acid base disorders

ACID BASE DISORDERS

F. Rashid FarokhiNephrologist

Masih Daneshvari Hospital

Extra cellular fluid H+ concentration

[H +] = 40 10 meq/lit = 40 10 Eq/litPH = - log [H+]PH = 7.35 - 7.45

- 9- 9- 6- 6

- 7- 7

meq

7.47.35 7.456.8 7.8

Arterial PH

How can the body regulate H+ concentration in such a low concentration despite of

Daily production of 15000 meq CO2 Daily production of 50-100 meq nonviolate acids Entrance of exogenous acids

?

CO2 +H2O H+ + HCO3-

circulation

Buffering systemsBuffering systems

H2CO3 H+ + HCO3- H2PO4 - H+ +H PO4 2- HAlb H+ + Alb- HHgb H+ + Hgb - HProt H+ + Prot – HPhosphate- H+ + phosphate -

H2CO3 H+ + HCO3- H2PO4 - H+ +H PO4 2- HAlb H+ + Alb- HHgb H+ + Hgb - HProt H+ + Prot – HPhosphate- H+ + phosphate -

H2CO3 H+ + HCO3 –V1 [H2CO3]

H+ + HCO3- 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-]


H+ + HCO3- H2CO3 V2 [H+] [HCO3-]

V1 =V2[H2CO3] [H+] [HCO3-]

[H+] [HCO3-][H2CO3]


= = =

= K= K

[H+] =[H+] =

BB=

12.2 × PCO2/(10 ) + [Albumin] ×(0.123×PH-0.0631) + [PO4]}×(0.309× PH-0.469)

BB=

12.2 × PCO2/(10 ) + [Albumin] ×(0.123×PH-0.0631) + [PO4]}×(0.309× PH-0.469)-PH

H20 + CO2 H2CO3 H+ + HCO3-

[CO2] [H+] = K ×

[HCO3-]

PCO2 × 0.03[H+] = 800 ×

[HCO3-]

PCO2= 24 ×

[HCO3-]

Example 1:Example 1:

PH=7.50 , HCO3 =28 , PCO2=40PH=7.50 , HCO3 =28 , PCO2=40

PCO2[H+] = 24 ×

[HCO3-]

40? = 24 ×

[HCO3-]

PCO2 [ HCO3-]

[H+] PH 40 1.25 1.25 1.25 = 80 7.1 40 1.25 1.25 = 63 7.2 40 1.25 = 50 7.3 40 7.4 40 0.8 = 32 7.5 40 0.8 0.8 = 26 7.6 40 0.8 0.8 0.8 = 20 7.7

PCO2 [ HCO3-]

[H+] PH 40 1.25 1.25 1.25 = 80 7.1 40 1.25 1.25 = 63 7.2 40 1.25 = 50 7.3 40 7.4 40 0.8 = 32 7.5 40 0.8 0.8 = 26 7.6 40 0.8 0.8 0.8 = 20 7.7

[H+] =24× [H+] =24×

PH=7.50 , HCO3 = 30 , PCO2=40PH=7.50 , HCO3 = 30 , PCO2=40

PCO2[H+] = 24 ×

[HCO3-]

4032 = 24 ×

30

The effect of respiratory system on acid base balance

The effect of respiratory system on acid base balance

C6H12O6 + 602 6CO2 +6H2O

CO2 + H2O H2CO3 H+ + HCO3-

C6H12O6 + 602 6CO2 +6H2O

CO2 + H2O H2CO3 H+ + HCO3-

Proximal tube

H+

HCO3

OH-

H+Na+

+ H20CO2 +

NaHCO3

Proxoimal tubuleProxoimal tubule

Distal tubules

H+H++A-

HA

OH-

H+

CO2

HCO3-

H+ + HCO3- H2O + CO2 + A-

HA

Acid base disordersAcid base disorders

What is the difference between acidemia and acidosis, alkalemia and

alkalosis?

What is the difference between acidemia and acidosis, alkalemia and

alkalosis?

