Mechanical ventilation is a common method of respiratory support for critically ill patients, and gastrointestinal dysfunction (GIDF) is a frequent complication. In the ICU, more than 60% of mechanically ventilated patients experience gastrointestinal dysfunction. Currently, the exact causes of mechanical ventilation-induced gastrointestinal dysfunction remain unclear, but they primarily include increased intra-abdominal pressure resulting from positive-pressure ventilation, which inhibits gastrointestinal motility; inflammatory responses, prolonged bed rest, electrolyte imbalances, and the use of sedatives, analgesics, and even muscle relaxants . Manifestations such as gastroparesis and constipation further lead to delayed gastric emptying, increased intra-abdominal pressure, and heightened risks of bacterial translocation, multiple organ failure, and ventilator-associated pneumonia. Primary Objective is to investigate, through a prospective randomized controlled trial, the efficacy of neostigmine injection at the Zusanli acupoint compared to Zusanli acupoint stimulation alone or subcutaneous neostigmine injection in improving gastrointestinal function in patients with mechanical ventilation and gastrointestinal dysfunction. Secondary objectives: （1）To evaluate the effects of acupoint injection of neostigmine on the duration of mechanical ventilation, enteral nutrition intake, and ICU length of stay in critically ill patients; （2）To assess the safety of acupoint injection of neostigmine.