The document provides detailed information on acid-base disorders, including metabolic and respiratory acidosis and alkalosis, along with normal value ranges for pH, HCO3−, and PaCO2. It outlines methods for analyzing arterial blood gas (ABG) values and identifying primary disturbances, compensation mechanisms, and specific conditions associated with various disorders. Additionally, it includes multiple exercises with example patient scenarios to illustrate the application of these concepts.

1. ACID BASE
DISORDER
DR. MOHAMMED HUMAYUN
KABIR
MBBS,
BCS(Health)
FCPS(Medicine)
MD(Pulmonology)-Resident
BSMMU

2. DISORDERS
⯈Metabolic
acidosis
⯈Metabolic alkalosis
⯈ Respiratory acidosis – Acute/Chronic
⯈ Respiratory alkalosis –
Acute/Chronic

4. NORMAL
VALUES
RANGE
⯈ pH : 7.35 – 7.45
⯈ HCO₃ˉ : 22 – 26
mmol/L
⯈ PaCO₂ : 34 – 45
mmHg
4.5 – 6.0 KPa
⯈ Na⁺ : 135 – 145
mmol/L
⯈ K⁺ : 3.5 – 4.5 mmol/L
⯈ Clˉ : 95 – 107 mmol/L
For ABG
analysis
⯈ pH - 7.40
⯈ HCO₃ˉ -
24
⯈ PaCO₂ -
40
⯈ AG - 14

5. ⯈ Anion gap (AG) : Measured cation – Measured anion
(Na⁺+k⁺) – (Cl⁻+HCO₃⁻)
=
> High AG suggest – Metabolic acidosis
⯈ HCO₃⁻ gap/Delta gap : Patient HCO₃⁻ + (Measured AG – Normal
AG)
=
> Adjusted HCO₃⁻ should be 24(±6) [18-30]
=
> HCO₃⁻ gap >30 suggest – additional metabolic alkalosis
=
> HCO₃⁻ gap <18 suggest – additional NAGMA
=
> HCO₃⁻ gap 18-30 suggest – no additional metabolic acidosis

6. Delta ratio(ΔΔ) = Δ Anion gap/Δ
HCO₃⁻ = (Pt. AG – Normal AG)/(Normal HCO₃⁻- Pt.
HCO₃⁻)
= (Pt. AG – 14)/(24- Pt. HCO₃⁻)
⯈ 0.0 – 0.4 : NAGMA
⯈ 0.4 – 0.8 : Mixed normal & high AGMA
⯈ 1 – 2 : HAGMA
⯈ >2 : Metabolic acidosis and coexistent metabolic alkalosis
or compensated respiratory acidosis

7. APPROACH TO ABG
1. pH : Acidosis or
Alkalosis?
2. Primary disturbance : Metabolic (HCO₃ˉ) or Respiratory
(PaCO₂)?
# For metabolic acidosis – anion gap?
# For respiratory disturbance – acute or chronic?
3. Look for compensation : Partial or full compensation?
Simple or mixed acid base
disorder?

8. BASIC
ABNORMALITY
⯈ Acidosis : pH <7.40
Metabolic : HCO₃⁻
<24 Respiratory :
PCO₂ >40
⯈ Alkalosis : pH >7.40
Metabolic : HCO₃⁻
>24 Respiratory :
PCO₂ <40
⯈ High AG : >14

9. COMPENSATORY CHANGE
⯈ For metabolic disturbance :
Expected PaCO₂ : (HCO₃⁻ + 15)
± 2
⯈ For respiratory acidosis :
Expected HCO₃⁻ : 24 + (PaCO₂ - 40) X 0.1 (Acute
case)
24 + (PaCO₂ - 40) X 0.4 (Chronic
case)
⯈ For respiratory alkalosis :
Expected HCO₃⁻ : 24 - (40 - PaCO₂) X 0.2 (Acute
case)

10. ⯈ FULLY COMPANSATED -> if pH is normal
⯈ PARTIALLY COMPANSATED -> if all three values are abnormal
⯈ UNCOMPANSATED -> if PaCO₂ or HCO₃⁻ is normal and the other
is abnormal
FULLYCOMPANSATED
Acidosis Normal Alkalosis
pH
HCO₃⁻ PaCO₂
PARTIALLY COMPANSATED
Acidosis Normal Alkalosis
pH
PaCO₂ HCO₃⁻
UNCOMPANSATED
Acidosis Normal Alkalosis
pH
PaCO₂ HCO₃⁻

