The Effects of CPB

1. The Effects of CPB Brian Schwartz, CCP November 5, 2002

2. Effects of CPB • To some degree or another, our patients who undergo CPB may suffer some type of injury. • The longer the bypass time….the better chance of having some type of injury

3. Innovative products to help decrease the incidence of injury • Membrane oxygenators • Filters • Bubble detectors • Coated circuits

4. Areas that are Effected The Lungs The Kidneys The Brain The Compliment System The Endocrine System The Hepatic System

5. Effects on the Lungs • Considered to be the most serious injury as a result of CPB • By placing our patients on CPB the lungs automatically undergo some type of abnormal physiologic changes • The lungs are subject to injury by the activation of the blood compliment system by coming into contact with foreign substances

6. Lungs (continued) • Compliment Activation of both C3a and C5a lead to the activation of leucocytes • Activation of Leucocytes • Leukoembolization may occur in the lungs with the release of oxygen free radicals and proteolytic enzymes released by the neutrophils

7. Things we might see: • Pump Lung • Congested lungs with intraalveolar edema, interstitial edema, and atelectasis • Atelectasis • Collapsed lung • Smoking, chronic bronchitis, obesity, and pulmonary edema predispose patients for injury

8. Donor Blood • Any time donor blood is added to the pump it should be filtered • It should be filtered mainly for leucocytes

9. Thrombocytopenia • Defined as low platelet count • Platelet count usually decreases during CPB, sometimes even below 50,000 • Because of such a low platelet count we will see a large blood loss • Due to decreased amount of platelets and function

10. Platelets (continued) • As the platelets are activated, they bind to the tubing, sequestered in the lungs, the spleen, and liver….all leading to thrombocytopenia

11. Effects on the Kidneys • Another common effect of CPB is renal dysfunction • Normally, 25% of the total C.O. is sent to the kidneys. On pump this amount is reduced due to: low flows and low pressures

12. Blood flow to kidneys is effected by: • Composition of Prime • The sympathetic nervous system • Hormones • Epinephrine • Angiotensin

13. Renal Failure • Acute renal failure • Nitrogen wastes accumulate in the blood rapidly • Chronic renal failure • Urine decreases in amount and failure signs begin… • Increase in fluid intake doesn’t affect output, mental status changes, seizures, GI bleeding, and yellowing of the skin

14. Best Indicator of Failure • Acute renal failure • Nitrogen wastes accumulate in the blood rapidly • mg/100ml • Elevated levels indicate creatine is not being expelled in the urine

15. Reasons for poor function post-op • Long bypass run • Poor pre-op function • Addition of blood • Exposure of angiographic dyes • IABP

16. Neurological Effects • These results are usually permanent as a result of an embolic event such as a CVA or Stroke • Embolus: defined as an air, blood clot, fat or calcium debris • Indicators of air embolism: • Seizures • Cardiac arrythmias • Ventricular dysfunction

17. CT Scan • Best method to determine extent of brain injury

18. Ways to prevent neurological injuries • Use filters • CO2 flush circuit • Watch temperature gradients • Vent heart when clamp is off

19. Major causes of cerebral injury • Low flows • Hypotension • Low pCO2…which leads to vasoconstriction of cerebral arteries • High p02…which also leads to vasoconstriction of cerebral arteries

20. Hematological Effects • Caused by exposing the patients to blood products in the circuit • Caused by using heparin • Caused by hemodiluting the patients

21. Hematological Effects (continued) • Patients with pre-existing hematological problems are at even more of a risk when having heart surgery • Platelet dysfunction may be a result of diluting the patients and the blood interaction between air or pump circuit • Disseminated Intravascular Coagulation • Rare, but seen in long pump runs • Coagulation factors inappropriately activated and bleeding occurs systemically

22. Effects on the Compliment System • CS involves complex proteins in the blood that bind with antibodies against infection and foreign bodies • When activated, over 18 plasma proteins are activated causing an immune response

23. Activation of the CS • Release of anaphylatoxins that increase vascular permeability (edema) and smooth muscle contraction • C3a and C5a cause migration of neutrophils onto walls of vessels • Arachidonic acid causes increase vascular permeability • Chemotactic factors cause WBC’s to migrate to the area causing inflammation • Release of enzymes and oxygen free radicals that destroy tissue

24. Effects on the Endocrine System • A system on ductless glands that secrete hormones directly into the blood • Adrenal: secretes epi/norepi • Thyroid: secretes T-3 and T-4 for metabolism • Pituitary: secretes vasopressin (ADH) • Pancreas: secretes insulin • Ovaries/Testis: maturation of eggs and sperm

25. Major Effect on Endocrine System • Insulin regulates the metabolism of glucose and regulates the processes for metabolism of fats, carb’s, and proteins • Under hypothermic conditions the insulin response in decreased and thus one’s blood glucose levels increase. During the re-warming phases of bypass the insulin response increases.

26. Hepatic Effects • The liver is the largest organ in the body • Consists of 4 lobes and supplied by 2 means • Hepatic artery- oxygen from the heart • Hepatic portal vein-nutrient filled blood from the stomach and intestines • Functions of the Liver • Processes glucose, proteins, and fats

27. Hepatic Injury • Patient becomes jaundice…excessive bilirubin due to blood transfusions or blood trauma. • Jaundice may clear up by itself within a week • Elevated liver enzymes indicate injury • As long as you keep your flows about an 2.2 index, hepatic oxygenation is maintained and injury may be avoided