Effectiveness of end-tidal carbon dioxide tension for monitoring thrombolytic therapy in acute pulmonary embolism.

Objective: In acute massive pulmonary embolism with hemodynamic instability, monitoring of pulmonary artery pressure can be used to assess the efficacy of thrombolytic therapy. As a noninvasive alternative to pulmonary artery catheterization, we investigated the efficacy of continuous monitoring of end-tidal CO 2 tension. Design: In 12 patients with massive pulmonary embolism who required mechanical ventilation, mean pulmonary arterial pressure (MPAP) and end-tidal carbon dioxide tension (ETCO 2 ) were registered continuously during thrombolytic therapy. PaCO 2 , cardiac index as estimated by thermodilution catheter and respiratory ratio of arterial oxygen tension and inhaled oxygen concentration (PaO 2 /FIO 2 ) were determined every 60 mins. Measurements and Main Results: Before thrombolysis, MPAP (34.5 ± 9.8 mm Hg) and the difference between PaCO 2 and ETCO 2 (10.1 ± 4.7 mm Hg) were markedly increased compared with normal values. Continuously monitored MPAP was related to ETCO 2 for both all patients (r2 = .42; p <.001) and individually (mean r2 =.92; range,.79-.98; p <.001). In ten survivors, the mean cardiac index and PaO 2 /FIO 2 increased during therapy from 1.7 ± 0.4 to 2.8 ± 0.6 L/min.m 2 and 125 ± 27 to 285 ± 50 mm Hg (p < .01, respectively). In these patients, the difference between PaCO 2 and ETCO 2 decreased from 9.8 ± 4.5 to 2.8 ± 0.9 mm Hg (p < .001). Recurrent embolism was detected in two patients by sudden reduction of ETCO 2 . Conclusions: Analysis of ETCO 2 allows monitoring of the efficacy of thrombolysis and may reflect recurrent embolism. Thus, on the basis of this small study, analysis of ETCO 2 appears to be useful for noninvasive monitoring in mechanically ventilated patients with massive pulmonary embolism.