ALS algorithm

- Scenario one – analysing the ABG results

Think again about the patient’s ABG results (you can review the results by selecting Essentials). Identify which of these statements are correct.
Select the correct statements and then choose Confirm.
A picture of an oropharyngeal airway and oxygen facemask.
 
 
 
 

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  • This patient’s PaO2 is >10kPa which means she is not hypoxaemic. However, we would expect a higher PaO[sub]2[/sub] breathing 40% oxygen (approximately 30 kPa), suggesting impaired oxygenation
  • Her pH level is 7.19 which is below the normal level (pH 7.35). This indicates that she does have an acidaemia
  • Her PaCO[sub]2[/sub] is increased well above normal. This is consistent with a low pH and therefore she does have a respiratory acidosis
  • Her bicarbonate is within normal limits and her base excess is just below normal. There is no significant metabolic abnormality and so she does not have a metabolic acidosis

In summary:

This patient has an acute respiratory acidosis with impaired oxygenation. Treatment will include improving her airway and ventilation to reduce the PaCO[sub]2[/sub], particularly as she may have a head injury.

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That is not right. Have another go.

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That is not right.

  • This patient’s PaO2 is >10kPa which means she is not hypoxaemic. However, we would expect a higher PaO[sub]2[/sub] breathing 40% oxygen (approximately 30 kPa), suggesting impaired oxygenation
  • Her pH level is 7.19 which is below the normal level (pH 7.35). This indicates that she does have an acidaemia
  • Her PaCO[sub]2[/sub] is increased well above normal. This is consistent with a low pH and therefore she does have a respiratory acidosis
  • Her bicarbonate is within normal limits and her base excess is just below normal. There is no significant metabolic abnormality and so she does not have a metabolic acidosis

In summary:

This patient has an acute respiratory acidosis with impaired oxygenation. Treatment will include improving her airway and ventilation to reduce the PaCO[sub]2[/sub], particularly as she may have a head injury.

Feedback

That is right.

  • This patient’s PaO2 is >10kPa which means she is not hypoxaemic. However, we would expect a higher PaO[sub]2[/sub] breathing 40% oxygen (approximately 30 kPa), suggesting impaired oxygenation
  • Her pH level is 7.19 which is below the normal level (pH 7.35). This indicates that she does have an acidaemia
  • Her PaCO[sub]2[/sub] is increased well above normal. This is consistent with a low pH and therefore she does have a respiratory acidosis
  • Her bicarbonate is within normal limits and her base excess is just below normal. There is no significant metabolic abnormality and so she does not have a metabolic acidosis

In summary:

This patient has an acute respiratory acidosis with impaired oxygenation. Treatment will include improving her airway and ventilation to reduce the PaCO[sub]2[/sub], particularly as she may have a head injury.

References

See chapter 15 of the ALS manual for further reading about arterial blood gas analysis.

Essentials: 5-step approach to ABG interpretation

Step 1 – how is the patient?

Step 2 – is the patient hypoxaemic?

Step 3 – is the patient acidaemic or alkalaemic?

Step 4 – what happened to the PaCO2?

Step 5 – what has happened to the base excess or bicarbonate?



Normal values

PaO[sub]2[/sub] > 10 kPa (75 mmHg) on air
pH 7.35 – 7.45
PaCO[sub]2[/sub] 4.7 – 6.0 kPa
HCO[sub]3[/sub] 22 – 26 mmol l-1
BE +/- 2 mmol l[sup]-1[/sup]

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