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## PowerPoint Slideshow about ' Acid-Base Disturbances' - marcia-barker

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Stepwise ApproachesStepwise ApproachesStepwise Approaches### Interpretation of Case 1

### How to differentiate normal gap acidosis resulting from GI HCO3 loss (diarrhea) vs dRTA?

Simple vs Mixed

- Simple
- When compensation is appropriate
- Mixed
- When compensation is inappropriate

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

- 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

- 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 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 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

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

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.

- 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

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

- 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

- 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 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

- 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

- 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 respiratory alkalosis & metabolic acidosis
- ASA overdose
- Sepsis
- Liver failure
- Mixed respiratory acidosis & metabolic alkalosis
- COPD with excessive use of diuretics

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

- 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

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

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

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

Patient has normal gap metabolic acidosis

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 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

History

Urine pH < 5.5

Negative urine anion gap

dRTA

History

Urine pH > 5.5

Positive urine anion gap

Diarrhea vs RTACase 2

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

- 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 2

- This patient has metabolic alkalosis with appropriate respiratory compensation

Interpretation of Case 2

- 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

Active vomiting

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 DiureticCase 3

- 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

- A normal pH suggests mixed disturbances

Interpretation of Case 3

- 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 3

- 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

- 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

- 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 4

- 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 4

- 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

- 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

- 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

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