Changes in Arterial-Alveolar Oxygen Gradient and Mixed Venous Oxygen Saturations in Mechanical Thrombectomy for Pulmonary Embolism: A Prospective Cohort Study.

Abstract

Large bore mechanical thrombectomy (LBMT) is an effective therapy for intermediate-high risk PE, however, objective physiological endpoints to guide intraprocedural decision-making remain poorly defined. The alveolar-arterial (A-a) oxygen gradient, mixed venous oxygen saturation (SvO₂), and cardiac index (CI) may provide clinically useful insights during LBMT. We sought to determine if changes in alveolar-arterial gradients and estimated cardiac index were sufficiently consistent to be used to inform clinical decision making. This was a single-center, prospective, pre-post cohort study of patients undergoing LBMT for intermediate-high risk PE. Arterial and mixed venous blood gases were aspirated immediately before and after thrombectomy. CI was estimated via the indirect Fick method. Primary outcomes were changes in A-a gradient and mixed venous oxygen saturations; secondary outcomes included estimated CI and Modified Borg Dyspnea Scale. Sensitivity analyses excluded physiologically implausible outliers and accounted for intraprocedural hemoglobin changes. Twenty-seven patients were included. LBMT was associated with a nonsignificant reduction in A-a gradient (-38.5 ± 129.9 mmHg, p = 0.052), which became significant after exclusion of outliers (-41.5 ± 62.9 mmHg, p = 0.0096). Mixed SvO₂ decreased in most patients by 3.8% ± 7.3% (p = 0.015), corresponding to a modest reduction in estimated CI (-0.16 ± 0.67 L/min/m², p = 0.032) which persisted after controlling for hemoglobin loss. Dyspnea scores improved in most patients with paired measurements. Acute improvements in oxygenation efficiency were reflected by reductions in A-a gradient, while paradoxical reductions in SvO₂ and estimated CI suggest altered oxygen extraction ratio post-procedure. These parameters may serve as novel intraprocedural physiological markers to complement thrombectomy endpoints.