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biomeoicus centrifugal

PUMP

biomeoicus centrifugal

PUMP

FEM 0. OUTFLOW

FEM 0. OUTFLOW

cardiopulmonary bypass foreign circuit. Hageman factor 12 activates four pathways: 1) fibrinolysis; 2) the clotting cascade such that even in the presence of heparin consumption of coagulation factors occurs to some degree; 3) the complement cascade including C3A and C5A resulting in increased vascular permeability, third spacing, and neutrophil migration; 4) the kallikrein/bradykinin system resulting in increased vascular permeability and pain.

Cardiopulmonary bypass is a stress on the body similar to the stress of trauma or surgery itself. The concentration of epinephrine in the plasma increases 10-fold in cardiopulmonary bypass and that of norepinephrine increases three to four times. ADH during cardiopulmonary bypass far exceeds that of other surgical procedures. There is increased lipolysis from the increased epinephrine and hy-perglycemia with impaired insulin responsiveness in cardiopulmonary bypass.

Bypass causes a 7-fold increase in thyroxin levels secondary to the hepariniza-tion. ACTH levels fall during cardiopulmonary bypass with resulting decrease in cortisol. Pulsatile cardiopulmonary bypass minimizes the fall of ACTH, and thus the ACTH and cortisol are closer to normal than during continuous flow perfusion.

Bleeding is common when coming off cardiopulmonary bypass because of sequestration of platelets, inactivation of coagulation factors from enzymatic injury, as well as stunning of the enzyme systems from hypothermia. Many techniques to achieve hemostasis in the operating room are utilized. Blood products including fresh frozen plasma, cryoprecipitate, and platelets may be utilized. Amicar (alpha-aminocaproic acid) is an antifibrinolytic and prevents clot destruction. DDAVP, Gelfoam and thrombin, and "cryoglue" (a combination of thrombin, calcium, and cryoprecipitate which coagulates when mixed together) may be used.

Special reference should be made to aprotinin (Trasylol) an anti-inflammatory, antifibrinolytic agent which appears to have a profoundly beneficial action in limiting coagulopathy-related bleeding. Aprotinin is a protease inhibitor with a variety of effects on the coagulation system. It blocks fibrinolysis by inhibiting plasmin and kallikrein. It inhibits the contact phase of coagulation and prevents consumption of coagulation factors. Aprotinin also preserves glycoproteins in the platelet membrane making them resistant to damage from cardiopulmonary bypass. It is used prophylactically in patients at high risk for bleeding, including reoperation, aortic dissections, and endocarditis.

Protamine is given after completion of cardiopulmonary bypass to reverse the heparin. A protamine reaction results in decreased systemic vascular resistance with hypotension and sometimes pulmonary vasocontriction that may lead to right heart failure. It may be related to a direct effect and/or an autoimmune or anaphylactic reaction. It also activates complement by the classical passway. The treatment of a full-blown protamine reaction is to administer isoproterenol, epi-nephrine or prostaglandin E1 into the right heart and calcium into the left heart. Intravenous Amrinone which acts as a cardiac inotrope and pulmonary vasodilator may be useful as well. Patients previously receiving the NPH form of insulin, containing protamine, may be presensitized and particularly susceptible to a protamine reaction.

The ACT (activated clotting time) for safe cardiopulmonary bypass without risk of clotting the oxygenator should be greater than 400 seconds. The ACT is inaccurate for high heparin doses or in hypothermia. The ACT may be prolonged with inadequate levels of clotting factors even if heparin concentrations are low.

Generally, during systemic cooling on bypass no greater than 10°C gradient (8°C for children) should exist between the heat exchanger and the venous blood. When cooling, the pO2 of the arterial blood should be less than 200 mmHg lest bubbles form when the cool blood enters warm tissue. Re-warming tends to be slower than cooling because the risk of air embolization is greatest on warming. The heat exchanger temperature should not be greater than 40°C. Cooling is generally done at a rate of 1°C per minute; rewarming is done at 1°C every 3-5 minutes.

Generally, it has been stated that for each hour of cross-clamp time, one needs approximately 10 minutes of reperfusion (supportive bypass). This is often not the case and weaning may frequently be done quite rapidly. Flow in cardiopulmonary bypass should be 2.4 liters/min/m2 at normothermia. This flow can be less with hypothermia. For each decrease in temperature of 1°C oxygen consumption by tissue decreases by 10%. Between 22-37°C, cerebral blood flow is not altered, but when the temperature becomes less than 22°C, cerebral blood flow is markedly less and is in the range of 15% of normothermic blood flow.

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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