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Acid-Base Disturbances. Clinical Approach 2006 Pravit Cadnapaphornchai. Simple vs Mixed. Simple When compensation is appropriate Mixed When compensation is in appropriate. Simple Acid-Base Disturbances. When compensation is appropriate Metabolic acidosis ( ↓ HCO 3 , ↓ pCO 2 )

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Acid base disturbances

Acid-Base Disturbances

Clinical Approach

2006

Pravit Cadnapaphornchai


Simple vs mixed
Simple vs Mixed

  • Simple

    • When compensation is appropriate

  • Mixed

    • When compensation is inappropriate


Simple acid base disturbances
Simple Acid-Base Disturbances

  • When compensation is appropriate

    Metabolic acidosis (↓ HCO3, ↓ pCO2)

    Metabolic alkalosis (↑ HCO3, ↑ pCO2)

    Respiratory acidosis (↑ pCO2, ↑ HCO3)

    Respiratory alkalosis (↓ pCO2, ↓ HCO3)


Stepwise approaches
Stepwise Approaches

  • History & physical examination

  • Arterial blood gas for pH, pCO2, (HCO3)

    • Use the HCO3 from ABG to determine compensation

  • Serum Na, K, Cl, CO2 content

    • Use CO2 content to calculate anion gap

  • Calculate anion gap

    • Anion gap = {Na - (Cl + CO2 content)}

  • Determine appropriate compensation

  • Determine the primary cause


Organ dysfunction
Organ dysfunction

  • CNS – respiratory acidosis (suppression) and alkalosis (stimulation)

  • Pulmonary – respiratory acidosis (COPD) and alkalosis (hypoxia, pulmonary embolism)

  • Cardiac – respiratory alkalosis, respiratory acidosis, metabolic acidosis (pulmonary edema)

  • GI – metabolic alkalosis (vomiting) and acidosis (diarrhea)

  • Liver – respiratory alkalosis, metabolic acidosis (liver failure)

  • Kidney – metabolic acidosis (RTA) and alkalosis (1st aldosteone)


Organ dysfunction1
Organ Dysfunction

  • Endocrine

    • Diabetes mellitus – metabolic acidosis

    • Adrenal insufficiency – metabolic acidosis

    • Cushing’s – metabolic alkalosis

    • Primary aldosteronism – metabolic alkalosis

  • Drugs/toxins

    • Toxic alcohols – metabolic acidosis

    • ASA – metabolic acidosis and respiratory alkalosis

    • Theophylline overdose – respiratory alkalosis


Stepwise approaches1
Stepwise Approaches

  • History & physical examination

  • Arterial blood gas for pH, pCO2, (HCO3)

    • Use the HCO3 from ABG to determine compensation

  • Serum Na, K, Cl, CO2 content

    • Use CO2 content to calculate anion gap

  • Calculate anion gap

    • Anion gap = {Na - (Cl + CO2 content)}

  • Determine appropriate compensation

  • Determine the primary cause


Acid base disturbances

pH

< 7.35 7.4 >7.45

Acidosis

Metabolic

Respiratory

Mixed

Alkalosis

Metabolic

Respiratory


Stepwise approaches2
Stepwise Approaches

  • History & physical examination

  • Arterial blood gas for pH, pCO2, (HCO3)

    • Use the HCO3 from ABG to determine compensation

  • Serum Na, K, Cl, CO2 content

    • Use CO2 content to calculate anion gap

  • Calculate anion gap

    • Anion gap = {Na - (Cl + CO2 content)}

  • Determine appropriate compensation

  • Determine the primary cause


Acid base disturbances

CO2 content

LowNormalHigh

Metabolic acidosis Normal Metabolic alkalosis

Resp alkalosis Mixed Resp acidosis

A normal CO2 content + high anion gap = metabolic acidosis +

Metabolic alkalosis or metabolic ac + compensatory respiratory ac.


Stepwise approaches3
Stepwise Approaches

  • History & physical examination

  • Arterial blood gas for pH, pCO2, (HCO3)

    • Use the HCO3 from ABG to determine compensation

  • Serum Na, K, Cl, CO2 content

    • Use CO2 content to calculate anion gap

  • Calculate anion gap

    • Anion gap = {Na - (Cl + CO2 content)}

  • Determine appropriate compensation

  • Determine the primary cause


Calculation of anion gap in metabolic acidosis
Calculation of Anion Gap in Metabolic Acidosis

Anion gap = Na – (Cl + HCO3)

Normal 8 ± 2

Correction for low serum albumin

Add (4-serum albumin g/dL) X 2.5

to the anion gap


Stepwise approaches4
Stepwise Approaches

  • History & physical examination

  • Arterial blood gas for pH, pCO2, (HCO3)

    • Use the HCO3 from ABG to determine compensation

  • Serum Na, K, Cl, CO2 content

    • Use CO2 content to calculate anion gap

  • Calculate anion gap

    • Anion gap = {Na - (Cl + CO2 content)}

  • Determine appropriate compensation

  • Determine the primary cause


Compensations for metabolic disturbances
Compensations for Metabolic Disturbances

  • Metabolic acidosis

    • pCO2 = 1.5 x HCO3 + 8 ( ± 2)

  • Metabolic alkalosis

    • pCO2 increases by 7 for every 10 mEq increases in HCO3



How does the kidney compensate for metabolic acidosis1
How does the kidney compensate for metabolic acidosis?

