Heart Lung Machine.pptx

Human assist devices

1. Heart Lung Machine Unit – I

2. Purpose Heart–lung machine or cardiopulmonary bypass (CPB) machine is an equipment that temporarily takes over the function of the heart and lungs during cardiac surgery, maintaining the circulation of blood and the oxygen content of the patient’s body . Principle : Operations requiring the opening of the chambers of the heart require the use of the heart–lung machine to support the circulation during that period. The machine thus allows the surgeon to correct the defects in the heart, while the entire functions of the human heart and lungs are temporarily performed by the machine.

3. Block diagram The heart–lung machine does the same job that the heart and lungs do, but it is done outside the human body. The first step in the process is to draw and return blood to the human body circulation system. This is done by using special drainage and return catheters , known as cannulae. One or more venous cannulae are placed in a central vein or in the right atrium of the heart to empty the heart. The blood is then pumped to the oxygenator and the heat exchanger. Inside the oxygenator, oxygen bubbles up through the blood and enters the red blood cells and makes the blood oxygen‐rich. Then, a filter removes the air bubbles from the oxygen‐rich blood, which is returned via a plastic tube into the arterial system of the body, usually at the upper portion of the ascending aorta. From the aorta, the blood moves throughout the rest of the body . Inside the oxygenator, oxygen bubbles up through the blood and enters the red blood cells and makes the blood oxygen‐rich.

4. Components of CPB Reservoir: The function of the reservoir is to collect blood from the operative field and hold the excess blood volume, while the heart and lungs are stopped. The drainage of the blood takes place either by gravitational forces or sometimes it is achieved with vacuum. Pumps: Pumps are used to achieve flow of blood through the rest of the circuit. Many pump designs have been tried over the years, but currently roller pump and the centrifugal pump are mostly used. Both types of pumps can provide pulsatile or non‐pulsatile blood flow to the systemic circulation . Heat exchanger : A heat exchange system is used to first lower the blood and body temperature during heart surgery. The process is later reversed to rewarm the blood before its return to the body. The blood temperature isadjusted via the water temperature, which is controlled manually by the perfusionist.

5. Components of CPB Oxygenator An oxygenator is that part of the heart–lung machine that mimics the functions the patient’s natural lungs during the period of extracorporeal circulation besides adding oxygen to infused blood. In reality, the oxygenator is a gas exchanger because besides adding oxygen to the infused blood, it also removes carbon dioxide from the venous blood and transports anaesthetics, and possibly other gases into and out of the circulation. Besides, it has an integrated heat exchanger in it and also serves as the main reservoir for the blood. Thus, the oxygenator performs almost all major functions of the natural lungs. In an oxygenator, gas transfer from the gas to the liquid phase takes place by diffusion process based on the partial pressure difference of the particular gas. Thus, gas transfer would depend upon the resistance to diffusion of the particular gas when it passes through any substance, which could be a membrane, blood, or the gas itself. Other factors that also play a role in the gas exchange are the physical size and structure of the oxygenator .

6. Components of CPB Filter Finally , when blood is ready for return to the patient, it passes through an arterial line filter (typically 40μm). This filter prevents air and other particles from returning to the arterial circulation by filtering small air bubbles that may have entered, or been generated by, the heart–lung machine . Power Supply The machines are designed to operate on backup battery in case of a power failure. The capacity of the battery is sufficient to provide power to enable the finishing of the operation . All pump modules are designed to operate on 24V for ensuring patient and operator safety. Cannulae Multiple cannulae are sewn into the patient’s body in a variety of locations, depending on the type of surgery. Large vessels – veins and arteries – are required for cannulation , i.e . to insert the tubes (cannulae) that carry the blood from the patient to the heart–lung machine and to return the blood from the heart–lung machine to the patient.

7. Oxygenators An oxygenator is a medical device that is capable of exchanging oxygen and carbon dioxide in the blood of human patient during surgical procedures that may necessitate the interruption or cessation of blood flow in the body, a critical organ or great blood vessel . An oxygenator is typically utilized by a perfusionist in cardiac surgery in conjunction with the heartlung machine . Design Criteria for Oxygenators • The demands on an artificial lungs are great. • Every minute 5 liters of blood must be spread in layer then enough to ensure adequate gaseous exchange. • Enough oxygen must be transported to saturate hemoglobin . • The right amount of CO2 must be give off so that the acid base balance is not disturbed. • The oxygenated blood must have all bubbles removed, which would otherwise cause air emboli. • Throughout the process the blood must be carefully handled to reduce the damage of the delicate blood cells, otherwise the body would be unable to dispose of all the decomposition products from the demolished cells.

8. Bubble Oxygenators

9. Membrane Oxygenators

10. Liquid – Liquid Oxygenators

11. Rotating Disc type film Oxygenators