ACIDBASE BALANCE

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ACID-BASE BALANCE
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BASICS

• Acid-base balance is a dynamic relationship which
  reflects the concentration of hydrogen ions (H)
  in the body.
• Hydrogen ions are acids which must be maintained
  within strict limits
• Any deviation from the norm affects biochemical
  events.

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BASICS

• Acid-base relationship is measured in a logarithm
  (pH) which is inversely proportional to the
  hydrogen ion concentration
• High H ion concentration low pH
• Low H ion concentration high pH

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THE pH SCALE

• Scale ranges from 1 to 14
• 1 means only hydrogen ions are present
• 14 means no hydrogen ions present
• The pH of water is 7.0 which is neutral
• The normal range of the human body is 7.35 - 7.45
• A pH lt 7.35 indicates a state of acidosis
• A pH gt 7.45 indicates a state of alkalosis
• A variation of 0.4 in either direction can be
  fatal

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BODY REGULATION OF ACID-BASE BALANCE

• The body constantly produces acids through
  metabolism
• These acids must be constantly eliminated from
  the body
• Three systems perform this task
• Buffer system
• Respiratory system
• Renal system

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BUFFER SYSTEM

• The fastest performer, works in seconds
• Bicarbonate ions combine with excess hydrogen
  ions to form carbonic acid in a dynamic
  relationship
• HCO3 H H2CO3

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BUFFER SYSTEM

• For every molecule of carbonic acid, there are 20
  molecules of bicarbonate
• Any change in the this 201 ratio is immediately
  corrected to maintain pH
• An increase H causes an increase in H2CO3
• A decrease in H causes a decrease in H2CO3

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BUFFER SYSTEM

• Carbonic acid is a weak, volatile acid which must
  be eliminated
• The enzyme carbonic anhydrase causes the carbonic
  acid to convert to carbon dioxide and water
• The CO2 and the H2O are easily eliminated by the
  lungs and kidneys
• The system also works in reverse

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RESPIRATORY SYSTEM

• Works in minutes
• The lungs eliminate excess CO2 by increasing
  respirations, causing a decrease in H and an
  increase in pH
• The lungs can retain more CO2 by slowing
  respirations, causing an increase in H and a
  decrease in pH

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RENAL SYSTEM

• Can take hours to days to work
• Kidneys can retain bicarbonate ion, causing a
  decrease in H and an increase in pH
• Kidneys can excrete bicarbonate ion, causing an
  increase in H and a decrease in pH

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ACID-BASE DERANGEMENTS
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RESPIRATORY ACIDOSIS

• Lower than normal pH caused by retention of CO2
• Results in decreased ventilations due to problems
  in lungs or respiratory center of the brain
• CO2 is increased and the pH is decreased
• Treatment is aimed at improving ventilations

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RESPIRATORY ALKALOSIS

• Higher than normal pH from increased respiration
  and excessive elimination of CO2
• Can result from anxiety or following ascent to
  high altitude
• CO2 is decreased and pH is increased
• Treatment is aimed at increasing CO2 level by
  having patient rebreath CO2

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METABOLIC ACIDOSIS

• Lower than normal pH due to increase production
  of metabolic acids
• Can also result from diarrhea, vomiting,
  diabetes, medications (aspirin)
• pH is decreased and CO2 level is normal
• Treatment is aimed at improving ventilations to
  eliminate CO2
• Sodium bicarbonate may be administered on rare
  occasions

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METABOLIC ALKALOSIS

• Higher than normal pH caused by excessive
  elimination of H
• Caused by increased diarrhea, prolonged vomiting,
  overdosing on antacids
• pH is increased and CO2 remains normal
• Treatment is aimed at correcting underlying cause

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COMBINATIONS

• Usually both metabolic and respiratory components
  are present
• Only arterial blood gasses can accurately
  diagnose the problem

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