ABG Worksheet. Acid base balance wksh - NUR-152 - ECC - Studocu - Free Printable

Let's solve each of these arterial blood gas (ABG) interpretation questions step by step. We’ll use the standard approach for ABG analysis:

Step-by-step ABG Interpretation:

1. Check pH:
- Normal: 7.35–7.45
- <7.35 → Acidemia
- >7.45 → Alkalemia

2. Identify primary disturbance:
- Look at PaCO₂ (respiratory component):
- ↑ PaCO₂ → Respiratory acidosis
- ↓ PaCO₂ → Respiratory alkalosis
- Look at HCO₃⁻ (metabolic component):
- ↑ HCO₃⁻ → Metabolic alkalosis
- ↓ HCO₃⁻ → Metabolic acidosis

3. Determine compensation:
- In acute/chronic respiratory issues, kidneys compensate with HCO₃⁻ changes.
- In metabolic issues, lungs compensate via PaCO₂ changes.

4. Check for mixed disorders if both PaCO₂ and HCO₃⁻ are abnormal in the same direction (e.g., both high or both low).

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Now let’s go through each question:

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1. pH 7.56, PaCO₂ 20, HCO₃⁻ 20

- pH: 7.56 → Alkalemia
- PaCO₂: 20 → Low → Respiratory alkalosis
- HCO₃⁻: 20 → Low → Metabolic acidosis (but this is compensatory)
- Interpretation: Primary Respiratory Alkalosis with partial metabolic compensation
(Low HCO₃⁻ is expected as kidney tries to correct by excreting bicarbonate)

✔ Answer: Respiratory Alkalosis

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2. pH 7.23, PaCO₂ 37, HCO₃⁻ 18

- pH: 7.23 → Acidemia
- PaCO₂: 37 → Normal
- HCO₃⁻: 18 → Low → Metabolic acidosis
- Since PaCO₂ is normal, no significant respiratory compensation yet.
- This is a primary metabolic acidosis.

✔ Answer: Metabolic Acidosis

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3. pH 7.31, PaCO₂ 34, HCO₃⁻ 21

- pH: 7.31 → Acidemia
- PaCO₂: 34 → Low → Respiratory alkalosis (compensatory)
- HCO₃⁻: 21 → Low → Metabolic acidosis (primary)
- Low HCO₃⁻ = primary problem; low PaCO₂ = compensatory hyperventilation

✔ Answer: Metabolic Acidosis with Respiratory Compensation

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4. pH 7.50, PaCO₂ 32, HCO₃⁻ 24

- pH: 7.50 → Alkalemia
- PaCO₂: 32 → Low → Respiratory alkalosis
- HCO₃⁻: 24 → Normal
- Normal HCO₃⁻ suggests no metabolic compensation yet.
- This is acute respiratory alkalosis.

✔ Answer: Respiratory Alkalosis

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5. pH 7.46, PaCO₂ 36, HCO₃⁻ 32

- pH: 7.46 → Alkalemia
- PaCO₂: 36 → Normal
- HCO₃⁻: 32 → High → Metabolic alkalosis
- No change in PaCO₂? But it should be low in compensation (hyperventilation).
- Wait — PaCO₂ is normal, but HCO₃⁻ is elevated → this is early or uncompensated metabolic alkalosis

But wait — actually, in metabolic alkalosis, PaCO₂ *should* be high due to hypoventilation (compensation). Here, PaCO₂ is normal → incomplete compensation.

So: Primary metabolic alkalosis, no significant respiratory compensation.

✔ Answer: Metabolic Alkalosis

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6. pH 7.52, PaCO₂ 48, HCO₃⁻ 28

- pH: 7.52 → Alkalemia
- PaCO₂: 48 → High → Respiratory acidosis?
- But pH is high → not possible if respiratory acidosis is primary.

Wait: High PaCO₂ → respiratory acidosis would cause acidemia, but here pH is alkalemic.

So: High HCO₃⁻ (28) → metabolic alkalosis
High PaCO₂ → respiratory acidosis?

But pH is alkalotic → so metabolic alkalosis must be dominant.

→ Metabolic alkalosis with respiratory compensation (hypoventilation → ↑ PaCO₂ to buffer alkalemia)

✔ Answer: Metabolic Alkalosis with Respiratory Compensation

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7. pH 7.25, PaCO₂ 60, HCO₃⁻ 27

- pH: 7.25 → Acidemia
- PaCO₂: 60 → High → Respiratory acidosis
- HCO₃⁻: 27 → High → Metabolic alkalosis? But that doesn’t make sense with acidemia.

Wait: HCO₃⁻ is elevated but not enough to compensate for severe acidosis.

In acute respiratory acidosis, HCO₃⁻ rises slightly (by ~1 mmol/L per 10 mmHg rise in PaCO₂).
Here: PaCO₂ = 60 → ↑ from 40 → +20 mmHg → expected HCO₃⁻ ≈ 24 + 2 = 26 → observed is 27 → appropriate compensation

So: Primary Respiratory Acidosis with renal compensation

✔ Answer: Respiratory Acidosis with Metabolic Compensation

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8. pH 7.55, PaCO₂ 47, HCO₃⁻ 30

- pH: 7.55 → Alkalemia
- PaCO₂: 47 → High → Respiratory acidosis?
- But pH is high → contradiction.

HCO₃⁻ = 30 → High → Metabolic alkalosis

PaCO₂ = 47 → High → Hypoventilation → compensatory for metabolic alkalosis

So: Metabolic Alkalosis with respiratory compensation (hypoventilation)

✔ Answer: Metabolic Alkalosis with Respiratory Compensation

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9. pH 7.20, PaCO₂ 49, HCO₃⁻ 25

- pH: 7.20 → Severe acidemia
- PaCO₂: 49 → High → Respiratory acidosis
- HCO₃⁻: 25 → Normal → Not compensating yet?

Expected HCO₃⁻ in chronic respiratory acidosis:
For every 10 mmHg ↑ in PaCO₂, HCO₃⁻ ↑ by 3–4 mmol/L
PaCO₂ = 49 → ↑ 9 mmHg → expected HCO₃⁻ = 24 + 3 = 27 → but actual is 25 → less than expected

So: Primary Respiratory Acidosis with inadequate metabolic compensation

But also: HCO₃⁻ is normal → could be acute respiratory acidosis

Yes — acute respiratory acidosis has minimal HCO₃⁻ rise.

✔ Answer: Respiratory Acidosis

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10. pH 7.30, PaCO₂ 36, HCO₃⁻ 16

- pH: 7.30 → Acidemia
- PaCO₂: 36 → Low → Respiratory alkalosis (compensatory)
- HCO₃⁻: 16 → Low → Metabolic acidosis (primary)

So: Primary Metabolic Acidosis with respiratory compensation (hyperventilation → ↓ PaCO₂)

✔ Answer: Metabolic Acidosis with Respiratory Compensation

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✔ Final Answers:

1. Respiratory Alkalosis
2. Metabolic Acidosis
3. Metabolic Acidosis with Respiratory Compensation
4. Respiratory Alkalosis
5. Metabolic Alkalosis
6. Metabolic Alkalosis with Respiratory Compensation
7. Respiratory Acidosis with Metabolic Compensation
8. Metabolic Alkalosis with Respiratory Compensation
9. Respiratory Acidosis
10. Metabolic Acidosis with Respiratory Compensation

Let me know if you'd like a summary chart or explanation on how to memorize the patterns!