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Introduction to Clinical Biochemistry > L10 - Acid-Base Balance > Flashcards

L10 - Acid-Base Balance Flashcards

1
Q

What is the relationship between [H+] and pH?

A

pH is the negative log of hydrogen ion concentration

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2
Q

What concentrations of H+ are incompatible with life?

A

> 120nmol/L and <20nmol/L

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3
Q

What is the major way hydrogen ions are produced in the body?

A

Oxidation of ingested amino acids, as they contain sulphur

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4
Q

What is acidosis and alkalosis, in terms of pH and [H+]?

A

Acidosis - high [H+], low pH

Alkalosis - low [H+], high pH

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5
Q

How are excess H+ ions dealt with?

A

Excreted in urine or temporarily removed via buffers

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6
Q

What are the three main parameters measured to assess acid-base balance?

A

[H+] - hydrogen concentration
[HCO3] - bicarbonate
PCO2 - partial pressure of carbon dioxide

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7
Q

What are the main buffer systems?

What is the most important in the ECF?

A

Bicarbonate, proteins (e.g. haemoglobins), phosphate system

Bicarbonate is the main system

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8
Q

What three factors will cause [H+] to increase?

A

Adding H+, removing bicarbonate, increasing PCO2

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9
Q

What three factors will cause [H+] to decrease?

A

Removing H+, adding bicarbonate, decreasing PCO2

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10
Q

What 2 organs are responsible for maintaining acid-base balance?

How are they able to do this?

A

Kidneys - excrete H+, reabsorb bicarbonate

Lungs - remove CO2

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11
Q

In metabolic acidosis and alkalosis, what is the main organ involved?

A

Kidneys

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12
Q

In metabolic acidosis and alkalosis, what is the main test parameter involved?

How are the levels of this affected in each condition?

A

Bicarbonate (HCO3)

Decreases in metabolic acidosis
Increases in metabolic alkalosis

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13
Q

In respiratory acidosis and alkalosis, what is the main organ involved?

A

Lungs

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14
Q

In respiratory acidosis and alkalosis, what is the main test parameter involved?

How are the levels of this affected in each condition?

A

Partial pressure of CO2 (PCO2)

Increases in respiratory acidosis
Decreases in respiratory alkalosis

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15
Q

What is renal compensation?

A

When lung function is compromised, kidneys increase or decrease the amount of H+ excreted, increasing/lowering bicarbonate levels

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16
Q

What is respiratory compensation?

A

When renal function is compromised, the lungs can remove CO2 through hyperventilation, or reduce loss through hypoventilation

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17
Q

How does the bicarbonate buffer system control acid-base balance, and what enzyme is involved in this process?

A

H+ associates with bicarbonate to form carbonic acid (H2CO3). Carbonic anhydrase aids in the breakdown of carbonic acid to CO2 and water

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18
Q

Which is faster to take effect, respiratory or renal compensation

A

Respiratory compensation

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19
Q

Define complete compensation

A

When the compensation mechanism returns [H+] to within reference range, but the PCO2 and bicarbonate are abnormal

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20
Q

Define partial compensation

A

When compensation has occurred, but the [H+] has not returned to within reference range

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21
Q

What is metabolic acidosis?

A

Accumulation of H+, resulting in decreased bicarbonate

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22
Q

Give three causes of metabolic acidosis

A

Renal disease
Diabetic ketoacidosis
Lactic acidosis

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23
Q

What is the anion gap and how is it calculated?

A

The anion gap is an estimation of the concentration of unmeasured ions; it is the difference between the anions and the cations

[Na+] - [(Cl-) + (HCO3-)]

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24
Q

What is knowledge of the anion gap useful for?

A

Finding out the cause of a metabolic acidosis when it is not apparent from clinical history

25
Q

In chemical terms, a normal anion gap in metabolic acidosis is due to…

A

Chloride substituting for the lost bicarbonate, maintaining electrochemical balance

26
Q

What can a normal anion gap in metabolic acidosis indicate?

A

Bicarbonate is being lost e.g. diarrhoea

27
Q

In chemical terms, a raised anion gap in metabolic acidosis is due to…

A

Acids (anions) being produced which replace the bicarbonate being used up to buffer the H+ ions

28
Q

What can a raised anion gap in metabolic acidosis indicate?

A

There is excess production of organic acids e.g. lactic acid in lactic acidosis, ketoacids in diabetic ketoacidosis

29
Q

What type of compensation can be seen in metabolic acidosis?

