Background <p>Double-lumen endobronchial tube (DLT) displacement often occurs in patients undergoing thoracic surgery after lateral positioning. There are no clinical studies investigating the effect of disconnection of the breathing circuit with DLT on the incidence of displacement after lateral positioning. Therefore, the aim of this study is to investigate the effect of disconnection of the breathing circuit with DLT on the rate of DLT displacement after lateral positioning in patients undergoing thoracic surgery.</p> Methods <p>A single-blind, parallel-group, randomized controlled study will be conducted. We will recruit 256 patients who are scheduled to undergo elective thoracic surgery. The participants will be randomly allocated to the disconnected breathing circuit group and the connected breathing circuit group. The primary outcome is the rate of DLT displacement identified via the flexible bronchoscopy before and after lateral positioning. The secondary outcomes are the effect of lung collapse, peripheral oxygen saturation at 5 and 10 min after one-lung ventilation, and the length of stay in the post-anesthesia care unit (PACU).</p> Discussion <p>Several studies have shown promising results in reducing the incidence of DLT displacement during lateral positioning. However, no studies have investigated the effect of the disconnection of the breathing circuit from the DLT on the rate of DLT displacement after lateral positioning. We expect that disconnecting the breathing circuit when changing the patient from supine to lateral position will avoid unintended tube traction, thus reducing the incidence of DLT displacement.</p> Trial registration <p>The study protocol was registered at Clinical Trials (<a href="https://register.clinicaltrials.gov/">https://register.clinicaltrials.gov/</a>) with registration number: NCT06182371 on November 21, 2023.</p>