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

Bengt Gerdin 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.

Bengt Gerdin Terminology Oxygen demand/consumptionVO 2 Oxygen transportDO 2 Oxygen extraction rateO 2 ER

Bengt Gerdin Oxygen transport / Oxygen flux (DO 2 )

Bengt Gerdin Arterial oxygen content (CaO2) =20/100 ml O 2 /ml blood = 0,2 ml O 2 /ml blood

Bengt Gerdin Oxygen consumption (VO 2) Amount of oxygen transported out to the tissues minus amount of oxygen transported back to the heart. OutCO x SaO 2 % x Hb x 1.39 BackCO x SvO 2 % x Hb x 1.39 VO 2 = CO x (SaO 2 % - SvO 2 %) x Hb x 1.39

Bengt Gerdin Oxygen demand/consumption VO 2

Bengt Gerdin Oxygen extraction rateO 2 ER Relative amount of oxygen extracted from the blood during one passage through the tissues. OutCO x SaO 2 % x Hb x 1.39 BackCO x SvO 2 % x Hb x 1.39 O 2 ER ≈ (SaO 2 % -SvO 2 %)/SaO 2 % x 100 Example:SaO 2 = 95 % and SvO 2 = 70 % gives O 2 ER ≈ (95-70)/95 = 26 %

Bengt Gerdin Oxygen extraction rateO 2 ER Varies in different vascular beds Highly extracting beds: liver gut mucosa hippocampus Global O 2 ER is about 25 %, i.e. DO 2 /VO 2 is about 4:1

Bengt Gerdin From Nunn JF, Applied Respiratory Physiology

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

Bengt Gerdin Oxygen demand/consumption VO 2

Bengt Gerdin How do we know that oxygen transport is adequate? Global vs local assessment

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

Bengt Gerdin Global assessment of adequacy of oxygen transport Blood lactateBlood lactate related to survival in sepsis Oxygen saturation in mixed venous bloodOxygen saturation in mixed venous blood

Bengt Gerdin 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 SO 2

Bengt Gerdin DO 2 VO 2 Aerobic metabolism Anaerobic metabolism Critical DO 2 DO 2 -dependent DO 2 -independent

Bengt Gerdin DO 2 VO 2 Aerobic metabolism Anaerobic metabolism Critical DO 2 DO 2 -dependent DO 2 -independent -- normal -- sepsis

Bengt Gerdin General strategy: Improve oxygen transport; When in doubt: determine! (CO and O 2 ER) CO↑ Hb↑optimal viscosity (Hct close to 33) BV↑ CVP (LAP) ↑ vasoactive amines

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

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

Bengt Gerdin 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 (SaO 2 ?) Kidney perfusion parameter (hourly urinary output?) Other metabolic parameter (blood lactate?) Gut perfusion parameter (pH i ?)