS D5 0.45%NS D5 0.33% NS D5 0.18% NS
PlasmaLyte Characteristics
Closely mimics human plasma
Electrolytes, osmolality & pH (similar to human)
Buffer capacity
Anions: Acetate, gluconate, lactate converted to bicarb, Co2 and water
No evidence that it is superior to other crystalloids
Plasmalyte Advantages
Volume/Electrolyte deficit correction
Addresses acidoses
PlasmaLyte Disadvantages
Fluid overload Edema with weight gein Lung edema Worsening of ICP Magnesium: PVR, HR, worsen ischemia
Magnesium in Prime
Book says its a problem
Works in concert with calcium
Partially replenishes myocytes
No substantial effect on SVR based on research
Lactated Ringer’s
“Balanced” electrolyte solution with lactate added
Lactate converted into bicarbonate by a functioning liver into bicarbonate
Normal Saline (0.9% saline solution)
Must add bicarb because its so acidic
Matches blood tonicity
Just sodium chloride
Colloid Prime Characteristics
Contains protein or starch
Preserve high COP in the blood
Colloid Prime Advantages
Maintain COP and reduce tissue edema
Colloid Prime Disadvantages
Colloids associated with increased incidence of anaphylactoid reactions and clinical coagulopathy
Colloid Examples
Albumin
Dextrans
Gelatins
Hydroxyethyl starch (Hespan)
How is albumin sterilized?
Cold filtered
Hypertonic
Osmolarity > 350 mOsm/L
Solution cannot be “hypertonic” unless there is some indication of what it might be hypertonic to; greater amt of solbe more hypertonic
Is D10-10% Dextrose has what tonicity?
Hypertonic (temporarily)
Becomes hypotonic metabolizes sugar
Becomes water
Hypotonic
Osmolarity <250 mOsm/L
Distilled water is hypotonic to everything
Causes fluid to shift, lowers osmolarity, allows fluid to shift out of vessel into cells and interstitial space
Hypotonic fluids have the potential to cause sudden fluid shifts out of bloodvesels
Examples of Hypotonic Fluids
0.45% NS and 0.25% NS
Istonic
~285-295 mOsm/L
Freely move into and out of the intravascular compartments and increase circulating volume in the cells
Osmosis
Movement of water through a semipermeable membrane from an area of lower concentration of solute to higher concentration of solute
Osmotic Pressure
pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane
Oncotic Pressure
Created by the presence of large protein molecules such as albumin (55%) Immunoglobulins (38%) Fibrinogen (7%) and other regulatory and clotting factors tend to retain fluid in the capillaries
*Note: oncotic pressure is a type of osmotic pressure
Hydrostatic Pressure
pressure of the intravascular fluid against hte wall of the vein
How to convert L to kg?
1 Liter of H20 at 4 degrees C = 1 kg (2.205 lbs)
Advantages of Hemodilution
Decreased blood viscosity
Improved regional blood flow
Improved oxygen delivery to tissues
Decreased exposure to homologous blood products
improved blood flow at lower perfusion pressure (lower shear stress), especially during hypothermic perfusion
How much do you hemodilute?
Most centers try to achieve hematocrits below 30% during CPB.
What’s the normal priming volume range?
1000-1500 mL
Advantage of Albumin in Prime
Increases COP white at the same time (at least temporarily) attenuating the platelet-lowering effects of CPB
Basic Prime Constituents: Adults
Normosol/PlasmaLyte Hetastarch/Albumin Antibiotic NaHCO3 Mannitol Heparin 10k units
Basic Prime Constituents: Pediatrics
Normosol 25% Albumin Antibiotic Solumedrol NaHCO3 Heparin 100 units Mannitol CaCl PRBCs
25% Albumin
Large molecule Aids pacificiation of tubing Elevates COP and serum osmolarity Good osmotic "Pull" from tissues (1.3:1) A Jehovah's Witness "no-no"
Pacification
Foreign surface pacification may significantly reduce the detrimental effects of the CPB circuit
*Without albumin, pacification will lead to low circulating proteins
To date, albumin is the only intervention consistently shown to be beneficial
What two constraints does siphonage place on venous drainage?
- venous reservoir must be below the level of the patient
2. lines must be full of blood (or fluid) or an air lock can occur and disrupt the effect
What influences CVP?
