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Oxygenation in patients with exceptionally high oxygen demand - and the role of hemotherapy

Oxygenation in patients with exceptionally high oxygen demand - and the role of hemotherapy. Problem An increased oxygen demand reflects an increased overall metabolism - useful or not. An increased oxygen demand is often seen in patients with severe circulatory impairment.

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Oxygenation in patients with exceptionally high oxygen demand - and the role of hemotherapy

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  1. Oxygenation in patients with exceptionally high oxygen demand - and the role of hemotherapy

  2. Problem An increased oxygen demand reflects an increased overall metabolism - useful or not. An increased oxygen demand is often seen in patients with severe circulatory impairment. An increased oxygen demand must be matched by an adequate oxygen transport.

  3. Terminology Oxygen demand/consumption VO2 Oxygen transport DO2 Oxygen extraction rate O2ER

  4. Oxygen transport / Oxygen flux (DO2)

  5. Arterial oxygen content (CaO2)

  6. Oxygen consumption (VO2) Amount of oxygen transported out to the tissues minus amount of oxygen transported back to the heart. Out CO x SaO2% x Hb x 1.39 Back CO x SvO2% x Hb x 1.39 VO2 = CO x (SaO2% - SvO2%) x Hb x 1.39

  7. Oxygen demand/consumption VO2

  8. Oxygen extraction rate O2ER Relative amount of oxygen extracted from the blood during one passage through the tissues. Out CO x SaO2% x Hb x 1.39 Back CO x SvO2% x Hb x 1.39 O2ER ≈ (SaO2% -SvO2%)/SaO2% x 100 Example: SaO2 = 95 % and SvO2 = 70 % gives O2ER ≈ (95-70)/95 = 26 %

  9. Oxygen extraction rate O2ER • Varies in different vascular beds • Highly extracting beds: • liver • gut mucosa • hippocampus • Global O2ER is about 25 %, i.e. DO2/VO2 is about 4:1

  10. From Nunn JF, Applied Respiratory Physiology

  11. From Vincent JL et al. In: Pathophysiology of Shock, Sepsis and Organ Failure, Ed Schlag & Redl, Springer, 1993

  12. Oxygen demand/consumption VO2

  13. How do we know that oxygen transport is adequate? Global vs local assessment

  14. How do we know that oxygen transport is adequate? Global vs local assessment Adequate where???

  15. Global assessment of adequacy of oxygen transport • Blood lactate • related to survival in sepsis • Oxygen saturation in mixed venous blood

  16. Local assessment of adequacy of oxygen transport • Hypothesis: Deficient oxygen transport to a certain vascular bed is related to success of therapy • Liver? • Gut? • Brain? • Gut tonometry • Liver vein SO2

  17. DO2 -dependent DO2 -independent Anaerobic metabolism Aerobic metabolism VO2 Critical DO2 DO2

  18. DO2 -dependent DO2 -independent Anaerobic metabolism Aerobic metabolism VO2 Critical DO2 DO2 -- normal -- sepsis

  19. General strategy: Improve oxygen transport; When in doubt: determine! (CO and O2ER) CO↑ Hb↑ optimal viscosity (Hct close to 33) BV↑ CVP (LAP) ↑ vasoactive amines

  20. Burn injury Massive activation of all cascade systems Major effects of circulating and locally acting cytokines Major metabolic consequences, oxygen demand may increase to 200-300 % cytokine effects SIRS compensation for heat loss

  21. Strategy for adequate oxygenation in burns Diminish oxygen consumption diminish water loss diminish heat loss diminish shivering diminish fever Optimize oxygen transport

  22. How to monitor the acute intravenous treatment? The dream is to monitor by the parameter that gives the best information about the patient´s condition after 24 hours. -least risk for organ ischemia (e.g. kidneys) - least risk for bacterial translocation - least risk for causing progression of the burn Circulatory parameter (CVP?, MAP?, HR<120?) Oxygen transport parameter (SaO2?) Kidney perfusion parameter (hourly urinary output?) Other metabolic parameter (blood lactate?) Gut perfusion parameter (pHi?)

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