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F. Rashid Farokhi Nephrologist Masih Daneshvari Hospital
ACID base disorders F. Rashid Farokhi Nephrologist Masih Daneshvari Hospital
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Extra cellular fluid H+ concentration
[H +] = 40 meq/lit = 40 Eq/lit PH = - log [H+] PH = - 6 - 9 meq - 7
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6.8 7.35 7.4 7.45 7.8 Arterial PH
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How can the body regulate H+ concentration in such a low concentration despite of
Daily production of meq CO2 Daily production of meq nonviolate acids Entrance of exogenous acids ?
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circulation CO2 +H2O H+ + HCO3-
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HPhosphate- H+ + phosphate -
Buffering systems H2CO H+ + HCO3- H2PO H+ +H PO4 2- HAlb H+ + Alb- HHgb H+ + Hgb - HProt H+ + Prot – HPhosphate H+ + phosphate -
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K1[CO2] K2[Halb] K3[H2PO4-] Kn[HA] [HCO3-] [alb-] [HPO4-2] [A-]
H2CO H+ + HCO3 – V1 [H2CO3] H+ + HCO H2CO3 V2 [H+] [HCO3-] V1 =V2 [H2CO3] [H+] [HCO3-] [H+] [HCO3-] [H2CO3] K1[CO2] K2[Halb] K3[H2PO4-] Kn[HA] [HCO3-] [alb-] [HPO4-2] [A-] = K [H+] = = = =
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BB= 12.2 × PCO2/( ) + [Albumin] ×(0.123×PH ) + [PO4]}×(0.309× PH-0.469) -PH
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H20 + CO2 H2CO3 H+ + HCO3- [CO2] [H+] = K × [HCO3-] PCO2 × 0.03
= 24 × [HCO3-]
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Example 1: PH=7.50 , HCO3 =28 , PCO2=40 PCO2 [H+] = 24 × [HCO3-] 40
? = 24 × [HCO3-]
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[H+] =24× [ HCO3-] [H+] PH 40 1.25 1.25 1.25 = 80 7.1
PCO2 [ HCO3-] [H+] PH 40 1.25 1.25 1.25 = 40 1.25 1.25 = 40 1.25 = 40 0.8 = 40 0.8 0.8 = 40 0.8 0.8 0.8 = [H+] =24×
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PH=7.50 , HCO3 = , PCO2=40 PCO2 [H+] = 24 × [HCO3-] 40 32 = 24 × 30
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The effect of respiratory system on acid base balance
C6H12O CO2 +6H2O CO2 + H2O H2CO H+ + HCO3-
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Proximal tube NaHCO3 OH- H+ Na+ H+ Proxoimal tubule CO2 + H20 HCO3 +
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Distal tubules H+ + HCO3- H2O + CO2 + A- HA H+ + A- HA H+ H+ CO2 OH-
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Acid base disorders
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What is the difference between acidemia and acidosis, alkalemia and alkalosis?
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PH = 6.1+ log {HCO3- / [0.03 x PCO2]}
Metabolic acidosis HCO3 Respiratory Acidosis PCO2 PH = log {HCO3- / [0.03 x PCO2]} Acidemia PH
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PH = 6.1+ log {HCO3- / [0.03 x PCO2]}
Metabolic alkalosis HCO3 Respiratory Alkalosis PCO2 PH = log {HCO3- / [0.03 x PCO2]} Alkalemia PH
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Respiratory compensation in metabolic acidosis
PH = log {HCO3- / [0.03 x PCO2]} Acidemia PH Metabolic acidosis HCO3 PCO2 = (1.5×Hco3) + 8 ± 2 Or 1.25 mmHg fall in the PCO2 for every 1 meq/lit reduction in the bicarbonate
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Respiratory compensation in metabolic alkalosis
PH = log {HCO3- / [0.03 x PCO2]} Alkalemia PH Metabolic alkalosis HCO3 PCO2 = HCO3 + 15 Or 0.75 mmHg rise in the PCO2 for every 1 meq/lit elevation in the bicarbonate
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PH = 6.1+ log {HCO3- / [0.03 x PCO2]}
Respiratory Acidosis PCO2 PH = log {HCO3- / [0.03 x PCO2]} Acidemia PH Acute: HCO3 rises 1 meq/lit for every 10 mmHg elevation in PCO2 Chronic: HCO3 rises 4 meq/lit for every 10 mmHg elevation in PCO2
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PH = 6.1+ log {HCO3- / [0.03 x PCO2]}
Respiratory Alkaloosis PCO2 PH = log {HCO3- / [0.03 x PCO2]} Alkalemia PH Acute: HCO3 falls by 2 meq/lit for every 10 mmHg decline in PCO2 Chronic: HCO3 falls by 4 meq/lit for every 10 mmHg decline in PCO2
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Example 1: PH=7.50 , HCO3 = , PCO2=40 Mixed metabolic and respiratory alkalosis
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Examples 2: 1- PH =7.25 ,HCO3=12 , PCO2=25
compensated metabolic acidosis 2-PH=7.1 , HCO3 =12 , PCO2=30 mixed metabolic and respiratory acidosis
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Example 3: PH=7.35 , HCO3= 28 , PCO2=60 Acute respiratory acidosis + metabolic alkaosis Chronic respiratory acidosis +metabolic acidosis
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In a patient there is following arterial blood values:
PH=7.22 , PCO2 =70 , HCO3= 31 What is the acid base disorder?