Intravascular Volume
Venous compliance
What influences venous compliance?
Medications
Sympathetic Tone
Anesthesia
Solutions to Chattering/Fluttering/Chugging
Partially occlude clamp on venous line
Increase the systemic blood flow
What is the ultimate limit to venous flow?
Amount of blood returning to the great veins from the body
Newton’s Law of Universal Gravitaiton
F=G (m1m2/r^2)
F=ma
How to calculate mass
volume x density
How to calculate weight
mass x gravity
What is the constant for gravity
9.8 m/sec^2
What is the density of water
1 @ 37 degrees C
Principle of transmission of fluid-pressure
pressure exerted in a confined incompressible fluid is transmitted equally in all directions throughout the fluid so pressure variations remain the same
Pascal’s Law
1mmHg for every 13.6 mm heigh
Potential energy to do work
P=pgh
What is the normal siphon gradient?
30 to 40 mmHg
What three factors affect the siphon gradient?
CVP
Cannula Resistance
Height (to end of venous inlet tube)
Why use augmented venous return (AVR)?
- smaller diameter cannula and venous line (minimal volume)
- Long, narrow cannula (peripheral access)
- generate venous return using smaller heigh differential, smaller diameter cannula, smaller diameter venous line, no fluid in venous line
- Allow minimally invasive surgery
Methods of Augementation
VAVR
KAVR
Modified Roller Pump
Where do you monitor pressure in augmented return?
10 cm before pump inlet OR within hard-shell reservoir
Max negative pressure in augmented return
-60 to -100 mmHg
What could happen if the pump head is not occlusive?
Could pull retrograde
Why would you want shunt around roller pump to be partially occluded?
Prevent build-up of excessive negative pressure
Relief valve pressure limits
Low positive (+15 mmHg) High negative (-150 mmHg)
Augmented Venous Return complications
Hemolysis
Decreased flow
Damage to vascular structures
Air aspiration
Over-pressurization of hard-shell venous reservoir (too much positive pressure)
Under-pressurization of hard-shell venous reservoir (too much negative pressure)
Imbalance between venous and arterial flows
When do we use AVR?
Minimally invasive surgeries Femoral venous cannulation unprimed venous lines (w.o VAP) small heigh differential smaller prime circuits (3/8'' venous) pediatrics possibly all cases
Calculating Effective Negative Pressure Gradient
Effective negative pressure gradient = negative pressure (VAVR) + Gravity Drainage
Effective negative pressure = Negative pressure (KAVR) + Gravity drainage
Range from the regulator in VAVR
-20 to -80 mmHg Range from regulator
Because pressurization is a risk in CPB and VAVR, what should you set the alarm to?
+10
In KAVR, what RPMs relate to what pressure
700-1100 RPM related to -50 to -80 mmHg
Actions of the Real Lung
Gas exchange
Filtration
Immune Function
Biochemical function
Actions of the Artificial Lung
Gas exchange Secondary actions (filtration; drug delivery)
Diffusion proportion
Diffusion prop (PAS)/(Distance sq rt MW)
Only True membrane
Silicone
Surface Area of Natural vs Membrane
Natural= 70 m^2 Membrane= 0.6-4 m^2
Blood Path Width Natural vs Membrane
Natural 8 um
Membrane 200 um
Blood path length Natural vs membrane
Natural 200 um
Membrane 250,000 um
Membrane thickness Natural vs membrane
Natural 0.5 um
Membrane 150 um
Maximum O2 Transfer Natural vs membrane
Natural 2,000 ml/min
Membrane 400-600 ml/min
Oxygen gradient Natural vs membrane
Natural 105 (alv) - 40 (ven) = 65 Membrane [160 to 760] - 40= [120 to 720]
Carbon dioxide gradient natural vs membrane
Natural 40-45 = 5
Membrane 45 - 0 = 45
CO2 during gas exchange
Chemical Reaction 0.4 seconds
Red Cell (including chemical reaction)
Plasma (lease amount of time)
Alveolar Wall
O2 during gas exchange
Alveolar Wall (most time) 0.25 seconds Plasma (third most) 0.1 second Red Cell (second most) 0.2 seconds Chemical reaction (least)
Who made the film oxygenator?
