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Base Excess and Critical Care in the past and in the future

Base Excess and Critical Care in the past and in the future. Ivar Hejde Gøthgen M.D., D.M.Sc. Content. Acid-base basic Scientist in the acid-base story Instruments in the acid-base story The future and Base excess.

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Base Excess and Critical Care in the past and in the future

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  1. Base Excess and Critical Care in the past and in the future Ivar Hejde Gøthgen M.D., D.M.Sc. IHG 05

  2. Content • Acid-base basic • Scientist in the acid-base story • Instruments in the acid-base story • The future and Base excess IHG 05

  3. Acid Base (concept of neutrality)_______________________________________________________________________ pN = [H+] = [OH-] (=neutrality) pH = 6.80 [H+] = [OH-] = 160 nmol/l = neutrality at 37 oC pH = 7.40 [H+] = 40 nmol/l [OH-] = 640 nmol/l = Alkaline offset of 0.6 pH unit IHG 05

  4. Acid Base (the simple model)_______________________________________________________________________ Extracellular fluid pH = 7.40 pH = 6.8 H+ Blood and extracellular fluid serve as sink for metabolic produced acids IHG 05

  5. Acid Base (the acid production)_______________________________________________________________________ Fixed Acids production [H+] : 60 mmol/24 hour => 700 nmol/sec Volatile Acids production [H+] : 13 mol/24 hour => 150000 nmol/sec > 200 times the fixed acids Total extracellular free [H+] : 40 nmol/l * 15 l => 600 nmol IHG 05

  6. Acid Base(the Metabolic component I )_______________________________________________________________________ Buffer Base 50 mmol/l Buffer base = H+ acceptors_____________________________ Red cell Hemoglobin 35% Red cell Bicarbonate 18% Plasma Bicarbonate 35% Plasma Proteins 7% Others (Phosphate ect.) 5% IHG 05

  7. Acid Base (the Metabolic component II)_______________________________________________________________________ BASE EXCESS and the Acid-Base nomogram Base excess was introduced by Ole Siggaard­Andersen for almost 50 years ago. While pH and pCO2 are directly measured, the metabolic component, defined as Base excess, is calculated from pH and pCO2 using the Henderson-Hasselbalch equation and the Van Slyke equation. By using base excess the acid base status is made simple and clinical useful. IHG 05

  8. Acid Base (the Metabolic component III)_______________________________________________________________________ Can you go to a Pharmacy and buy a bottle of Base excess ? BASE EXCESS IHG 05

  9. Acid Base (the Metabolic component IV)_______________________________________________________________________ The Van Slyke equation (= The equation for the CO2 equilibration curve of blood in vitro) a-24.4 = -(2.3*b+7.7)*(c-7.40)+d/(1-0.023*b) where: a = bicarbonate concentration in plasma (mmol/l) b = hemoglobin concentration in blood (mmol/l) c = pH of plasma at 37 oC d = base excess concentration in blood (mmol/l) (Scand J Clin lab Invest 1977:37,Suppl 146:15-20) IHG 05

  10. Acid Base (the acid-base status)_______________________________________________________________________ pH: as a measure of the activity of free hydrogen ions. pCO2: as a measure of the respiratory component, the activity of free CO2 in the blood. Base Excess: as a measure of the metabolic component, (the concentration of titratable hydrogen ion in the extracellular fluid). IHG 05

  11. Acid Base (the acid-base status) IHG 05

  12. Acid Base (the acid-base status) Respiratory changes along The bufferlines IHG 05

  13. Acid Base (the acid-base status) Metabolic changes across The bufferlines IHG 05

  14. Bicarbonate IHG 05

  15. Content • Acid-base basic • Scientist in the acid-base story • Instruments in the acid-base story • The future and Base excess IHG 05

  16. Scientist in the acid-base story S.P.L. Sørensen 1868-1939 L.J. Henderson 1878-1942 K.A. Hasselbalch 1874-1962 Donald D van Slyke 1883-1971 Poul Astrup 1915-2000 John W. Severinghaus 1922- Ole Siggaard-Andersen 1932- IHG 05

  17. Scientist in the acid-base story Søren P. L. Sørensen 1868-1939 Protein Chemist at the Carlsberg brewery. To save having to write that H+ = 0.000000040M, he devised the scale of acid in terms of pH, as the negative log of H+ ion activity. (1907) IHG 05

  18. Scientist in the acid-base story IHG 05

  19. Scientist in the acid-base story Lawrence J Henderson Prof Biochemistry and Physiology. Theory of buffering and of bicarbonate-hydrogen ion-pCO2 relationship. The Henderson equation K = [H+][HCO3-]/[H2CO3] K is the dissociation constant of carbonic acid, about 10-3 M A constant 0.1% of dissolved CO2 in water is hydrated to carbonic acid. Therefore it can be simplified to H2CO3 = dissolved CO2 Where K’ is the apparent dissociation constant K’ = 10-6.1 IHG 05

  20. Scientist in the acid-base story IHG 05

  21. Scientist in the acid-base story Karl A Hasselbalch 1874-1962 Agricultural chemist, Denmark. Adapted Henderson’s equation to Sørensen’s logarithmic pH by replacing H2CO3 with S.pCO2 creating the Henderson-Hasselbalch equation: pH=pK’ + log[HCO3-/(S.pCO2)] 7.40 = 6.10 + log[24/{0.31.40}] Where S (solubility) = 0.031 mM/liter/mmHg at 37oC IHG 05

