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tACCP > Resp Physiology Part 3 - ABG > Flashcards

Resp Physiology Part 3 - ABG Flashcards

1
Q

What is the Henderson-Hasselbalch equation?

A

pH = pKa + log10 ([HCO3-] / 0.03 x PaCO2)

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2
Q

What is the anion gap equation?

A

Anion Gap = (Na+ + K+) – (Cl- + HCO3-)

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3
Q

What is the significance of the anion gap?

A

Used to evaluate metabolic acidosis and identify unmeasured anions.

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4
Q

What are the two types of lactic acidosis?

A

Type A: Caused by hypoxia.

Type B: Caused by metabolic or toxic derangements.

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5
Q

Define base excess.

A

The amount of acid or base required to return blood pH to 7.4 at standard PaCO2.

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6
Q

What are common causes of respiratory acidosis?

A

Hypoventilation, obstructive lung diseases, and neuromuscular impairment.

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7
Q

What are common causes of respiratory alkalosis?

A

Hyperventilation, anxiety, and pain.

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8
Q

What are the normal arterial blood gas (ABG) parameters for pH and PaCO2?

A

pH: 7.35 - 7.45
PaCO2: 4.7 - 6.0 kPa.

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9
Q

What is the normal bicarbonate (HCO3-) range?

A

22 - 26 mmol/L.

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10
Q

What is the A-a gradient?

A

The difference between alveolar and arterial oxygen pressure, used to assess oxygen exchange.

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11
Q

What does a low pH with high PaCO2 indicate in ABG interpretation?

A

Respiratory acidosis.

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12
Q

What does a low pH with low HCO3- indicate?

A

Metabolic acidosis.

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13
Q

What does a high pH with low PaCO2 indicate?

A

Respiratory alkalosis.

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14
Q

How is metabolic alkalosis identified on ABG?

A

High pH and high HCO3- (>26 mmol/L).

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15
Q

What is the significance of PaO2 in ABG interpretation?

A

Determines oxygenation status; PaO2 <10 kPa on air indicates hypoxemia.

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16
Q

What is the definition of a buffer?

A

A solution that minimizes changes in pH when an acid or base is added.

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17
Q

What are examples of physiological buffers?

A
  • Bicarbonate buffer system
  • Haemoglobin
  • Plasma proteins
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18
Q

What is the role of bicarbonate in acid-base balance?

A

Bicarbonate acts as a base in the carbonic acid-bicarbonate buffer system to regulate pH.

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19
Q

What is lactic acidosis, and how is it produced?

A

Lactic acidosis is caused by the accumulation of lactic acid, a product of anaerobic metabolism.

(Debated!)

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20
Q

What are the causes of Type A lactic acidosis?

A

Hypoxia, shock, severe anemia, or respiratory failure.

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21
Q

What are the causes of Type B lactic acidosis?

A

Liver failure, sepsis, medications (e.g., metformin), or malignancy.

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22
Q

What is the PaO2/FiO2 (P/F) ratio used for?

A

To assess the severity of hypoxemia, commonly in ARDS.

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23
Q

What is the P/F Ratio equation.

A

PaO2/FiO2

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24
Q

How is the P/F ratio severity scaled?

A
  • Severe <100
  • Moderate 101-200
  • Mild 201-300
  • Non ARDS >301
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25
Q

What is the clinical significance of the A-a gradient?

A

Helps differentiate hypoxemia due to V/Q mismatch, diffusion impairment, or shunting.

26
Q

What does a high A-a gradient indicate?

A

Issues like pulmonary embolism, pneumonia, or ARDS.

27
Q

What would a:
pH 7.19
PaCO2 10.2 kPa
HCO3 23.6 mmol/L
indicate?

A

Acute respiratory acidosis

28
Q

In ABG interpretation, what does a PaO2 of 7.5 kPa with a pH of 7.10 suggest?

A

Hypoxemia and severe acidosis

29
Q

What would a PaCO2 of 18 kPa and a pH of 7.10 in a COPD patient suggest?

A

Acute respiratory acidosis superimposed on chronic respiratory acidosis

30
Q

Define “Base Excess” in ABG interpretation.

A

The amount of acid or base needed to return blood pH to 7.4 at standard PaCO2 and temperature.

31
Q

What is the significance of hypoalbuminemia in acid-base disorders?

A

It reduces the sensitivity of the anion gap in detecting metabolic acidosis.

