Evidence-based On-call

Pulmonary embolism

Investigations

Capnography ^a

.
Measure the waveform area (area under curve produced by one expiration) .

Why?

A low capnogram waveform area makes a pulmonary embolism much more likely

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability
suspected pulmonary embolism ^a (pre-test probability: 14%)	pulmonary embolism (v/q scan, angiography, or follow-up)	capnogram waveform area < 25 Hg.sec	13 (4.2 to 38)	67%
		25-50 Hg.sec	1.2 (0.81 to 1.9)	16%
		> 50 Hg.sec	0.0 (0.0 to 0.29)	0%