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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
Why do we assess HCO3- and base excess?
An abnormal base excess and HCO3- indicates a primary or compensatory metabolic acid-base disturbance
26
What 3 reasons are there for assessing PaCO2?
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
List 5 different additional analytes that you would review?
1. Electrolytes 2. Calculation of anion gap to further assess any metabolic acidosis 3. Haemoglobin 4. Glucose 5. Lactate
28
What does air bubbles in the specimen cause?
Falsely raises PaO2 and pH and lowers PaCO2
29
Give 5 causal examples of metabolic/mixed acidosis?
1. Lactic acidosis 2. Diabetic ketoacidosis 3. Chronic renal failure 4. Self poisoning (drugs) 5. Chloride excess (iatrogenic saline infusion)
30
Give 3 causal examples of respiratory acidosis?
1. Opiate excess 2. Severe acute ventilatory failure 3. Airway obstruction
31
Give a causal example of respiratory acidosis with renal compensation?
Long term respiratory diseases; - COPD - Thoracic abnormalities
32
Give 4 causal examples of metabolic/mixed alkalosis with respiratory compensation?
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
Give 3 causal examples of respiratory alkalosis?
1. Anxiety 2. Central causes (brain injury) 3. Drugs (salicylate, caffeine)
34
Give 2 causal examples of respiratory alkalosis with renal compensation?
1. Pregnancy | 2. Central causes
35
What would the ABG's be for a mixed respiratory and metabolic acidosis?
- pH <7.35 - Negative base excess or low HCO3- - High PaCO2
36
What would the ABG's be for a metabolic acidosis?
- pH <7.35 - Negative base excess or low HCO3- - Normal PaCO2
37
What would the ABG's be for a metabolic acidosis with respiratory compensation?
- pH <7.35 - Negative base excess or low HCO3- - Low PaCO2
38
What would the ABG's be for a respiratory acidosis?
- pH <7.35 - Normal base excess or HCO3- - High PaCO2
39
What would the ABG's be for a respiratory acidosis with renal compensation?
- pH <7.35 - Positive base excess or high HCO3- - High PaCO2
40
What would the ABG's be for a metabolic alkalosis with respiratory compensation?
- pH >7.45 - Positive base excess or high HCO3- - High PaCO2
41
What would the ABG's be for a metabolic alkalosis?
- pH >7.45 - Positive base excess or high HCO3- - Normal PaCO2
42
What would the ABG's be for a mixed respiratory and metabolic alkalosis?
- pH >7.45 - Positive base excess or high HCO3- - Low PaCO2
43
What would the ABG's be for a respiratory alkalosis?
- pH >7.45 - Normal base excess or HCO3- - Low PaCO2
44
What would the ABG's be for a respiratory alkalosis with renal compensation?
- pH >7.45 - Negative base excess or low HCO3- - Low PaCO2
45
If the arrows are going in the same direction, then the primary problem is what?
Metabolic
46
If the arrows are going in different directions, then the primary problem is what?
Respiratory
47
What does a P/F ratio of >50 suggest?
Healthy
48
What does a P/F ratio of <40 suggest?
Acute lung injury
49
What does a P/F ratio of <26.7 suggest?
Acute respiratory distress syndrome (ARDS)
50
What does an increased anion gap signal?
A metabolic acidosis
51
What is the normal anion gap?
16
52
What are the 4 causes of lactic acidosis?
1. Product of anaerobic metabolism 2. Severe acute hypoxia 3. Severe convulsions (respiratory arrest) 4. Strenuous exercise (dehydration)
53
What 2 exogenous acid loads can lead to an increased anion gap?
1. Methanol (industrial solvent, windscreen wash) | 2. Ethylene glycol (anti freeze)
54
What 2 things can cause a normal anion gap with metabolic acidosis?
1. Diarrhoea | 2. Renal tubular acidosis
55
What are the 2 possible initiating processes for metabolic alkalosis?
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
What process maintains the metabolic alkalosis?
Impair kidney's ability to excrete bicarb by chloride/potassium depletion groups

MD4003 (22 decks)

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