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HCO3 can be measured by adding a powerful acid to serum:
HCO3- +H H20+CO2+CL × 41.7= = 19.151
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What are the problems with PCO2/HCO3 in evaluation of acid base condition
It can not determine the: Severity of metabolic disturbance can not be determined The etiology of acid base disorder
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anion gap in approach of metabolic acidosis
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All Anions = All cations Measured Anions +Unmeasured Anions
= Measured Cation +Unmeasured Cations M C – MA = UA - UC [Na+] – { [CL-] +[HCO3-] } = UA-UC = AG Anion gap should be corrected with albumin
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Example 4: A previously well 55 year old woman is admitted with a complaint of severe vomiting for 5 days. Physical examination reveals postural hypotension, tachycardia and diminished skin turgor. The laboratory findings include: PH=7.23 , PCO2 =22 , HCO3= 9 Na: 140, K: 3.4, Cl: 77, Cr: 2.1, Ketone: trace what is the metabolic disturbances?
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High anion gap metabolic acidosis
H+ + HCO H2O + CO2 + A- HA
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Hyperchloremic metabolic acidosis
H+ + HCO H2O + CO2 + Cl- HCl
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[Na+] – { [CL-] +[HCO3-] } = UA-UC = AG
HCL + NaHCO NaCl +H2O+CO2 HA + NaHCO NaA +H2O+CO2 ∆ AG ∆ HCO3
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[Na+] – { [CL-] +[HCO3-] } = UA-UC = AG
HCL + NaHCO NaCl +H2O+CO2 HA + NaHCO NaA +H2O+CO2 ∆ AG ∆ HCO3
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[Na+] – { [CL-] +[HCO3-] } = UA-UC = AG
HCL + NaHCO NaCl +H2O+CO2 HA + NaHCO NaA +H2O+CO2 ∆ AG ∆ HCO3 AG / HCO3 > 2 : metabolic alkalosis + high anion gap metabolic acidosis
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[Na+] – { [CL-] +[HCO3-] } = UA-UC = AG
HCL + NaHCO NaCl +H2O+CO2 HA + NaHCO NaA +H2O+CO2 ∆ AG ∆ HCO3 AG / HCO3 <1 : hyperchloremic metabolic acidosis + high anion gap metabolic acidosis or urine loss of organic anions
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Example 4: A previously well 55 year old woman is admitted with a complaint of severe vomiting for 5 days. Physical examination reveals postural hypotension, tachycardia and diminished skin turgor. The laboratory findings include: PH=7.23 , PCO2 =22 , HCO3= 9 Na: 140, K: 3.4, Cl: 77, Cr: 2.1, Ketone: trace what is the metabolic disturbances? ∆ HCO3 = 24-9= 15 ∆ AG ∆ HCO3 AG=140-86=54 ∆ AG = 54-10=44 44/15=3
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Example 5: A 58 year old man with a history of chronic bronchitis develop severe diarrhea. The volume of diarrheal fluid is approximately 1 lit/hour. Results of the initial laboratory test is: PH=6.97 , PCO2 =40 , HCO3= 9 Na: 138, K: 3.8, Cl: 115, aibumin: 2 What is the acid base disorder? ∆ HCO3 = 24-9= 15 ∆ AG ∆ HCO3 AG= =14 14+5+=19 ∆ AG = 19-10= 9 9/15 <1
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Example 6: A 25 years woman complains of easy fatigability and weakness. She has no other complains. The physical examination is unremarkable, with the blood pressure being normal. The following laboratory data are obtained: plasma [Na+]: 141 meq/lit [K=]: 2.1 meq/lit [Cl-]:85meq/lit [HCo3]: 45 meq/lit urine [Na+]: 80 meq/lit urine [K+]: 170 meq/lit what are your differential diagnosis? What test would you order next?