A

Hyperventilation, to lower PCO2

Kussmaul breathing is the type of respiratory pattern seen (deep, rapid, gasping breaths)

30
Q

What can occur as a result of metabolic acidosis?

A

Increased neuromuscular irritability
Arrhythmias progressing to cardiac arrest (more likely if there is also hyperkalaemia)
Depression of consciousness can progress to coma and death

31
Q

What acid-base disorder can result in hyperkalaemia?

A

Metabolic acidosis

32
Q

What acid-base disorder can result in hypokalaemia?

A

Metabolic alkalosis

33
Q

What is metabolic alkalosis?

A

A decrease in [H+] resulting in elevated bicarbonate levels

34
Q

Give three causes of metabolic alkalosis

A

Loss of H+ through vomiting
Absorbable alkali ingestion e.g. sodium bicarbonate
Potassium deficiency

35
Q

What cause of metabolic alkalosis results in acidic urine?

How does this occur?

A

Potassium deficiency - H+, rather than potassium, are exchanged for reabsorption of Na in kidneys

36
Q

What can occur as a result of metabolic alkalosis?

A

Confusion and coma

Decrease in unbound calcium - causes muscle cramps, tetany (muscle spasms) and paraesthesia (pins and needles)

37
Q

Which acid base disorder is associated with hypocalcaemia?

A

Metabolic alkalosis

38
Q

What is respiratory acidosis?

A

H+ ion excess due to insufficient gas exchange, resulting in increased PCO2

39
Q

What type of compensation can be seen in metabolic alkalosis?

A

Hypoventilation

40
Q

What type of compensation can be seen in respiratory acidosis?

A

Kidney excretes more H+ and reabsorbs bicarbonate

Only in chronic as it is slow to develop

41
Q

What can cause acute respiratory acidosis?

A

Choking
Bronchopneumonia
Acute exacerbation of asthma

42
Q

What can cause chronic respiratory acidosis?

A

Chronic bronchitis
Emphysema
COAD/COPD

43
Q

What is respiratory alkalosis?

A

Decrease in [H+] due to excessive gas exchange, resulting in lowered PCO2

44
Q

What type of compensation can be seen in respiratory alkalosis?

A

Kidney excretes less H+ and doesn’t absorb as much bicarbonate

This is only if the cause is chronic (usually acute)

45
Q

Give three causes of respiratory alkalosis?

A

Hysteric hyperventilation
Raised intracranial pressure
Hypoxia (lack of oxygen)

46
Q

What is a mixed acid-base disorder?

A

A combination of more than one disorder

47
Q

In terms of mixed acid-base disorders, why must care be taken if the patient displays signs of compensation?

A

The patient may have antagonistic disorders, where one disorder can mimic the compensatory response

48
Q

Give an example of antagonistic mixed acid-base disorders, where one mimics the compensatory response

A

COPD (respiratory acidosis) causing an increase in PCO2, along-side thiazide induced potassium deficiency (metabolic alkalosis) causing an increase in bicarbonate

49
Q

What is PO2 and what does it show?

A

Partial pressure of oxygen (PO2) is proportional to the total unbound oxygen in blood

50
Q

What is oxygen saturation?

A

Percentage of haemoglobin that is bound to oxygen

51
Q

Define ventilation

A

The mechanical process of moving air into and out of the respiratory tract

52
Q

What is respiratory failure?

A

Blood PO2 < 8kPa in patient breathing room air at rest

53
Q

What is seen in type 1 respiratory failure?

A

Hypoxia with CO2 retention

54
Q

What is seen type 2 respiratory failure?

A

Hypoxia without CO2 retention (normal levels)

55
Q

What contributes to type 1 respiratory failure?

A

Impaired diffusion and some ventilation / perfusion imbalances e.g. lobar pneumonia

56
Q

What contributes to type 2 respiratory failure?

A

Some ventilation/perfusion imbalances e.g. chronic bronchitis or bronchial pneumonia

57
Q

What results in impaired diffusion?

A

Fluid (oedema) or thickened alveolar walls (fibrosis) inhibit oxygen diffusion

CO2 is less affected so may be within normal range

58
Q

What occurs in lobar pneumonia to contribute to a ventilation/perfusion imbalance?

A

Some blood in the lungs does not reach functional alveoli; this increase in CO2 stimulates hyperventilation, making the functional alveoli work harder

Introduction to Clinical Biochemistry (11 decks)

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