ABB

1. Mr. Azher

2. Blood pH Regulation
Acid Base Balance
(ABB)
Professor Dr. Mohammad Shafique
MBBS, M.Phil, Ph.D.

3. The important aspect of clinical biochemistry is
information on a patient’s
 pH regulation
 Acid base balance
 Blood gas homeostasis.
These data often are used to assess patients in
life- threatening situations.

4. Normal pH of Blood is 7.4 Life compatible pH 7 – 7.7
Importance of pH regulation
1. For normal enzyme activity
2. Acidosis – affects enzyme activity. Causes depression of CNS –
coma, death may occur in severe case
3. Alkalosis – causes stimulation of CNS, excitation and convulsions.
Body’s tendency is towards acidosis, producing inorganic and
organic acids continuously. Cells produce 50-100 mmol/L H+ daily

5. MCQs
1. The normal pH of the blood is
(A) 7.0 (B) 7.1
(C) 7.2 (D) 7.4
2. The normal concentration of bicarbonate in blood is
(A) 21 meq/L (B) 24 meq/L
(C) 26 meq/L (D) 30 meq/L
3. At the pH of blood 7.4, the ratio between the carbonic acid and
bicarbonate fractions is
(A) 1 : 10 (B) 1 : 20
(C) 1 : 30 (D) 1 : 40

6. 4. Important buffer system of extracellular fluid is
(A) Bicarbonate/carbonic acid
(B) Disodium hydrogen phosphate/sodium dihydrogen phosphate
(C) Plasma proteins
(D) Organic Phosphate
5. The pH of body fluids is stabilized by buffer systems.
The compound which will be the most effective buffer
at physiologic pH is
(A) Na2HPO4 pKa = 12.32 (B) Na2HPO4 pKa=7.21
(C) NH4OH pKa = 7.24 (D) Citric acid pKa = 3.09

7. 6. In a solution having a pH of 7.4, the hydrogen ion concentration is
(A) 7.4 nmol/L (B) 40 nmol/L
(C) 56 nmol/L (D) 80 nmol/L
7. In a solution containing phosphate buffer, the pH will be 7.4, if the
ratio of monohydrogen phosphate : dihydrogen phosphate is:
(A) 4 : 1 (B) 5 : 1
(C) 10 : 1 (D) 20 : 1
8. Buffering action of haemoglobin is mainly due to its:
(A) Glutamine residues (B) Arginine residues
(C) Histidine residues (D) Lysine residues

8. Mechanism of regulation
Blood pH is regulated by the following mechanisms:
Chemical buffers include inorganic and organic pairs. They are first line
of defense and act within seconds.
Physiological buffers include lungs and kidneys. Lungs deal with
respiratory acid I.e. CO2 (H2CO3) they act within hours. Kidneys deal with
HCO3 component mainly by its reabsorption or excretion by renal tubules.
They act within days and cause final compensation.

9. Chemical buffers are further classified as
I.Extra cellular buffers
Bicarbonate buffer: NaHCO3/H2CO3 (Main in ECF)
Phosphate buffers: Na2HPO4/NaH2PO4
Protein buffer: B.Protein/H.Protein
II. Intracellular buffers
Phosphate buffer ( Main in ICF and more powerful)
Bicarbonate buffer (Less important in ICF)
Protein buffer (also present in ICF)

10. III. RBC’s Buffer: Hemoglobin acts as special
buffer and carries O2 & CO2.
IV. Other Chemical Buffers
Which are commonly used in vetro as well
Acetate buffer: CH3COONa/CH3COOH.
Citrate buffer: Sodium citrate/ Citric acid.
Ammonium buffer: NH4Cl/NH4OH.
Barbitone buffer: Na barbiturate/ Barbituric acid

11. Chemical Buffers
NON VOLATILE OR FIXED ACIDS
Main buffer involved is bicarbonate which deals the various acids produced
continuously in the body – HCl, H2PO4, & K. Bodies – actoacetate.
3–hydroxy butyrate , H2SO4, Pyruvate , lactic acid.
For this acids , the buffer used is HCO3/ H2CO3.
- HCl + NaHCO3 NaCl + H2CO3
- H2SO4 + NaHCO3 Na2SO4 + H2CO3
- H2PO4 + NaHCO3 Na2HPO4 + H2CO3
- Pyruvic acid + NaHCO3 Na- Pyruvate + H2CO3
- Lactic acid + NaHCO3 Na-Lactate + H2CO3
- Acetoacetic acid + NaHCO3 Na-acetoacetate + H2CO3
H2CO3 is a weak acid and is broken down into CO2 + H2O
NaHCO3 is an alkali reserve which is decreased
and is finally compensated by kidneys.

