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MD4003 > ABG's > Flashcards

ABG's Flashcards

1
Q

What are the 6 steps to interpreting arterial blood gasses?

A
  1. Assess oxygenation
  2. Assess pH
  3. Assess standard bicarbonate (sHCO3-) and base excess
  4. Assess arterial partial pressure of carbon dioxide (PaCO2)
  5. Assess additional analytes
  6. Reassess
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2
Q

What is PaO2?

A

Partial pressure of oxygen in arterial blood

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3
Q

What is FiO2?

A

Inspired oxygen concentration expressed as a fraction

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4
Q

Why is the PaO2/FiO2 or P/F ratio helpful?

A

For determining the presence and severity of impaired alveolar gas exchange and is easier to calculate

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5
Q

When does intrapulmonary shunting occur?

A

When areas of lung are perfused without adequate ventilation- for example; after consolidation, fluid accumulation, or acute inflammation of lung tissue

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6
Q

What is the normal pH range?

A

7.35-7.45

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7
Q

What would you expect to see in metabolic acidosis?

A
  • Reduction in the HCO3− concentration

- Negative base excess (commonly termed a base deficit)

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8
Q

What would you expect to see in a metabolic alkalosis?

A
  • Raised HCO3- concentration

- Positive base excess

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9
Q

What is the anion gap equation?

A

((Na+) + (K+)) − ((Cl−) + (HCO3−))

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10
Q

What is the normal reference range for the anion gap?

A

6-14mmol/L

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11
Q

List 4 possible causes for a raised anion gap metabolic acidosis?

A
  1. Lactic acidosis
  2. Ketoacidosis
  3. Renal failure
  4. Toxins
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12
Q

What does a raised anion gap suggest?

A

Excess of unmeasured anions, which are responsible for the underlying acidosis

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13
Q

What is a metabolic acidosis with a normal anion gap usually accompanied by?

A

Hyperchloraemia

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14
Q

What are the 3 usual causes of hyperchloraemia?

A
  1. Iatrogenic saline infusion
  2. Gastrointestinal loss of bicarbonate from diarrhoea
  3. Renal loss of bicarbonate (such as renal tubular acidosis type I and II)
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15
Q

What will a raised PaCO2 contribute towards?

A

Acidosis

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16
Q

What does a low PaCO2 indicate about the type of acidosis?

A

Its not respiratory in origin

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17
Q

What would happen in metabolic acidosis if the respiratory drive was normal?

A

Compensatory hypocarbia

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18
Q

Give 4 different examples which can cause inadequate ventilatory response?

A
  1. Opioid analgesia
  2. Coexistent chronic obstructive pulmonary disease
  3. Severe abdominal pain splinting breathing 4. Incipient ventilatory failure
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19
Q

What is a more sensitive marker of ventilatory failure

A

PaCO2 value is better than pulse oximetry or PaO2

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20
Q

What can hypokalaemia precipitate?

A

Atrial fibrillation which will impair cardiac output

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21
Q

What does a low Hb in a patient with metabolic acidosis suggest?

A
  • Occult haemorrhage with inadequate tissue oxygen delivery might have caused the metabolic acidosis
  • This is a particular risk in the postoperative setting when oxygen demand is increased
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22
Q

What can you do if getting an arterial supply is difficult?

A

Venous blood sample will provide a reasonable substitute for all analytes other than PaO2

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23
Q

What 3 ways can we assess the patients oxygenation?

A
  1. Record the inspired oxygen concentration
  2. Calculate the P/F ratio, particularly if receiving supplemental oxygen.
  3. Assess haemoglobin saturations
24
Q

Why do we assess the pH?

A

To see if the patient is acidaemic or alkalaemic

25
Q

Why do we assess HCO3- and base excess?

A

An abnormal base excess and HCO3- indicates a primary or compensatory metabolic acid-base disturbance

26
Q

What 3 reasons are there for assessing PaCO2?

A
  1. To see if its a primary respiratory acidosis or alkalosis?
  2. Is low or high PaCO2 compensating for a metabolic acidosis or alkalosis respectively?
  3. The respiratory system will not normally overcorrect a metabolic acid-base disturbance, and so if this is the case, consider a mixed metabolic and respiratory disorder
27
Q

List 5 different additional analytes that you would review?

A
  1. Electrolytes
  2. Calculation of anion gap to further assess any metabolic acidosis
  3. Haemoglobin
  4. Glucose
  5. Lactate
28
Q

What does air bubbles in the specimen cause?

A

Falsely raises PaO2 and pH and lowers PaCO2

29
Q

Give 5 causal examples of metabolic/mixed acidosis?

