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

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Presentation on theme: "Base Excess and Critical Care in the past and in the future"— Presentation transcript:

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 = 6.8 pH = 7.40 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 => 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 % 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/( *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 Ole Siggaard-Andersen 1932-
Scientist in the acid-base story S.P.L. Sørensen L.J. Henderson K.A. Hasselbalch Donald D van Slyke Poul Astrup John W. Severinghaus 1922- Ole Siggaard-Andersen 1932- IHG 05

17 Søren P. L. Sørensen 1868-1939 Scientist in the acid-base story
Protein Chemist at the Carlsberg brewery. To save having to write that H+ = M, 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 Lawrence J Henderson Scientist in the acid-base story
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’ = IHG 05

20 Scientist in the acid-base story
IHG 05

21 pH=pK’ + log[HCO3-/(S.pCO2)] 7.40 = 6.10 + log[24/{0.31.40}]
Scientist in the acid-base story Karl A Hasselbalch 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 = log[24/{ }] Where S (solubility) = mM/liter/mmHg at 37oC IHG 05

22 Scientist in the acid-base story
IHG 05

23 Donald D Van Slyke Scientist in the acid-base story
Major developer of clinical chemistry in the 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 Prof of Clinical Chemistry Univ. of Copenhagen
Scientist in the acid-base story Poul Astrup 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 John W Severinghaus Scientist in the acid-base story 1922
Prof of Anestesia University of California San Francisco Major developer of blood gas measurents since 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 Micro-Astrup pH and reference electrodes, 1957
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 First blood gas apparatus. Severinghaus and Bradley (1958)
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 How to interpret the difference in Acid Base Status after
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 Acidosis versus 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 Gilleleje 2003 IHG 05

51 Advice from your brain and body: ”Use me or loose me”
IHG 05


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