12. Buffering by lungs
Regulate the amount of CO2 that is removed by expiration or retained. It
takes 3-6hours for the maximum effect of respiratory compensation. It is
mediated through CNS chemo receptors in contact with CSF. Peripheral &
central chemo receptors are sensitive to small changes of pH & PCO2.
Main respiratory acid is CO2 (H2CO3) which is volatile , produced in tissues
during metabolism. Production is 200 ml/min=288 L/day which is equal
to 2.6N HCL (damage wise)
Lung Level Blood Tissue Level
RBC RBC
O2
HbO2
Hb
H HHb
H2CO3
H2O + CO2 HCO3
-
Cl-
HbO2
HHb
HCO3
Cl- Cl-
H2O + CO2
HbO2 O2
Hb
HHb H2CO3
H+ + HCO3
-
Cl-
Expired Out
HCO3- Cl- Shift
Hamburger’s Phenomenon
CO2 is also transporetd as Hb NH2 CO2
Carbonic
Anhydrase
tissues

13. Interrelation of HCO3
- & Hb

14. Role of Kidney’s regarding ABB
- Reabsorbtion or excretion of HCO3 by kidneys
- Reabsorption and excretion of chlorides
- Generation of HCO3
-
- Formation of NH3
- Acidification of urine
- Excretion or conservation of H+ as free acid
- Na & H+ exchange
- K+ & H+ or Na+ exchange

15. RBC
STOMACH

16. The bicarbonate system is the most important buffer in the
body because:
• It accounts for more than 60 per cent of the blood buffering
capacity,
• H+ secretion by the kidney depends on it,
• It is necessary for efficient buffering by Hb, which provides
most of the rest of the blood buffering capacity.
Urinary Buffers:
Bicarbonate buffer pKa = 6.1
Phosphate buffer pair pKa = 6.8
NH3 / NH4 buffer pair pKa = 9.8

17. Tubular Lumen
(Urine)
Renal Tubular Cells Peritubular Fluid
(Plasma)
NaHCO3
Na + HCO3
H+
Na +
H2CO3
H2O + CO2
Chief Inorganic component
of Urine
H2O + CO2
H2CO3
H+ + HCO3
-
Na +
Na: H Exchange
HCO3
- Retention
HCO3
-
Na +
Buffering by Kidneys
Tabel I: Reabsorption & Generation of HCO3
Carbonic
Anhydrase

18. Reabsorbtion & Generation of Bicarbonate

19. Table II: Dealing of Fixed ions or Phosphates (Na2HPO4)
Na2HPO4
Na+ + NaHPO4
H+
Na+
NaH2PO4
Acidification of Urine
H2O + CO2
H2CO3
H+ + HCO3
-
HCO3
- and Cl-
excretion is
reciprocal
HCO3
-
Na+
Carbonic
Anhydrase

20. Acidification of Urine

21. Role of Ammonia

22. Table III Neutral Salts ( Na2SO4, NaCl, NaA-)
Tubular Lumen Renal Tubular Cells
Peritubular Fluid
(Plasma)
Na A- NaCl Na2SO4
Na + A- Na++ Cl- 2Na+ + SO4
2Na+
NH4
H2O + CO2
Carbonic
Anhydrase
H2CO3
H+ + HCO3
-
NH3 Glutamine
K+
H+
NH4
+ weak acid & NH3 is
strong base
NH3 eliminates H+
It conserves Na+
NH3 is Increased in acidosis
and decreased in alkalosis.
HCO3
-
2 Na+
Glutamine
In Alkalosis
K:Na / K:H Exchange
H+
May cause hypokalemia, Ca2+
can also ( Tetany can occur)
NH4 A-
NH4Cl
(NH4)2 SO4
K2SO4
KCl
URINE

