Acid-Base Disturbances

1
Acid-Base Disturbances

• Clinical Approach
• 2006
• Pravit Cadnapaphornchai

2
Simple vs Mixed

• Simple
• When compensation is appropriate
• Mixed
• When compensation is inappropriate

3
Simple Acid-Base Disturbances

• When compensation is appropriate
• Metabolic acidosis (? HCO3, ? pCO2)
• Metabolic alkalosis (? HCO3, ? pCO2)
• Respiratory acidosis (? pCO2, ? HCO3)
• Respiratory alkalosis (? pCO2, ? HCO3)

4
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

5
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)

6
Organ Dysfunction

• Endocrine
• Diabetes mellitus metabolic acidosis
• Adrenal insufficiency metabolic acidosis
• Cushings metabolic alkalosis
• Primary aldosteronism metabolic alkalosis
• Drugs/toxins
• Toxic alcohols metabolic acidosis
• ASA metabolic acidosis and respiratory
  alkalosis
• Theophylline overdose respiratory alkalosis

7
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

8
pH
lt 7.35 7.4 gt7.45
Acidosis Metabolic Respiratory
Mixed
Alkalosis Metabolic Respiratory
9
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

10
CO2 content
Low Normal High 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.
11
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

12
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
13
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

14
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

15
How does the kidney compensate for metabolic
acidosis?
16
How does the kidney compensate for metabolic
acidosis?

• By reabsorbing all filtered HCO3
• By excreting H as NH4 (and H2PO4- )
• Interpretations
• Urine pH lt 5.5
• Urine anion gap Negative

17
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 dont have kidneys, can you have chronic
  respiratory acidosis?

18
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 dont have kidneys can you have chronic
  respiratory alkalosis?

19
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

20
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

21
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

22
Generation of Metabolic Acidosis
Loss of HCO3 diarrhea
Administration of HCl, NH4Cl, 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
23
Loss of H from GI Vomiting, NG
suction Congenital Cl diarrhea Loss of H from
kidney 1st 2nd aldosterone ACTH Diuretics Bartte
rs, Gitelmans, Liddles Inhibition of ß OH
steroid deh
H HCO3
Compensations
Buffer Respiratory Forget the kidney
Gain of HCO3 Administered HCO3, Acetate,
citrate, lactate Plasma protein products
24
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
25
Interpretation of Case 1

• Patient has normal gap metabolic acidosis

26
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 patients pCO2 is 30
• The respiratory compensation is inappropriate

27
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

28
How to differentiate normal gap acidosis
resulting from GI HCO3 loss (diarrhea) vs dRTA?
29
Diarrhea vs RTA

• Diarrhea
• History
• Urine pH lt 5.5
• Negative urine anion gap

• dRTA
• History
• Urine pH gt 5.5
• Positive urine anion gap

30
Case 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
31
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 patients pCO2 43

32
Interpretation of Case 2

• This patient has metabolic alkalosis with
  appropriate respiratory compensation

33
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

34
Vomiting vs Diuretic

• Active vomiting
• ECF depletion
• Metabolic alkalosis
• High UNa, UK, low UCl
• Urine pH gt 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

35
Case 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

36
Interpretation of Case 3

• A normal pH suggests mixed disturbances

37
Interpretation of Case 3

• His pCO2 is 25, his HCO3 15
• 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

38
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

39
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.

40
Interpretation of Case 4

• Pts 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

41
Interpretation of Case 4

• Pts 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

42
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
  3/1038 and not 48
• He had combined metabolic alkalosis and
  respiratory acidosis after treatment of CHF

43
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

44
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 4/1017
• For acute respiratory alkalosis, HCO3 21
• Patients 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