Different Interpretation Approaches To Acid Base -
Transcript of Different Interpretation Approaches To Acid Base -
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Different Interpretation Approaches To Acid BaseDisturbances
Mohamad Atef Radwan
April 27, 2011
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In The Name Of ALLAH
Mohamad Atef Radwan Different Interpretation Approaches To Acid Base Disturbances
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Introduction
”If anyone killed a person not in retaliation of
murder, or (and) to spread mischief in the land - it
would be as if he killed all mankind, and if anyone
saved a life, it would be as if he saved the life of all
mankind”
Al-Maidah-32
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Objectives
Understanding basic concept of pH, and Hydrogen ion activity.
Understanding different definitions of acidosis, alkalosis.
Development of traditional approach using combination ofHenderson-Haselblach equation, the base excess and its clinicalapplication.
Development of Stewart approach, its mathematical concept and itsclinical application.
Unification of acid-base physiology.
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Introduction
The body produces more acids than bases (food, protein, lipidmetabolism,.... ).
Its critical to keep hydrogen ion concentration in certain range.
Management of Acidbase disorders begins with accurate diagnosis.
Main organs responsible for controlling hydrogen ion concentration arelungs, kidney, GIT, liver.
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Traditional Approach
Boston School ”Henderson-Hasselbalch”
Copenhagen School ”Base Excess”
Acid And Base
Acid: Proton donor
Base: Proton acceptor
pH: Negative logarithm of hydrogen ion concentration
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Boston School
Henderson-Hasselbalch equation
pH = 6.1 + log10[HCO−3 ]
0.03× PaCO2
Described six primary states of acid-base imbalance
Chronic/Acute respiratory acidosis
Chronic/Acute respiratory alkalosis
Metabolic Acidosis
Metabolic Alkalosis
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Winters Rules
Rules established interrelationships among the degree of primary reductionof the metabolic component
The clinical question the rules are designed to answer in this situation is,”whether the patients respiratory compensation is within the range tobe expected or whether there is an additional component of respiratorydisturbance, too”
Winter Equation
PCO2 = 1.54× [HCO−3 ] + 8± 2
Albert MS, Dell RB, Winters RW. Quantitative displacement of acid-base equilibrium in metabolic acidosis. Ann. Intern.
Med. 1967 Feb;66(2):312-322.
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Anion Gap
The term anion gap (AG) represents theconcentration of all the unmeasuredanions in the plasma.
Na+−(Cl−+HCO3−) = UA−UC = AnionGap
Value : 10 to 12 mEq/L
Help differentiate between causes of ametabolic acidosis: high anion gap versusnormal anion gap.
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Copenhagen Approach
Acid-base disorders are classified as being of respiratory origin (primary changein PaCO2) or of metabolic origin (primary change in fixed acids). Some basicquestions to be answered by any approach are:
How can the magnitude of a respiratory disorder be determined?
How can the magnitude of a metabolic disorder be determined?
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Van Slyke
Henderson persuaded his friend Van Slyke to placehis equation on quantitative footing.
Van Slyke realized that the plot of log PaCO2 VsPlasma pH was Linear.
By adding known amount of acid or base andreading value of pH vs log PaCO2, A line of ”nonrespiratory pH” could be obtained which wasknown as ”base excess”.
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Siggaard-Andersen Nomogram
1960,Ole Siggard Anderson 25 year old, rotating intern, helped to produce analignment nomogram relating PaCO2 and pH to base Excess
Point A : measured pH at high PaCO2
Point B : measured pH at low PaCO2
Point F : actual pH of the anaerobicallydrawn blood and allows the calculation ofthe actual PaCO2.
Point C : the BE ”Base Excess”
Point D : the Buffer Base
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BE
Definition
The miliequivalents of strong acid or bases that is needed to titrate one liters(in vitro) of blood or plasma
Has been equlibrated to PaCO2 = 40 mmHg
At physiological pH of 7.4
At temperature 37 C
Full O2 saturation
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BE & SBE
By using the previous informations Siggard Andersonproduced formula for calculating BE as re-expressionof data and called it ”Van Slyke equation”
BE
Base excess = 0.93×([
HCO−3]− 24.4 + 14.8× (pH − 7.4)
)SBE
SBE = 0.9287× (HCO−3 − 24.4 + 14.83× ([pH − 7.4]))
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Base excess using computing methods.
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Algorithm
Anticipate the acid base disturbance from the causes and history that mayhave effect.
Check pH, PaCO2, HCO3, If one of these are abnormal:Check pH
If pH less than 7.4, the primary disorder is acidosisIf pH more than or equal 7.4, The primary disorder is alkalosis
Metabolic Or RespiratoryIf HCO3− is responsible for changing the pH , the cause is MetabolicIf PaCO2 is responsible for changing pH, the cause is Respiratory
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Algorithm Cont.
