patholophysiology of acid base disturbance Pathophysiology（病理生理学） Pathology uploaded by prabesh 杰诗

1. Dept. of PathologyDept. of Pathology
Medical CollegeMedical College
Hunan Normal UniversityHunan Normal University
(( 湖南 范大学医学院病理学教研室师湖南 范大学医学院病理学教研室师 )) 1
Chapter 3Chapter 3
Acid-Base Balance andAcid-Base Balance and
ImbalanceImbalance
（酸 平衡紊乱）碱（酸 平衡紊乱）碱

2. 22
Acid-Base Balance and ImbalanceAcid-Base Balance and Imbalance
a.a. Acid-base homeostasisAcid-base homeostasis
b.b. Parameters of acid-baseParameters of acid-base
balancebalance
c.c. Simple acid-base disturbanceSimple acid-base disturbance
 Metabolic acidosisMetabolic acidosis
 Respiratory acidosisRespiratory acidosis
 Metabolic alkalosisMetabolic alkalosis
 Respiratory alkalosisRespiratory alkalosis

3. §1. Concept ：
Decrease of pH induced by primary increase in PaCO2
(or plasma H2
CO3
).
§2. Causes ：
Hypoventilation (inside) ：
Air way obstructed
Paralysis of respiratory muscle
Fibrosis of the lungs
Insufficient ventilation (outside)
Excessive inspiration of CO2 (e.g, mine workers)
Respiratory acidosis

4. §3. Compensation ：
1) Acute respiratory acidosis:
Often decompensated because kidneys play their roles in
compensation slowly.
2) Chronic respiratory acidosis:
The secondary HCO3
-
↑ shows after 3 ～ 5 days.
Respiratory acidosis
Lungs and bicarbonate buffer system can’t play their roles in
compensation.
Mainly depends upon non-bicarbonate systems and the
kidneys.

5. 2.1 Pulmonary heart disease patient ：
pH 7.34, HCO3
-
31 ， PaCO2
60 ；
Predict HCO3
-
= 24 + 0.4(60 - 40)±3 = 29 ～ 35
Measured HCO3
-
= 31, within predicted, simple RAc
Equation ： predict HCO3
-
= 24 + 0.4 PaCO△ 2
±3
Example
Judgement ：
If measured HCO3
-
insofar as predict HCO3
-
, simple RAc
If measured > predict maximum, HCO3
-
retention, RAc +MAl
If measured < predict minimum, HCO3
-
too less, RAc + MAc
Respiratory acidosis

6. 2.2 Pulmonary heart disease patient given bicarbonate ：
pH 7.40 ， HCO3
-
40 ， PaCO2
67 ；
Predict HCO3
-
= 24 + 0.4(67 - 40)±3 = 31.8 ～ 37.8
Measured HCO3
-
= 40, exceed predict maximum ，
RAc + MAl
2.3 Pulmonary heart disease patient ：
pH 7.22 ， HCO3
-
20 ， PaCO2
50
Predict HCO3
-
= 24 + 0.4(50―40)±3 = 25 ～ 31
Measured HCO3
-
=20, below predict minimum ，
RAc + MAc
Respiratory acidosis

7. §4. Changes of blood gas parameters ：
Respiratory acidosis
pH ↓
PaCO2
↑↑
HCO3
-
↑
AB ↑
SB ↑
BB ↑
BE ↑ (positive value increased)
(in the case of simple RAc)

8. §5. Effects on organism ：
Respiratory acidosis
1) Cardiovascular system ：
Similar to MAc
Cardiac arrhythmias
Negative inotropic action
Blood vessel dilatation
2) Nervous system ： quite prominent
Pulmonary encephalopathy :
PaCO2
↑ CO2
retention (>80 mmHg, narcosis)

9. 1) Correction of underlying disorders ：
Improve ventilation
2) Correction of acidosis ：
Tris (THAM) should be used with caution after ventilation
improved. (Instead of NaHCO3)
Tris+ H2CO3→TrisH+
+ HCO3
-
§6. Principles of prevention and treatment
：
Respiratory acidosis

