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

Introduction

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.

Methods

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.

Results

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.

Conclusions

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.