  • By reabsorbing all filtered HCO3

  • By excreting H+ as NH4+ (and H2PO4- )

    Interpretations

    Urine pH < 5.5

    Urine anion gap Negative


Compensations for respiratory acidosis
Compensations for Respiratory Acidosis

  • Acute respiratory acidosis

    • HCO3 increases by 1 for every 10 mm increases in pCO2

  • Chronic respiratory acidosis

    • HCO3 increases by 3 for every 10 mm increases in pCO2

      If you don’t have kidneys, can you have chronic respiratory acidosis?


Compensations for respiratory alkalosis
Compensations for Respiratory Alkalosis

  • Acute respiratory alkalosis

    • HCO3 decreases by 2 for every 10 mm decrease in pCO2

  • Chronic respiratory alkalosis

    • HCO3 decreases by 4 for every 10 mm decrease in pCO2

      If you don’t have kidneys can you have chronic respiratory alkalosis?


Mixed acid base disorders
Mixed Acid-Base Disorders

  • Mixed respiratory alkalosis & metabolic acidosis

    • ASA overdose

    • Sepsis

    • Liver failure

  • Mixed respiratory acidosis & metabolic alkalosis

    • COPD with excessive use of diuretics


Mixed acid base disorders1
Mixed Acid-Base Disorders

  • Mixed respiratory acidosis & metabolic acidosis

    • Cardiopulmonary arrest

    • Severe pulmonary edema

  • Mixed high gap metabolic acidosis & metabolic alkalosis

    • Renal failure with vomiting

    • DKA with severe vomiting


Stepwise approaches5
Stepwise Approaches

  • History & physical examination

  • Arterial blood gas for pH, pCO2, (HCO3)

    • Use the HCO3 from ABG to determine compensation

  • Serum Na, K, Cl, CO2 content

    • Use CO2 content to calculate anion gap

  • Calculate anion gap

    • Anion gap = {Na - (Cl + CO2 content)}

  • Determine appropriate compensation

  • Determine the primary cause


Generation of metabolic acidosis
Generation of Metabolic Acidosis

Loss of HCO3

diarrhea

Administration of

HCl, NH4+Cl, CaCl2, lysine HCl

Exogenous acids

ASA

Toxic alcohol

Endogenous acids

ketoacids

DKA

starvation

alcoholic

Lactic acid

L-lactic

D-lactate

H+

HCO3-

Compensations

Buffers

Lungs

Kidneys

High gap

Normal gap

If kidney function is normal, urine anion gap Neg


Acid base disturbances

Loss of H+ from GI

Vomiting, NG suction

Congenital Cl diarrhea

Loss of H+ from kidney

1st & 2nd aldosterone

ACTH

Diuretics

Bartter’s, Gitelman’s, Liddle’s

Inhibition of β – OH steroid deh

H

HCO3

Compensations

Buffer

Respiratory

Forget the kidney

Gain of HCO3

Administered HCO3,

Acetate, citrate, lactate

Plasma protein products


Case 1
CASE 1

A 24 year old diabetic was admitted for weakness.

Serum Na 140, K 1.8, Cl 125, CO2 6, anion gap 9.

pH 6.84 (H+ 144) pCO2 30, HCO3 5


Interpretation of case 1

Interpretation of Case 1

Patient has normal gap metabolic acidosis


Interpretation of case 11
Interpretation of Case 1

  • Next determine the appropriateness of respiratory compensation

    • pCO2 = 1.5 x HCO3 + 8 ( ± 2)

    • pCO2 = 1.5 x 5 + 8 + 2 = 17.5

      • The patient’s pCO2 is 30

  • The respiratory compensation is inappropriate


Interpretation of case 12
Interpretation of Case 1

  • This patient has normal anion gap metabolic acidosis with inappropriate respiratory compensation

  • The finding does not fit DKA but is consistent with HCO3 loss from the GI tract or kidney



Diarrhea vs rta

Diarrhea HCO

History

Urine pH < 5.5

Negative urine anion gap

dRTA

History

Urine pH > 5.5

Positive urine anion gap

Diarrhea vs RTA


Case 2
Case 2 HCO

A 26 year old woman, complains of weakness.

She denies vomiting or taking medications.

P.E. A thin woman with contracted ECF.

