ChemPath: Acid-Base Handling Flashcards

1
Q

What is the normal range for H+ concentration? What is normal pH

A

35-45 nmol/L in ECF

pH 7.35-7.45

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2
Q

What equation links H+ concentration to pH?

A

pH = log1/[H+]

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3
Q

What are the three main physiological buffers?

A
  • Bicarbonate (ECF, renal tubular fluid)
  • Haemoglobin (RBC)
  • Phosphate (renal tubular fluid/intracellular)

NOTE: also protein and bone

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4
Q

What is the rate of production of H+ ions per day?

A

50 - 100 mmol/day

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5
Q

Describe how the kidneys excrete H+ ions. Where does this occur?

A

Via bicarbonate through the production of carbonic acid
Occurs in proximal tubules

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6
Q

Describe how H+ ions pass through the renal epithelial membrane.

A

H+ ions cannot pass through the membrane itself so a transport system is necessary (Na+/H+ transporter)

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7
Q

What is the rate of production of carbon dioxide per day?

A

20,000-25,000 mmol/day

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8
Q

Describe the relationship between CO2 and repiratory rate

A
  • Respiration is controlled by chemoreceptors in the hypothalamic respiratory centre
  • An increase in CO2 will stimulate an increase in ventilation which then brings down CO2 concentration
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9
Q

What information is provided by ABGs?

A
  • pO2
  • pCO2
  • pH
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10
Q

What are 3 mechanism of metabolic acidosis?

A

Caused by:

  • Increased H+ production (e.g. DKA)
  • Decreased H+ excretion (e.g. renal tubular acidosis)
  • Bicarbonate loss (e.g. diarrhoea)
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11
Q

Describe the ABG results in a metabolic acidosis

A
  • Low pH / increased H+
  • Low pCO2
  • Low HCO3-
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12
Q

What are 3 mechanisms of respiratory acidosis?

A

Caused by:

  • Decreased ventilation
  • Poor lung perfusion
  • Impaired gas exchange

E.g. chronic lung disease (COPD), opioids, sedatives, neuromuscular weakness

NOTE: metabolic compensation is slower than respiratory compensation

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13
Q

Describe the ABG results in a respiratory acidosis

A
  • Low pH / increased H+
  • High pCO2
  • High HCO3-
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14
Q

What happens in chronic respiratory acidosis?

A

Metabolic compensation will drive H+ down to near normal range, however pCO2 and bicarbonate will remain elevated

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15
Q

What are 3 mechanisms of metabolic alkalosis?

A

Caused by:

  • H+ loss (e.g. pyloric stenosis)
  • Hypokalaemia
  • Ingestion of bicarbonate
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16
Q

Describe the ABG results in a metabolic alkalosis

A
  • High pH / low H+
  • High pCO2
  • High HCO3-
17
Q

What is the main mechanism behind respiratory alkalosis, and what are 3 causes?

A

Main mechanism is hyperventilation, which can be due to:

  • Voluntary
  • Artificial ventilation
  • Stimulation of the respiratory centre
18
Q

Describe the ABG results in a respiratory alkalosis

A
  • High pH / low H+
  • Low pCO2
  • Low HCO3-
19
Q

What derangement of acid-base balance would be caused by pyloric stenosis?

A

Metabolic alkalosis due to loss of H+ from profuse vomiting

20
Q

Which condition classically causes a mixed respiratory alkalosis and metabolic acidosis?

A
  • Aspirin overdose
  • Aspirin causes high anion gap metabolic acidosis whilst simulataneously causing respiratory alkalosis by stimualting the respiratory centre
21
Q

What is the cause of an elevated anion gap in metabolic acidosis?

A
  • Ketoacidosis
  • Lactic acidosis
  • Uraemia
  • Toxins (ethylene glycol, methanol, salicylates)