GAS EXCHANGE AND OXYGENATORS

Maria Helena L. Souza, CCP (Br)

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QUESTIONS

1. Through common usage, the term "oxygenator" has come to mean that portion of the perfusion apparatus that serves the functions of the patient's natural lungs during the period of extracorporeal circulation. More correctly, in order to define its function, the device should be called:

artificial lung
gas exchanger
cooler oxygenator
all of the above
none of the above

2. The artificial lung has a much larger surface area in comparison to the natural lung.

true
false

3. Five students discussed the basic knowledge related to the natural and the artificial lungs. Andy stated that the surface area of a membrane lung varies between 0.5 and 4.0 m². Barbara said that blood path width of membrane lungs is about 200 micron. Clark stated that the maximum O2 transfer of natural lung is 2,000 ml/min. Daisy stated that membrane thickness of membrane lungs is approximately 150 micron. Finally Edward said that membrane thickness of natural lung equals that of membrane lungs. In your opinion which student made a wrong statement ?

Andy
Barbara
Clark
Daisy
Edward

4. The partial pressure of gases present in a mixture of gases occupying a volume acts as if each individual gas is occupying the volume independently. This statement is known as the law of:

Boyle
Dalton
Newton
Gay-Lussac
Fick

5. Five students discussed the basic knowledge related to gas exchange and transport. Andy stated that the efforts to improve gas exchange have focused on reducing the diffusion barrier. Edward said that increasing the driving pressure gradient is limited to 760 mmHg minus the oxygen tension in the blood. Clark stated that pressures above the atmospheric pressure risk bulk gas transport accross the membrane with resultant gas embolism. Daisy stated that decreasing the diffusion path has been used very successfully to enhance gas transfer. Finally Barbara said that the easiest measure to enhance gas exchange would be to increase pressure gradiente to above atmospheric pressures, which in her opinion does not accentuate the risk of gas embolism. In your opinion which student made an incorrect statement ?

Andy
Barbara
Clark
Daisy
Edward

6. "True" membrane oxygenators provide a complete barrier between the gas and blood phases so that gas transfer depends totally on diffusion of gas through the membrane material.

true
false

7. The Kolobow spiral coil membrane lung is the only true membrane oxygenator currently manufactured. Its membrane is made of:

cellophane
polyethylene
teflon
nylon
none of the above

8. Five students discussed the basic knowledge related to membrane configuration and gas/blood flow manifolds. Andy stated that pore size of hollow polypropylene fiber is less than 1 micron. Barbara said that such a minimal pore size has the capacity to avoid gas and serum leakage across the membrane. Clark stated that the most common pattern in modern oxygenators has blood flowing outside of fibers. Daisy said that microporous membrane avoids the occurrence of a direct blood-gas interface. Finally Edward said that microporous membrane oxygenators should not be used for long-term applications. In your opinion which student made a wrong statement ?

Andy
Barbara
Clark
Daisy
Edward

9. In contrast to bubble oxygenators, control of ventilation and oxygenation is relatively independent in membrane oxygenators. Increasing the total gas flow rate changes ventilation by reducing the gas phase CO2 partial pressures and probably by decreasing the gas phase boundary layers for CO2 transfer.

true
false

10. After the first hour of CPB, the SvO2 decreased to 48% during a 5 minutes interval. The parameter likely to indicate the most accurate evaluation and correction is:

pH
BE
SaO2
SAO2
pCO2

11. The first membrane oxygenator was a very small capacity polyethylene coil that was, surprisingly, used successfully. This device was designed and constructed by:

Bramson
Clowes
Kolff
Landé
Melrose

12. A drop in platelet count during CPB may be due to:

destruction
adhesion
sequestration
activation
all of the above

13. In a retrospective study of approximately 573,000 patients collected by Kurusz et al, reporting causes of CPB accidents, oxygenator failure ranked as:

first
second
third
fourth
fifth

14. Any microporous membrane oxygenator that is placed distal to the arterial pump can be used with pulsatile perfusion.

true
false

15. Five students discussed the basic knowledge related to the use of oxygenators. Andy stated that increasing the flow of oxygen into a bubble oxygenator will increase the number of bubbles generated and the surface available for gas transfer, resulting in increased PO2 in the blood. Barbara said that bubble oxygenators are less traumatic to blood formed elements and proteins. Clark stated that one vital aspect of using a bubble oxygenator is maintaining an adequate volume of blood in the reservoir. Daisy said that the arterial reservoir enhances debubbling of the blood by giving the bubbles the opportunity to rise to the top of blood pool. Finally Edward said that the arterial reservoir also acts as a compliance chamber for the system. In your opinion which student made a wrong statement ?

Andy
Barbara
Clark
Daisy
Edward

16. The comparison between membrane and bubble oxygenators has demonstrated that all membrane oxygenators better preserve platelet function as measured by the release of ß-thromboglobulin.

true
false

17. Coating of blood-contacting surfaces of membrane oxygenators has been demonstrated to improve all of the following, except:

biocompatibility
platelet activation
hemolysis
pressure gradient
embolism

18. All of the following are reference conditions to describe oxygenator performance, except:

CO2 reference blood flow
O2 reference blood flow
index of hemolysis
plasma levels of C3a
static priming volume

19. Under steady blood flow conditions, if a perfusionist reduces the sweep gas in a membrane oxygenator, the pH will:

decrease
increase
not change

20. In a bubble oxygenator large bubbles enhance O2 transfer while smaller bubbles favor CO2 removal.

true
false

C.E.Quiz is dedicated to the Continuing Education in Extracorporeal Technology.

Your comments on C.E. Quiz are appreciated. Please contact: Maria Helena L. Souza