Acid-base balance II: Whole body acid-base balance Flashcards by Emma Williams

what is the first priority if normal acid-base balance is disrupted?

restore pH to 7.4 as soon as possible- compensation

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what is compensation?

the restoration of pH irrespective of what happens to [HCO3-]p and PCO2

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what is correction?

restoration of pH and [HCO3-]p and PCO2 to normal

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what are the 2 classification of disturbances or respiratory origin?

-respiartory acidosis (plasma pH falls)
-Respiratory alkalosis
(plasma pH rises)

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what are the 2 classification of disturbances or non-respiratory origin?

-Metabolic acidosis
(plasma pH falls)
-Metabolic alkalosis
(plasma pH rises)

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what is immediate buffering of a pH change?

Immediate dilution of the acid or base in ECF
Blood buffers (i.e. Hb, HCO3-. Acidosis would reduce [HCO3-]p)
Buffers in the ECF (particularly HCO3-)

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what happens once buffer stores are quickly depleted?

kidney has to rectify stores

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what can measure pH and Pco2?

blood-gas analyser

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what is pH proportional to?

[HCO3-]/ [CO2]

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what diagram can we plott variables on?

Davenport diagram

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what are the normal values in the davenport diagram?

plasma pH- 7.4

[HCO3-]p - 25mmol/l

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what is respiratory acidosis?

retention of CO2 by the body e.g. chronic bronchitis

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how do respiratory disorders generate acidosis?

Co2 retention drives equilibrium to the right

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what happens during respiratory acidosis?

-Both [H+]p and [HCO3-]p rise
-The increased [H+]p results in acidosis
(remember that pH is only a measure of free [H+])

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how is uncompensated respiratory acidosis indicated?

pH < 7.35 and PCO2 > 45 mmHg

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where does respiratory acidosis sit on the davenport diagram?

top left

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what system compensates for respiratory acidosis?

since respiratory system is the cause- renal system must compensate

how does the renal system compensate for respiratory acidosis?

H+ secretion is stimulated
All filtered HCO3- is reabsorbed (i.e. no HCO3- excretion)
H+ continues to be secreted and generates titratable acid (TA) and NH4+
Acid is excreted and “new” HCO3- is added to the blood

why does the [HCO3-] rise in respiratory acidosis?

(a) as a result of the disorder (b) as a result of the renal compensation

what does correction of respiratory acidosis require?

requires lowering PCO2 by restoration of normal ventilation

what is respiratory alkalosis?

Excessive removal of CO2 by the body e.g. hyperventilation

How do these disruptions to ventilation cause respiratory alkalosis?

-Excessive CO2 removal drives equilibrium to the left and so Both [H+]p and [HCO3-]p fall

where does respiratory alkalosis sit on the davenport diagram?

bottom right

How does the renal system compensate for respiratory alkalosis?

The H+ secretion is insufficient to reabsorb the filtered HCO3-, even though the load is lower than normal
HCO3- is excreted and urine is alkaline
No titratable acid (TA) and NH4+ is formed, so no “new” HCO3- is generated

what is the overall compensation and correction by the renal system for respiratory alkalosis?

- Renal compensation further lowers [HCO3-]p | - Correction requires the restoration of normal ventilation

what is metabolic acidosis?

Excess H+ from any source other than CO2 e.g. ingestion of acids

how is Uncompensated respiratory alkalosis is indicated?

pH > 7.45 and PCO2 < 35 mmHg

how does metabolic acidosis effect [HCO3-] p?

[HCO3-]p is depleted as a result of buffering excess H+ or loss of HCO3- from the body

how is uncompensated metabolic acidosis indicated?

pH < 7.35, [HCO3-]p is low

where is metabolic acidosis found on the davenport diagram?

bottom left

what compensates for metabolic acidosis?

The respiratory system is not the cause so can participate in compensation

How does the respiratory system compensate for metabolic acidosis?

- A decrease in plasma pH stimulates peripheral chemoreceptors - Ventilation is quickly increased and more CO2 is blown off - [H+]p is lowered raising pH towards normal - [HCO3-]p is also lowered

what is the correction for metabolic acidosis?

- Filtered HCO3- is very low and very readily reabsorbed - H+ secretion continues and produces TA & NH4+ to generate more “new” HCO3- - The acid load is excreted (urine is acidic) and [HCO3-]p is restored - Ventilation can then be normalised

why is respiratory compensation in metabolic acidosis essential?

Acid load cannot be excreted immediately

what is metabolic alkalosis?

Excessive loss of H+ from the body e.g. loss of HCl from the stomach

how does metabolic alkanosis effect [HCO3-] p?

As a result of loss of H+ or addition of base, [HCO3-]p rises

what is uncompensated metabolic alkalosis indicated by?

pH > 7.45, [HCO3-]p is high

where does metabolic alkalosis sit on the davenport diagram?

top right

what is the respiratory compensation for metabolic alkalosis/

- Increased pH slows ventilation (peripheral chemoreceptors) - CO2 retained, PCO2 rises - [H+]p rises, lowering pH - [HCO3-]p also rises further

what is the correction for metabolic alkalosis?

- Filtered HCO3- load is so large compared to normal that not all of the filtered HCO3- is reabsorbed - No TA or NH4+ is generated - HCO3- is excreted (urine is alkaline) - [HCO3-]p falls back towards normal