Arterial to end-tidal CO2 (PaCO2–EtCO2) gradient as a monitoring parameter of efficacy during thrombolytic therapy for massive pulmonary embolism (PE) in spontaneously breathing patients
© BioMed Central Ltd 2003
Published: 3 March 2003
Alveolar dead space is increased in PE and can be evaluated by measuring the PaCO2–EtCO2 gradient during time-based capnography. The evolution of this gradient during thrombolysis in six spontaneously breathing patients with massive PE follows.
Six patients with massive PE were assigned to thrombolysis. Diagnosis was comfirmed by V/Q lung scanning and/or CT angiography. The 'massive' feature was attributed to the presence of acute right ventricular pressure overload or pulmonary hypertension signs on the twodimensional and Doppler transthoracic echocardiography: pulmonary hypertension with a trans-tricuspid gradient (RA/RV gradient) > 30 mmHg, paradoxic septal wall motion, right to left ventricle size ratio > 0.6 and loss of inspiratory collapse of the inferior vena cava. The PaCO2–EtCO2 gradient was monitored during and several hours after the treatment. Echocardiography was repeated about 12–24 hours after thrombolysis to assess the treatment's efficacy.
Two patients showed a large decrease in the PaCO2–EtCO2 gradient (mean gradient from 17 mmHg before treatment to 7 and 1.5 mmHg, respectively, at 2–4 hours and at 12–24 hours) and a nearly complete disappearance of right cardiac signs with, in particular, a normalization of RA/RV gradient for one patient and a 62% reduction for the other one. Three patients had no significant change in the PaCO2–EtCO2 gradient (from 11.5 mmHg to 12 mmHg at 2–4 hours and 12–24 hours) and showed partial improvement of echocardiographic findings (mean RA/RV gradient from 61 to 44 mmHg). One patient had a stable PaCO2–EtCO2 gradient in contrast with echocardiographic improvement (RA/RV gradient from 56 to 28 mmHg) but the echocardiographic control was performed 10 days after thrombolysis.
To our knowledge, this small series is the first to investigate the interest of capnography as monitoring for thrombolysis in spontaneously breathing patients with massive pulmonary embolism. The decrease of PaCO2–EtCO2 gradient suggests the efficacy of thrombolysis, and an elevated persistent PaCO2–EtCO2 gradient may question the efficacy of the treatment. Capnography could be a promising noninvasive and bedside application in the monitoring of thrombolysis for massive pulmonary embolism.