11. Exercise – 01 :
pH : 7.36
HCO₃⁻ : 20
mmol/L PaCO₂ :
35 mmHg Na⁺ :
140 mmol/L K⁺ :
4.0 mmol/L
Clˉ : 114 mmol/L

12. Ans :
Normal anion gap metabolic acidosis with partial
compensation
Examples:
⯈ RTA
⯈ Diarrhea
⯈ Small bowel fistula
⯈ Carbonic anhydrase inhibitor therapy

13. Exercise – 02 :
pH : 7.32
HCO₃⁻ : 15
mmol/L PaCO₂ :
30 mmHg Na⁺ :
140 mmol/L
K⁺ : 4.0 mmol/L
Clˉ : 106 mmol/L

14. Ans :
High anion gap metabolic acidosis with partial
compensation
Examples :
⯈ Diabetic ketoacidosis
⯈ Lactic acidosis
⯈ Starvation ketosis
⯈ Uremia

15. Exercise – 03 :
pH : 7.43
HCO₃⁻ : 30
mmol/L PaCO₂ :
45 mmHg

16. Ans :
Metabolic alkalosis with partial
compensation
Examples :
⯈ Conn’s syndrome
⯈ Cushing’s syndrome
⯈ Corticosteroid therapy
⯈ Vomiting
⯈ Diuretics

17. Exercise – 04 :
pH : 7.37
HCO₃⁻ : 32
mmol/L
PaCO₂ : 60
mmHg

18. Ans :
Respiratory acidosis with partial compensation
Examples :
⯈ COPD
⯈ Muscular dystrophy
⯈ Sleep apnea
⯈ Ankylosing spondylosis
⯈ Kyphoscoliosis

19. Exercise – 05 :
pH : 7.42
HCO₃⁻ : 20
mmol/L
PaCO₂ : 30
mmHg

20. Ans :
Respiratory alkalosis with partial
compensation
Examples :
⯈ Psychogenic hyperventilation
⯈ Pulmonary embolism
⯈ Pregnancy
⯈ CLD
⯈ Salicylate poisoning

21. Exercise – 06 :
pH : 7.35
HCO₃⁻ : 14
mmol/L
PaCO₂ : 24
mmHg

22. Ans :
Metabolic acidosis with respiratory
alkalosis
Examples :
⯈ Acute pulmonary embolism
⯈ Salicylate poisoning

23. Exercise –
07 :
pH : 7.38
HCO₃⁻ : 20
mmol/L PaCO₂ :
38 mmHg

24. Ans :
Metabolic acidosis with respiratory acidosis
Examples :
⯈ Severe pneumonia with pulmonary
edema
⯈ Severe pneumonia with renal failure
⯈ AKI with fluid overload
⯈ Renopulmonary syndrome

25. Exercise –
08 :
pH : 7.48
HCO₃⁻ : 29
mmol/L PaCO₂ :
30 mmHg

26. Ans :
Respiratory alkalosis with metabolic
alkalosis
Examples :
⯈ Pregnancy with diuretics
⯈ CLD on diuretics

27. Exercise –
09 :
pH : 7.39
HCO₃⁻ : 32
mmol/L PaCO₂ :
55 mmHg

28. Ans :
Respiratory acidosis with metabolic
alkalosis
Examples :
⯈ COPD on diuretics

29. Exercise – 10 :
pH : 7.40
HCO₃⁻ : 26
mmol/L PaCO₂ :
40 mmHg
Na⁺ : 140 mmol/L
K⁺ : 3.0
mmol/L Clˉ :
95 mmol/L

30. Ans :
High anion gap metabolic acidosis with metabolic
alkalosis
Examples :
⯈ Uremia with vomiting

31. Arterial Blood Gases:
pH = 7.58
pCO₂ = 21 mmHg
pO₂ = 154 mmHg
HCO₃ = 19 mmol/l
Exercise – 11:
A 70-year-old man was admitted with severe congestive cardiac failure. He
has been unwell for about a week and has been vomiting for the previous
5 days. He was on no medication. He was hyperventilating and was
very distressed. Admission biochemistry is listed below. He was on
high concentration oxygen by mask.
Biochemistry results: Na+ 127, K+ 5.2, Cl- 79, HCO3- 19, urea 50.5, creatinine
0.38 & glucose 9.5 mmol/L.

32. Ans
:
Respiratory alkalosis with high AG metabolic acidosis with metabolic
alkalosis

33. Exercise – 12 :
A 60 year old women was admitted with lobar pneumonia. She was
on a thiazide diuretic for 9 months following previous admission
with CCF. The admission ABG results were:
pH = 7.64
Pco2 = 32 mmHg
Po2 = 75 mmHg
HCO3 = 33 mmol/L
K+ = 2.1 mmol/L

34. Ans
:
Respiratory alkalosis with metabolic
alkalosis