10. 1010
Acid-Base Balance and ImbalanceAcid-Base Balance and Imbalance
a.a. Acid-base homeostasisAcid-base homeostasis
b.b. Parameters of acid-baseParameters of acid-base
balancebalance
c.c. Simple acid-base disturbanceSimple acid-base disturbance
 Metabolic acidosisMetabolic acidosis
 Respiratory acidosisRespiratory acidosis
 Metabolic alkalosisMetabolic alkalosis
 Respiratory alkalosisRespiratory alkalosis

11. §1. Concept ：
Increase of pH induced by primary increase in plasma HCO3
-
.
§2. Causes ：
Acids too little
Bases too much
Metabolic alkalosis

12. H+
Loss ↑ from the stomach ： bad vomiting and/or
gastric suction
H+
Loss ↑ from the
kidneys
Long term use of diuretics:
primary or secondary
hyperaldosteronism
Cushing Syndrome
(↑ cortisol →↑ glucocorticoid
[similar to ADS])
Hypokalemia: H+
exchanged into cells
ADS↑:
1) Acids
too little
Metabolic alkalosis
Ammonia (NH3) poisoning during hepatic failure
NH3 + H+
→ NH4
+

13. 2) Bases
too much
Excessive intake of alkaline drugs
(e.g., NaHCO3)
Excessive intake of stored blood
(rich in sodium citrate)
Loss of a lot of fluid
Compensatory HCO3
-
↑:
 Hyperaldosteronism → ↑ ADS →
reabsorption of Na+
and HCO3
-
 Compensation after chronic respiratory
acidosis (e.g., mechanical ventilation)
Metabolic alkalosis

14. §3. Classification ：
1) Saline-responsive alkalosis ：
The replacement of saline (0.9%NaCl) is effective.
Cl-
helps excrete HCO3
-
Seen in vomiting, gastric suction and use of the diuretics.
(causing loss of H+
)
2) Saline-resistant alkalosis ：
The replacement of saline is not effective.
Seen in ADS↑, Cushing syndrome.
Causative diseases need to be treated first.
Metabolic alkalosis

15. §3. Compensation ：
1) Buffer systems ：
 Plasma buffer systems
 Cells
May cause hypokalemia
H+
↓ Hypokalemia
K +
H+
Metabolic alkalosis

16. 2) Regulation by the kidneys:
↓ excretion of H+
/NH4
+
↓ HCO3
-
reabsorption
Alkaline urine
3) Regulation by the lungs - main mechanism ：
H+
↓→(-) breathing PaCO2
↑ (secondary)
Metabolic alkalosis
Na+
Capillary Epithelial Cell Tubule
H2O + CO2
H+
Na+
H2CO3
HCO3
-
H+

17. 3.1 Pyloric obstruction patient ： pH 7.49 ， HCO3
-
36 ， PaCO2
48 ；
Predict PaCO2
= 40 + 0.7(36-24)±5 = 43.4 ～ 53.4
Measured PaCO2
= 48, within predicted, simple MAl
Equation ： predict PaCO2
= 40 + 0.7 HCO△ 3
-
±5
Example
Judgement ：
If measured PaCO2 insofar as predict PaCO2 , simple MAl
If measured > predict maximum, CO2 retention, MAl + RAc
If measured < predict minimum, CO2 too less, MAl + RAl
Metabolic alkalosis

18. 3.2 Septic shock patient given excessive bicabonate and
mechanical ventilation ：
pH 7.65 ， HCO3
-
32 ， PaCO2
30 ；
Predict PaCO2
= 40 + 0.7(32-24)±5 = 40.6 ～ 50.6
Measured PaCO2
= 30, below predict minimum
MAl + RAl
3.3 Pulmonary heart disease patient used the diuretics ：
pH 7.40 ， HCO3
-
36 ， PaCO2
60 ；
Predict PaCO2
= 40 + 0.7(36-24)±5 = 43.4 ～ 53.4
Measured PaCO2
=60, exceed predict maximum
MAl + RAc
Equation ： predict PaCO2
= 40 + 0.7 HCO△ 3
-
±5
Metabolic alkalosis

19. §4. Changes of blood gas parameters ：
pH ↑
HCO3
-
↑↑
PaCO2
↑
AB ↑
SB ↑
BB ↑
BE ↑ (positive value increased)
Metabolic alkalosis
(in the case of simple MAl)

