NEUROANANTOMY AND NEUROPHYSIOLOGY

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BLOOD CONSERVATION STRATEGIES Niki M Dietz,
MD Department of Anesthesiology Mayo Clinic,
Rochester, MN
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Blood Conservation Strategies

• Allogeneic blood use
• Blood substitutes
• Autologous
• Hemodilution/lower hematocrit
• Enhanced donation

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RBC Transfusion (2005)

• 14 million units/year
• 60 - 70 perioperatively
• 50 of total to patients gt 65 years

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RBC Transfusion--Impact of Age
Percent
41 - 65
lt41
gt65
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Blood Use -- Future Demand

• Safety no longer major issue
• HIV 1250,000 to 11,000,000
• hepatitis screening better
• blood safer than pre-AIDS era
• Demographic pressure -- major issue
• aging population
• inadequate donor rates
• logistics of blood donation/storage

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Projected Changes in Age Distribution of the U.S.
Population
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Blood Use -- Future Demand
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Blood Conservation Strategies

• Allogeneic blood use
• Blood substitutes
• Autologous
• Hemodilution/lower hematocrit
• Enhanced donation

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Blood Substitutes -- Types

• Hemoglobin solutions
• Perfluorocarbons
• Liposome-encapsulated hemoglobin

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Blood Substitutes -- Hemoglobin Solutions

• Raw material hemoglobin molecule
• Outdated banked blood
• Bovine blood
• Molecular modifications
• Larger molecule more oxygen
• Enhanced oxygen transport characteristics
• cross-link / polymerization / conjugation

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Hemoglobin Solutions -- Physiologic Effects

• Variables unaffected
• O2 consumption
• CO2 production
• cardiac output
• Variables affected
• mean arterial pressure -- increased
• pulmonary artery pressure -- increased
• systemic vascular resistance -- increased

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Hemoglobin Solutions -- Limitations

• Vasoconstriction
• Limited intravascular half-life
• Renal effects
• Some promise in trauma setting

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Blood Substitutes -- Perfluorocarbons

• Synthetic solvents of oxygen
• Solvents of carbon dioxide and nitrogen
• Insoluble in plasma
• emulsification
• Surfactant
• Limited oxygen-carrying capacity

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Blood Substitutes -- Liposome-encapsulated
Hemoglobin

• Lipid-based pseudomembrane
• Mimics erythrocyte in size and structure
• Ability to add allosteric effectors
• Major limitation -- uptake by RES

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Blood Substitutes -- Limitations

• Half-life
• Expense
• Metabolism
• Oxygen content
• Co-existing disease

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Blood Conservation Strategies

• Allogeneic blood use
• Blood substitutes
• Autologous
• Hemodilution/lower hematocrit
• Enhanced donation

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Autologous -- Types

• Pre-donation
• Intraoperative salvage

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Pre-Donation

• Major risk of blood from blood bank clerical
  error
• Cost for pre-donated unit 250
• Cost for allogeneic unit 100
• Increased cost due to much greater clerical work
  tracking unit

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Cell-Salvage

• Reclaims 40-50 of blood
• High initial equipment cost
• Cost effective for blood loss of gt1000 ml

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Cell-Salvage -- Mayo Clinic
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Blood Conservation Strategies

• Allogeneic blood use
• Blood substitutes
• Autologous
• Hemodilution/lower hematocrit
• Enhanced donation

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Factors Affecting Transfusion Decision
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Ideal Hematocrit

• Maximal oxygen capacity
• rheology
• hematocrit
• Spiess, et al.
• post-CABG
• HCt lt 24 best
• need more hemoglobin/outcome studies

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Hemodilution

• Theoretically sound
• Withdraw units of blood prior to incision
• Blood lost of lower hematocrit
• Give blood back when wound closed
• Lack of efficacy data
• Paucity of large trials
• Cost?

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Blood Conservation Strategies

• Allogeneic blood use
• Blood substitutes
• Autologous
• Hemodilution/lower hematocrit
• Enhanced donation

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Blood Donation

• Blood ideal blood substitute
• Supply safe
• Recruitment of donors
• United States (age 18-65)
• 1990-2000 -- 0.67 donation rate
• 2001 -- increase to 0.89 donation rate
• Donation rate gt Transfusion rate
• Rochester, MN -- 15 donation rate
• older donors (gt65) safe (Pindyck, et al., JAMA,
  1987)

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Summary

• Predicted RBC shortage
• Blood substitutes -- not feasible
• efficacy
• side effects
• cost
• Autologous -- feasible
• Hemodilution -- feasible
• Increase donations -- best

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Thank you