Cpb oxygenators DR NIKUNJ R SHEKHADA (MBBS,MS GEN SURG ,DNB CTS SR)

1. CPB OXYGENATOR
BY DR NIKUNJ
(CTS RESIDEaNT STAR HOSPITAL)
(Coordinator:DR P.SATYENDRANATH PATHURI)
(16/10/18)

2. OXYGENATOR
• The primary components are the circulation device, termed the pump, and
the gas exchange device, termed the oxygenator.
• The fundamental purpose of the oxygenator is to arterialize venous blood
by removing excess carbon dioxide and increase the partial pressure of
oxygen (PO2)
• Oxygenators are complex devices made up of distinct components such as
membrane modules, heat exchangers, and reservoirs.
• Oxygenators can be categorized by two uses
• either extracorporeal life support (ECLS) or extracorporeal membrane
oxygenation (ECMO):The use of oxygenators for long-term sup port (>6
hours)
• as traditional CPB oxygenators :Short-term devices (<6 hours) are
described.

3. OXYGENATOR
• traditional CPB oxygenators have integral heat exchangers, while ECLS/ECMO
oxygenators may have external heat exchangers located distal to the
oxygenator.
• most cardiac surgical procedures employ some level of hypothermia during
extracorporeal circulation to protect underperfused regions from ischemic
damage.
• Most oxygenators are sold with a venous reservoir that may be either a hard-
shell (noncollapsible) or soft-shell (collapsible) variety. The latter will collapse
upon itself when emptied, reducing the risk of air being pumped to the
patient if the reservoir inadvertently empties.
• Both systems allow the sequestration of excess volume (i.e., volume from the
decompressed heart) and provide a mechanism for rapid replacement of lost
volume

4. OXYGENATOR
• early oxygenators were complex and relied upon vast amounts of surface area and
a direct blood-to-gas interface to function.
• The pioneering work by C. Walton Lillehei et al. from the University of Minnesota
in the late 1950s made ‘‘bubbler’’ oxygenators both disposable and cheap, and
they were easily made from simple components.
• Regulation of the gas mixture is through the ventilation components of the heart–
lung machine, which include a gas blender, a flowmeter, an inhalation anesthesia
canister, an oxygen monitor, and associated tubing. The quantities of these gases
are measured in the circulating blood by the use of in-line monitoring systems or
by intermittent sampling of arterial and venous blood samples
• Secondary considerations in oxygenator design include flow characteristics to
minimize blood trauma but still minimize the priming volume and surface area of
the device (i.e., the amount of liquid that must be added to fill the oxygenator
before operation). The oxygenator heat exchanger must also efficiently transfer
heat energy

6. BUBBLE OXYGENATORS
• Desaturated blood first enters passively
(without active pressure) into a mixing
chamber, where 100% oxygen flows across a
disparager plate into the stream of blood,
which causes small bubbles to form.
• The blood becomes oxygenated and carbon
dioxide is reduced as the stream of gas
percolates through the blood.
• A second session coalesces the bubbles,
which then pass through a defoaming
section where most of the gas separates
from the blood. Blood is defoamed by the
presence of silicone antifoam-A, which
consists of the liquid polymer
dimethylpolysiloxane (96%) and particulate
silica (4%), which destabilizes the bubbles,
causing them to implode.
• The arterialized blood is collected in an
arterial reservoir that is then actively
pumped from a collection reservoir into the
patient.

7. FLOW THROUGH AN OXYGENATOR
• Blood flowing through oxygenators
passes through two continuous or
sequential compartments: the heat ex-
changer and the gas bundle.
• Blood flows first through the HEAT
EXCHANGER, which is separated from a
temperature- regulated water source by
either a metal or plastic heat exchanger,
and then into the gas bundle (Fig. 1).
THE GAS BUNDLE makes up the core of
the membrane oxygenator, and is most
frequently made of microporous
polypropylene fibers or less frequently a
silicone sheet (Fig. 2). Gas moves into the
liquid (blood) phase by diffusion,

8. GAS DIFFUSION
• Gas transfer in oxygenators occurs due
to diffusion. Diffusion can be defined as
the random motion of the atoms or
molecules of the diffusing gas as they
move from regions of higher
concentration to regions of lower
concentration.
• Fick law is used to describe the rate at
which gases diffuse through gases,
liquids, or solids. The rate of diffusion is
proportional to the partial pressure
gradient of the gas in the direction of
diffusion (i.e., the difference of the
partial pressure of the gas per unit
distance)
• the rate of gas transfer can be increased
by increasing the difference in partial
pressure

10. PRINCIPLES OF HEAT TRANSFER
• Heat transfer is the transfer of kinetic energy from molecules with higher
energy (higher temperature) to molecules with lower energy (lower
temperature).
• In practice, heat transfer can occur in one of three ways:
• conduction (from solid to solids),
• convection (from solids to liquids),
• and radiation (an electromagnetic mechanism).
• Within the CPB heat exchanger, the primary form of heat transfer is forced
convection (the water and blood of the heat exchanger are actively
pumped past the stainless steel interface, hence the term forced), with
conduction occurring within the stainless steel.

