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TAS Emergencies and Critical Care ✅ > Blood Gas Abnormalities ✅ > Flashcards

Blood Gas Abnormalities ✅ Flashcards

1
Q

What is the normal blood pH?

A

7.34-7.44

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2
Q

What is the normal blood CO2?

A

4.6-6

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3
Q

What happens to the blood CO2 in respiratory acidosis?

A

It is high

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4
Q

What happens to the blood CO2 in uncompensated metabolic acidosis?

A

It is normal

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5
Q

What happens to the blood CO2 in compensated metabolic acidosis?

A

It is low

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6
Q

What is the normal blood HCO3?

A

22-26mmol/L

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7
Q

What happens to the blood HCO3 in metabolic acidosis?

A

It is low

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8
Q

What happens to the blood HCO3 in uncompensated respiratory acidosis?

A

It is normal

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9
Q

What happens to blood HCO3 in compensated respiratory acidosis?

A

It is high

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10
Q

What is the normal base excess?

A

-2 to +2 mmol/L

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11
Q

What happens to base excess in uncompensated respiratory acidosis?

A

It is normal

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12
Q

What happens to base excess in uncompensated respiratory acidosis?

A

It is high

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13
Q

What happens to base excess in metabolic acidosis?

A

It is low

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14
Q

What is pH defined as?

A

A decimal logarithm of the reciprocal of the hydrogen ion activity or concentration in a solution

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15
Q

How is pH maintained in the range of 7.34-7.44?

A

By several buffering systems

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16
Q

What is the main buffering system that maintains blood pH in range?

A

The carbonic acid-bicarbonate system

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17
Q

What is the equation for the carbonic acid-carbonate system

A

HCO3- + H+ ↔ H2CO3 ↔ H2O + CO2

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18
Q

What equation describes the relationship between pH, HCO3, and CO2?

A

The Henderson-Hasselbach equation

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19
Q

What is the Henderson-Hasselbach equation?

A

pH = 6.1 + log10 ( HCO3- / 0.03xpCO2)

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20
Q

What causes respiratory alkalosis?

A

Hyperventilation

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21
Q

How does hyperventilation cause respiratory alkalosis?

A

Because in hyperventilation, CO2 is blown off and pH increases

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22
Q

What causes respiratory acidosis?

A

Hypoventilation

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23
Q

How does hypoventilation cause respiratory acidosis?

A

Because CO2 is retained and the blood becomes acidotic

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24
Q

Do respiratory changes have a fast or slow effect on the blood pH?

A

Fast

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25
Q

What is the importance of HCO3- in the. blood?

A

It is the base and a buffer of hydrogen ions

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26
Q

Where do hydrogen ions in the body come from?

A

They are a product of normal cellular metabolism

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27
Q

What causes metabolic acidosis?

A

Excess production of hydrogen ions

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28
Q

How does excess production of hydrogen ions cause metabolic acidosis?

A

The buffering effect of HCO3 is overcome, and the blood becomes acidotic

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29
Q

Give 4 examples of causes of excess acid?

A
  • Lactic acid
  • Ketone production
  • Acid administration
  • Bicarbonate loss
30
Q

When might there be excess lactic acid?

A

In shock

31
Q

When might there be excess ketones?

A

Diabetic ketoacidosis

32
Q

When might there be acid administration?

A

Salicylic acid in aspirin positioning

33
Q

When might there be excess bicarbonate loss?

A

From the gut in gastroenteritis, or urine in renal tubular disease

34
Q

What organ can compensate for respiratory acidosis in chronic respiratory failure?

A

Kidneys

35
Q

How can the kidneys compensate for respiratory acidosis in chronic respiratory failure?

A

Increasing the amount of HCO3 in the blood and extracellular fluid

36
Q

What will be found on blood gas in compensated respiratory acidosis?

A

Normal pH

High CO2 and HCO3

37
Q

How long does compensation in respiratory acidosis take?

A

Several days

38
Q

What organ can compensate for metabolic acidosis?

A

Lungs

39
Q

How can the respiratory system compensate for metabolic acidosis

A

Can blow off CO2 to normalise pH

40
Q

What mediates respiratory compensation for metabolic acidosis?