A
  1. Lactic acidosis
  2. Diabetic ketoacidosis
  3. Chronic renal failure
  4. Self poisoning (drugs)
  5. Chloride excess (iatrogenic saline infusion)
30
Q

Give 3 causal examples of respiratory acidosis?

A
  1. Opiate excess
  2. Severe acute ventilatory failure
  3. Airway obstruction
31
Q

Give a causal example of respiratory acidosis with renal compensation?

A

Long term respiratory diseases;

  • COPD
  • Thoracic abnormalities
32
Q

Give 4 causal examples of metabolic/mixed alkalosis with respiratory compensation?

A
  1. GI loss (vomiting, loss of colonic secretions)
  2. Electrolyte disturbance (hypokalaemia, hypomagnesaemia, hypercalcaemia)
  3. Drug ingestion (calcium carbonate, thiazide, loop diuretics)
  4. Endocrine (hyperaldosteronism)
33
Q

Give 3 causal examples of respiratory alkalosis?

A
  1. Anxiety
  2. Central causes (brain injury)
  3. Drugs (salicylate, caffeine)
34
Q

Give 2 causal examples of respiratory alkalosis with renal compensation?

A
  1. Pregnancy

2. Central causes

35
Q

What would the ABG’s be for a mixed respiratory and metabolic acidosis?

A
  • pH <7.35
  • Negative base excess or low HCO3-
  • High PaCO2
36
Q

What would the ABG’s be for a metabolic acidosis?

A
  • pH <7.35
  • Negative base excess or low HCO3-
  • Normal PaCO2
37
Q

What would the ABG’s be for a metabolic acidosis with respiratory compensation?

A
  • pH <7.35
  • Negative base excess or low HCO3-
  • Low PaCO2
38
Q

What would the ABG’s be for a respiratory acidosis?

A
  • pH <7.35
  • Normal base excess or HCO3-
  • High PaCO2
39
Q

What would the ABG’s be for a respiratory acidosis with renal compensation?

A
  • pH <7.35
  • Positive base excess or high HCO3-
  • High PaCO2
40
Q

What would the ABG’s be for a metabolic alkalosis with respiratory compensation?

A
  • pH >7.45
  • Positive base excess or high HCO3-
  • High PaCO2
41
Q

What would the ABG’s be for a metabolic alkalosis?

A
  • pH >7.45
  • Positive base excess or high HCO3-
  • Normal PaCO2
42
Q

What would the ABG’s be for a mixed respiratory and metabolic alkalosis?

A
  • pH >7.45
  • Positive base excess or high HCO3-
  • Low PaCO2
43
Q

What would the ABG’s be for a respiratory alkalosis?

A
  • pH >7.45
  • Normal base excess or HCO3-
  • Low PaCO2
44
Q

What would the ABG’s be for a respiratory alkalosis with renal compensation?

A
  • pH >7.45
  • Negative base excess or low HCO3-
  • Low PaCO2
45
Q

If the arrows are going in the same direction, then the primary problem is what?

A

Metabolic

46
Q

If the arrows are going in different directions, then the primary problem is what?

A

Respiratory

47
Q

What does a P/F ratio of >50 suggest?

A

Healthy

48
Q

What does a P/F ratio of <40 suggest?

A

Acute lung injury

49
Q

What does a P/F ratio of <26.7 suggest?

A

Acute respiratory distress syndrome (ARDS)

50
Q

What does an increased anion gap signal?

A

A metabolic acidosis

51
Q

What is the normal anion gap?

A

16

52
Q

What are the 4 causes of lactic acidosis?

A
  1. Product of anaerobic metabolism
  2. Severe acute hypoxia
  3. Severe convulsions (respiratory arrest)
  4. Strenuous exercise (dehydration)
53
Q

What 2 exogenous acid loads can lead to an increased anion gap?

A
  1. Methanol (industrial solvent, windscreen wash)

2. Ethylene glycol (anti freeze)

54
Q

What 2 things can cause a normal anion gap with metabolic acidosis?

A
  1. Diarrhoea

2. Renal tubular acidosis

55
Q

What are the 2 possible initiating processes for metabolic alkalosis?

A
  1. Loss of H+ ions from the gut (above pylorus) or kidney (furosemide & thiazide)- COMMON
  2. Gain of exogenous alkali ie. massive blood transfusion- LESS COMMON
56
Q

What process maintains the metabolic alkalosis?

A

Impair kidney’s ability to excrete bicarb by chloride/potassium depletion groups

MD4003 (22 decks)

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