Low End-Tidal CO ₂ Identifies High-Severity Pulmonary Embolism and Shock-Level Hemodynamics

Objective End-Tidal CO 2 (EtCO 2 ) may be reduced when lung units are ventilated but under-perfused, as occurs in Pulmonary Embolism (PE). We sought to determine whether early EtCO 2 measurement reflects PE severity according to European Society of Cardiology (ESC) risk categories and identifies shock level hemodynamics among patients undergoing catheter directed therapy (CDT). Methods Patients admitted with acute PE confirmed by computed tomography pulmonary angiogram were enrolled in this prospective observational study. EtCO 2 was measured using nasal capnography within 24 h of presentation or immediately prior to urgent CDT. EtCO 2 was compared between lower and higher severity PE groups and between patients referred for CDT or not. In patients undergoing mechanical thrombectomy(CDT) with invasive hemodynamic assessment, pulmonary artery pressures and Cardiac Index were recorded. A subgroup analysis evaluated patients with cardiogenic shock defined as a cardiac index <1.8 L/min·m −2 . Results Sixty-two patients were analyzed. EtCO 2 was significantly lower in the combined Higher-risk group compared with the combined lower-risk group (21.7 mmHg 95%CI (20.2–23.3) versus 30.2 mmHg 95%CI (27.8–32.6) p<0.001). EtCO 2 was also lower in patients referred for CDT compared to those not referred (20.4 mmHg 95%CI (18.7–22.0) versus 28.2 mmHg 95%CI (26.2–30.1), p<0.001). Among patients who underwent CDT and met hemodynamic criteria for cardiogenic shock (n=16), EtCO 2 was the lowest (18.6 mmHg (16.1–21.1). Conclusions EtCO 2 can be rapidly obtained early in PE evaluation and reflects ESC-defined severity. An EtCO 2 level< 20 mmHg was associated with shock level hemodynamics among normotensive Intermediate-high-risk patients undergoing CDT. EtCO 2 may serve as a non-invasive marker of physiologic severity.