Handling the Whole Patient: A Case of Asthma Exacerbation
Arterial Blood Gas 1
Blood Gas:
On 15L oxygen via non-rebreathe face mask
pH 7.47 (7.35-7.45)
pO2 20 kPa (11-14)
pCO2 3 kPa (4.5-6)
HCO3- 22 mM (22-28)
Else normal
What is this blood gas indicating?
Well done, correct.
Feedback:
The raised pH makes this an alkalosis
Her pCO2 is lower than normal which makes this a respiratory alkalosis
She is blowing off the carbon dioxide with her tachypnoea
This is an acute respiratory alkalosis, which is expected in non-life-threatening asthma exacerbations
NB In this situation a 'normal' pCO2 is of concern and not reassuring
This in an important learning point which can mislead clinicians in clinical practice
These patients are almost always tachypnoeic and this "blows off" CO2
When the patient starts to tire and their respiratory rate drops or their airflow obstruction prevents movement of air through the lungs then their CO2 will rise: in other words a normal pCO2 in this ABG would signify a 'tiring' patient or such severe airflow obstruction that they are barely moving any air; in this case an immediate referral to intensive care is warranted, even while you continue to manage the patient
