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1. Acid-Base Balance & Disorders
.
Part II .
Respiratory & Mixed Acid Base Disorders
ABG Interpretation
Presented By
dr. Mohammed Abdel Gawad
Nephrologist
2-2-2012

3. To download the lecture contact me
drgawad@gmail.com
More lectures on www.NephroTube.com

4. Acid Base Balance & Disorders
• Normal Acid Base Balance
• Metabolic Acidosis
• Metabolic Alkalosis
• Respiratory Acidosis
• Respiratory Alkalosis
• Mixed Acid Base Disorders
• ABG Interpretation
4
Part I
Part II

5. 5
CO2
Red Blood Cell
Systemic Circulation
H2O
H+ HCO3-
carbonic
anhydrase
Plasma
CO2 CO2 CO2 CO2 CO2CO2
+ +
Tissues
H+
Cl-
Hb
H+ is buffered by
Hemoglobin
Tissue side

6. 6
Red Blood Cell Pulmonary Circulation
CO2 H2O
H+
+ + HCO3-
Cl-
Alveolus
Plasma
CO2 H2O
Hb
Lung side

7. Respiratory regulation of acid-base balance

8. Classification of Acid-basic Disorders
pH PCO2 HCO3
Metabolic
Acidosis
↓ ↓
(compensation)
↓
(1ry disorder)
Metabolic
Alkalosis
↑ ↑
(compensation)
↑
(1ry disorder)
Respiratory
Acidosis
↓ ↑
(1ry disorder)
↑
(compensation)
Respiratory
Alkalosis
↑ ↓
(1ry disorder)
↓
(compensation)

9. is PO2 low?
PCO2
low
is HCO3 low?
NO
1ry
hyperventilation
YES
Respiratory
alkalosis
high
Type II
respiratory
impairment
is HCO3 high?
NO
Acute
YES
pH normal
Chronic
pH low
Acute on top of
chronic
PCO2
high Low/normal
Type I
respiratory
impairment
Acute or Chronic?

10. I- Approved respiratory acidosis:
• pH < 7.35
• PCO2 > 45 mmHg
• HCO3 > 26 mEq/L (compensation)
• 1. Acute respiratory acidosis:
▫ HCO3 rises 1 mEq/L for each 10 mm Hg rise in PCO2 (in minutes).
• 2. Chronic respiratory acidosis:
▫ HCO3 rises 3.5 mEq/L for each 10 mm Hg rise in PCO2 (over days).
• In absence of full compensation, this is
called:
▫ A- partial compensation
▫ or better called:
II- Expected compensation:

13. Acid Base Balance & Disorders
• Normal Acid Base Balance
• Metabolic Acidosis
• Metabolic Alkalosis
• Respiratory Acidosis
• Respiratory Alkalosis
• Mixed Acid Base Disorders
• ABG Interpretation
13
Part I
Part II

14. I- Approved respiratory alkalosis:
• pH > 7.45
• PCO2 < 35 mmHg
• HCO3 < 22 mEq/L (compensation)
• 1. Acute respiratory alkalosis:
▫ HCO3 falls 2 mEq/L for each 10 mm Hg fall in PCO2 (in minutes).
• 2. Chronic respiratory alkalosis:
▫ HCO3 falls 5 mEq/L for each 10 mm Hg fall in PCO2 (over days).
• In absence of full compensation, this is
called:
▫ A- partial compensation
▫ or better called:
II- Expected compensation:

17. Acid Base Balance & Disorders
• Normal Acid Base Balance
• Metabolic Acidosis
• Metabolic Alkalosis
• Respiratory Acidosis
• Respiratory Alkalosis
• Mixed Acid Base Disorders
• ABG Interpretation
17
Part I
Part II

18. All acid base disorders can be combined in a
double or triple disorders
BUT NEVER COMBINE
respiratory acidosis with respiratory alkalosis

19. Acid Base Balance & Disorders
• Normal Acid Base Balance
• Metabolic Acidosis
• Metabolic Alkalosis
• Respiratory Acidosis
• Respiratory Alkalosis
• Mixed Acid Base Disorders
• ABG Interpretation
19
Part I
Part II

20. Step 1 - pH
If it falls into the normal range:
< 7.4 = normal/acidic,
> 7.4 = normal/alkalotic.

21. Parameter Normal value
PCO2 35 – 45 mmHg
HCO3 22- 26 mEq/L
Step 2 – PCO2 & HCO3 analysis
pH PCO2 HCO3
Metabolic
Acidosis
↓ ↓ ↓
Respiratory
Alkalosis
↑ ↓ ↓
Metabolic
Alkalosis
↑ ↑ ↑
Respiratory
Acidosis
↓ ↑ ↑
Mixed Acidosis ↓ ↑ ↓
Mixed Alkalosis ↑ ↓ ↑

22. If Metabolic Acidosis

23. I- Approved metabolic acidosis:
• pH < 7.35
• HCO3 < 22 mEq/L
• PCO2 < 35 mmHg (compensation)
• for each 1 HCO3 1.2 CO2↓ → ↓
▫ or
• Δ ↓ Pco2 = 1.2 x ΔHCO3
• In absence of full compensation, this is
called:
▫ A- partial compensation
▫ or better called:
▫ B- mixed metabolic & respiratory acidosis:
as the lung not washing enough CO2 as needed, which mean that it is actually accumulating CO2
II- Expected compensation:

24. NormocholeremicHypercholeremic
III-
Calculate
Anion Gap

25. III- Calculate Anion Gap
• Equations:
▫ AG = (Na + K) – (Cl + HCO3) = 12 ± 4 mmol/l
▫ or
▫ AG = (Na) – (Cl + HCO3) = 12 ± 2 mmol/l
• Corrected Anion Gap:
▫ anion gap is decreased by 4 mmol/l for each 1 g/dl decrease in the
serum albumin concentration below normal.
• The result:
▫ Wide (high) anion gap metabolic acidosis
▫ or
▫ Non (normal) anion gap metabolic acidosis

26. High AG acidosis
•
•
•
•
•
•
•
•
K
U
S
S
M
A
L
E
Ketoacidosis (starvation, DM, alcohol)
Uremia
Sepsis
Salicylate & other drugs e.g.paraldhyde
Methanol
Alcohol (Ethanol)
Lactic acidosis
Ethylene glycol
Wide Anion Gap Causes
Normocholeremic

27. 4- uretrosigmoid-
ostomy
Non Anion Gap Causes
Hypercholeremic

28. To remember
• I- Approved Metabolic Acidosis
• II- Calculate Compensation
• III- Calculate Anion Gap
• IV-
– a- if high anion gap calculate delta gap→
– b- if normal anion gap calculate urinary AG→

29. ●
IV- a- if high anion gap calculate delta gap→
∆ Gap = ∆AG / ∆HCO3
▫ > 1
= high AG metabolic acidosis mixed with metabolic
alkalosis
▫ < 1
= high AG metabolic acidosis mixed with non AG
metabolic acidosis
▫ = 1
= simple high AG metabolic acidosis
Ketoacidosis
Uremia
Sepsis
Salicylate & other drugs
Methanol
Alcohol (Ethanol)
Lactic acidosis
Ethylene glycol
AG
HCO3
Cl
12
24
105

30. ●
IV- b- if normal anion gap calculate urinary→
AG
4- uretrosigmoid-
ostomy
urine AG = u[Na + K] – u[Cl]
If –ve:
so the loss is non renal
If zero or +ve:
so the loss is renal
N.B.
Normally it is +ve ranging from
+30 to +50 mmol/L

31. To remember
• I- Approved Metabolic Acidosis
• II- Calculate Compensation
• III- Calculate Anion Gap
• IV-
– a- if high anion gap calculate delta gap→
– b- if normal anion gap calculate urinary AG→

32. Bicarbonate Deficit – Equation 1

33. Bicarbonate Deficit – Equation 2

34. If Metabolic Alkalosis

35. I- Approved metabolic alkalosis:
• pH > 7.45
• HCO3 > 26 mEq/L
• PCO2 > 45 mmHg (compensation)
• for each 1 HCO3 0.7 CO2↑ → ↑
▫ or
• Δ ↑ Pco2 = 0.7 x ΔHCO3
• In absence of full compensation, this is
called:
▫ A- partial compensation
▫ or better called:
▫ B- mixed metabolic & respiratory alkalosis:
as the lung can not retain enough CO2 as needed, which mean that it is actually washing CO2 even if
the PCO2 is higher than normal.
II- Expected compensation:

36. III- Causes
• A- Chloride Depletion (urine Cl < 10 mEq/L)
• B- Corticosteroid & Apparent Corticosteroid
Induced (chloride resistant) (urine Cl > 10 mEq/L)
• C- Alkali Administration or Ingestion

37. A- Chloride Depletion
(urine Cl < 10 mEq/L)

38. B- Corticosteroid & Apparent Corticosteroid Induced
(chloride resistant)
(urine Cl > 10 mEq/L)

39. C- Alkali Administration
or
Ingestion

41. If Respiratory Disorder

42. is PO2 low?
PCO2
low
is HCO3 low?
NO
1ry
hyperventilation
YES
Respiratory
alkalosis
high
Type II
respiratory
impairment
is HCO3 high?
NO
Acute
YES
pH normal
Chronic
pH low
Acute on top of
chronic
PCO2
high Low/normal
Type I
respiratory
impairment
Acute or Chronic?
NO YES

43. If Respiratory Acidosis

44. I- Approved respiratory acidosis:
• pH < 7.35
• PCO2 > 45 mmHg
• HCO3 > 26 mEq/L (compensation)
• 1. Acute respiratory acidosis:
▫ HCO3 rises 1 mEq/L for each 10 mm Hg rise in PCO2 (in minutes).
• 2. Chronic respiratory acidosis:
▫ HCO3 rises 3.5 mEq/L for each 10 mm Hg rise in PCO2 (over days).
• In absence of full compensation, this is
called:
▫ A- partial compensation
▫ or better called:
II- Expected compensation:

46. If Respiratory Alkalosis

47. I- Approved respiratory alkalosis:
• pH > 7.45
• PCO2 < 35 mmHg
• HCO3 < 22 mEq/L (compensation)
• 1. Acute respiratory alkalosis:
▫ HCO3 falls 2 mEq/L for each 10 mm Hg fall in PCO2 (in minutes).
• 2. Chronic respiratory alkalosis:
▫ HCO3 falls 5 mEq/L for each 10 mm Hg fall in PCO2 (over days).
• In absence of full compensation, this is
called:
▫ A- partial compensation
▫ or better called:
II- Expected compensation:

51. Thank You