PH = 6.1+ log {HCO3- / [0.03 x PCO2]}

AcidemiaPH

Metabolic acidosis

HCO3

Respiratory Acidosis

PCO2

PH = 6.1+ log {HCO3- / [0.03 x PCO2]}

AlkalemiaPH

Metabolic alkalosis

HCO3

Respiratory Alkalosis

PCO2

Respiratory compensation in metabolic acidosis

PH = 6.1+ log {HCO3- / [0.03 x PCO2]}

AcidemiaPH

Metabolic acidosis

HCO3

PCO2 = (1.5×Hco3) + 8 ± 2Or

1.25 mmHg fall in the PCO2 for every 1 meq/lit reduction in the bicarbonate

PCO2 = (1.5×Hco3) + 8 ± 2Or

1.25 mmHg fall in the PCO2 for every 1 meq/lit reduction in the bicarbonate

Respiratory compensation in metabolic alkalosis

PH = 6.1+ log {HCO3- / [0.03 x PCO2]}

AlkalemiaPH Metabolic

alkalosis HCO3

PCO2 = HCO3 + 15Or

0.75 mmHg rise in the PCO2 for every 1 meq/lit elevation in the bicarbonate

PCO2 = HCO3 + 15Or

0.75 mmHg rise in the PCO2 for every 1 meq/lit elevation in the bicarbonate

PH = 6.1+ log {HCO3- / [0.03 x PCO2]}Acidemia

PH

Respiratory Acidosis

PCO2

Acute: HCO3 rises 1 meq/lit for every 10 mmHg elevation in PCO2Chronic: HCO3 rises 4 meq/lit for every 10 mmHg elevation in PCO2Acute: 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

PH = 6.1+ log {HCO3- / [0.03 x PCO2]}Alkalemia

PH

Respiratory Alkaloosis

PCO2

Acute: HCO3 falls by 2 meq/lit for every 10 mmHg decline in PCO2Chronic: HCO3 falls by 4 meq/lit for every 10 mmHg decline in PCO2Acute: 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


PH=7.50 , HCO3 = 30 , PCO2=40

Mixed metabolic and respiratory alkalosis

PH=7.50 , HCO3 = 30 , PCO2=40

Mixed metabolic and respiratory alkalosis

Examples 2: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

1- PH =7.25 ,HCO3=12 , PCO2=25 compensated metabolic acidosis

2-PH=7.1 , HCO3 =12 , PCO2=30 mixed metabolic and respiratory acidosis


PH=7.35 , HCO3= 28 , PCO2=60

Acute respiratory acidosis + metabolic alkaosisChronic respiratory acidosis +metabolic acidosis

PH=7.35 , HCO3= 28 , PCO2=60

Acute respiratory acidosis + metabolic alkaosisChronic respiratory acidosis +metabolic acidosis

In a patient there is following arterial blood values:

In a patient there is following arterial blood values:

PH=7.22 , PCO2 =70 , HCO3= 31 What is the acid base disorder?

PH=7.22 , PCO2 =70 , HCO3= 31 What is the acid base disorder?

HCO3 can be measured by adding a powerful acid to serum:

HCO3- +H+ H20+CO2+CL

17.9 + 0.03× 41.7=17.9 + 1.251=

19.151

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



anion gap in approach of metabolic acidosis

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

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

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:



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?

PH=7.23 , PCO2 =22 , HCO3= 9


High anion gap metabolic acidosisHigh anion gap metabolic acidosis

H+ + HCO3- H2O + CO2 + A-

H+ + HCO3- H2O + CO2 + A-

HA

Hyperchloremic metabolic acidosisHyperchloremic metabolic acidosis

H+ + HCO3- H2O + CO2 + Cl-

H+ + HCO3- H2O + CO2 + Cl-

HCl

[Na+] – { [CL-] +[HCO3-] } = UA-UC = AG

HCL + NaHCO3 NaCl +H2O+CO2HA + NaHCO3 NaA +H2O+CO2

[Na+] – { [CL-] +[HCO3-] } = UA-UC = AG


∆ AG

∆ HCO3

[Na+] – { [CL-] +[HCO3-] } = UA-UC = AG


[Na+] – { [CL-] +[HCO3-] } = UA-UC = AG


∆ AG

∆ HCO3 AG / HCO3 > 2 : metabolic alkalosis + high anion gap metabolic acidosis

[Na+] – { [CL-] +[HCO3-] } = UA-UC = AG


[Na+] – { [CL-] +[HCO3-] } = UA-UC = AG


∆ AG

∆ HCO3 AG / HCO3 <1 : hyperchloremic metabolic acidosis + high anion gap metabolic acidosis or urine loss of organic anions



turgor. The laboratory findings include:



turgor. The laboratory findings include: PH=7.23 , PCO2 =22 , HCO3= 9


PH=7.23 , PCO2 =22 , HCO3= 9


∆ AG

∆ HCO3

AG=140-86=54 ∆ AG = 54-10=44

∆ HCO3 = 24-9= 15

44/15=3

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:

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?

PH=6.97 , PCO2 =40 , HCO3= 9

Na: 138, K: 3.8, Cl: 115, aibumin: 2 What is the acid base disorder?

∆ AG

∆ HCO3

AG=138-124=1414+5+=19

∆ AG = 19-10= 9

∆ HCO3 = 24-9= 15

9/15 <1

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?

