ACID - BASE PHYSIOLOGY

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ACID - BASE PHYSIOLOGY

• PROFESSOR. ASHRAF HUSAIN
• DEPT. OF PHYSIOLOGY
• COLLEGE OF MEDICINE
• KING SAUD UNIVERSITY
• RIYADH.

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Acid Base Physiology

• Definition
• pH is defined as potential of H Ion
  concentration in body fluid. The amount of H
  ion concentration is so low in the body hence it
  is expressed as ve logarithm to base of the H
  ion concentration in mEq/lit.
• pH log 1/ H
• - log H

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NORMAL VALUE

• Arterial blood 7.35 7.45
• Can be explained as follows
• Normal value of H ion conc. is about
  40nEq/lit.
• 40 nEq/lit 0.00000004 Eq/lit.
• Therefore pH - log 0.00000004
• 7.4

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pH and H ion concentration

• pH
• 6.0
• 7.0
• 8.0
• 9.0

• H ion in nmol/lit
• 1000
• 100
• 10
• 1.0

Note one point drop in pH results in a ten fold
decrease in H ion conc.
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Scale of pH measurement

• The pH scale is between 0 14.
• Zero onwards below 7 is acidic.
• After 7 upto 14 the solution is alkaline.
• At 7 (neutral e.g. water) where the amount of H
  and Hydroxyl ion are equal at 23o

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• Examples of pH zero, one two.
• pH 0 1 lit. of HCl contains 1gm of H 10o
• pH 1 10 lit. of N/10 HCl contains 1gm of H
• Therefore 1 lit. will contain 1/10gm of H 10-1
• pH 2 100 lit. of N/100 HCl contains 1gm of H
• Therefore 1 lit. will contain 1/100gm of H 10-2
• And so on..
• It will be noted that a solution of pH 2 does not
  have twice the H ion conc. at a pH of 4 rather
  it has 100 times H ion conc.

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• Since pH is inversely related to H ion conc. so
  a low pH corresponds to high H ion conc.
  (Acidic) and a high pH corresponds to low H ion
  conc. (Alkaline)

Acidic
Neutral
Alkaline
14
7
0
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The Negative logarithmic relationship between
H and pH
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About H

• H are derived from hydrogen atoms. Hydrogen atom
  has proton a positive electrical charge with a
  negative charge electron which is revolving
  around it. The hydrogen ion is formed when
  negative ion 9electron) is lost and it contains
  only proton. The H is the smallest ionic
  particle, highly reactive with a very short life
  and unable to survive on its own.

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• A very tight control is needed for normal
  metabolic functions.
• eg. Enzymatic activity, blood clotting and
  neuromuscular activity.
• Hydrogen ions are the toxic end product of
  metabolism and they adversely affect all physical
  and biochemical cellular process in our body.

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Hydrogen Ion Excretion in Kidney
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Buffering of hydrogen ions in urine
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• A 44-year old woman with a long history of
  indigestion begins to vomit at home. She becomes
  unwell after 4 days and is admitted to hospital
  because of marked muscle weakness. Her arterial
  blood gases are H 28nmol/l,
• PaCO2 6.5kPa,
• HCO3- 40mmol/l,
• PaO210.3kPa,
• plasma potassium 2.1 mmol/l.
• Q. What is the likely diagnosis and what
  treatment is required?

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• Metabolic alkalosis is less common than metabolic
  acidosis. It is characterized by an increase in
  plasma bicarbonate, a fall in H, and a small
  compensatory rise in PaCO2.

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• 2. A 32 year-old man is admitted in a very ill
  state. He had been drinking with friends, but had
  not been seen for some hours. On admission he is
  barely conscious and breathing heavily.
• His arterial blood gases are
• H 98nmol/l,
• PaCO2 2.7kPa,
• HCO3- 6mmol/l,
• PaO2 13kPa.
• Q. What is likely diagnosis, how should it be
  confirmed, and what treatment is required?

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• Metabolic acidosis is characterized by a
  reduction in plasma bicarbonate and a rise in
  H. The PaCO2 is reduced secondarily by
  hyperventilation, which mitigates the rise in
  H.

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• 3. a 56-year-old man, who has smoked heavily for
  many years, develops a worsening cough with
  purulent sputum, and is admitted to hospital
  because of difficulty in breathing. He is drowsy
  and cyanosed. His arterial blood gases are
• H 65nmol/l,
• PaCO2 9.5kPa,
• HCO3- 28mmol/l,
• PaO26.2kPa,
• Q. What is likely diagnosis and what treatment is
  required?

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• Respiratory acidosis arises when effective
  alveolar ventilation fails to keep pace with the
  rate of CO2 production. As a result PaCO2, blood
  HCO3- and H all rise.

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• 4. a 13-year-school boy is brought the casualty
  department, having become acutely unwell in the
  headmasters office. He is alert and agitated,
  the respiratory rate is 35/min, and he complains
  of tingling in his hands. His arterial blood
  gases are
• H 29nmol/l,
• PaCO2 2.8kPa,
• HCO3- 22mmol/l,
• PaO2 16kPa.
• Q. What is the likely diagnosis and what
  treatment is required?

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• Respiratory alkalosis occurs when there is
  excessive loss of CO2 due to over-ventilation of
  the lungs. PaCO2 and H fall. The low PaCO2
  results in reduced renal Na/H exchange.

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REASONS FOR METABOLIC ACIDOSIS AND ALKALOSIS
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METABOLIC ACID BASE DISORDERS
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COMPENSATION IN PRIMARY METABOLIC DISORDERS
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RESPIRATORY AND MIXED ACID BASE DISORDERS
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WHY AN INCREASED PCO2 CAUSES AN ACIDOSIS
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RENAL COMPENSATION IN PRIMARY RESPIRATORY ACIDOSIS
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CAUSES OF RESPIRATORY ACIDOSIS AND ALKALOSIS
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ACID BASE DISORDERS DIAGNOSIS AND MANAGEMENT
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THE 95 COFIDENCE INTERVALS FOR ARTERIAL BLOOD
GASES IN PRIMARY ACID BASE DISORDERS
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THANK YOU