23. Disturbed Acid Base Balance
pH = pKa + Log Salt/Acid = NaHCO3/H2CO3
pH = Salt/Acid = 20/1 = 40/2 = 10/5
Salt component is related with metabolism and
controlled by kidneys
Acidic component is related with respiration and is
controlled by respiration. Center in medulla
oblongata of brain
If salt component is disturbed then Metabolic Acidosis
/ Metabolic Alkalosis
If acidic component is disturbed then Respiratory
Acidosis / Respiratory Alkalosis

24. Respiratory Alkalosis
It is rare. pH high, CO2N, PCO2 low & HCO3/H2CO3normal sometimes
It is due to increased hyperventilation both rate and depth.
Causes:
Head injuries: CNS is stimulated
Anxiety, nervousness, apprehension, hysteria.
Hepatic failure, CCF, thyrotoxicosis, hypoxia,
Exercise, Salicylate poisoning, high altitude.
Compensation: By lungs : Already Defected.
By Kidneys : Less HCO3
- Reabsorbed
More HCO3 exertion
More H+ conserved
NH3 synthesis is depressed
So Na+ : K exchange
K low in plasma ( Hypokalemia)
Also Ca+ may be low in plasma
So tetany may occur

25. Exercise:
The following are the blood gas results of a patient who has
been on a respirator for the past week—pH : 7.5
pCO2: 24 mm of Hg
pO2: 88 mm of Hg
HCO3
-: 18 mmol/L.
A. What is the acid-base status of the patient?
B. Explain the nature of the disturbance and the alteration in each
parameter.
C. What is the nature of the compensatory change?
R.Al
Normal values-Arterial blood
pH 7.35-7.45
pO2 (mmHg) 80-110
pCO2(mmHg) 35-45
HCO3 (mmol/L) 22-26
O2Hb (%) >95

26. Respiratory Acidosis
It is rare but is an emergency. In it pH is low, PCO2 high & HCO3/H2CO3 low.
It is due to hypoventilation.
Causes:
Air passage obstruction. Respiratory distress syndrome.
Chronic obstructive pulmonary disease of lungs and pleura.
Pneumonia, pneumothorax, pulmonary edema & asthma.
Abdominal muscle disease, myasthenia gravis.
General anesthesia, narcotics & barbiturates, high CO Hb.
Compensation: Lungs already defected.
Kidneys play role.
Na:H exchange
CO2+H2O H2CO3 HCO3 + H+
HCO3
_
all conserved.
H+ is excreted in urine
Plasms Urine

27. EXERCISE:
The following results were obtained by blood gas analysis on the arterial blood of a
patient admitted in an unconscious state with suspected barbiturate poisoning.
pH: 7.24
pCO2: 60 mm of Hg
HCO3", 27 mmol/L
A. What is the nature of acid-base disturbance Explain.
B. Why barbiturates cause acid-base disturbance?
C. What will be the nature of compensation?
D. What are the enzyme levels that are likely to be elevated in this patient?
E. Define the term base deficit.
F. What is the effect of barbiturates on heme synthesis?
R.Ac
Normal values-Arterial blood
pH 7.35-7.45
pO2 (mmHg) 80-110
pCO2(mmHg) 35-45
HCO3 (mmol/L) 22-26
O2Hb (%) >95

28. EXERCISE:
The laboratory results of a patient with chronic obstructive pulmonary disease
(COPD) are:
pH : 7.26
pCO2: 65 mm of Hg
pO2: 60 mm of Hg
bicarbonate: 36 mmol/L.
A. What is the nature of the disturbance?
B. How is it compensated?
D. What are the major buffer systems of plasma?
E. Explain the role of hemoglobin in buffering.
Ch.R.Ac
Normal values-Arterial blood
pH 7.35-7.45
pO2 (mmHg) 80-110
pCO2(mmHg) 35-45
HCO3 (mmol/L) 22-26
O2Hb (%) >95

29. Metabolic Acidosis
In it low pH, PCO2N,PCO2 Low, HCO3/H2CO3 Low
Causes:
Prolonged diarrhea, loss of pancreatic juice & bile.
Uncontrolled DM, ketoacidosis, lactic acidosis.
Chronic renal failure, tissue hypoxia, CA inhibitor.
Ammonia Cl ingestion, hypoaldosteronism.
For causes, remember DR MAPLES:
D= DKA , R= reanal disease /injury, M= methanol,
A= alcoholic A, P= Paracetamole, L= Lactic acidois ,
E= ethylene glycol, S= salicylates
Compensation:
By Lungs: Hyperventalation, So PCO2 low by exhalation.
By Kidneys: HCO3 reabsorbed. H+ is excreted in NH4 forms. NH3
formation is increased

