Exam 3 - Oxygenators Flashcards
Actions of Real Lung
- Gas Exchange (O2 and CO2)
- Filtration (small capillary diameter and heparin in lining)
- Immune Function (Macrophages: Innate / Lymphocytes: adaptive)
- Biochemical function (metabolism of drugs)
Oxygenator vs Lung Surface Area
Lungs: 70m^2
Oxygenator: 1.8m^2
Function of artificial lung
- Gas Exchange
- Filtration
- Drug delivery
Factors that affect diffusion rate in Oxygenators
- Pressure gradient: increases / changed by perfusionist
- Surface Area: increases / set my manufacturer
- Solubility: increases / usually constant (increase with increase temp)
- Distance: decreases rate / set by manufacturer
- Sqrt of MW: decrease rate / pretty constant in perfusion
Transfer of O2 and CO2 in blood
- O2: hemoglobin
- CO2: bicarb
- Diffusion of CO2 is much faster than O2 but conversion of CO2 to bicarb and back in RBC takes much longer….
Natural vs Artificial Lung Capillary
Diameter: 7-8um vs 150-250um (25x)
Surface Area: 70m2 vs 1.8 m2 (2.5% of)
How to maintain Natural lung O2 in Artificial Lung
1 - Dwell time
2 - Secondary flow (make blood swirl toward edges)
3 - O2 Pressure gradient (much higher in Artificial…110-680 vs 65)
-CO2 pressure gradient also higher (5 vs 45)
4 - Decrease metabolic demand of patient (cool down/anesthesia)
Cardiac Surgery History
- Began in 40’s without CPB
- 50’s had high mortality rates with ASD surgeries (17/18 died)
Early artificial oxygenation
- Isolated monkey lungs
- Film oxygenators (1/4 survived….Gibbon)
- Rotating disc oxygenators (Kay-Cross…50’s)
- Cross circulation
Father of Heart Surgery
- C. Walton Lillehei
- 1954
Richard De Wall
- First perfusionist
- Made Dewall-Lillehei Bubble oxygenator in 1955
- Replaced cross circulation
Parts of bubble oxygenator
- Gas Sparger (bubble size)
- Mixing column
- De-foaming/de-bubbling area (steel wool, silicone, poly foam)
- Heat exchanger (also a secondary place for gas exchange)
- Arterial reservoir
- Resistance usually low so had a low pressure drop
Bubble O2 bubble size
- Small (high SA:V ratio, high O2 exchange, low CO2 exchange, high GME potential)
- Large (low SA:V, low O2 exchange, high CO2 exchange, low GME)
Bubble O2 gas flow vs. FiO2
- FiO2 always 100% (did not want N2 mixed into blood)
- Flow rate determined # of bubbles
- usually start 1:1 gas flow to blood flow ratio
- low ratio: transfer of O2/CO2 decrease -> PO2a down, PCO2a up)
- high ratio: opposite
Bubble Oxygenators facts
- Balanced O2 / CO2 transfer difficult to achieve
- GME
- Increased foreign surface exposure and turbulence increases immune responses
Oxygenator Useage
- By 1986…more membrane Oxygenators in use than bubble
- By 2000…no more bubble Oxygenators in use
Types of membranes in membrane Oxygenator
- Capillary: made of Polypropylene/Polymethylpentene (PMP)
- Flat plate folds: made of silicone
- Coils: made of silicone
- Silicone and PMP are not porous aka “true membrane”
- Polypropylene is porous
Prime volume comparison
Hollow fibers
True Membrane advantages
- More efficient gas exchange
- More balanced gas exchange (high O2 across and low CO2)
- Minimal GME
- Imrpoved blood flow path
- No direct blood:gas interaction (better biocompatibility)
Membrane Oxygenator induced turbulence
- Small jagged wall in membrane capillary to:
- Induce turbulence (better gas exchange)
- Decrease distance (higher diffusion rate)
Bubble vs Membrane
- Independent CO2/O2 control: Yes M / No B
- FiO2: Variable for M / 100% for B
- Gas:Blood flow ratio: affects PaO2/PaCO2 for B / Just PaCO2 for M
- Increase flow -> more CO2 transfer - Also can add 100% CO2 to gas flow in Bubble
- Type of system: Open for B / Open or closed for M
Hollow Fiber Oxygenation
- Made of PMP
- Blood flow can be extraluminal or intraluminal
- Intraluminal is not used anymore (high R, less SA, high prime)
True membrane vs porous membrane Oxygenators
- True can last 14 days and is selectively permeable
- Porous lasts 6 hrs and is not selectively permeable (relies only on pressure gradients)
Blood phase pressure vs Gas phase pressure
- Need to keep higher blood phase pressure otherwise gas moves into blood in the oxygenator and air gets into system
- Higher blood phase pressure allows blood to keep higher surface tension over holes in hollow fibers
Wetting of membrane surface in hollow fiber Oxygenators
- Prolonged use leads to this
- Get plasma leakage through pores
- Bubbles form on Oxygenator
- Very bad
Hollow fiber oxygenators
- Good but still 2-8x less efficient than natural lungs
(Still need dwell time, pressure gradient, decrease metabolism) - Primary limitation to exchange is diffusion into blood phase
(Blood to viscous to push through single file)
Minimum and Maximum O2 levels in blood
Min: 21%
Max: 100%
Blood gas control
- O2 too low….Increase FiO2
- O2 too high….Decrease FiO2
- CO2 too low….Decrease Gas:Blood flow ratio
- CO2 too high….Increase Gas:Blood flow ratio
- SvO2 too low….Increase Blood flow (60-80%)
How to tell a failing Oxygenator
- PO2 drops even with increase in FiO2
- PCO2 increase even with increase in blood flow (sweep rate)
- Rising pressure gradient across Oxygenator
What to do before an Oxygenator change out
- Check all gas tubing, lines, connections
- Consult with Anesthesiologist that patient is knocked out
- Draw A and V blood gases
- Check Hbg/Hct
- Calculate O2 transfer rate
[ 1.34 * (X gm Hgb / 100) * (Art sat - Ven sat) * ml/min ]- If lower than IFU recommended rate, could be failing
Rated Blood Flow
- Max flow at which you get 95% O2 in A and 65% O2 in V
CO2 Reference Blood Flow
- Flow rate in which CO2 content is decreased by 38 mL per Liter of flow
O2 Reference Blood Flow
- Flow rate in which O2 is increased by 45mL per Liter of blood flow
Reference Blood Flow
- Lowest O2/CO2 Reference flow, manufacturers recommended flow, or 8 L/min
Index of Hemolysis
- Mg of plasma free Hgb generated per 100 L of blood pumped through Oxygenator
Initial Priming Volume
- Volume needed to fill Oxygenator and heat exchanger to minimal reservoir volume (set by manufacturer)
Oxygenator Thrombosis
- Random increase in Oxygenator inlet pressure of up to 900mmHg within 10-15 min of starting CPB despite adequate anticoagulation
- 1 in 230 cases
- Can prime with Albumin to minimize this
- Can cool slower
- Can cause oxygenator change out
