Cardiopulmonary Bypass Chapter 5

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Questions and Answers

What is the primary purpose of a cross-clamp in cardiac surgery?

To aspirate blood from the cardiac chambers

To manage acute volume shifts during CPB

To filter particulate materials from banked blood

To provide a dry, motionless operative area (correct)

What is the function of a cardiotomy reservoir in cardiac surgery?

To filter blood from the cardiac chambers

To manage acute volume shifts during CPB

To recycle suctioned blood from the surgical field (correct)

To pump blood to the heart-lung machine

What is the purpose of a venous reservoir in cardiac surgery?

To pump blood to the heart-lung machine

To filter blood from the cardiac chambers

To aspirate blood from the surgical field

To manage acute volume shifts during CPB (correct)

What type of pump is characterized by a rotor with a number of rollers attached to the external circumference?

Peristaltic pump Signup and view all the answers

What is the result of the rotor turning in a peristaltic pump?

The fluid is pumped to move through the tube Signup and view all the answers

What is the purpose of the impeller vanes in a centrifugal pump?

To force fluid into a circular movement Signup and view all the answers

What is the function of the air-fluid separation chamber in a cardiotomy reservoir?

To separate air from fluid Signup and view all the answers

What is the purpose of the temporary storage reservoir in a cardiotomy reservoir?

To store priming solutions Signup and view all the answers

What is the primary function of cardiopulmonary bypass during surgery?

To maintain the circulation of blood and oxygen content Signup and view all the answers

Who operates the cardiopulmonary bypass pumps?

Perfusionists Signup and view all the answers

Why is cardiopulmonary bypass commonly used in heart surgery?

Because of the difficulty of operating on the beating heart Signup and view all the answers

What is the benefit of using cardiopulmonary bypass for the induction of total body hypothermia?

It allows the body to be maintained for up to 45 minutes without perfusion Signup and view all the answers

What is the consequence of stopping blood flow at normal body temperature?

Permanent brain damage in 3-4 minutes Signup and view all the answers

What is the primary mechanism by which an impeller pump increases the pressure of the fluid?

Centrifugal force Signup and view all the answers

What surgical procedures commonly use cardiopulmonary bypass?

Coronary artery bypass surgery, cardiac valve repair and/or replacement, and heart transplantation Signup and view all the answers

What is the purpose of the heat exchanger in a cardiopulmonary bypass system?

To regulate the temperature of the blood Signup and view all the answers

What is the material used to manufacture the tubing for cardiopulmonary bypass?

Clear polyvinyl chloride (PVC) Signup and view all the answers

What is the ideal range of cardiac index for a patient during cardiopulmonary bypass?

1.8 to 2.4 L/min/m2 Signup and view all the answers

What is the primary function of the impeller vanes in a pump?

To transfer mechanical work to the fluid Signup and view all the answers

What is the purpose of the pump in cardiopulmonary bypass?

To return oxygenated blood to the aorta Signup and view all the answers

What is the term used to describe the reduction of the body temperature during cardiopulmonary bypass?

Hypothermia Signup and view all the answers

What is the maximum duration of circulatory arrest possible at a temperature of 12–22°C?

45 minutes Signup and view all the answers

What is the equation that describes the properties of an ideal blood pump?

Poiseuille equation Signup and view all the answers

What is the purpose of the external heater-cooler in a cardiopulmonary bypass system?

To pump temperature-controlled water into the heat exchanger Signup and view all the answers

What is the primary mechanism of heat transfer in the CPB heat exchanger?

Convection Signup and view all the answers

What is the maximum temperature that arterial blood should reach during CPB?

37.5°C Signup and view all the answers

What is the purpose of the oxygenator in CPB?

To add oxygen to and remove carbon dioxide from the blood Signup and view all the answers

What is the minimum temperature that some patients may be cooled to during CPB?

12°C Signup and view all the answers

What is the maximum temperature gradient between the water and blood in the CPB heat exchanger?

10°C Signup and view all the answers

What type of oxygenator is used when CPB is needed for less than 2 hours?

Bubble oxygenator Signup and view all the answers

How does gas exchange occur in a bubble oxygenator?

Through direct contact between blood and oxygen bubbles Signup and view all the answers

What is the purpose of the diffusion plate in a bubble oxygenator?

