Capnographic trend curve monitoring can detect 1-ml pulmonary emboli in humans

To evaluate the potential of trend monitoring of end-tidal PCO2 (PETCO2) to detect pulmonary embolization, the capnograms of 24 mechanically ventilated patients were monitored during simulation of 1-ml pulmonary embolization by inflation of the balloons of their pulmonary artery catheters. Within 1 minute of balloon inflation, PETCO2 showed an exponential decrease to a new equilibrium. This response is characteristic of a CO2 wash-out curve produced by a step increase in dead space. Because of a steady baseline, the depression of the trend line during balloon inflation was apparent to a naive reader repeatedly in 20 of the 24 patients (sensitivity, 85%; specificity, 94%; positive predictive value, 98%; negative predictive value, 89%), despite a small mean decrease in PETCO2 (2 +/- 1.97 mm Hg). The PETCO2 trend curve did not reliably allow detection of balloon inflation in 4 patients whose capnograms were poorly formed. In conclusion, during constant ventilation, PETCO2 trend curve monitoring might provide clinically useful "on line" information regarding pulmonary embolization.