Effectiveness of end-tidal carbon dioxide tension for monitoring of 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 efficac y of thrombolytic therapy. As a noninvasive alternative to pulmonary artery catheterization, we investigated the efficacy of continuous monitoring of end-tidal CO2 tension. Design: In 12 patients with massive pulmonary embolism who required mechani cal ventilation, mean pulmonary arterial pressure (MPAP) and end-tidal carb on dioxide tension (ETco(2)) were registered continuously during thrombolyt ic therapy. Pacco(2), cardiac index as estimated by thermodilution catheter and respiratory ratio of arterial oxygen tension and inhaled oxygen concen tration (Pao(2)/Flo(2)) were determined every 60 mins. Measurements and Main Results: Before thrombolysis, MPAP (34.5 +/- 9.8 mm H g) and the difference between Paco(2) and ETco(2) (10.1 +/- 4.7 mm Hg) were markedly increased compared with normal values. Continuously monitored MPA P was related to ETco(2) for both all patients (r(2) = .42; p < .001) and i ndividually (mean P = .92; range, .79-.98; p < .001). In ten survivors, the mean cardiac index and Pao(2)/Flo(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 Pace, and ETco(2) decreased from 9.8 +/- 4.5 to 2.8 +/- 0.9 mm Rg (p <.061). Recurrent embol ism was detected in two patients by sudden reduction of ETco(2). Conclusions: Analysis of ETco(2) allows monitoring of the efficacy of throm bolysis and may reflect recurrent embolism. Thus, on the basis of this smal l study, analysis of ETco(2) appears to be useful for noninvasive monitorin g in mechanically ventilated patients with massive pulmonary embolism.