An 8yo boy has longstanding asthma. He has admitted with a severe episode and is tired and
drowsy. He has not improved on oxygen, inhaled B2 agonist and IV hydrocortisone. CXR shows
bilateral hyperinflation. He is too breathless to use a peakflow meter and is O2 sat <90%. What
is the single most appropriate inv?
a. CBG
b. CXR
c. CT chest
d. Pulse oximetry
e. Spirometry
answer: A
To find out if PaCo2 is normal or decreased, normally it should be increased, if not that signifies respiratory muscle fatigue and inability to hyperventilate > rapid transfer to ICU.