25-08-2017, 09:32 PM
Cardiopulmonary Bypass machine
Cardiopulmonary Bypass.ppt (Size: 1.04 MB / Downloads: 39)
Objectives
The components and operation of perfusion systems
The humoral response to cardiopulmonary bypass,
The consequences of extracorporeal perfusion in terms of organ damage
Definition
Cardiopulmonary bypass (CPB) is a technique that temporarily takes over the function of the heart and lungs during surgery , maintaining the circulation of blood and the oxygen content of the body. The CPB pump itself is often referred to as a heart-lung machine or "the pump".
Uses of cardiopulmonary bypass
Cardiopulmonary bypass is commonly used in heart surgery because of the difficulty of operating on the beating heart .
CPB can be used for the induction of total body hypothermia .
Venous Cannulation and Drainage
Venous blood usually enters the circuit by gravity or siphonage into a venous reservoir placed 40 to 70 cm below the level of the heart (Negative pressure is sometimes applied to the venous lines to provide assisted venous drainage using a roller pump or centrifugal pump)
The amount of drainage is determined by central venous pressure(IV volume,ven.compliance); the height differential; resistance in cannulas, tubing, and connectors; and absence of air within the system.
If inadequate blood volume …wall collapse ..fluttering… add volume to pnt .
Complications
Complications associated with venous cannulation and drainage, These include:-
Atrial arrhythmias.
Atrial or caval tears and bleeding.
Air embolization, injury or obstruction due to catheter malposition.
Reversing arterial and venous lines, and unexpected decannulation.
Placing tapes around the cavae may lacerate branches, nearby vessels (e.g., the right pulmonary artery), or the cava itself.
Arterial Cannulation
The tip of the arterial cannula is usually the narrowest part of the perfusion system
High-velocity jets may damage the aortic wall, dislodge atheroemboli, produce dissections, disturb flow to nearby vessels, and cause cavitation and hemolysis.
Venous Reservoir
The venous reservoir serves as volume reservoir.
This reservoir serves as a high-capacitance receiving chamber for venous return;
facilitates gravity drainage; is a venous bubble trap;
provides a convenient place to add drugs, fluids, or blood; and adds storage capacity for the perfusion system, as much as 1 to 3 L of blood may be translocated from patient to circuit when full CPB is initiated.
The venous reservoir also provides several seconds of reaction time if venous return is suddenly decreased or stopped during perfusion.
Disadvantages include the use of silicon antifoam compounds, which may produce microemboli.
Filters and Bubble Traps
During clinical cardiac surgery with CPB the wound and the perfusion circuit generate gaseous and biologic and nonbiologic particulate microemboli (<500 µm diameter).
Microemboli produce much of the morbidity associated with cardiac operations using CPB.
Gaseous emboli contain oxygen or nitrogen and may enter the perfusate from multiple sources (stopcocks, sampling and injection sites, priming solutions, priming procedures, intravenous fluids, vents, the cardiotomy reservoir, tears or breaks in the perfusion circuit, loose sutures, rapid warming of cold blood, cavitation, oxygenators) and pass through other components of the system.
Blood produces a large number of particulate emboli related to thrombus formation (clots), fibrin, platelet and platelet-leukocyte aggregation, hemolyzed red cells, cellular debris, fat particles and denatured proteins.
Starting Cardiopulmonary Bypass
CPB is started at the surgeon’s request with concurrence of the anesthesiologist and perfusionist. As venous return enters the machine, the perfusionist progressively increases arterial flow while monitoring the patient’s blood pressure and volume levels in all reservoirs. Six observations are critical:
Is venous drainage adequate for the desired flow?
Is pressure in the arterial line acceptable?
Is arterial blood adequately oxygenated?
Is systemic arterial pressure acceptable?
Is systemic venous pressure acceptable?
Is the heart adequately decompressed?
Once full stable cardiopulmonary bypass is established for at least 2 minutes, lung ventilation is discontinued, perfusion cooling may begin, and the aorta may be clamped for arresting the heart.