32
Q

What is the normal range for the anion gap?

A

4 to 12 mmol/L.

33
Q

What are the derived and measured values from an ABG machine?

A
  • Derived: Bicarbonate.
  • Measured: pH, PaO2, and PaCO2.
34
Q

What are the key steps in ABG interpretation?

A

1) Assess patient’s condition.
2) Assess oxygenation (PaO2).
3) Check pH (acidosis or alkalosis).
4) Determine respiratory component (PaCO2).
5) Determine metabolic component (HCO3-).

35
Q

What diagnosis is consistent with a pH of 6.89, PaCO2 of 2.48 kPa, and HCO3- of 4.7 mmol/L in a diabetic patient?

A

Severe diabetic ketoacidosis with partial respiratory compensation

36
Q

How is metabolic acidosis compensated?

A

By hyperventilation, which reduces PaCO2 levels.

37
Q

What does a normal PaO2 value indicate in a healthy individual breathing air?

A

PaO2 > 10 kPa (~75 mmHg).

38
Q

What does a base excess value outside +/-2 mmol/L indicate?

A

A disturbance in the metabolic component of acid-base balance.

39
Q

Why is the bicarbonate level important in ABG interpretation?

A

It reflects the metabolic component of acid-base balance.

40
Q

How does hyperventilation affect ABG values?

A

Decreases PaCO2, leading to respiratory alkalosis.

41
Q

What is the expected relationship between pH and PaCO2 in respiratory acid-base disorders?

A
  • Respiratory acidosis: Decreased pH and increased PaCO2.
  • Respiratory alkalosis: Increased pH and decreased PaCO2.
42
Q

What are the clinical causes of metabolic acidosis with a normal anion gap?

A
  • Diarrhea
  • Renal tubular acidosis
  • Early kidney injury
43
Q

What are clinical causes of metabolic acidosis with an increased anion gap?

A
  • Diabetic ketoacidosis
  • Lactic acidosis
  • Toxic ingestions (methanol, ethylene glycol)
44
Q

How can chloride loss lead to alkalosis?

A

Loss of chloride (e.g., via vomiting) reduces acid equivalents, causing metabolic alkalosis.

45
Q

What does a PaCO2 of 2.65 kPa with a pH of 7.62 indicate?

A

Severe respiratory alkalosis.

46
Q

What is the likely diagnosis with pH 7.17, PaO2 8.2 kPa, and HCO3- 12 mmol/L?

A

Sepsis-induced metabolic acidosis.

47
Q

What is the compensation for a metabolic alkalosis?

A

Hypoventilation to retain CO2 and lower pH.

48
Q

What is the primary buffer system in the blood?

A

The carbonic acid-bicarbonate buffer system.

49
Q

What role does hemoglobin play in buffering?

A

Hemoglobin buffers hydrogen ions released during oxygenation of blood.

(?)

50
Q

Why are plasma proteins considered buffers?

A

Their amino acid residues can donate or accept hydrogen ions to stabilize pH.

51
Q

What is the physiological role of lactate under normal conditions?

A

Lactate serves as an energy source during anaerobic metabolism.

52
Q

How does Type A lactic acidosis differ from Type B?

A
  • Type A: Hypoxic causes (e.g., shock, hypovolemia).
  • Type B: Non-hypoxic causes (e.g., sepsis, liver dysfunction).
53
Q

Why is lactate accumulation clinically significant?

A

It signifies tissue hypoxia or impaired metabolic pathways, often seen in critical illnesses.

54
Q

How does hypoalbuminemia affect the anion gap?

A

It reduces the sensitivity of the anion gap in detecting metabolic acidosis.

(?)

55
Q

What anion gap value suggests an unmeasured anion accumulation?

A

An anion gap >12 mmol/L.

56
Q

What are common unmeasured anions in metabolic acidosis?

A

Lactate, ketones, or toxins like methanol and ethylene glycol.

57
Q

How can you determine if an acid-base disorder is mixed?

A

If both pH and compensatory mechanisms are abnormal (e.g., acidosis with inappropriate PaCO2 response).

58
Q

What does a PaO2 of <10 kPa on FiO2 >0.21 suggest?

A

Impaired oxygenation, likely due to V/Q mismatch or shunting.

59
Q

What does a low PaCO2 with normal pH indicate?

A

A compensated metabolic acidosis or respiratory alkalosis.

60
Q
A

tACCP (4 decks)

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