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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
In chemical terms, a normal anion gap in metabolic acidosis is due to...
Chloride substituting for the lost bicarbonate, maintaining electrochemical balance
26
What can a normal anion gap in metabolic acidosis indicate?
Bicarbonate is being lost e.g. diarrhoea
27
In chemical terms, a raised anion gap in metabolic acidosis is due to...
Acids (anions) being produced which replace the bicarbonate being used up to buffer the H+ ions
28
What can a raised anion gap in metabolic acidosis indicate?
There is excess production of organic acids e.g. lactic acid in lactic acidosis, ketoacids in diabetic ketoacidosis
29
What type of compensation can be seen in metabolic acidosis?
Hyperventilation, to lower PCO2 Kussmaul breathing is the type of respiratory pattern seen (deep, rapid, gasping breaths)
30
What can occur as a result of metabolic acidosis?
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
What acid-base disorder can result in hyperkalaemia?
Metabolic acidosis
32
What acid-base disorder can result in hypokalaemia?
Metabolic alkalosis
33
What is metabolic alkalosis?
A decrease in [H+] resulting in elevated bicarbonate levels
34
Give three causes of metabolic alkalosis
Loss of H+ through vomiting Absorbable alkali ingestion e.g. sodium bicarbonate Potassium deficiency
35
What cause of metabolic alkalosis results in acidic urine? How does this occur?
Potassium deficiency - H+, rather than potassium, are exchanged for reabsorption of Na in kidneys
36
What can occur as a result of metabolic alkalosis?
Confusion and coma | Decrease in unbound calcium - causes muscle cramps, tetany (muscle spasms) and paraesthesia (pins and needles)
37
Which acid base disorder is associated with hypocalcaemia?
Metabolic alkalosis
38
What is respiratory acidosis?
H+ ion excess due to insufficient gas exchange, resulting in increased PCO2
39
What type of compensation can be seen in metabolic alkalosis?
Hypoventilation
40
What type of compensation can be seen in respiratory acidosis?
Kidney excretes more H+ and reabsorbs bicarbonate Only in chronic as it is slow to develop
41
What can cause acute respiratory acidosis?
Choking Bronchopneumonia Acute exacerbation of asthma
42
What can cause chronic respiratory acidosis?
Chronic bronchitis Emphysema COAD/COPD
43
What is respiratory alkalosis?
Decrease in [H+] due to excessive gas exchange, resulting in lowered PCO2
44
What type of compensation can be seen in respiratory alkalosis?
Kidney excretes less H+ and doesn't absorb as much bicarbonate This is only if the cause is chronic (usually acute)
45
Give three causes of respiratory alkalosis?
Hysteric hyperventilation Raised intracranial pressure Hypoxia (lack of oxygen)
46
What is a mixed acid-base disorder?
A combination of more than one disorder
47
In terms of mixed acid-base disorders, why must care be taken if the patient displays signs of compensation?
The patient may have antagonistic disorders, where one disorder can mimic the compensatory response
48
Give an example of antagonistic mixed acid-base disorders, where one mimics the compensatory response
COPD (respiratory acidosis) causing an increase in PCO2, along-side thiazide induced potassium deficiency (metabolic alkalosis) causing an increase in bicarbonate
49
What is PO2 and what does it show?
Partial pressure of oxygen (PO2) is proportional to the total unbound oxygen in blood
50
What is oxygen saturation?
Percentage of haemoglobin that is bound to oxygen
51
Define ventilation
The mechanical process of moving air into and out of the respiratory tract
52
What is respiratory failure?
Blood PO2 < 8kPa in patient breathing room air at rest
53
What is seen in type 1 respiratory failure?
Hypoxia with CO2 retention
54
What is seen type 2 respiratory failure?
Hypoxia without CO2 retention (normal levels)
55
What contributes to type 1 respiratory failure?
Impaired diffusion and some ventilation / perfusion imbalances e.g. lobar pneumonia
56
What contributes to type 2 respiratory failure?
Some ventilation/perfusion imbalances e.g. chronic bronchitis or bronchial pneumonia
57
What results in impaired diffusion?
Fluid (oedema) or thickened alveolar walls (fibrosis) inhibit oxygen diffusion CO2 is less affected so may be within normal range
58
What occurs in lobar pneumonia to contribute to a ventilation/perfusion imbalance?
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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