Non-Invasive Respiratory Monitoring to Predict Successful Separation From Mechanical Ventilation Following Upper Abdominal Surgery

Postoperative patients undergoing upper abdominal surgery frequently require mechanical ventilation and are at increased risk of extubation failure because of impaired respiratory mechanics, postoperative pain, diaphragmatic dysfunction, and atelectasis. Failure of separation from mechanical ventilation is associated with prolonged intensive care unit (ICU) stay, increased healthcare utilization, and mortality. Although prophylactic high-flow nasal cannula (HFNC) is commonly used to reduce the risk of respiratory deterioration after extubation, clinicians currently lack reliable bedside tools that provide real-time physiological information to predict successful separation from mechanical ventilation and guide individualized respiratory support.

A preceding quality improvement audit conducted at King Chulalongkorn Memorial Hospital demonstrated a composite post-extubation failure rate of approximately 32% among postoperative upper abdominal surgery patients requiring mechanical ventilation. In addition, the investigators' precursor VISION study showed that an electrical impedance tomography (EIT)-derived absolute ventral-to-dorsal ventilation difference greater than 20% during a spontaneous breathing trial was associated with failure of liberation from mechanical ventilation. These findings provide the rationale for evaluating non-invasive physiological monitoring in this high-risk surgical population.

The VALUE study is a prospective, two-phase clinical investigation designed to determine the prevalence of separation failure from mechanical ventilation and to evaluate the predictive performance of non-invasive respiratory monitoring parameters. The study will enroll approximately 40 adult patients who require postoperative mechanical ventilation following upper abdominal surgery.

During the first phase, participants will undergo physiological assessment while receiving mechanical ventilation during spontaneous breathing. An EIT belt will be applied to continuously measure regional lung ventilation. Simultaneously, ventilator-derived indices of respiratory drive and inspiratory effort, including airway occlusion pressure (P0.1) and end-expiratory occlusion pressure-derived measurements (ΔPocc), will be recorded using standardized measurement procedures.

Following successful extubation, participants will enter the second phase, which consists of a prospective physiological crossover study. Oxygen therapy will be administered according to routine clinical practice, with the treating clinical team selecting the initial oxygen delivery device. Participants will then undergo an ABA crossover sequence between conventional nasal prong oxygen therapy and high-flow nasal cannula, with each intervention maintained for a standardized 10-minute period. This design allows comparison of physiological responses while minimizing potential carryover effects without requiring an unsafe room-air washout period.

Throughout both study phases, EIT will continuously measure regional ventilation distribution, while additional non-invasive physiological variables, including respiratory drive, inspiratory effort, respiratory rate, oxygenation indices, and clinical respiratory distress scores, will be collected using standardized protocols. Participants will be followed for seven days after extubation to evaluate clinical outcomes related to separation from mechanical ventilation and postoperative pulmonary complications.

The study is designed to determine whether bedside physiological monitoring using EIT and complementary non-invasive respiratory measurements can improve prediction of successful separation from mechanical ventilation and provide insights into the physiological effects of different post-extubation oxygen delivery strategies in patients undergoing upper abdominal surgery.