  22. Scientist in the acid-base story IHG 05

  23. Scientist in the acid-base story Donald D Van Slyke 1883-1971 Major developer of clinical chemistry in the 1910-50 period. His manometric blood gas apparatus (1924) was used to measure the content in blood of oxygen, carbon dioxide and many other variables. Laboratories calculated pCO2 using the Henderson-Hasselbalch equation after measuring pH of blood and the total plasma CO2 by the Van Slyke apparatus until the polio epidemics resulted in two new methods: Astrup’s equilibration scheme and Severinghaus modification of the Stow CO2 electrode. IHG 05

  24. Scientist in the acid-base story IHG 05

  25. Scientist in the acid-base story Poul Astrup1915-2000 Prof of Clinical Chemistry Univ. of Copenhagen New method for pCO2 To avoid need for the VanSlyke and Henderson-Hasselbalch method, he devised a method for graphically calculating pCO2 by measuring pH before and again after equilibration of the blood to a known pCO2 IHG 05

  26. Scientist in the acid-base story IHG 05

  27. Scientist in the acid-base story John W Severinghaus 1922 Prof of Anestesia University of California San Francisco Major developer of blood gas measurents since 1950. His modification (invention) of the CO2 electrode, the first blood gas apparatus (1958), the blood gas ruler, transcutaneous blood gas measurement and pulsoximetry, as well as important work in high altitude respiratory physiology IHG 05

  28. Scientist in the acid-base story IHG 05

  29. Scientist in the acid-base story Ole Siggaard Andersen 1932 Prof of Clinical Chemistry Univ. of Copenhagen A student of Astrup, he devised the micro-method and the concept of base excess and ECF base excess, now called SBE, for standard base excess. His equation for SBE is now used in most blood gas apparatus. Photo 1999 by JWS IHG 05

  30. Scientist in the acid-base story IHG 05

  31. Content • Acid-base basic • Scientist in the acid-base story • Instruments in the acid-base story • The future and Base excess IHG 05

  32. Instruments in the acid-base story First Astrup pH apparatus for equilibration of blood sample with known Pco2, then repeated pH measurement 1953 IHG 05

  33. Instruments in the acid-base story Micro-Astrup pH and reference electrodes, 1957 Radiometer Co, Copenhagen, Denmark The widely used Astrup equilibration method for estimating blood pCO2 by pH measurement before and after equilibration with gas of known pCO2. The glass pH capillary is “A”, filled by suction from “G”, and then connected to reference electrode “K” in saturated KCl “I”. IHG 05

  34. Instruments in the acid-base story First blood gas apparatus. Severinghaus and Bradley (1958) O2 electrode consumed so much oxygen it needed stirring and calibration with equilibrated blood. CO2 electrode tonometer stirrer O2 electrode IHG 05

  35. Instruments in the acid-base story ABL-1 IHG 05

  36. Instruments in the acid-base story BMS-2 , OSM-3 and ABL-4 ( incl. Ole Siggaard-Andersen at work) IHG 05

  37. Instruments in the acid-base story ABL-700 IHG 05

  38. Critical care treatment and the acid-base story Polio victim in Copenhagen epidemic being ventilated manually by medical student through tracheostomy, 1952. Invasive ventilation IHG 05

  39. Critical care treatment and the acid-base story Non-invasive ventilation in Critical Care around 1955 IHG 05

  40. Critical care treatment and the acid-base story To put a patient into a ventilator IHG 05

  41. Critical care treatment and the acid-base story Invasive ventilation in Critical Care in 2003 IHG 05

  42. Content • Acid-base basic • Scientist in the acid-base story • Instruments in the acid-base story • The future and Base excess IHG 05

  43. The future and Base excess Acid-Base status and Normal Saline versus Lactated Ringer’s solution ? IHG 05

  44. The future and Base excess IHG 05

  45. The future and Base excess IHG 05

  46. The future and Base excess IHG 05

  47. The future and Base excess • How to interpret the difference in Acid Base Status after • Infusion of Normal Saline and Lactated Ringer’s Solution: • - Dilutional Acidosisversus HyperChloremic Acidosis • - Brønsted’s definition versus Arrhenius definition • Buffer Base (BB) versus Strong Ion Difference (SID) • When adding Lactate and Chloride measument, the interpretation of acid base status may be simple and illustrates that • - Buffer base equals SID • as well as • - Changes in Buffer Base equals Base Excess IHG 05

  48. The future and Base excess Electrolyte balance of arterial plasma showing columns of cations and anions of equal height (law of electro-neutrality). The equality of the strong ion difference (SID) and buffer base (BB) is illustrated. The change in concentration of buffer base from normal (at pH = 7.40, pCO2 = 5.3 kPa, and T = 37 C) with opposite sign equals the concentration of titratable hydrogen ion. IHG 05 (O. Siggaard-Andersen in Encylopedia of Respiratory Medicine 2006)

  49. The future and Base excess Base Excess is a virtual parameter, making some very complex matter simple and clinical useful Base Excess may continue to exist as the metabolic parameter in Acid-Base status IHG 05

  50. Thanks to John W Severinghaus for his kind advice and help Reykjavik june 2005 Thanks to Ole Siggaard-Andersen for his kind advice and help IHG 05 Gilleleje 2003

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