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

Adam D. Walsh, James Warner, Anna Dunn, Kabir Ahmad

https://doi.org/10.1002/pul2.70345 

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.

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