Investigations

• pulse oximetry ^c  

Why?

• Patients with an oxygen saturation > 92% are less likely to be hypoxic. ^c
• Significant hypoxia produces minimal changes in vital signs in healthy people. ^c

Pulse oximetry can help rule out hypoxia, but further tests may be required.

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
acute severe asthma c (pre-test probability: 9%)	hypoxia (pO2 < 8 kPa arterial blood gas)	SaO2 ≤ 92%	6.7 (3.2 to 13)	38%	0.3 (0.08 to 0.94)	2%