Story, David — The Meaning of Acidosis
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Story, David — The Meaning of Acidosis

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Story, David — The Meaning of Acidosis Story, David — The Meaning of Acidosis Presentation Transcript

  • Dave Story MBBS, MD, BMedSci, FANZCA Professor and Chair of Anaesthesia Head of Anaesthesia, Perioperative and Pain Medicine Unit (APPMU) Melbourne Medical School The University of Melbourne The Meaning of Acidosis?
  • Conflict of Interest I think I have no conflict of interest associated with this presentation
  • The OED Acid: from “acidus”, Latin: “sour” 1625 Boswell: “Rather an acid expression of countenance”
  • Definitions of acid Like other definitions “sour” is still used today in parallel with other acid definitions Depends on context
  • Strong ion acidosis- Stewart Bicarbonate and hydrogen ions dependent factors Bicarbonate is a marker not a mechanism Base-excess is a marker Sirker et al. Anaesthesia, 2002 Miller’s Anesthesia H+ / HCO3 CO2 SID Weak acids Kw + Ka
  • Definitions of acid Faraday, 1830s English electrochemist, -metal ions (sodium): base forming -ions like chloride: acid forming
  • Definitions of acid Arrhenius, 1870s Swedish Chemist • Electrolytic theory for ions (Almost failed PhD but later Nobel Prize) • First suggested CO2 greenhouse effect General acid definition: Substance that increases [H+] when added to a solution
  • The next step Naunyn, 1890s German Diabetes physician Combined Arrhenius definition of acid with Faraday’s ideas: plasma acid-base status partly determined by electrolytes -particularly sodium and chloride
  • Henderson and Hasselbalch Henderson, 1908 Boston Physician H+ = Ka X [H2CO3] [NaHCO3] Henderson, Am J Phys, 1908 Hasselbalch, 1916 Danish gentleman farmer and chemist pH = pKa + log [HCO3 -]  pCO2 Astrup and Severinghaus, The history of blood gasses, acids and bases. 1986
  • Van Slyke US Clinical Chemist 1910 -1960s “... the roles played…anions other than bicarbonate, and by the cations, in determining the acid-base balance and the bicarbonate content of the blood.” Peters and Van Slyke, Quantitative Clinical Chemistry 1935
  • Bicarbonate and carbon dioxide Henderson and Hasselbalch (before 1920) knew challenge: To assess effects of disease on bicarbonate, must account for effects on carbon dioxide: Isolate non-respiratory effects
  • The rise of bicarbonate The Modern Way in 1950s Calculate bicarbonate using Henderson-Hasselbalch equation: Measure pH, pCO2 + know constants pH = pKa + log [HCO3 -]  pCO2 Carbonic acid true Bronstead-Lowry acid Describe plasma pH ([H+]) with two measurable variables Simple maths (B.C. - before calculators) CO2 and bicarbonate = meaning of life, the universe, and everything Christensen, Am J Med 1957
  • Intensive Care born 1952
  • Bicarbonate and carbon dioxide (again) Siggaard-Andersen, Denmark, 1960s onward Base Excess = amount of acid (mmol/l) added to return blood to pH 7.40 after equilibration with pCO2 of 40 mmHg at 37oC Quantify change in non-respiratory component www.osa.suite.dk
  • But… Schwarz and Relman, NEJM 1963 Boston Physicians Found flaws in (original) base-excess: ABE CO2 and bicarb “rules-of-thumb” and “The Great Trans-Atlantic Acid-Base Debate” Bunker, Anesthesiology, 1965
  • Then we have… Siggaard-Andersen (fights back) -Altered the “buffering” component “Standard base-excess” -Gained support form Severinghaus (US) Severinghaus, Am J Respir Crit Care Med, 1998
  • Peter Stewart 1921-1993 Canadian physiologist working in USA Stewart. Can J Physiol Pharmacol 1983 Acid base chemistry: “…piecemeal, qualitative, confusing…” Returned to Arrhenius, Naunyn, Van Slyke QUANTITATIVE Used principles of chemistry: electroneutrality conservation of mass dissociation of electrolytes
  • Strong ion acidosis- Stewart Bicarbonate and hydrogen ions dependent factors Bicarbonate is a marker not a mechanism Base-excess is a marker Sirker et al. Anaesthesia, 2002 Miller’s Anesthesia H+ / HCO3 CO2 SID Weak acids Kw + Ka
  • The Gamblegram Gamble , 1950s - chloride = acid - Gamblegram - important aid to Stewart Gamble, Chemical Anatomy, Physiology and Pathology of Extracellular Fluid 1954 Watson: www.ppn.med.sc.edu/watson/Acidbase/
  • Fencl Boston based Physician Originally suggested dividing base-excess into effects of: • Sodium • Chloride • Albumin • Unmeasured ions Gilfix J Crit Care 1993
  • Figge Boston Physician -quantified the base-excess effect of albumin Complex version Albumin effect (mmol/L) = (0.123pH- 0.631) X [42-albumin (g/l)]. Simple version: Albumin effect (meq/L) = 0.25 X (42-Albumin) Figge, Crit Care Med 1998 Value for anion gap increasingly understood (even by Boston Physicians) Fencl-Stewart = Figge-Fencl www.acid-base.org
  • Kellum and the SIG (NOT) Boston physician Strong ion gap: Sum of all measured strong ions, and weak anions albumin, phosphate, bicarbonate “anion-gap” on steroids Kellum J Crit Care 1995 Net unmeasured ions Lloyd, Crit Care Resus, 2005
  • Then I came along… 1. SBE = overall metabolic effect 2. Principal SID = Na – Cl (simplify Fencl), 140 – 102 = 38 (35) 3. Principal Weak acid = albumin (use simple Figge), 4. Rest = other ions SBE = NaCl efffect + Albumin Effect + Other ion effect For bedside use, not for the OCD Not a Boston Physician
  • Simplify
  • In 2014 add lactate… Plasma lactate now routinely measured SBE = NaCl Effect + Albumin Effect + Lactate Ion Effect + Other Ions Lactate is a strong anion so effect on SBE = negative [lactate] Median Reference Range = 1 mmol/L (ie when SBE = 0) SBE effect = 1 – lactate, mmol/L Eg Lactate ion effect of lactate of 4 mmol/L = - 3 mmol/L Story, Anesthesia and Analgesia, 2006
  • SBE = NaCl + Albumin + Lactate + OI 78 yr old female with AAA post op Na = 142, Cl = 110, Albumin = 26, Lactate = 6, SBE = - 8 mmol/L NaCl effect = 142 - 110 - 38 = - 6 mmol/l Albumin effect = 0.25 x (42-26) = 0.25 x (16) = 4 mmol/l Lactate effect = 1 - 6 mmol/L = -5 mmol/L Other ions = SBE – NaCl effect – Albumin – Lactate OI = -8 – (-6) - 4 – (-5) = - 1 mmol/L
  • How will clinical acid-base evolve? • Readily understood • Clinically useful • Quantifiable • Identifiable • Modifiable Try different approaches in YOUR clinical practice! But, in my view…
  • Rules-of-thumb The Neanderthals
  • Base-excess The “sapiens” way forward
  • But can the US cope?
  • …and add Stewart! Thank you !!