ABSTRACT
End-tidal CO2 (ETCO2) can represent dead space ventilation. The authors aimed to define the optimum ETCO2 to conclusively exclude a pulmonary embolic event. One hundred consecutive patients with suspected pulmonary embolisms (PEs) were enrolled over 6 months in 2012. Symptoms, demographic date, Wells' score, D-dimer levels and the gold standard computed tomography pulmonary angiogram (CTPA) results were collated for analysis. ETCO2 was measured within 24 hours of presentation in all 100 patients. Patient ages ranged from 18 years to 93 years. PE was diagnosed in 38% of cases. The average ETCO2 in patients with a positive CTPA was 3.35 kPa (range 2.4-4.2 kPa, SD 0.50). The average ETCO2 in patients without a PE was 4.41 kPa (range 1.3-6.6 kPa, SD 1.10). All patients positive for a PE obtained an ETCO2 <4.3 kPa (32.3 mmHg). This point (4.3 kPa) had a sensitivity and specificity (100% and 68% respectively), with a negative predictive value of 100% and positive predictive value of 66%. ETCO2 may reliably be used to screen and exclude patients with suspected PEs. If used in combination with D-dimer with clinical probability as a screening tool, CTPA will be required in only a minority of patients.