A

The carotid chemoreceptors

41
Q

What is found on blood gas in compensated metabolic acidosis?

A

Normal pH

Low CO2 and HCO3

42
Q

What is the main limitation of the Henderson-Hasselbach approach to considering pH?

A

Buffers other than HCO3 exist

43
Q

Give 2 buffers of pH other than HCO3?

A
  • Albumin

- Haemoglobin

44
Q

What is the result of HCO3 not being the only buffer of pH?

A

HCO3 and CO2 are not independent

45
Q

What happens to hydrogen ions when there is a rise in CO2?

A

There is a rise in hydrogen ions

46
Q

Why is there a rise in hydrogen ions when there is a rise in CO2?

A

CO2 + H2O ↔ H+ + HCO3-

47
Q

What happens to HCO3 when there is a rise in CO2?

A

There is a rise in HCO3

48
Q

Why is there a rise in HCO3 when there is a rise in CO2?

A

CO2 + H2O ↔ H+ + HCO3, and there are other buffers for H+, so not all the HCO3-reforms with H+

49
Q

What is the result of HCO3 rising with an increase in CO2?

A

Respiratory acidosis could be mistaken for metabolic alkalosis

50
Q

How can respiratory acidosis be differentiated from metabolic alkalosis?

A

Base excess

51
Q

How is base excess determined?

A

By equilibrating the sample to a normal pCO2 (5.33kPa), then titrating it to pH 7.4 = the number of mmol/L needed to do this is the base excess

52
Q

What is base excess a measure of?

A

How acidotic or alkaloid the sample is without any contribution of CO2

53
Q

How is the anion gap calculated?

A

(Na + K) - (Cl + HCO3)

54
Q

What is the purpose of calculation of the anion gap?

A

It allows classification of a metabolic acidosis into those with normal or increased anion gap

55
Q

What is the anion gap a measure of?

A

The concentration of unmeasured anions

56
Q

Give 3 examples of unmeasured anions?

A
  • Plasma proteins
  • Ketones
  • Lactate
57
Q

What theory is the anion gap based on?

A

Electrical neutrality

58
Q

What is the theory of electrical neutrality?

A

The sum of positive ions must equal the sum of negative ions

59
Q

What is considered to be an increased anion gap?

A

> 16mmol/L

60
Q

What does an increased anion gap suggest?

A

The presence of unmeasured organic acid

61
Q

What does a normal anion gap suggest?

A

Bicarbonate loss and/or increase in chloride concentration

62
Q

Give 9 causes of metabolic acidosis with increased anion gap

A
  • Diabetic ketoacidosis
  • Alcohol poisioning
  • Starvation
  • Inborn errors of metabolism
  • Hyperosmolar non-ketotic coma
  • Lactic acidosis
  • Methanol
  • Ethylene glycol
  • Salicylate
63
Q

Give 8 causes of metabolic acidosis with a normal anion gap

A
  • Diarrhoea
  • Parenteral nutrition
  • Carbonic anhydrase inhibitors
  • Dilutional acidosis
  • Ingestion of HCl or other acid
  • Renal tubular acidosis
  • Ileostomy
  • Sodium chloride administration
64
Q

Who is hyperchloraemic acidosis common in?

A

Patients given normal-saline containing fluids

65
Q

Why is hyperchloraemic acidosis common in patients given normal-saline containing fluids?

A
  • Normal saline is acidic, and has little buffering capacity

- Volume expansion causes plasma bicarbonate dilution

66
Q

What is the pH of normal saline?

A

5-6

67
Q

What is the acidic pH of normal saline due to?

A

‘Grotthuss mechanism’

68
Q

What is the Grothuss mechanism?

A

Ions high dissociated when dissolved in water, i.e. Na and Cl ions, cause disruption of the ionic bonding of H2O, leading to greater dissociation and generation of H+

69
Q

Why is it important to recognise hyperchloraemia as a cause of acidosis?

A

To avoid administration of fluids when further fluid therapy is unnecessary and will exacerbate the problem

70
Q

What findings on bloods should indicate hyperchloraemia as the cause of acidosis?

A
  • Normal anion gap
  • Raised chloride concentration
  • Low bicarbonate

TAS Emergencies and Critical Care ✅ (8 decks)

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