A multicenter comparative study of saline contrast electrical impedance tomography method versus CTPA for the diagnosis of acute pulmonary embolism: a trial protocol

Life-threatening acute pulmonary embolism (PE) requires rapid diagnosis, but the current gold standard, CT pulmonary angiography (CTPA), involves radiation, contrast, and patient transport risks. Bedside saline contrast electrical impedance tomography (EIT) offers non-invasive, radiation-free, rapid assessment of ventilation-perfusion matching and previous case reports and single-center pilot study showed its promising value for diagnosing PE; however, robust multicenter validation is lacking. This multicenter nationwide study aims to further validate the diagnostic performance of saline contrast EIT compared with CTPA for detecting acute PE. This diagnostic test is conducted across multiple hospitals of varying tiers in China. Patients with acute respiratory failure suspected of acute PE will be screened. Within 24 hours, each participant receives both CTPA and saline contrast EIT, the latter involving a bolus injection of either 10 mL 10% NaCl via a central venous catheter or 15 mL 5% NaHCO₃ via a peripheral vein. Using CTPA as the gold standard, saline contrast EIT data are analyzed offline to derive key diagnostic parameters—including dead space percentage, intrapulmonary shunt percentage, and ventilation/perfusion (V/Q) match percentage—whose diagnostic performance for acute PE will be subsequently evaluated. The continuous variables dead space%, intrapulmonary shunt%, and V/Q match% will be assessed using receiver operating characteristic curves with area under the curve calculations to differentiate PE from non-PE patients. Optimal diagnostic thresholds will be determined using the point closest to the top-left corner or maximum Youden’s index, followed by calculation of sensitivity, specificity, Youden’s index, accuracy, Kappa statistic, positive predictive value, negative predictive value, positive likelihood ratio, and negative likelihood ratio at these thresholds. We hypothesize that in our national multicenter diagnostic trial, parameters derived from saline contrast EIT may exhibit favorable diagnostic performance for CTPA-confirmed PE, particularly massive PE. If this hypothesis is validated, saline contrast EIT could provide prompt, noninvasive, convenient, and rapid bedside evaluation for critically ill patients with clinically suspected PE who are hemodynamically unstable and difficult to transport. The study was registered at ClinicalTrials.gov (NCT07190079) on 22 September 2025.