What is base excess?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 mmHgthis calculation is accurate invitro but not

invivo, so SBE is calculated

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 mmHgthis calculation is accurate invitro but not

invivo, so SBE is calculated

Base excess in acid base disordersBase excess in acid base disorders

Metabolic acidosis: SBE<-5 PCO2 = 40 + SBEMetabolic alkalosis: SBE>+5 PCO2= 40+ 0.6 SBEAcute respiratory acidosis: SBE=0Chronic respiratory acidosis: SBE=0.4(PCO2-40)Acute respiratory alkalosis: SBE=0 Chronic respiratory alkalosis: SBE=0.4(PCO2-40)

Metabolic acidosis: SBE<-5 PCO2 = 40 + SBEMetabolic alkalosis: SBE>+5 PCO2= 40+ 0.6 SBEAcute respiratory acidosis: SBE=0Chronic respiratory acidosis: SBE=0.4(PCO2-40)Acute respiratory alkalosis: SBE=0 Chronic respiratory alkalosis: SBE=0.4(PCO2-40)

Example 7:In a patient there is following arterial

blood values:

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?

PH=7.22 , PCO2 =70 , HCO3= 31 BE: 5.7 What is the acid base disorder?

Pitfalls of ABG resultsPitfalls of ABG results

1- air bubbles in the syringe Decreased PCO2 and increased PO2 due to

existence of bubbles in the sample

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

Prevention: gentle removal of bubbles, rapid sample anaysis


2- the effect of heparin Dilution of blood parameters , CO2

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

Prevention: Use of minimum amount of heparin, no less than 2 cc of blood should be obtained


3- Specimen transport without ice Decreased PO2 due to oxygen consumption of

leukocytes Decreased PH and HCO3 due to anaerobic metabolism

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

Prevention: Rapid cooling of specimen, rapid sample anaysis

Comparison of normal arterial and venous blood gas parameters

Comparison of normal arterial and venous blood gas parameters

ABG mmHg VBG mmHg Pco2 35-45 42-50 HCO3 22-26 23-27 PH 7.35-7.45 7.32-7.38

ABG mmHg VBG mmHg Pco2 35-45 42-50 HCO3 22-26 23-27 PH 7.35-7.45 7.32-7.38

STRONG ION DIFFERENCES

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

Acid is a proton donor Base is a proton acceptor

DEFINITION OF ACIDS AND BASES BASED ON TRADITIONAL APPROACH

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-

Pure Water

H20 H+ + OH-

Body

H20 H+ + OH-

Pure Water

H20 H+ + OH-

Body

H20 H+ + OH-

H+ = 10

H+ = 4 ×10

-7

-8

Strong cations : Na, Ca, Mg, KWeak cations: H

Strong Anions: Cl, Lactate, Weak Anions: Albumin, Phosphate, HCO3

Strong cations : Na, Ca, Mg, KWeak cations: H

Strong Anions: Cl, Lactate, Weak Anions: Albumin, Phosphate, HCO3

[ Na + Ca + Mg + K] - [Cl + lactate] = SID( apparent) SID>40 : metabolic alkalosis

[ Na + Ca + Mg + K] - [Cl + lactate] = SID( apparent) SID>40 : metabolic alkalosis

H2O

OH- H+ H20 H+ + OH-

[ Na + Ca + Mg + K] > [Cl + lactate]

[ Na + Ca + Mg + K] - [Cl + lactate] = SID( apparent) SID<40 : metabolic acidosis [ Na + Ca + Mg + K] - [Cl + lactate] = SID( apparent) SID<40 : metabolic acidosis

H2O

OH- H+ H20 H+ + OH-

[ Na + Ca + Mg + K] < [Cl + lactate]

According to modified SID theory variables responsible for change in acid

base balance are :

According to modified SID theory variables responsible for change in acid

base balance are :

PCO2 Nonvolatile weak acids Strong Ions

PCO2 Nonvolatile weak acids Strong Ions

Strong Cations + weak cations = Strong Anions + Weak Anions Strong Cations - Strong Anions= Weak Anions - Weak Cations

[ Na + Ca + Mg + K] - [Cl + lactate] = Weak anions

Strong Cations + weak cations = Strong Anions + Weak Anions Strong Cations - Strong Anions= Weak Anions - Weak Cations

[ Na + Ca + Mg + K] - [Cl + lactate] = Weak anions


H+ + HCO3- H2CO3 V2 [H+] [HCO3-]

V1 =V2[H2CO3] [H+] [HCO3-]

[H+] [HCO3-][H2CO3]



H+ + HCO3- H2CO3 V2 [H+] [HCO3-]

V1 =V2[H2CO3] [H+] [HCO3-]

[H+] [HCO3-][H2CO3]


= = =

= K= K

[H+] = [H+] =

[ Na + Ca + Mg + K] - [Cl + lactate] = SID( apparent)[ Na + Ca + Mg + K] - [Cl + lactate] = SID( apparent)

SID app – SID eff = SID gap

If we consider anion gap and serum albumin

in traditional approach stewart approach does not appear a

clinically significant advantage

acid base disorders

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