20. §5. Effects on organism ：
1) Central nervous system (CNS) ： excitatory, such as
restlessness, mental derangement, delirium and disorder of
consciousness.
Mechanism ：↓ γ-GABA (inhibitory neurotransmitter)
2) Neuromuscular excitability ： The patient may
manifest tendon hyperreflexia and convulsion.
Mechanism ： Plasma free Ca2+
↓ in alkalosis
Glutamate decarboxylase
↑ pH
Glu GABA
Metabolic alkalosis

21. 4) Hypokalemia (arrhythmia) ：
5) Urine: usually alkali
But in hypokalemia-alkalosis:
paradoxical acidic urine
Metabolic alkalosis
3) Hypoxia ：
pH ↑→ affinity of O2 to Hb ↑ (ODC left shift)

22. §6. Principles of prevention and treatment ：
1) Saline-responsive MAl
Saline (NaCl or KCl) infusion
2) Saline-resistant MAl
 Carbonic anhydrase (CA) inhibitor
- Acetazolamide (diamox)
- Inhibits generation and secretion of H+
 ADS inhibitor
- Spironolactone [ 螺内脂 ]
- Inhibits reabsorption of Na+
and H2CO3
+
Metabolic alkalosis

23. 2323
Acid-Base Balance and ImbalanceAcid-Base Balance and Imbalance
a.a. Acid-base homeostasisAcid-base homeostasis
b.b. Parameters of acid-baseParameters of acid-base
balancebalance
c.c. Simple acid-base disturbanceSimple acid-base disturbance
 Metabolic acidosisMetabolic acidosis
 Respiratory acidosisRespiratory acidosis
 Metabolic alkalosisMetabolic alkalosis
 Respiratory alkalosisRespiratory alkalosis

24. §1. Concept ：
Increase of pH induced by primary decrease in PaCO2
(or plasma
H2CO3).
§2. Causes ： Hyperventilation is the fundamental
mechanism of respiratory alkalosis.
1) Excitement of respiratory center
Fever, hysteria.
2) Hypoxia
3) Lung diseases
ARDS, interstitial pneumonia.
4) Misuse of mechanical ventilator
Respiratory alkalosis

25. §3. Classification ：
１ ) Acute respiratoy alkalosis ：
High fever, misuse of mechanical ventilator
2) Chronic respiratory alkalosis ：
Chronic hypoxia, lung diseases
Respiratory alkalosis

26. 2) Chronic respiratory alkalosis ：
Kidneys are main organs in compensation.
−↓ excretion of H+
−↓ reabsorption of HCO3
-
§3. Compensation ：
1) Acute respiratory alkalosis ：
 Buffers in plasma and cells.
 Often decompensated because the lungs and kidneys fail
to play their roles in compensation.
Respiratory alkalosis

27. 4.1 Hysteria patient ： pH 7.42 ， HCO3
-
19 ， PaCO2
29 ；Predict HCO3
-
= 24 + 0.5(40 - 29)±2.5 = 16 ～ 21
Measured HCO3
-
= 19, within predicted, simple RAl
Equation ： predict HCO3
-
= 24 + 0.5 PaCO△ 2
±2.5
Example
Judgement ：
If measured HCO3
-
insofar as predict HCO3
-
, simple RAl
If measured > predict maximum, HCO3
-
retention, RAl + MAl
If measured < predict minimum, HCO3
-
too less, RAl + MAc
Respiratory alkalosis

28. 4.2 ARDS patient with shock:
pH 7.41 ， HCO3
-
10.2, PaCO2
18 ；
Predict HCO3
-
= 24 + 0.5(18 - 40)±2.5 = 10.5 ～ 15.5
Measured HCO3
-
= 10.2, below predict minimum,
RAl + MAc
Respiratory alkalosis

29. §4. Changes of blood gas parameters
：
pH ↑
HCO3
-
↓
AB↓
SB↓
BB↓
BE ↓ (negative value increased)
Respiratory alkalosis
(in the case of simple RAl)
PaCO2
↓↓

