the meaning of acidosis by story
DESCRIPTION
Is base excess the new bicarb ? David Story's breakdown of an often complicated and confusing topic.TRANSCRIPT
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Dave StoryMBBS, MD, BMedSci, FANZCA
Professor and Chair of AnaesthesiaHead of Anaesthesia, Perioperative and Pain Medicine Unit (APPMU)
Melbourne Medical SchoolThe University of Melbourne
The Meaning of Acidosis?
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Conflict of Interest
I think I have no conflict of interest associated with this presentation
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The OED
Acid: from “acidus”, Latin: “sour” 1625
Boswell: “Rather an acid expression
of countenance”
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Definitions of acid
Like other definitions “sour” is still used today
in parallel with other acid definitions
Depends on context
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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, 2002Miller’s Anesthesia
H+ / HCO3
CO2
SID
Weak acids
Kw + Ka
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Definitions of acid
Faraday, 1830s
English electrochemist,
-metal ions (sodium): base forming
-ions like chloride: acid forming
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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
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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
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Henderson and Hasselbalch
Henderson, 1908Boston Physician
H+ = Ka X [H2CO3] [NaHCO3]
Henderson, Am J Phys, 1908
Hasselbalch, 1916Danish gentleman farmer and chemist
pH = pKa + log [HCO3-]
pCO2
Astrup and Severinghaus, The history of blood gasses, acids and bases. 1986
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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
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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
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The rise of bicarbonateThe 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
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Intensive Care born 1952
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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 componentwww.osa.suite.dk
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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
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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
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Peter Stewart 1921-1993Canadian physiologist working in USA
Stewart. Can J Physiol Pharmacol 1983
Acid base chemistry:“…piecemeal, qualitative, confusing…”
Returned to Arrhenius, Naunyn, Van Slyke QUANTITATIVEUsed principles of chemistry:
electroneutrality conservation of massdissociation of electrolytes
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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, 2002Miller’s Anesthesia
H+ / HCO3
CO2
SID
Weak acids
Kw + Ka
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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/
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Fencl
Boston based Physician
Originally suggested dividing base-excess into effects of:
• Sodium• Chloride• Albumin• Unmeasured ions
Gilfix J Crit Care 1993
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FiggeBoston 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-Fenclwww.acid-base.org
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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
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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
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Simplify
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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
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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
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How will clinical acid-base evolve?
• Readily understood• Clinically useful• Quantifiable• Identifiable• Modifiable
Try different approaches in
YOUR clinical practice!
But, in my view…
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Rules-of-thumb
The Neanderthals
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Base-excess
The “sapiens”
way forward
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But can the US cope?
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…and add Stewart!
Thank you !!