12. MEMBRANE OXYGENATORS
• A variety of membrane materials have been used for gas transfer and have
included cellophane, nylon, polyethylene, ethyl cellulose, Teflon, butyl rubber,
silicon, polypropylene, and polymethyl pentene.
• However, the membrane materials that have been found to provide the best gas
transfer characteristics with minimal cellular trauma have been SILICONE and
POLYPROPYLENE, and have become the standard materials used for oxygenators
currently.

15. SILICONE
• The silicone barrier separated the gas and blood phases so that gas transfer was
totally dependent upon the diffusion of gas through the membrane material. This
was termed a true membrane, as opposed to oxygenators made of materials with
microscopic pores throughout the membrane material.
• The silicone polymer is a bioinert material that provided improved
biocompatibility, enhancing its utility for longterm support
• They also had gas exchange characteristics that were inferior to that of
polypropylene materials, requiring greater surface areas and larger prime volumes.
• Owing to compatibility issues, silicone membranes continue to be the membrane
of choice for long-term procedures such as ECLS/ECMO.
• Silicone membranes avoid plasma leakage.

16. POLYPROPYLENE
• Microporous polypropylene membrane oxygenators are the predominant
design used for CPB in the world currently
• Wetting of the membrane module is termed plasma leakage and occurs
when blood plasma slowly fills the pores of the fiber wall and leaks into
gas pathways, increasing the diffusion distance and decreasing gas
exchange
• One of the major problems with using microporous membrane materials
for periods greater than 24 hours is their propensity to develop plasma
leakage and membrane wet-out

17. POLYPROPYLENE
• There are two major types or configurations of the membrane material—hollow
fiber designs and folded sheets with hollow fibers making up the predominance of
devices .

18. POLYPROPYLENE
• The polypropylene comes from a variety of manufacturers but is relatively
consistent in its size and dimensions.

19. MEMBRANE OXYGENATORS
• The micropores making up the membrane material are created by a
process of extrusion, where the membrane material is stretched and then
heated creating microchannels .
• These microchannels are pores less than 1 μm in diameter, although the
size varies among manufacturers.
• The membrane is initially porous, before being exposed to proteins in
plasma, which allows at least a transient direct blood–gas interfacing at
the initiation of CPB. After a short time, protein coating of the membrane
and gas interface takes place, and no further direct blood and gas contact
exists.
• The surface tension of the blood prevents plasma water from entering the
gas phase of the micropores during CPB. Likewise, surface tension of the
blood prevents gas leakage into the blood phase, which would create
gaseous microemboli and denature the blood proteins.
• The surface tension of the blood at the micropores can be overcome if
the gas compartment pressures are allowed to the exceed blood
compartment pressure, raising the risk of gas emboli.

20. • After several hours of use, however, the functional capacity of micropore
membrane oxygenators decreases because of evaporation and subsequent
condensation of serum that leaks through the micropores.

21. MEMBRANE CONFIGURATION
• in the hollow fiber design, blood flow is around the fiber bundle while gas flows
through the hollow fibers, which have a cylindrical shape similar to that seen in
straws.
• The manufacture of the membrane module of a hollow fiber oxygenator occurs by
wrapping hollow fibers around a central mandrel in a precise and reproducible
manner, assuring consistency in fiber bundle geometry.
• The ends of the fiber bundle are then dipped in a vat of polyurethane and allowed
to dry, creating a seal at each end of the bundle. A high-speed saw is then used to
make precise slices at right angles to the fiber bundle, creating sealed ends on
each side of the membrane module with only the fibers open to atmosphere.
These ends then become the gas inlet and outlet sections of the membrane
bundle

22. OPERATION AND CONTROL OF MEMBRANE OXYGENATORS
• The control of ventilation and
oxygenation is relatively
independent in membrane
oxygenators.
• Increasing the total gas flow, or
sweep rate, increases CO2
elimination by reducing the gas
phase CO2 partial pressures and
likely decreasing the gas phase
boundary layers.
• Gas flow is regulated by the use of
the flowmeter with a gas mixture of
medical grade air (a mixture of
oxygen and nitrogen gases) and
oxygen through the gas blender.

26. • The oxygenator, composed of several different types of synthetic
materials, represents the largest surface area within the extracorporeal
circuit
• The nonendothelialized surfaces of the circuit elicit an SIR.
• In the early 1980s several cardiopulmonary device manufacturers began
heparin coating common perfusion supplies including the oxygenator
•

27. • Sorin inspire
• Capiox(Terumo)
• Affinity(medtronics)
• Vital(edwards)

28. REFERENCES
• Principles of Oxygenator Function: Gas Exchange, Heat Transfer, and Operation
• Alfred H. Stammers and Cody C. Trowbridge Chapter 4
• Cardiopulmonary Bypass Principles and Practice
• Third Edition
• GLENN P. GRAVLEE, MD

29. THANK YOU