30. A 7-year-old boy was admitted unconscious to a casualty
department. On examination he was found to be
hyperventilating. He had inadvertently consumed ethylene
glycol antifreeze, which he had found in his parents' garage
stored in a lemonade bottle. Blood results were as follows:
Plasma
Sodium 134mmol/L(135-l45)
Potassium 6.0mmol/L (3.5-5.0)
Bicarbonate 10 mmol/L (24-32)
Chloride 93 mmol/L (95-105)
Glucose 5.3 mmol/L (3.5-6.0)
Arterial blood gases
pH 7.2 (7.35-7.45)
pCO2 3.18kPa (4.6-6.0) kPa = kilopascals
pO2 13.1kPa (9.3-13.3) 1kPa = 7.5mmHg
M.Ac

31. Metabolic Alkalosis
pH High, PCO2N,HCO3/H2CO3 high.
Causes:
Gastric vomiting, HCl loss, nasogastric suction, citrate transfusion.
Excessive intake of alkali, milk alkali syndrome, licorice abuses.
Diuretics like chlorothiazides, steroid treatment, Cushing
syndrome, hyperaldosteronism
Compensation:
By Lungs: Hypoventilation, so PCO2 is conserved.
By Kidneys: HCO3 are excreted.
H+ is reabsorbed as K:H exchange,
so Hypokalemia.
Na and K are lost in urine

32. A baby girl a few days old had had projectile vomiting since
birth clue to pyloric stenosis. Her blood results were as
follows:
Plasma:
Sodium 137 mmol/L (135-145)
Potassium 3.0 mmol/L (3.5-5.0)
Bicarbonate 40mmol/L (24-32)
Chloride 82 mmol/L (95-105)
Arterial blood gases:
pH 7.52 (7.35-7.45)
Paco2 6.2kPa (4.6-6.0)
Pao2, l2.9kPa (9.3-13.3)
M.Alk

33. Electrolytes in meq/L
Cat-ions An-ions
Na+= 144 Cl- = 103
HCO3
- = 27
K+ = 4 Proteinate = 16
Organic
Ca2+= 5 acid anions = 6
Phosphate = 2
Mg2+= 2 Sulfate = 1
Total = 155meq/L Total = 155meq/L
****************

34. Anion Gap in ABB
It is calculated by the difference between
measured cations and anions:
[Na+K]-[HCO3+Cl]=AG
It’s importance relates to differentiate the type
and cause of metabolic acidosis. We know that
in serum:
Na + K + Other cations = HCO3
- + Cl- + Other Anions
 The major unmeasured cations are Ca, Mg.
 The major unmeasured anions are PO4, SO4,
Lactate and negatively charged albumin and other
organic anions.

35. An increased Anion Gap is found when there is an increase in
unmeasured anions such as proteins, PO4 and SO4.
Lactic acidosis, ketoacidosis (DM), starvation, renal failure.
Intoxation of methanol, ethanol, salicylates, ethylene glycol,
hypernatremia.
For Causes, remember the word DR MAPLES

36. A decreased anion gap
 May be due to an increase in unmeasured
cations as in Hypercalcemia &
hypermagnesemia or lithium toxicity.
 Increase in hyperimmunoglobulemenia (IgG)
due to net positive charge.
 Decreased unmeasured anions with
hypoalbuminemia.

37. Anion Gap (A- or X- ) is calculated by
Na – [ HCO3
- + Cl-] = 12mEq/L (8 – 16) Normal Value
[Na + K] - [ HCO3
- + Cl-] = 15mEq/L (10-20) Normal Value
[Na] + [K] = [ HCO3-] + [Cl] + [A-]
140 + 4 = 25 + 100 + 19
141 + 4 = 15 + 100 + 29
130 + 4 = 15 + 100 + 19
140 + 4 = 15 + 110 + 19
[Na] + [K] = [ HCO3-] + [Cl] + [A-] + [X-]
140 + 4 = 15 + 100 + 19 + 10 mEq/L
Anion Gap