To produce thousands of small oxygen bubbles Signup and view all the answers

What type of oxygenator is used when CPB is needed for more than 2-3 hours?

Membrane oxygenator Signup and view all the answers

How does gas exchange occur in a membrane oxygenator?

Oxygen diffuses from the gas side into the blood Signup and view all the answers

What law does gas exchange in an artificial lung obey?

Fick's law of diffusion Signup and view all the answers

What is the relationship between the diffusion constant D and the specific gas solubility (Sol)?

D is proportional to Sol Signup and view all the answers

What is the advantage of using a hollow fiber membrane oxygenator?

It increases surface area for gas exchange with limited impact on blood trauma Signup and view all the answers

Why is it challenging to design an artificial lung?

Red blood cells pass through pulmonary capillaries one at a time, making the distance for O2 diffusion much shorter Signup and view all the answers

What is the thickness of the wall in a hollow fiber membrane oxygenator?

50 μm Signup and view all the answers

What is the outer diameter of the hollow fiber in a hollow fiber membrane oxygenator?

300 μm Signup and view all the answers

Study Notes

Introduction to Cardiopulmonary Bypass (CPB)

CPB is a technique that temporarily takes over the function of the heart and lungs during surgery, maintaining blood circulation and oxygen content in the body.
Perfusionists, specialized healthcare professionals, operate the heart-lung machine during cardiac surgery to manage the patient's physiological status.

Importance of CPB in Heart Surgery

CPB is commonly used in heart surgery because of the difficulty of operating on the beating heart.
Operations requiring the opening of the heart chambers require CPB to support circulation during that period.
CPB can nourish blood cells and allow them to continue cellular respiration even through surgery.

CPB Applications

CPB can be used for:
- Coronary artery bypass surgery
- Cardiac valve repair and/or replacement
- Heart transplantation
- Pulmonary thrombectomy (remove blood clots from the pulmonary arteries)
CPB can also be used to rewarm individuals suffering from hypothermia.

Cardiopulmonary Bypass Circuit

Blood is gravity-drained from the heart to a reservoir via venous tubing and returned oxygenated to the aorta using a pump.
The tubing is manufactured from clear polyvinyl chloride (PVC).
A cross-clamp is placed across the ascending aorta above the coronary ostia and proximal to the aortic cannula to provide a dry, motionless, operative area.

Cardiotomy Reservoir

The cardiotomy reservoir is used to aspirate blood from the cardiac chambers to provide adequate exposure of the surgical field.
The reservoir includes an air-fluid separation chamber, a temporary storage reservoir for priming solutions, filtration of particulate materials, and the addition of fluids and pharmacological agents to the perfusion circuit.

Venous Reservoir

The venous reservoir acts as a capacitance chamber to manage acute volume shifts experienced during CPB due to hypothermia operating mode.
Filtered venous blood is drawn from the reservoir and pumped toward the heat exchanger and oxygenator block.

Pump

There are two types of arterial pumps commonly used:
- Peristaltic pump: uses a rotor to compress a flexible tube, forcing fluid to move through the tube.
- Centrifugal pump: uses an impeller to transfer mechanical work to the fluid, increasing pressure and velocity.

Heat Exchanger

Heat exchangers are integral components of all oxygenators used for CPB.
The heat exchanger regulates the temperature of the blood perfusing the patient, which raises or lowers the body temperature depending on the type of surgical procedure being performed.
The heat exchanger can cool the patient's blood to a temperature of 25-32°C or lower for more challenging operations.

Oxygenator

An oxygenator is a device used to add oxygen to and remove carbon dioxide from the blood.
There are two types of oxygenators:
- Bubble oxygenator: used for CPB lasting less than 2 hours, where oxygen is directly infused into the oxygenator chamber through a diffusion plate.
- Membrane oxygenator: used for CPB lasting more than 2-3 hours, where gas doesn't come into direct contact with the blood.

Gas Exchange and Diffusion

Gas exchange occurs across the blood-gas interface in the oxygenator.
The physical process of diffusion that occurs during gas exchange in the natural lung also applies to the artificial lung, but is less efficient.
Gas exchange obeys Fick's law of diffusion.

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Description

This quiz covers the basics of cardiopulmonary bypass, a technique used in cardiac surgery to temporarily replace the heart and lungs' functions. Learn about the role of perfusionists and the heart-lung machine.