Check pH acceptance (pH range from 7.3 to 7.5):In respiratory disorder
If pH is accepted, it is chronic respiratory disorder
If pH is Unaccepted, it is acute respiratory disorder
In metabolic disorderAccepted pH , indicates compensated metabolic disorder
Unaccepted pH, without change in PaCO2 indicates uncompensated metabolic disorder
Unaccepted pH, with change in PaCO2 indicates partially compensated metabolic
disorder
Check appropriateness using winter rules (for diagnosis of Mixed disorder)
Further analysis for specific disorders:
In Metabolic acidosis, calculate Anion Gap
In metabolic alkalosis, check chloride in urine.
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Stewart Approach
What is the role of bicarbonate inacid-base balance?
The answer is simply:
None!
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Stewart Approach
Quantitative analysis of pH deviation
How much each element of acid base controllersubstances will affect pH deviation
Variables
Independent variables (PaCO2, SID, ATOT )
Dependent variables (pH, H, HCO3−,......)
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Mathematical Concept Of Stewart Approach
The Simplest Acid-Base System : Pure water
[H2O]⇐⇒ H+ + OH−
[H+]x[OH−] = KW × [H2O]
As KW is highly temperature dependent and very small
K ′W = KW × [H2O]
[H+]× [OH] = K ′W
H+ − OH− = 0
H+ = OH−
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Mathematical Concept Of Stewart Approach
Cont.[H+]× [H+] = K ′W
[H+] =√
K ′W
[OH−] =√
K ′W
The following definitions were introduced :
1 Solution is acid-base neutral if the hydrogen ionconcentration is equal to the square root of the K ′W .
2 A solution is acidic if [H+] >√
(K ′W )
3 A solution is basic if [H+] <√
(K ′W )
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Strong Ion Difference ”SID”
Adding specified amount of NaCl to Water [H2O],so solution will only contain Na+,Cl−,H+ AndOH−
By application of electrical neutrality:
Na+ − Cl− + H+ − OH− = 0
[H]× [OH−] = K ′W
By substitution of OH− by [K ′W ]/[H]
H+ − (K ′W /H+) + Na+ − Cl− = 0
By multiplying the previous equation by H+ andrearrangement
[H+]2 + [H+]([Na+]− [Cl−])− K ′W = 0
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SID Cont.
ax2 + bx + c = 0
the quadratic equation can by solved as
[H+] = −([Na+]−[Cl−])2 +
√(([Na+]− [Cl−])2/4 + K ′W )
SID
[H+] =√
(K ′W + SID2/4)− SID/2
And by application to OH−
[OH−] =√
(K ′W + SID2/4) + SID/2
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SID Cont.
Reproduced from original Stewart textbook using JAVA programming language and Gnuplot
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SID
Strong Ion Difference
”The sum of all strong base cation concentration minus the sum of all stronganion concentration, all expressed in equivalents per Liter.”
SID = (∑
StrongBaseCation)− (∑
StrongAcidAnions)
Sodium minus Chloride = 40-42
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SID Cont.
What is really happening ???
Adding HCL to water ??Traditionaly : H+ ion was added .., so solutionbecame more acidic .Stewart : Cl− was added, SID decreased , so solutionbecame more acidic .
Why !!
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Adding Weak Acid
Weak electrolytes
Substance that partially dissociate when dissolved in water, i.e the moleculesof parent substance as well as the product of dissociation will exist .
Weak acid solution contains molecular species [HA] and [A−].
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ATOT
Weak acid dissociationHA⇐⇒ H+ + A−
Water dissociation
[H+]× [OH−] = K ′W
Weak acid dissociation
[H+]× [A−] = KA × [HA]
Weak acid conversion
[HA] + [A−] = [ATOT ]
For achieving electrical neutrality
[H+] + [OH−] + [SID] + [A−] = 0
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ATOT
Cubic equation like
f (x) = ax3 + bx2 + cx + d
[H+]3 + KA + [SID]× [H+]2 + KA
×([SID]− [ATOT ])− K ′W × [H+]− KA × K ′W = 0
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pH VS SID plus ATOT
Reproduced from original Stewart textbook using JAVA programming language and Gnuplot
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pH VS SID plus ATOT
Reproduced from original Stewart textbook using JAVA programming language and Gnuplot
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SID plus CO2
[SID] + [H+]− [OH−]− [HCO−3 ]− [CO−23 ] = 0
by substituting and clearing, cubic equation like syntax will be produced
H3 + [SID]× H2 − (KC x PC + K ′W )× H − K3 x KC x PC = 0
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SID + CO2
Reproduced from original Stewart textbook using JAVA programming language and Gnuplot
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SID + ATOT + CO2
SID + H+ + HCO−3 − A− − CO−23 − OH− = 0
H4 + KA + SID ∗ H3 + KA × (SID)− ATOT )
- (KC ×PC + K ′W ) ∗H2−KA × (KC × PC + K ′W + K3
×KC × PC × H − KA × K3 × KC × PC = 0
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Full Picture
Acid-base Balance :is set of mechanisms by which parts of the body, notablylungs, kidneys, and gastrointestinal track, control thecomposition of circulating blood plasma, so its H+ liesgenerally within range from 2× 10−7 to 1× 10−7 Eq/L orpH 7.7 to 7.0
Regulators
Lung
Kidney
GIT
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Lungs
::::::
CO2 regulator
::::::
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Lungs Cont.
