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

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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

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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

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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

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Donor Blood

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

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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

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Platelets (continued)

• As the platelets are activated, they bind to the
  tubing, sequestered in the lungs, the spleen, and
  liver.all leading to thrombocytopenia

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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

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Blood flow to kidneys is effected by

• Composition of Prime
• The sympathetic nervous system
• Hormones
• Epinephrine
• Angiotensin

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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 doesnt affect output,
  mental status changes, seizures, GI bleeding, and
  yellowing of the skin

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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

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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

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CT Scan

• Best method to determine extent of brain injury

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Ways to prevent neurological injuries

• Use filters
• CO2 flush circuit
• Watch temperature gradients
• Vent heart when clamp is off

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Major causes of cerebral injury

• Low flows
• Hypotension
• Low pCO2which leads to vasoconstriction of
  cerebral arteries
• High p02which also leads to vasoconstriction of
  cerebral arteries

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Hematological Effects

• Caused by exposing the patients to blood products
  in the circuit
• Caused by using heparin
• Caused by hemodiluting the patients

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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

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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

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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 WBCs to migrate to the
  area causing inflammation
• Release of enzymes and oxygen free radicals that
  destroy tissue

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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

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Major Effect on Endocrine System

• Insulin regulates the metabolism of glucose and
  regulates the processes for metabolism of fats,
  carbs, and proteins
• Under hypothermic conditions the insulin response
  in decreased and thus ones blood glucose levels
  increase. During the re-warming phases of bypass
  the insulin response increases.

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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

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Hepatic Injury

• Patient becomes jaundiceexcessive 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