30. 1) central nervous system ：
PaCO2
↓ （ hypocapnia ）→ cerebrovascular
contraction → blood content in brain↓ →
disturbances in CNS, such as vertigo (dizzy),
unconsciousness, coma.
§5. Effects on organism ：
2) Increased neuromuscular excitability
(↓GABA)
such as convulsion, etc.
3)Hypokalemia
Respiratory alkalosis

31. §6. Principles of prevention and treatment ：
1) Treatment of primary diseases;
2) Prevention of mechanical hyperventilation
(ataractic used);
3) Inspiration of oxygen containing 5% CO2.
Respiratory alkalosis

32. Guidelines for the Diagnosis of Acid-Base Disturbances
1. According to the changes of pH, an acidosis or alkalosis can be
determined.
2. According to the case history (or/and H-H equation), primary
disorders of HCO3
–
or PaCO2 can be determined.
3. According to the primary disorders, a respiratory or metabolic
disturbance can be determined.
If a primary HCO3
-
↑or ↓, a metabolic alkalosis or acidosis can be
determined.
If a primary PaCO2 ↑or ↓, a respiratory acidosis or alkalosis can be
determined.
4. According to AG↑ , the types of metabolic acidosis can be
determined.
5. According to compensation equations, simple or mixed acid-base

33. Changes of Blood Gas ParametersChanges of Blood Gas Parameters
pHpH PaCOPaCO22
--
HHCOCO33
--
ABAB SBSB BBBB BEBE
AcidosisAcidosis
MetabolicMetabolic ↓↓ ↓↓ ↓↓↓↓ ↓↓ ↓↓ ↓↓ ↓↓
RespiratoryRespiratory ↓↓ ↑↑↑↑ ↑↑ ↑↑ ↑↑ ↑↑ ↑↑
AlkalosisAlkalosis
MetabolicMetabolic ↑↑ ↑↑ ↑↑↑↑ ↑↑ ↑↑ ↑↑ ↑↑
RespiratoryRespiratory ↑↑ ↓↓↓↓ ↓↓ ↓↓ ↓↓ ↓↓ ↓↓
Metabolic: changes of pH and others at the same direction;
Respiratory: changes of pH and other at the opposite direction.

34. Example ：
A 45-year-old women was admitted to the local hospital with nausea,
vomiting, anorexia. She has suffered a 5-year history of hypertension
and a 3-year history of albuminuria. Doctor told her kidneys damaged
one year ago. Now edema and hypertension has been checked out. Her
laboratory results were as follows: pH 7.30 ， PaCO2 20
mmHg ， HCO3
–
9 mmol/ L ， Na+
127 mmol/L ， K+
6.7 mmol/L ， Cl-
88
mmol/L ， BUN 1.5g/L [0.09 – 0.2] 。
1 ， Is there acid-base disorders?
2 ， Why does PaCO2 decrease too ？
3 ， Why her AG ↑ ?
[acids not eliminated from damaged kidneys]
4 ， Is there any other acid-base disorders except metabolic
acidosis ？
Equation ： predict PaCO2
= 1.5×[HCO3
-
] ＋ 8±2

36. 1, A patient suffered from pulmonary heart disease ：
pH 7.35 ， HCO3
-
36 mmol/L ， PaCO2 66 mmHg ，
1, PaCO2 ↑↑ , primary RAc
2, AG=140-(75+36)=29 , MAc
3, Also MAl , why ？ △ AG↑ ＝△ HCO3
-
↓ AG=29-12=17△
So, HCO3
-
(before buffering)= 36+17 = 53
RAc Equation:
predict HCO3
-
=24+0.4(66―40)±3= 34.4 ±3
HCO3
-
(before buffering) =53 > 37.4 , MAl
Conclusion ： RAc+MAc+MAl
Na+
140 mmol/L ， K+
4.5 mmol/L ， Cl-
75 mmol/L 。

37. H+: hydrogen ion
 H+: hydrogen ions
 K+: potassium ions
 Na+: sodium ions
 Cl-: chloride ions
 Ca2+:Calcium ions
 NH4+: ammonium ions
 HCO3-:bicarbonate ions
 HPO2- :phosphatic ions
 CO2: carbon dioxide
 H2CO3:carbonic acid
 NH3: ammonia
 mmol: millimol
 nmol: nanomol
 mmHg: millimetre of
mercury column