Base Excess and Critical Care in the past

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

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

Acid Base (concept of neutrality) ____________________________________ p. N = [H+] = [OH-] (=neutrality) p. H = 6. 80 [H+] = [OH-] = 160 nmol/l = neutrality at 37 o. C p. H = 7. 40 [H+] = 40 nmol/l [OH-] = 640 nmol/l = Alkaline offset of 0. 6 p. H unit IHG 05

Acid Base (the simple model) ____________________________________ Extracellular fluid p. H = 6. 8 p. H = 7. 40 H+ Blood and extracellular fluid serve as sink for metabolic produced acids IHG 05

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

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

Acid Base (the Metabolic component II) ____________________________________ BASE EXCESS and the Acid Base nomogram Base excess was introduced by Ole Siggaard Andersenfor almost 50 years ago. While p. H and p. CO 2 are directly measured, the metabolic component, defined as Base excess, is calculated from p. H and p. CO 2 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

Acid Base (the Metabolic component III) ____________________________________ Can you go to a Pharmacy and buy a bottle of Base excess ? BASE EXCES S IHG 05

Acid Base (the Metabolic component IV) ____________________________________ The Van Slyke equation (= The equation for the CO 2 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 = p. H of plasma at 37 o. C d = base excess concentration in blood (mmol/l) (Scand J Clin lab Invest 1977: 37, Suppl 146: 15 -20) IHG 05

Acid Base (the acid-base status) ____________________________________ p. H: as a measure of the activity of free hydrogen ions. p. CO 2: as a measure of the respiratory component, the activity of free CO 2 in the blood. Base Excess: as a measure of the metabolic component, (the concentration of titratable hydrogen ion in the extracellular fluid). IHG 05

Acid Base (the acid-base status) IHG 05

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

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

Bicarbonate IHG 05

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

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

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. 000000040 M, he devised the scale of acid in terms of p. H, as the negative log of H+ ion activity. (1907) IHG 05