class: title-slide, left, bottom # Physiology of gas exchange during VV-ECMO ---- ## **Determinants of oxygenation** ### Maurizio Passariello ### 25th of March 2022 --- class: middle, center # Ecmo orders  Why is this important? --- class: inverse, middle # Objectives <br> <br> ### - Review physiology of oxygen transport (Oxygen delivery) -- ###- Determinants of oxygenation -- ###- Determinants of oxygenation during VV-ecmo -- ###- Carbon dioxide removal --- class: middle, center # Question # 1  --- class: inverse, middle # Review physiology of oxygen transport # Oxygen delivery --- # Oxygen consumption  -- ## Is VO2 fixed? ## What is the relationship between DO2 and VO2 --- # Is VO2 fixed? .pull-left[ ### VO2 increased by: <br> - Muscular activity - Infection - Hyperthermia - Catecolamines - Thyroid hormones ] .pull-right[ ### VO2 decreased by: <br> <br> <br> - Rest - Paralysis - Hypothermia ] --- class: middle # What is the relationship between VO2 and DO2? <br> ### First let's see what DO2 is: ####- DO2 = CaO2 x CO -- ####- CaO2 = Dissolved O2 + O2 bound to Hb -- ####- Dissolved O2 = 0.0031 x pO2 ---> Negligible amount -- ####- O2 bound to Hb = 0.34 x SaO2 x [Hb] ---> Significant amount -- ###- Hence: DO2 = 0.34 x SaO2 x [Hb] x CO --- # What is the relationship between VO2 and DO2? ### Now let's see how DO2 is influenced by Hb: --  --- class: middle,center  --- class: middle, center # What is the relationship between VO2 and DO2?  In normal conditions DO2:VO2 = 5: 1 --- class:middle # How do we know if VO2 and DO2 are matched? <br> #### - Tachycardia #### - Oliguria #### - High lactate #### - Mentation/confusion/delirium #### - Low SvO2. (caveat: recirculation) --- class: middle, center  --- class: inverse, middle # So...What are the determinants of oxygenation in normal conditions? .pull-left[ <br> <br> ## Cardiac output ## [Hb] ## SO2 ] -- .pull-right[ <br> <br> <br> <br> ## VO2 ] --- class: inverse, middle, center # What are the determinants of Oxygenation during VV-ECMO? --- class: center, middle  --- class: center, middle  --- class: center ## Effects of CO .pull-left[  ] -- .pull-right[ <br> <br> <br> ## To obtain adequate oxygenation: ## ECBF/CO>60% ] --- # Lastly...let's see effects of metabolic rate <br> <br> <br> -- ### Increase in VO2 -- ### Increase in CO -- ###Increase in O2 demand -- #### .bottom-left[Possible solutions: increase ECBF, sedation +/- paralysis, cooling, Hb, 3rd cannula] --- class: middle, center # Effect of recirculation  --- class: middle # What are the determinants of Oxygenation during VV-ECMO? .pull-left[ <br> <br> ### Assuming oxygenator performs well ### Assuming no recirculation ### Ignoring dissolved O2 ] -- .pull-right[ ## VO2 ##.red[Hb] ## .red[ECBF] ## CO ] --- class: middle, center # Question # 2  --- class: inverse, middle, center # Carbon dioxide --- class: middle # Carbon dioxide <br> <br> #### - Odourless, colourless gas #### - 0.039% of air #### - Co2 productio approx=O2 consumption #### - RQ= CO2 prod/O2 consumed depends on nutrition --- # Carbon dioxide transport <br> <br> #### Dissolved --> 5% <br> #### As bicarbonate --> 80-90 % .pull-right[High concentration of carbonic anhydrase in red blood cells] <br> #### Bound to heamoglobin --- # CO2 removal during ECMO <br> <br> <br> #### CO2 is dissolvable and diffusable -- ####CO2 transport does not rely on Hb saturation -- ####Complete removal of CO2 is possible with ECMO even with low flows (0.5-1.5 lt/min) -- ###Change pCO2 gradually! -- ## .red[CO2 removal depends on SWEEP GAS FLOW] --- class: middle, center # Question # 3  --- # .center[Take home messages] ### .red[What really matters is DO2 and DO2/VO2] #### Assess when DO2 is low! Don’t assume because pO2 is <8! #### If oxygenation is a problem assess: - Oxygenator performance - Recirculation - High VO2 - Low ECBF/CO (patient has a high CO) ####.red[DO2] during VV ecmo depends on .red[EC Blood Flow] (ratio with patient’s CO) and .red[Hb] #### Remember Vvecmo is hemodynamically .red[neutral] #### CO2 removal is .red[NOT] a problem during VV-ECMO #### CO2 removal is effective at low ECBF. #### CO2 removal depends on sweep gas flow. .red[Correct pCO2 slowly]! --- # Reading  #### .footnote[Bartlett RH. Physiology of Gas Exchange during ECMO for Respiratory Failure. Journal of Intensive Care Medicine. 2017] ---  #### .footnote[Bartlett RH. Physiology of extracorporeal gas exchange. Comprehensive Physiology. 2020;10(3):879–91. ] ---  --- # http://icuecmo.ca