Alveolar ventilation could be changes inseconds.
Elevation of CO2 level lead to elevation of H+
value ”Respiratory Acidosis”.
Decrease of CO2 level lead to decrease of H+
value ”Respiratory Alkalosis”.
Sustained change in CO2 level leads to changeof SID Value. Role which is played by thekidneys.
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Kidney
SID=(Na++K+)-Cl−
1 Circulating plasma is perfusing the kidneys atan average rate of about 500 mL/min.
2 Every Cl− filtered but not reabsorbed meanscorresponding increase in plasma SID.
3 Every Na+ or K+ not reabsorbed means adecrease in plasma SID.
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Kidney
SID=(Na++K+)-Cl−
Sustained change of PaCO2 level
1 Acute Respiratory Acidosis = PaCO2 upbriefly, so plasma H+ is up
2 Acute Respiratory Alkalosis = PaCO2 downbriefly, so plasma H+ is down
3 Chronic Respiratory Acidosis = PaCO2 up”sustained” , SID up ,H+ up slightly
4 Chronic Respiratory Alaklosis = PaCO2 down”sustained”, SID down, H+ down slightly
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GIT
Cl− is removed from the plasma circulating throughthe gastric mucosa and secreting into the lumen asgastric acid.
SID in the plasma is increasing (Na+-Cl−).
that effect on total circulating plasma is small, butdetectable, the classic name for this phenomena is(Alkaline tide).
Disturbance:
transferred Cl− is lost from body and never returned to plasma.
Plasma SID is elevated.
Decrease of H+ ”Rise in pH”.
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Figge and Fencl
Figge and Fencl concentrated in their work on major species of weak acid andtheir conjugate base.
Weak acids
phosphoric acid (phosphate system)
Citric acid (citrate system)
Dissociatable amino acid side chain of albumin
Fencl Model
pH = f(pH){SID,PCO2, [PiTOT ], [Albumin], [CitrateTOT ]}
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Figge and Fencl. Cont.
Important values to be caculated
SID And ATOT
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ATOT
Albumin & Phosphorus participation :
[Alb] = [Alb]× (0.123× pH − 0.631)
[Pi ] = [Pi ]× (0.309× pH − 0.469)
New SID : SIDe
SID = [HCO3−] + [Alb] + [Pi ]
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SID
Electrical neutrality
Na++K++Ca+2+Mg+2 =HCO3−+Alb−+Pi−+Cl−+XA−
SIDa
SIDa=Na++K++Ca+2+Mg+2-Cl−
XA−
XA−=SIDa-SIDe=SIG
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Classification of disturbances
FENCL V, JABOR A, KAZDA A, FIGGE J. Diagnosis of Metabolic Acid-Base Disturbances in Critically Ill Patients. Am. J. Respir. Crit. Care Med.2000 Dec 1;162(6):2246-2251.
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Algorithm
Check history for detecting expected acid base deviation
The following data are required for interpretation
Na+,Cl−,K +,Albumin,PCO2
Calculate corrected chloride ”Corrected Cl” for assessment of volumestatus incorporation in acid base status
Corrected Cl− = Observed Cl− × (Normal Na+/Observed Na+)
Calculate apparent SID ”SIDa”
SIDa = (Na+ + K + + 6)− Cl−
(6) = value for presentation of Ca+2 and Mg+2 value ”provided theyare normal”
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Algorithm Cont.
Calculated effective SID ”SIDe”
SIDe = HCO3− + 2.8× Albumin in g/dL + 2
(2) in SIDe equation for substitution of phosphorus [Pi] value as it notroutinely measured
HCO3− usually measured by arterial blood gas machine or it could becalculated using Hasselbalch equation
Calculate strong ion gap (SIG) or effect exerted by unknown anions”XA−”
SIG = XA− effect = SIDa − SIDe
Make comparison for calculated data to its reference range
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Stewart application using computing method
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Stewart application using computing method
Mohamad Atef Radwan Different Interpretation Approaches To Acid Base Disturbances
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Stewart application using computing method
Mohamad Atef Radwan Different Interpretation Approaches To Acid Base Disturbances
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Stewart application using computing method
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Summay
It was long way for achieving accurate interpretation of acid basedisorders.
Story started since 100 year ago by Handerson-Haselblach Equation .
Later Boston school tried to classify different disorder as respiratory andmetabolic.
BE approach concentrated on metabolic element, Introduced BE andBuffer base definitions .
80s, Stewart presented his radical theory for explaining disturbances .
For rapid interpretation traditional approach may be used, for moredetailed interpretation quantitative approach could be used .
Mohamad Atef Radwan Different Interpretation Approaches To Acid Base Disturbances
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Idea From acidbase.org
Mohamad Atef Radwan Different Interpretation Approaches To Acid Base Disturbances
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Mohamad Atef Radwan Different Interpretation Approaches To Acid Base Disturbances