Serum Na 133, K 3.1, Cl 90, CO2 content 32, anion gap11.

pH 7.48 (H+ 32), pCO2 43, HCO3 32.

UNa 52, UK 50, UCl 0, UpH 8


Interpretation of case 2
Interpretation of Case 2 HCO

  • Determine the appropriateness of respiratory compensation

    • For every increase of HCO3 by 1, pCO2 should increase by 0.7

    • pCO2 = 40 + (32-25) x 0.7 = 44.9

      • The patient’s pCO2 = 43


Interpretation of case 21
Interpretation of Case 2 HCO

  • This patient has metabolic alkalosis with appropriate respiratory compensation


Interpretation of case 22
Interpretation of Case 2 HCO

  • Urine Na+ 52, UK+ 50, Cl- 0, pH 8

    • Urine pH = 8 suggests presence of large amount of HCO3. The increased UNa and UK are to accompany HCO3 excretion. The kidney conserves Cl

  • The findings are consistent with loss of HCl from the GI tract

  • Final diagnosis = Self-induced vomiting


Vomiting vs diuretic

Active vomiting HCO

ECF depletion

Metabolic alkalosis

High UNa, UK, low UCl

Urine pH > 6.5

Remote vomiting

ECF depletion

Metabolic alkalosis

Low UNa, high UK, low Cl

Urine pH 6

Active diuretic

ECF depletion

Metabolic alkalosis

High UNa, UK and Cl

Urine pH 5-5.5

Remote diuretic

ECF depletion

Metabolic alkalosis

Low UNa, high UK, low Cl

Urine pH 5-6

Vomiting vs Diuretic


Case 3
Case 3 HCO

  • A 40 year old man developed pleuritic chest pain and hemoptysis. His BP 80/50. pH 7.4, pCO2 25, HCO3 15 and pO2 50


Interpretation of case 3
Interpretation of Case 3 HCO

  • A normal pH suggests mixed disturbances


Interpretation of case 31
Interpretation of Case 3 HCO

  • His pCO2 is 25, his HCO315

    • If this is acute respiratory alkalosis his HCO3 should have been 25-{(40-25) x 2/10}= 22

    • If this is chronic respiratory alkalosis, his HCO3 should have been 25 – {(40-25) x 4/10} = 19

    • If this is metabolic acidosis, his pCO2 should have been 1.5 x 15 + 8 = 30-31


Interpretation of case 32
Interpretation of Case 3 HCO

  • He has combined respiratory alkalosis and metabolic acidosis

  • The likely diagnosis is pulmonary embolism with hypotension and lactic acidosis or pneumonia with sepsis and lactic acidosis

  • Other conditions are ASA overdose, sepsis, liver failure


Case 4
Case 4 HCO

  • A patient with COPD developed CHF. Prior to treatment his pH 7.35, pCO2 was 60 and HCO3 32. During treatment with diuretics he vomited a few times. His pH after treatment was 7.42, pCO2 80, HCO3 48.


Interpretation of case 4
Interpretation of Case 4 HCO

  • Pt’s data pH 7.35, pCO2 60 and HCO3 32

  • For acute respiratory acidosis

    • For every 10 mm elevation of pCO2, HCO3 increases by 1, his HCO3 should have been 25 + (60-40) x 1/10 = 27

  • He did not have acute respiratory acidosis


Interpretation of case 41
Interpretation of Case 4 HCO

  • Pt’s data pH 7.35, pCO2 60 and HCO3 32.

  • For chronic respiratory acidosis

    • For every 10 mm elevation of pCO2, HCO3 increases by 3

    • His HCO3 should have been 25 + (60-40) x 3/10 = 31

      • His HCO3 is 32

  • He had well compensated chronic respiratory acidosis


Interpretation of case 42
Interpretation of Case 4 HCO

  • His pH is now 7.42, pCO2 80, HCO3 48

  • If pCO2 of 80 is due to chronic respiratory acidosis, HCO3 should only be 32 +(80-60) x 3/10=38 and not 48

  • He had combined metabolic alkalosis and respiratory acidosis after treatment of CHF


Case 5
Case 5 HCO

  • A cirrhotic patient was found to be confused. Serum Na 133, K 3.3, Cl 115, CO2 content 14, anion gap 4

  • pH 7.44 (H+ 36), pCO2 20, HCO3 13


Interpretation of case 5
Interpretation of Case 5 HCO

  • Determine the respiratory compensation

    • For chronic respiratory alkalosis, every 10 reduction in pCO2, HCO3 should decrease by 4

    • HCO3 should be 25 - (40-20) x 4/10=17

    • For acute respiratory alkalosis, HCO3 = 21

    • Patient’s HCO3 is 13, suggesting a metabolic acidotic component is present

  • Anion gap is 4, even corrected for low albumin, is still low suggesting a normal gap metabolic acidosis

  • Patient had combined metabolic acidosis and respiratory alkalosis