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What is base excess? the amount of base that should be removed from whole blood invitro to restore PH of it to 7.4, while pco2 is held at 40 mmHg this calculation is accurate invitro but not invivo, so SBE is calculated
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Base excess in acid base disorders
Metabolic acidosis: SBE<-5 PCO2 = 40 + SBE Metabolic alkalosis: SBE>+5 PCO2= SBE Acute respiratory acidosis: SBE=0 Chronic respiratory acidosis: SBE=0.4(PCO2-40) Acute respiratory alkalosis: SBE=0 Chronic respiratory alkalosis: SBE=0.4(PCO2-40)
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Example 7: In a patient there is following arterial blood values:
PH=7.22 , PCO2 =70 , HCO3= 31 BE: 5.7 What is the acid base disorder?
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Pitfalls of ABG results
1- air bubbles in the syringe Decreased PCO2 and increased PO2 due to existence of bubbles in the sample Prevention: gentle removal of bubbles, rapid sample anaysis
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Pitfalls of ABG results
2- the effect of heparin Dilution of blood parameters , CO2 Prevention: Use of minimum amount of heparin, no less than 2 cc of blood should be obtained
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Pitfalls of ABG results
3- Specimen transport without ice Decreased PO2 due to oxygen consumption of leukocytes Decreased PH and HCO3 due to anaerobic metabolism Prevention: Rapid cooling of specimen, rapid sample anaysis
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Comparison of normal arterial and venous blood gas parameters
ABG mmHg VBG mmHg Pco HCO PH
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Strong Ion Differences
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What are the problems with PCO2/HCO3 in evaluation of acid base condition
It can not determine the: Severity of metabolic disturbance can not be determined The etiology of acid base disorder
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Strong Ion Differences approach to acid base disorders
Most internists traditional approach to acid base disorders considering : H+ = K× PCO2/HCO3 popularized by Relman and Schwartz in 1960s Many surgeons, critical care specialists and anesthesiologists are interested in an alternative approach, termed strong ion differerences introduced by Stewart in 1981
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Acid is a proton donor Base is a proton acceptor
Definition of Acids and Bases based on traditional approach Acid is a proton donor Base is a proton acceptor
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Definition of Acids and Bases In Stewart approach:
Acid is as ion that shift the dissociation equilibrium of water to: higher concentration of H+ and lower concentration of OH- Base is as ion that shift the dissociation equilibrium of water to: lower concentration of H+ and higher concentration of OH-
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Pure Water H20 H+ + OH- Body
-7 -8 H+ = 4 ×10
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Strong cations : Na, Ca, Mg, K
Weak cations: H Strong Anions: Cl, Lactate, Weak Anions: Albumin, Phosphate, HCO3
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[ Na + Ca + Mg + K] - [Cl + lactate] = SID( apparent)
SID>40 : metabolic alkalosis [ Na + Ca + Mg + K] > [Cl + lactate] OH- H+ H H OH- H2O
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[ Na + Ca + Mg + K] - [Cl + lactate] = SID( apparent)
SID<40 : metabolic acidosis [ Na + Ca + Mg + K] < [Cl + lactate] OH- H+ H H OH- H2O
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[ Na + Ca + Mg + K] - [Cl + lactate] = SID( apparent)
SID<40 : metabolic acidosis [ Na + Ca + Mg + K] < [Cl + lactate] OH- H+ H H OH- H2O
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According to modified SID theory variables responsible for change in acid base balance are :
PCO2 Nonvolatile weak acids Strong Ions
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Strong Cations + weak cations = Strong Anions + Weak Anions
Strong Cations - Strong Anions= Weak Anions - Weak Cations [ Na + Ca + Mg + K] - [Cl + lactate] = Weak anions
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K1[CO2] K2[Halb] K3[H2PO4-] Kn[HA] [HCO3-] [alb-] [HPO4-2] [A-]
H2CO H+ + HCO3 – V1 [H2CO3] H+ + HCO H2CO3 V2 [H+] [HCO3-] V1 =V2 [H2CO3] [H+] [HCO3-] [H+] [HCO3-] [H2CO3] K1[CO2] K2[Halb] K3[H2PO4-] Kn[HA] [HCO3-] [alb-] [HPO4-2] [A-] = K = [H+] = = =
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[ Na + Ca + Mg + K] - [Cl + lactate] = SID( apparent)
SID app – SID eff = SID gap
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anion gap and serum albumin in traditional approach
If we consider anion gap and serum albumin in traditional approach stewart approach does not appear a clinically significant advantage
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