Gibbon
Who made the rotating screen?
Dennis
Who made the bubble oxygenator?
DeWall-Lillehei
Who made the coil membrane?
Kolf
How do you remove bubbles with a bubble oxygenator?
Separation
Absorption
How do you defoam a bubble oxygenator?
Silicon Antifoam-A (96% liquid polymer dimethylpoysiloxane and 4% particulate silica)
Bubble mechanically restrained by mesh net
Area low blood flow velocity-allow bubble chance to rise to surface
Pressure drops for bubble oxygenator & membrane oxygenator
30 mmHg bubble oxygenator
100 + mmHg membrane oxygenator
Where is a bubble oxygenator placed?
Placed before the arterial pump head
What materials does the defoaming/dububbling area have?
Steel wool
Polyurethane foam
Silicone Antifoam-A
What does a heat exchanger do in a bubble oxygenator?
Transfer heat
Additional gas exchange
Additional air removal
Basic components of a bubble oxygenator system
Gas sparger Mixing column (turbulence) Defoaming/Debubbling area Heat exchanger Arterial reservoir
Archimedes Principle
principle that states that a body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid.
Buoyancy- used to eliminate air bubbles in the arterial reservoir
Bubble Size and Surface Area
Small: Surface: Volume ratio is high
Large: Surface: Volume ratio is low
What size bubbles has faster equilibration?
Small bubbles
Bubble size and O2 exchange
Small: O2 exchange efficient
Larger: O2 exchange less efficient
Bubble size and CO2 exchange
Small: Co2 exchange inefficient
Large: CO2 exchange efficient
Bubble size and GME potential
GME potential is high with small bubbles and low with large bubbles
What is FiO2 always set to?
100%
What is the purpose of turbulence?
Increases efficiency of gas exchange
Where does secondary gas exchange occur?
Heat exchanger/ defoamer
LOW Gas:Blood Flow
Decrease O2 transfer
Decreased CO2 transfer
Arterial PO2 goes down
Arterial PCO2 goes up
HIGH Gas: Blood Flow
Increased O2 transfer
increased co2 transfer
arterial PO2 goes up
arterial PCO2 goes down
Bubble Oxygenator Disadvantages
Balance O2 and CO2 transfer difficult to achieve
GME
Defoaming/filter increase foreign surface exposure w.o significant contribution to gas exchange efficiency
Direct blood:gas interaction damaging to plasma proteins and blood components
Membrane Types
Coil
Flat Plate
Capillary
“True Membrane”
Complete barrier between the gas side and the blood side
Ex. Silicon
Hollow Fiber Oxygenators
Fibers: 200-250um in diameter 10-15 cm long 25-50 um thick Blood flow Extra luminal/Intraluminal
Extraluminal Blood Flow
Blood outside, gas inside
Greater surface area: less prime volume, decrease resistance to blood flow
Intraluminal Blood Flow
Blood inside, gas outside
Permeability Equation
Solubility x Rate of diffusion
Membrane Performance
Gas transfer characteristics of "membrane" (gas exchange occurs at "pores") Surface area Fiber design- size & flow pattern Gas flow: Blood flow ratio (Influence co2 exchange only) Gas blender (100% oxygen & room air) FiO2:O2
Hollow Fiber Oxygenator Durability
long term use leads to “wetting” of the membrane surface resulting in plasma leakage through the pores; deterioration of oxygenator performance
Hollow Fiber Oxygenator Efficiency
Still 2-8 times less efficient as the natural lung
Primary limitation to gas exchange is gas diffusion in the blood phase
Capillaries: Natural Lung
0.5 to 1.0 um length
3 to 7 um diameter
Capillaries: Artificial Lung
10-15 cm in length
150-250 um diameter
Flow Patterns: Natural Lung
Minimize shear forces
Maximize RBC contact with capillary (1:1)
Flow Patterns: Artificial Lung
High shear forces
RBC contact with “capillaries” is low
Contact Time: Natural Lung
Not a limitation in gas exchange even at extreme exercise
Contact Time: Artificial Lung
Gas exchange efficiency decrease with higher blood flows
Biocompatibility is associated with…
Type and composition of surface Shear Forces Pressure drop across oxygenator surface area-to-volume ratio Duration of exposure patient status...
